lUUL) gigT7éz45-7 ' » 5-1604 A NO.1604 i. ~ “i T" l. | B R A R Y JUL 2 5 1988 i u‘ ‘i. a____< ;__ .1; J l_ ems AMA ilniversiliv IyKflLS ffizrminfl Qrs/ems qisearzfi) m he Texas Blackland THE TEXAS AGRICULTURAL EXPERIMENT STATION/ Neville P. Clarke, Director! The Texas A&M University System/College Station, Texas Major Findings O Rotated grain sorghum produced higher yields than equally fertilized con- tinuous grain sorghum. O Position of sorghum in a rotation containing cotton, sorghum, and wheat did not influence grain yield. O Clover fixed adequate nitrogen for the first crop after clover but did not fur- nish adequate nitrogen for the second crop. O Wheat grown in a cotton-sorghum-wheat rotation with no fertilizer applied produced lower yields than nonfertilized continuous wheat. O Cotton grown in a cotton-sorghum-wheat rotation without fertilizer produced higher yields than continuous cotton receiving 45-45-0. O Rotated cotton resulted in less cotton root rot than continuous cotton. O Soil organic carbon was increased by manure application or growth of fer- tilized continuous wheat but was decreased by all other systems measured. O Soil available phosphorus and potassium were increased by manure applica- tion. O Rate of water infiltration into soil was higher after continuous grain sorghum than after continuous cotton, continuous wheat, and cotton-sorghum-wheat rotation. Cover photo: Aerial view of the Texas Blackland farming systems in June 1975. ps5 arming Systems ‘Quench; |n the Texas Blackland by Billy w. Hipp Professor Texas A&M University Research and Extension Center at Dallas Texas Agricultural Experiment Station and Benny J. Simpson Research Scientist Texas A&M University Research and Extension Center at Dallas Texas Agricultural Experiment Station Table of Contents \J Page Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Materials and Methods . . . ._ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .~ . . . . . . . . . . . . . 4 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i Crop Response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Grain Sorghum Yield . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Grain Sorghum Protein . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Wheat Yield . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Wheat Protein . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Cotton Yield . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Cotton Root Rot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 ' Corn Yield . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Soil Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Organic Carbon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Total Nitrogen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Nitrogen Mineralization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Soil Phosphorus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Exchangeable Potassium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Soil Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Bulk Density and Water Infiltration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Literature Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21‘ \-& Summary Farming system and fertilizer studies were initiated by the Texas Research Foundation at Dallas in 1947 and con- tinued by the Texas Agricultural Experiment Station from 1972 through 1982. The study site was on Blackland Prairie soils consisting of Houston Black clay, Dalco clay, and Austin silty clay. All three soils have high montmoril- lonite clay content, shrink when dry, swell when wet, and are typical Blackland soils. The study consisted of combinations of fertilized and nonfertilized continuous cotton, corn, sorghum and wheat, and fertilized and nonfertilized cotton-sorghum- wheat in rotation. A cotton-corn-corn rotation (fertil- ized) was also included. Seven of the treatments were un- changed during the study. Each treatment was replicated three times in a randomized block design and enough plots were included that each crop would appear every year in a rotation, i.e., cotton-sorghum-wheat required three plots/replication. Conventional farm equipment was used in planting, harvesting, fertilizing, and main- taining the crops; none of the crops received irrigation. Continuous grain sorghum without fertilization pro- duced an average grain yield of 2,120 kilograms per hec- tare (kg/ha) (kg/ha >< 0.89 =lbs/acre) during the 35-year period. Grain yields were increased by rotation and by fertilizer application. The 35-year average grain yield for sorghum in a cotton-sorghum-wheat rotation fertilized with 45-45-0 (kg N, P205, KgO/ha) was 3,716 kg/ha. Ro tated sorghum produced higher yields than continuous” sorghum, but yield increase due to rotation was partially offset by fertilizer. Position of sorghum in a rotation con- taining cotton, sorghum, and wheat did not influence w grain yields over a 22-year period. Highest grain sorghum yields during 1971-1981 were obtained from rotated sorghum fertilized with 90-90-0 ox” more or from fertilizer plus manure. Substitution 0f ,¢Qclover for wheat in a cotton-sorghum-wheat system did not influence yields of sorghum if 45-45-0 was applied to cotton and sorghum. If the cotton and sorghum were not fertilized, clover fixed adequate nitrogen (N) for the first crop (cotton) after clover but did not furnish adequate N for the second crop (sorghum). Increased protein pro- duction by grain sorghum was generally associated with higher yields. A Wheat grown in a nonfertilized cotton-sorghum- wheat rotation produced significantly less wheat yields than all other systems. Yields from continuous wheat re- ceiving 22-45-0 and rotated wheat receiving 67-45-0 were comparable for the 35-year period, but these fer- tilizer rates were too low for maximum yields. There was a yearly increase in wheat yield from fertilized rotated systems, probably due to development and use of higher yielding cultivars. Of the four cotton systems that were not changed dur- ing the study, highest lint yield (383 kg/ha) was obtained from cotton-sorghum-wheat rotation with application of 45-45-0. Rotated and nonfertilized cotton produced higher yields than continuous cotton receiving 45-45-0. Increasing the fertilizer application rate above 45-45-0 on rotated cotton produced only a small yield increase (about 6 percent at 90-90-0). During 1971-1981, cotton grown in a cotton-sorghum-wheat rotation and fertilized with at least 45-45-0 produced higher yields than con- tinuous cotton fertilized with 180-180-0. /" 7‘ Rotating cotton with sorghum and wheat resulted in less cotton root rot than did continuous cotton regard- less of fertilization rate. The nonfertilized cotton-sorghum- wheat rotation resulted in the least cotton root rot. Corn grown continuously without fertilizer produced an average yield of 2,065 kg/ha from 1957 to 1982. Rota- tion of corn with cotton produced higher corn yields than continuous corn, but no definite trends emerged re- garding yields as a function of time for any of the treat- ments involving corn. Soil organic carbon was increased by several years of manure application or growth of fertilized continuous wheat but was decreased by all other systems measured. All systems measured contained at least 1.5 percent or- ganic carbon after 32 years in the farming system treat- ments. All treatments measured decreased total soil ni- trogen except the rotation receiving manure. Soil from the treatments receiving high N rates during the last 12 years of the study, however, was not analyzed. Nitrogen mineralization rate was a function of applied N and was not influenced by rotated or continuous sorghum. Mineralization rates were 0.47 and 1.6 milligrams per kilogram per day (mg/kg/day) for nonfertilized soils and soils fertilized with 1,620 kg N/ha/ 11 years, respectively. Soil available phosphorus (P) and potassium (K) at the 15-centimeter (cm) depth were increased by applica- tion of 11,200 kg manure/ha/year. Soil K was very high after 34 years under all treatments measured. Soil strength was affected by soil depth, cropping sys- tem, and location of measurement, but there was not a depth X farming system interaction. Water infiltration rate was higher after continuous sorghum than after con- tinuous cotton, rotated sorghum, and continuous wheat. Introduction The Blackland Prairie is one of the major farming re- gions of Texas. Approximately 5.1 million hectares (12.6 million acres) are included in the Blackland Prairie which extends from the Red River to near San Antonio. About 2.4 million hectares (5.8 million acres) of the Blackland Prairie are the Houston Black-Heiden-Austin association. Other major soil associations in the Black- land Prairie include the Wilson-Crockett-Burleson (Graylands) association, Burleson-Heiden-Crockett as- ‘Fsociation and the Austin-Stephen-Eddy association. Blackland soils are dark colored, high in montmorillo- nite clay, swell when wet, and shrink when dry. Cracks one meter deep and eight centimeters wide are common during dry periods. The primary crops grown in the Blackland Prairie are @wheat, forages, cotton, grain sorghum, corn, and legumes. Cotton was intensively grown from 1900 to 1960, but cotton acreage has declined and wheat acreage has increased in recent years. Rainfall limits production of cotton, sorghum, and corn in some years because of low or erratic rainfall dur- ing the summer growing period. Small grains are more adaptable to the fall and spring rainfall pattern. A sum- mary of the description and use of Blackland Prairie soils is provided by Godfrey (11). Continued cropping of the Blacklands and other lands is assumed to be detrimental to productivity probably because of fertility loss and deterioration of soil physical properties. Research was conducted from 1947 to 1982 to study the effects of farming systems and fertilizer practices on crop yield and soil properties. Materials and Methods Studies were initiated in the fall of 1947 and spring 0f 1948 by Texas Research Foundation at Renner, TX (an- nexed by Dallas in 1970) to evaluate the effects of farm- ing systems and fertilizer treatments on Blackland Prairie soil. The experiment was maintained by Texas Re- search Foundation, a privately funded research organi- zation, until 1972 when Texas Research Foundation was donated to Texas A&M University. The Texas Agricultural Experiment Station at Dallas maintained the study until it was terminated in the fall of 1982. \J Crops involved in the study were those common to the area, namely, cotton, grain sorghum, wheat, and clover. Corn was also included at a later date. The crops, fer- tilizer treatments, and year that each treatment was ini- tiated are indicated in Table 1 and on the inside back cover. The fertilizer sources used were ammonium nit-~* rate and ordinary or triple superphosphate. Sufficient plots were included so that each crop in a system ap- peared every year, i.e., cotton-sorghum-wheat required three plots per replication. Treatments were replicated three times in a randomized block design. Table 1. Description of the farming systems and fertilizer treatments used in the long-term cropping system studies at Dallas, TX, 1948-1982. System Fertilizer N-P2O5-K2O Year no. Crops (kg/ha/yr) initiated 1 continuous cotton none 1948 2 continuous corn none 1956 3* continuous cotton 45-45-0 1948 4 continuous grain sorghum none 1948 5 continuous wheat none 1948 6 continuous wheat 17-100-17, 1948-53 (overseeded with Hubam clover) 1948 22-45-0, 1954-82 7 continuous wheat 22-45-0, 1956-58 1956 50-45-0, 1959-62 67-45-0, 1963-82 "“ 8 cotton-sorghum-wheat none 1948 9 cotton-sorghum-wheat 45-45-O and 11,200 kg/ha manure/yr cotton & sorghum, 1956 67-45-0 wheat i 10* cotton-sorghum-clover 45-45-0, cotton & sorghum 1952 O-67-O clover, 1952-79 0-67-0 clover, 1980-82 11 cotton-sorghum-clover 0-67-0 clover, 1952-70 1952 cotton-sorghum-wheat 180-180-0 cotton & sorghum 1971 67-45-0 wheat, 1971-81 12* cotton-sorghum-wheat 45-45-0 cotton & sorghum 1948 67-45-0 wheat (plots switched to new location in 1953) 13 cotton-sorghum-wheat 45-O-0 cotton & sorghum 1961 67-45-0 wheat 14 cotton-wheat-sorghum 45-0-O cotton & sorghum 1961 67-45-O wheat 15 cotton-sorghum-wheat 90-90-0 cotton & sorghum 1971 67-45-0 wheat 16 cotton-sorghum-wheat 134-134-0 cotton & sorghum 1971 67-45-0 wheat 17 continuous corn 45-45-0, 1957-78 1957 90-45-0, 1979-82 18-1“ cotton-gqn-corn 45-45-0, 1964-78 1964 90-45-0, 1979-82 w 18-2 cotton-corn-cml 45-45-O, 1964-78 1964 90-45-O, 1979-82 19 continuous sorghum 45-45-O 1957 20 continuous sorghum 45-0-0 1960 "9 21 continuous cotton 45-O-O 1971 38 continuous sorghum 134-134-0 1971 39 continuous sorghum 90-90-0 1971 40 continuous sorghum 180-180-O 1971 ‘J ‘Systems 3, 10, and 12 received 22 kg KzO/ha/yr, 1948-52. “System 18-1 was first year of corn after cotton; 18-2 was second year of corn after cotton. ln previous publications (2, 19, 20, 23, 24) the experi- r4\mental site has been referred to as Houston Black clay. Q However, the area was mapped in detail in 1976 by the USDA Soil Conservation Service and the results indi- cated the experimental site was about 15 percent Hous- ton Black clay, 35 percent Dalco clay, and 50 percent Aus- tin silty clay. Management techniques, fertilizer, and crops grown are essentially the same for all three soil types. Plots were initially 7.62 >< 30.5 meters (m) (25 X 100 ft) but were later changed to 6.1 x 21.3 m (20 >< 70 ft). A detailed description of the procedure for establishing the crops and initial treatments was provided by Laws and Simpson (19). Conventional farming equipment typical for the area was used in planting, maintaining, and harvesting the plots. Insects were controlled as necessary using ap- propriate insecticides, but herbicides were not applied for weed control. Plant cultivars were changed as new and improved cultivars became available. Cultivars and dates of yearly plantings are indicated in Table 2. These data were not available for the early years of the study. Soil samples were taken from the 0-15 cm depth of each plot in 1947 and 1966 and stored air dry in cardboard containers. Soils were sampled at various other times for specific analyses. Rainfall data were taken a few meters from the experimental site and the monthly totals are presented in Table 3. Organic carbon was estimated in 1979 on selected plots (from stored and/or fresh samples) by the Walkley- Black method (1), and total soil N was determined in 1979 by digestion, as described by Gallaher, et al. (7), and by conventional distillation and titration. Nitrogen mineralization rate was determined by placing 10 grams (g) of air dry soil in test tubes and moistening it with 3.5 g of water. Moisture level was maintained by weighing every 3 days and adding water if necessary. Tubes were stoppered with loose fitting cotton and incubated for 3 weeks. Nitrate was not removed but was determined ini- tially and again after 3 weeks. Phosphorus analyses were conducted in 1977 on selected treatments according to the procedure de- scribed by Chapman and Pratt (5). Exchangeable K was Table 2. Cultivar and date of planting for farming systems from 1948-1982. Cotton Planting Sorghum Planting Wheat Planting Corn Planting g Year cultivar date cultivar date cultivar date cultivar date 1948 open pollinated April Austin 1949 open pollinated April Austin 1950 open pollinated Austin 1951 open pollinated Austin 1952 open pollinated Quanah 10/15 1953 open pollinated Quanah 10/20 1954 open pollinated Quanah 1955 open pollinated 1956 Hybrid TX 601 5/8 TRF 3 3/8 1957 FlS 610 3/14 Crockett 10/31 TRF9 3/13 1958 RS 610 3/22 Crockett 10/2 TRF 9 3/21 1959 RS610 3/17 Crockett 10/29 TRF9 3/17 1960 RS 610 3/21 Crockett 10/19 TRF 9 3/22 1961 Lankart 57 4/18 RS 610 4/6 Crockett 10/19/60 TRF 9 3/15 1962 Lan kart 57 4/17 RS 610 3/ 1 9 Crockett 10/20/61 TRF 9 3/ 1 6 1963 Lankart 57 4/9 RS 610 3/18 Crockett 10/18 TFlF 9 3/18 1964 Lankart 57 4/7 NK 222 3/17 Kaw 11/7 TRF9 3/16 1965 Lankart 57 4/ 1 4 NK 222 3/16 Kaw 10/28 Asgrow 105W 3/ 1 5 1966 Lankart57 4/13 NK222 3/15 Caddo 11/1 Asgrow105W 3/14 1967 Lankart 57 4/20 NK 222 3/9 Caddo 11/2 Asgrow 105W 3/10 1968 Lankart 57 4/8 NK 222 3/28 Caddo 11/20 Asgrow 305W 3/28 1969 Lan kart 3840 4/16 N K 222 3/28 Caddo 10/22 Asgrow 305W 3/27 1970 Lankart 3840 4/7 NK 222 3/31 Caddo 11/11 Asgrow 305W 3/31 "‘ 1971 Lankart 57 4/26 NK 222 3/9 Sturdy 11/12 Asgrow 305W 3/8 1972 Lan kart 57 4/26 NK 222 3/1 Sturdy 11/30 Asgrow 305W 2/29 1973 ~ NK 222 Sturdy 11/10 Asgrow 305W 1974 SP 37 4/8 NK 266A 3/ 18 Sturdy N/A TX 4O 3/ 19 Q 1975 SP 37 4/24 NK 266A 4/4 Sturdy N/A TX 40 3/20 1976 SP 37 4/23 NK 266A 3/22 Sturdy 11/18 TX 40 3/2 1977 SP 37 4/5 WAC692R 3/9 Sturdy 11/9 TX 40 3/9 % 1978 SP 37 4/4 Harpool 8409 3/28 Sturdy 12/2 TX 50 3/22 1979 GP 3755 5/ 15 Harpool 8409 4/ 19 Sturdy 10/20 TX 50 4/9 1980 GP 3774 4/17 Harpool 8409 3/20 Sturdy 11/16 TX 50 3/20 1981 GP 3774 4/14 NK 2244 3/27 TAM 106 11/10 NKPX 74 3/24 1982 GP 3774 4/15 NK 2778 3/23 TAM 106 11/19 NKPX 69A 3/15 determined on samples taken in 1981 by extracting with normal ammonium acetate and analysis by atomic ab- sorption. Water infiltration and bulk density measure- ments were made in April 1981 (soil at approximately field capacity) by procedures described in USDA Hand- book 6O (27). Field soil strength measurements were made when soil was wet (field capacity) in 1981 on selected treatments using a soil penetrometer driven by a hydraulic soil sampler. Data were obtained through a transducer-recorder arrangement as described by Gerard and Mehta (9). Cotton root rot was evaluated at the end of each growxa?’ ing season (1959-1982) by visually estimating the per- centage of each cotton plot exhibiting cotton root rot symptoms. Data were subjected to appropriate statistical analysis, primarily analysis of variance, and regression analysis. w Table 3. Monthly precipitation (cm) during the farming system and fertilizer studies at Dallas, TX. Year Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Total 1947* 3.07 1.14 6.25 10.95 7.06 18.19 0.02 28.88 7.54 7.57 7.54 14.00 112.22 48 1.52 6.40 6.07 3.66 6.81 11.05 5.28 1.65 0.20 2.18 1.40 5.74 51.97 49 21.84 9.04 10.82 4.29 16.05 29.41 0.15 5.54 5.87 17.93 0.13 3.86 124.94 5O 13.18 5.31 4.06 10.59 13.31 7.39 10.29 5.76 11.81 0.86 0.25 0.33 83.16 51 4.90 6.58 3.78 2.79 8.99 15.52 7.54 5.18 6.02 5.94 1.88 1.98 71.12 52 4.57 7.39 4.55 14.07 12.65 0 4.95 0.38 0.53 0.08 24.76 8.53 82.47 53 1.63 4.78 9.63 17.17 9.24 1.96 1.80 5.94 5.16 7.95 8.05 3.18 76.48 54 6.15 1.65 1.30 12.80 10.46 4.60 1.78 0.64 5.79 9.58 2.92 2.24 59.89 55 3.84 4.75 4.55 4.57 9.35 10.97 6.60 1.88 7.90 2.59 2.18 0 59.18 56 2.72 9.47 0.23 8.38 8.38 1.22 1.60 1.32 0.25 4.93 8.26 5.99 52.76 57 6.48 2.41 13.94 33.04 22.30 5.77 0.10 1.73 11.89 10.57 9.55 6.65 124.43 58 4.85 1.57 13.72 19.30 9.47 8.18 4.19 1.70 11.25 2.06 6.45 2.26 85.01 59 0.30 4.16 3.18 2.79 5.64 8.81 13.11 2.31 5.23 19.33 4.01 11.02 79.91 60 4.55 5.13 2.29 4.85 13.03 4.39 12.06 10.95 4.27 3.43 1.30 14.68 80.92 61 6.70 6.32 11.43 3.40 3.20 19.00 1.65 0.56 9.91 6.10 9.30 6.22 83.79 62 2.62 5.61 4.24 14.76 3.89 17.04 21.94 4.19 17.80 18.49 7.34 2.11 120.04 63 0.96 0.53 2.24 13.49 11.79 2.62 6.78 0.76 1.42 0.48 4.09 3.99 49.15% 64 6.78 3.66 12.17 9.47 14.78 1.24 0.25 9.12 43.61 0.53 15.49 2.39 119.51 65 5.28 13.36 3.66 5.31 24.54 9.96 1.37 3.78 12.22 3.58 5.38 3.76 92.20 66 3.43 5.92 6.07 48.44 2.74 8581 11.02 16.74 7.49 4.27 1.42 3.43 119.79 67 091i 1.73 5.89 12.45 16.05 4.27 5.23 0.41 17.93 12.90 2.13 7.29 87.20 68 7.47 3.86 18.52 6.22 10.67 12.42 4.42 9.55 6.81 3.10 10.26 2.87 96.16 69 5.64 5.18 11.20 7.70 23.62 2.39 0.13 2.26 8.41 16.38 2.26 7.75 92.91 70 1.93 12.67 10.06 13.54 11.53 2.69 0.74 7.42 20.32 8.33 1.02 4.06 94.31 71 0.36 5.21 0.76 5.61 9.91 4.75 7.62 11.07 6.86 23.44 4.19 20.17 99.95 72 2.18 0.71 2.72 7.42 4.09 6.45 0.30 2.26 4.47 18.42 7.54 2.46 59.03 73 9.24 5.49 8.41 13.94 18.03 19.23 9.19 0 16.23 17.93 4.04 2.84 124.59 74 4.39 2.79 2.34 11.79 2.46 12.98 4.57 8.76 21.23 14.12 9.07 4.88 99.39 75 11.12 3.56 7.14 9.17 16.81 8.30 10.39 5.18 0.91 0 3.94 3.28 79.81 76 0.71 2.36 6.53 14.22 15.32 4.80 6.17 3.22 5.92 8.53 0.96 7.90 76.66 77 5.77 5.64 18.21 12.75 1.88 5.23 6.02 5.38 5.03 2.51 4.98 0.58 73.99 78 3.81 7.67 5.66 3.96 18.57 1.73 1.83 9.40 4.01 0.76 9.07 3.15 69.62 79 10.57 6.58 18.34 5.38 19.23 3.20 3.50 8.43 3.53 6.45 1.45 7.47 94.13 80 6.86 2.36 3.00 6.35 8.97 4.37 0.13 0 19.63 3.25 3.45 4.55 62.92 81 2.29 5.08 8.15 8.43 16.86 23.42 11.61 3.96 8.71 35.69 3.33 0.46 127.99 82 6.76 4.52 3.33 8.48 28.75 11.66 5.99 1.24 3.00 8.89 11.15 10.87 104.65 83 6.71 3.48 9.32 1.32 13.74 5.97 6.35 7.67 0.30 8.89 5.61 2.74 72.11 Mean 5.19 4.97 7.13 10.62 12.17 8.65 5.32 5.28 8.90 8.60 5.57 5.29 87.69 *1947-1973 data from Brawand, Hans. 1977. Plant Environment Data; long-time measurements and recording at Fienner, TX, TAES TR 53. p. 7. ‘a Results and Discussion Crop Response Grain Sorghum Yield A There was a distinct influence of cropping system and fertilizer application on grain sorghum yields from sys- tems that were not changed during the entire study period (Table 4). Continuous grain sorghum without fer- tilization produced an average grain yield of 2,120 kg/ha during the 35-year period. Growing grain sorghum with- out fertilizer in rotation with cotton and wheat (System 8) increased yields by 815 kg/ha over continuous grain sorghum (System 4), but yields were increased by 1,596 kg/tta if sorghum was rotated and fertilized with 45-45-0 (System 12). Average yearly grain yield for the 35-year period was 3,716 kg/ha for the rotated and fertilized (45- 45-0) sorghum. In 1959, Laws and Simpson (19) con- Table 4. Influence of farming system and fertilizer practices on grain sorghum yield at Dallas, TX, 1948-1982. System* Grain yield no. (kg/ha) 12 cotton-sorghum-wheat 45-45-0 3,716 a** 8 nonfertilized cotton-sorghum-wheat 2,935 b 4 nonfertilized continuous sorghum 2,120 c K 4Q ‘For complete system description, refer to Table 1 or the inside back cover. “Means followed by the same letter are not significantly different at the 0.05 level according to Duncans multiple range test. cluded that rotated sorghum, whether fertilized or not, produced higher yields than nonfertilized continuous sorghum. They also concluded that fertilizer in a farming system was more important than crop rotation for grain sorghum production. Brawand and Hossner (2) reported on the nutrient contents of sorghum leaves and grain as influenced by 13 of the systems described in this publica- tion. They concluded that sufficient information was not available to adequately interpret their data. The effects of cropping system and fertilizer applica- tion on grain sorghum during a 22-year period (1961- 1982) are indicated in Table 5. Highest yields were from rotated sorghum fertilized with yearly application of 45- 45-0 and 11,200 kg manure/ha applied to cotton and sor- ghum in the rotation (System 9). Average yields for this system were 4,566 kg/ha and were significantly higher than all other systems that were not changed from 1961- 1982. During a 22-year period, rotated systems that re- ceived 45 kg N/ha produced significantly more grain than continuous systems receiving 45 kg/ha of N/yr. Yield re- ""sponse to P applied to grain sorghum was not significant in rotations (Systems 12 and 13) or with continuous sor- ghum (Systems 19 and 20). Position of grain sorghum in the rotation did not significantly affect yields during this 22-year period. Sorghum yield following cotton (System Table 5. Influence of farming system on yield of sorghum at Dallas, TX, 1961-82. System* Grain yield no. (kg/ha) 9 cotton-sorghum-wheat 45-45-0+manure 4,566 a“ 12 cotton-sorghum-wheat 45-45-0 4,049 b 14 cotton-wheat-sorghum 45-0-0 4,039 b 13 cotton-sorghum-wheat 45-0-0 3,965 b 19 continuous sorghum 45-45-0 3,289 c 20 continuous sorghum 45-0-0 3,144 c 8 nonfertilized cotton-sorghum-wheat 3,053 c 4 nonfertilized continuous sorghum 2,013 cl *For complete system description, refer to Table 1 or the inside back cover. “Means followed by the same letter are not significantly different at the 0.05 level according to Duncan's multiple range test. 12) was 4,049 kg/ha, and sorghum yield following wheat (System 14) was 4,039 kg/ha. Continuous sorghum grown without fertilizer during 1961-1982 produced lower yields (2,013 kg/ha) than all other systems. Fifteen of the systems involving grain sorghum were not changed during 1971-1981 (Table 6). Highest yields were obtained from rotated sorghum fertilized with at least 90-90-0 (Systems 11, 15, and 16) or 45-45-0 plus ma- nure (System 9). Rotated sorghum fertilized with 45-45-0 (System 12) produced yields as high as any of the con- tinuous sorghum systems receiving up to 180-180-0 (Sys- tems 19, 38, 39, and 40). Substitution of clover, plowed Table 6. Influence of farming system and fertilizer practice on grain sorghum at Dallas, TX, 1971-1981. System* Grain yield no. (kg/ha) 16 cotton-sorghum-wheat134-134-0 4,222 a“ 11 cotton-sorghum-wheat180-180-0 4,112 a 9 cotton-sorghum-wheat 45-45-0+manure 4,061 a 15 cotton-sorghum-wheat 90-90-0 4,041 a 12 cotton-sorghum-wheat 45-45-0 3,658 b 10 cotton-sorghum-clover 45-45-0 3,654 b 38 continuous sorghum 134-134-0 3,648 b 14 cotton-wheat-sorghum 45-0-0 3,632 b 40 continuous sorghum 180-180-0 3,618 b 13 cotton-sorghum-wheat 45-0-0 3,521 b 39 continuous sorghum 90-90-0 3,515 b 19 continuous sorghum 45-45-0 2,8320 20 continuous sorghum 45-0-0 2,767 c 8 nonfertilized cotton-sorghum-wheat 2,660 c 4 nonfertilized continuous sorghum 1,792 d *F0r complete system description, refer to Table 1 or the inside back cover. “Means not followed by the same letter are significantly different at the 0.05 level according to Duncan's multiple range test. under as green manure, (System 10) for wheat (System 12) did not increase yield of sorghum if 45-45-0 was applied to cotton and sorghum. As indicated in Figure 1, yield of continuous sorghum was less than rotated sor- ghum at all fertilizer rates during 1971-1981. Parabolic re- gression equations showed that fertilizer rate accounted for about 87 percent and 92 percent of the variations in rotated and continuous sorghum yield, respectively. 5000i Y=2699+10.3BX—0.017Xz ROTATED g 4000 Raw-l" G c0 5 3000 urmuous a Y=179B+12.20X—O.019X2 E! R2=0.92 >- 2000 E é u 1000 GRAIN soncriuu 1911-1901 0 O 100 200 300 400 500 FERTILIZER RATE (kg/ha of fertilizer with an analysis equivalent to 45—45—0) Figure 1. Influence of fertilizer application rate on yield of ro- tated and continuous grain sorghum. Data from Table 5 suggest that the yield increases were due primarily to N application. The relationship between fertilizer application rate and increase in yield due to ro- tation is provided in Figure 2. The greatest yield increase due to rotation over monoculture systems was about 40 percent without fertilizer application. Application of 180-180-0 reduced the effect of rotation on yield to about 15 percent, but the equation describing the relationship between fertilizer application rate and percent yield in- crease due to rotation suggests that fertilizer rate cannot compensate ior rotation at normal fertilizer application rates. Yearly grain sorghum yields for the duration of the studies are presented in Table 7. The magnitude of thr inherent fertility of the blackland soils used in the studyw can be gleaned from yearly yield data. After 27 years without fertilization, sorghum produced almost 4,000 kg/ha (System 8) in 1974. Average yields were higher from rotated nonfertilized sorghum than from nonfer- tilized continuous sorghum every year except 1956 and 1960. A plot of the 5-year average yield (to reduce vari- ation due to weather) vs. years (Figure 3) showed that.‘ yields of nonfertilized continuous sorghum changed very little during the experimental period but the yield declined beginning after about 13 years. Yields of rotated nonfertilized sorghum began to decline after about 16 years, while rotated sorghum fertilized with 45-45-0 began to decline after 19 years. The period between 1953 and 1957 was not included in the figure or analysis be- cause of low yields due to severe drought during much of the period. A comparison of System 10 (cotton-sorghum-clover with fertilizer 0n cotton and sorghum) and System 11 (nonfertilized cotton-sorghum-clover) from 1952 through 1970 (Table 7) indicates that clover did not fix sufficient N for the subsequent sorghum crop. System 10 with fer- tilizer applied produced an average of 504 kg/ha/yr more than System 11 (Student’s t test = 6.38, significant at 0.001 level). Recent studies indicate that clover grown in blackland soil may furnish adequate N for the first crop after clover but not for the second crop. % Grain Sorghum Protein Protein production by each of the systems involving sorghum during 1980- 1982 is indicated in Table 8. Protein production was closely related to yield because the pro- tein concentrations were not changed as much by treat- ment as were yield levels. System 9 produced 488 kg pro- tein/ha/yr during 1980-1982. This was more than all the continuous systems regardless of fertilizer rate. The low- est protein yields/ha were produced by the rotated sys- tem with no fertilizer or by the continuous sorghum sys- tems. Protein production ranged from 153 to 488 kg/ha. léarly protein concentration varied considerably (Table 9) ranging from 6.75 percent to 13.52 percent. Low con- centrations were generally associated with low N fer- “ ‘inizei \eve\s as snggesteoloy Ymneson, et a\. (B) 0r niiin continuous sorghum. High rainiall during the growing season can also re- duce protein concentration. The relationships between fertilizer applied to sorghum and protein production during 1980-1981 could be described by parabolic regres- sion curves (Figure 4). Fertilizer application accountedv (or about 53 percent and 67 percent of the variation in protein yields of rotated and continuous sorghum, re- 30 R2=0.67 20 10 1971-191 protein production could be expected with 127-127-0 on rotated sorghum. Extrapolation oi the equation for con- tinuous sorghum showed the fertilizer rate for maximurr production would be 225-225-0. ‘if’ O j l 1 1 . 1 A l . 0 100 200 300 400 500 FERTlLlZER RATE _ (kg/ ha of fertilizer with an analysis equivalent to 45-45-0) z INCREASE IN new out: T0 ROTATmN Figure 2. Influence of fertilizer application on grain sorghum yield increase due t0 rotation. spectively. The regression curves indicated maximum Table 7. influence of farming system and fertilizer practice on grain sorghum yields at Dallas, TX, 1948-1982. A Year System no.* 4 8 9 10 11 12 13 14 15 16 19 20 38 39 40 kg/ha 1948 3,163 3,614 3,036 49 2,331 3,591 3,700 50 2,335 3,666 4,774 51 2,026 2,575 4,079 Q 52 1,597 1,959 2,133 2,006 2,529 1953 1,670 1,763 1,935 1,721 2,287 54 55 2,260 2,648 3,302 2,938 2,342 56 1,091 925 1,325 1,467 1,003 1,128 57 1,710 1,857 3,113 2,436 1,785 1,972 1958 2,712 3,450 4,673 4,839 3,881 3,687 59 3,054 3,650 3,460 3,632 3,740 3,650 60 3,813 2,465 4,610 4,185 3,932 3,608 61 2,990 3,975 5,873 5,454 4,653 4,879 5,511 5,556 4,292 4,173 62 2,212 4,201 4,852 4,656 4,380 4,640 4,730 4,125 3,586 3,369 1963 2,080 2,993 4,606 4,112 3,358 4,330 3,689 4,169 3,849 3,284 64 1,696 3,035 4,262 3,192 2,825 2,876 3,075 3,460 3,238 2,696 65 3,149 4,097 3,609 4,171 4,029 3,865 4,109 3,432 3,754 3,541 66 2,830 4,489 6,331 5,980 5,501 5,833 5,385 5,427 4,577 4,587 67 1,507 3,004 5,807 4,485 3,693 4,760 4,927 5,298 3,386 3,788 1968 3,177 4,610 6,679 6,153 4,939 6,254 6,487 6,582 5,675 5,189 69 873 1,807 4,186 2,951 2,349 3,373 3,162 2,951 2,439 2,078 70 1,746 3,063 5,111 3,910 3,187 3,974 3,920 3,863 3,274 2,511 71 2,982 3,467 2,894 3,799 4,580 4,420 4,263 4,116 3,808 3,853 3,953 3,468 4,589 4,604 4,399 72 2,228 3,256 5,439 5,087 4,884 5,140 4,140 4,070 4,652 4,721 3,802 3,362 4,146 4,996 4,185 1973 955 1,970 3,709 3,158 3,890 3,085 2,984 3,169 3,597 3,664 2,182 2,078 3,329 3,046 3,894 74 2,879 3,979 5,537 4,160 5,617 4,297 5,167 4,517 5,680 5,816 3,675 4,000 4,608 5,341 5,383 75 1,541 2,506 3,733 3,545 4,532 2,855 3,475 3,939 4,403 4,553 2,503 3,207 4,319 3,347 4,043 76 1,206 2,653 5,027 5,034 5,013 4,919 4,057 4,664 5,215 4,992 3,197 2,827 4,346 4,636 4,581 77 1,645 3,071 4,981 4,033 4,284 4,640 3,876 4,043 4,545 5,061 2,928 2,942 3,611 2,729 3,214 1978 1,987 2,646 2,897 2,565 3,039 2,569 2,771 2,133 3,364 3,339 2,325 2,496 2,671 2,472 2,479 79 1,369 1,942 2,914 2,336 2,379 2,192 1,737 2,514 1,881 3,033 2,055 1,376 2,623 1,846 2,092 80 518 1,656 3,364 2,843 3,254 2,920 2,858 3,079 3,558 3,654 1,419 1,609 2,109 1,835 1,638 81 2,462 2,108 4,180 3,636 3,759 3,202 3,402 3,702 3,750 3,761 3,110 2,075 3,775 3,822 3,888 82 2,240 3,194 4,461 3,752 3,864 4,060 3,503 4,056 4,528 4,975 3,130 3,523 4,426 3,652 3,243 *For complete system description, refer to Table 1 or the inside back cover. Table 8. Influence of farming system and fertilizer on average protein production by grain sorghum at Dallas, TX, 1980-1982. A 5000 2 System* A i Y=2691+1B7.'7X—4.98X R2=o62 no_ kg protein/ha 5 4000 ' LS 9 cotton-sorghum-wheat45-45-0+manure 488 a“ 5 12 11 cotton-sorghum-wheat180-180-0 421 ab g 3000 - Y=2556+124~2X-3-B4X2 15 cotton-sorghum-wheat90-90-0 412 ab 2 R2=O.B4 8 16 cotton-sorghum-wheat134-134-0 389 abc g 2000 , 14 cotton-wheat-sorghum 45-0-0 381 abc A g Y=2179+58.14X—2.24X 4 12 cotton-sorghum-wheat45-45-0 375 abc 0 R2=o49 13 cotton-sorghum-wheat 45-0-0 325 bcd 2 1000 ' _ 10 cotton-sorghum-clover 45-45-0 322 bcd f5 f 38 continuous sorghum 134-134-0 307 bcd \ v O ' ‘ ‘ ' ‘ ‘ ' 39 continuous sorghum 90-90-0 305 bcd O 5 1O 15 2O 25 3O 35 4O 20 continuous sorghum 45-0-0 27s cd YEAR 40 continuous sorghum 180-180-0 270 cde ,\ 19 continuous sorghum 45-45-0 265 cde 'F' ure 3 Grain sor hum ield as a function of ear for three 2 nonfertmzed Cotton-Sorghum-wheat 222 d2 ‘g . ' g . y y _ . 4 nonfertilized continuous sorghum 153 e farming systems (12 is cotton-sorghum-wheat 45-45-0, 8 is nonfertilized cotton-sorghum-wheat; and 4 is nonfertilized *For complete system description, refer to Table 1 or the inside back cover. Qontinuous sorghum), “Means followed by the same letter are not significantly different at the 0.05 level according to Duncan’s multiple range test. Table 9. Influence of farming system and fertilizer on protein concentration in sorghum grain and protein production at Dallas, TX, 1980-1982. Syfrm 1980 1981 1982 1980 1981 1982“ ------------- -- % protein--------------- kg protein/ha 4 nonfertilized continuous sorghum 12.92 8.52 8.48 65 210 185 8 nonfertilized cotton-sorghum-wheat 12.13 9.43 10.77 197 196 275 9 cotton-sorghum-wheat 45-45-0+ manure 12.83 1 1 .96 1 1 .75 431 504 528 10 nonfertilized cotton-sorghum-clover 1 1 .85 10.46 10.31 337 381 250 1 1 cotton-sorghum-wheat 180-180-0 13.06 12.77 1 1 .58 425 481 358 w, 1 2 cotton-sorghum-wheat 45-45-0 1 2.77 10.79 9.85 374 351 400 13 cotton-sorghum-wheat 45-0-0 12.25 7.27 1 0.87 349 252 375 14 cotton-wheat-sorghum 45-0-0 13.02 6.75 10.93 401 252 490 15 cotton-sorghum-wheat 90-90-0 13.33 1 1 .77 9.81 477 442 317 16 cotton-sorghum-wheat 134-134-0 12.69 7.98 12.81 464 322 382 19 continuous sorghum 45-45-0 12.46 10.00 10.43 171 311 312 20 continuous sorghum 45-0-0 13.21 9.04 9.90 202 281 345 .38 continuous sorghum 134-134-0 13.18 11.38 9.92 277 431 213 39 continuous sorghum 90-90-0 13.52 9.98 9.92 248 382 285 40 continuous sorghum 180-180-0 12.36 7.37 9.19 210 302 298 *For complete system description, refer to Table 1 or the inside back cover. 50o A A Y=182.'7+1.78X—(3.14X10_3)X2 ROTATED i 40o- E v 300 _ CONTINUOUS 5 E‘ A ; 200 _ Y=1O9.1+.1.07X—(1.19X10_3)X2 E R2=0.67 g 10o - n‘ GRAIN SORGHUN 1960-81 O l A 1 l O 100 ZOO 300 400 500 _ FERTILIZER RATE (kg/ha of fertilizer with an analysis equivalent. to 45-45-0) Figure 4. Relationship between fertilizer application rate and protein yield by continuous and rotated grain sorghum. Wheat Yield Four of the cropping systems involving wheat were not changed from inception to termination of the study (Table 10). They were Systems 5 (nonfertilized continu- ous wheat), 6 (continuous wheat with 22-45-0), 8 (non- fertilized cotton-sorghum-wheat), and 12 (fertilized cot- ton-sorghum-wheat). Average yields for the 35-year period indicated that wheat grown in rotation with cot- ton and sorghum, in which none of the crops received fertilizer, produced significantly less (1,015 kg/ha) than all other systems. Nonfertilized continuous wheat (Sys- tem 5) produced 337 kg/ha (5 bu/ac) more than nonfer- tilized rotated wheat (System 8). Yields from continuous wheat receiving 22-45-0 and rotated wheat receiving 67- 45-0 were comparable for the 35-year period. l0 Table 10. Influence of farming system and fertilizer practice on wheat yield at Dallas, TX, 1948-1982. System* Grain yield no. kg/ha 12 cotton-sorghum-wheat 67-45-0 1,979 a“ 6 continuous wheat 22-45-0 1,925 a 5 nonfertilized continuous wheat 1,352 b 8 nonfertilized cotton-sorghum-wheat 1,015 c *For complete system description, refer to Table 1 or the inside back cover. “Means followed by the same letter are not significantly different at the 0.05 level according to Duncan’s multiple range test. A possible explanation of the higher fertilizer require- ment of rotated wheat is the short time between row crop harvest and wheat planting in which N mineraliza- tion and moisture accumulation can occur. The fallow time between wheat crops is about 5 months (June 1 - Nov. 1), but the fallow period between cotton and wheat is about l month, while the period between sorghum har- vest and wheat planting is about 2% months. Nitrogen accumulation during fallow periods between continuous sorghum or continuous cotton precluded response to N in South Texas (14). Laws and Simpson (19) found that wheat yield from nonfertilized rotation was the same as yield from nonfer- tilized continuous wheat for the first ll years. However, continuation of the same studies resulted in yield de- cline from rotated nonfertilized wheat (Table ll). Yields were very low during the first 11 years of the study (less than 1,000 kg/ha for 7 of ll years). Higher yields in later years would be more conducive to manifestation of the difference in the rotated and continuous systems. Longnecker and Longstaff (24) evaluated the effects of 4 farming systems (5, 6, 8, and 9 of the present study, ex- cept System 9 received green manure rather than cow % % %l 4K Table 11. Influence of farming system and fertilizer practices on yearly wheat yields at Dallas, TX, 1948-1982. Year System* 5 6 7 8 9 11 12 13 14 15 16 kg/ha 1948 1,073 1,897 1,232 1,465 49 54 316 150 248 50 752 1 ,277 562 1 ,O98 51 52 847 2,397 652 1 ,624 1953 1 ,868 2,789 1 ,879 2,457 54 1 ,436 2,582 1 ,964 2,079 55 801 757 625 206 56 976 1 ,456 235 645 569 677 57 688 896 632 1 ,351 320 934 1958 1,570 1,736 1,310 2,020 1,335 2,043 59 2,153 2,276 2,742 1,044 2,645 2,068 60 1,317 1,960 2,594 1,528 2,834 2,912 61 1,662 2,209 2,721 1,239 3,138 3,004 3,219 3,017 62 1 ,530 1 ,996 2,162 985 2,650 1 ,994 2,063 2,755 1963 1,080 1,593 1,474 475 1,678 1,169 1,357 1,667 64 2,139 2,273 2,215 1,100 1,964 2,984 2,843 2,560 65 782 1 ,028 956 658 813 820 712 1 ,008 66 847 1,176 1,644 854 1,290 1,434 1,956 1,915 67 1,825 2,213 2,596 820 2,493 1,996 2,204 2,137 1968 1 ,376 2,009 1 ,702 896 2,128 1 ,982 2,372 2,345 69 1,631 2,715 2,690 831 2,784 2,531 2,789 3,078 70 1,495 1,682 2,279 1,249 2,352 2,411 2,587 2,513 71 1,835 2,190 2,199 1,526 3,050 2,880 2,936 3,023 2,692 3,147 3,214 72 771 1,376 1,238 1,286 1,481 1,377 1,542 1,463 1973 2,256 3,089 3,070 1,119 3,683 3,657 3,077 2,979 3,504 3,586 3,571 74 1,644 2,230 2,308 1,260 2,984 2,896 2,692 2,920 2,740 3,137 3,041 75 1,965 2,334 2,605 1,206 3,197 3,303 2,939 2,915 3,246 2,687 3,412 76 1,833 1,793 2,580 759 1,640 1,821 1,662 1,984 1,917 1,886 1,828 77 948 2,599 3,146 513 3,822 3,681 2,337 2,631 2,981 3,228 3,583 1978 998 1 ,640 1,685 1 ,043 2,320 2,199 2,222 1,962 2,045 2,277 2,380 79 1,268 1,748 2,141 902 3,672 3,549 2,332 2,962 3,313 3,494 3,695 80 1,834 2,614 3,040 777 2,957 2,975 2,641 2,847 2,562 3,279 3,228 81 1,673 2,610 3,183 1,335 3,073 2,721 3,235 3,550 3,206 3,499 3,169 82 468 1,398 1,662 524 1,868 1 ,702 1 ,799 1,877 1 ,776 1 ,675 1 ,595 *For complete system description, refer to Table 1 or the inside back cover. manure). They found that including fertilizer and green manure in a rotation increased yields over rotation alone. In their study, overseeding continuous wheat with “Hubam” clover increased yields, but the clover crop failed in 3 of 6 years; thus, they summarized that it was not feasible to grow a good crop of wheat and clover at the same time. Laws (18) found that the primary limita- tion to overseeding small grains with sweet clover in the Blacklands was lack of stand establishment because clover seedlings could not compete with fertilized wheat. f An analysis of “systems that were not changed from 1961 to 1982 (Table 12) indicates that wheat grown in ro- tation with cotton and sorghum and fertilized with 45- a 45-0 and 11,200 kg/ha manure on row crops (System 9) produced higher yields than all other systems evaluated during the time period. Average yields for the 22-year period for System 9 were 2,497 kg/ha (37 bu/ac). Highest yield for this system was 3,822 kg/ha (57 bu/ac) pro- duced in 1977 (Table 11). The ranking of yields for Sys- tems 5 (nonfertilized continuous wheat), 6 (continuous wheat 22-45-0), 8 (nonfertilized cotton-sorghum-wheat), and 12 (cotton-sorghum-wheat with 67-45-0) was the same as during 1948-1982. However, during 1961-1982 the Table 12. Comparison of wheat yields at Dallas, TX from farming systems that were not altered during 1961-1982. System‘ Grain yield no. (kg/ha) 9 cotton-sorghum-wheat 67-45-0 + manure 2,497 a“ 7 continuous wheat 67-45-0 2,289 b 12 cotton-sorghum-wheat 67-45-0 2,249 b 6 continuous wheat 22-45-0 2,093 c 5 nonfertilized continuous wheat 1 ,480 d 8 nonfertilized cotton-sorghum-wheat 947 e ‘For complete system description, refer to Table 1 or the inside back cover. “Means followed by the same letter are not significantly different at the 0.05 level according to Duncan's multiple range test. 11 Grain sorghum in the highest yielding system (9 on left) and the lowest yielding system (4 on right) in 1979. Continuous grain sorghum fertilized with 134-134-0 (left) and rotated sorghum with 134-134-0 (right) in 1979. Nonfertilized rotated wheat in 1975. This system produced the lowest wheat yields of all treatments. Nonfertilized continuous wheat in 1975. Wheat residue from the nonfertilized cotton-sorghum-wheat rotation in 1980. 12 ‘Wheat residue from the cotton-sorghum-wheat rotation fertilized with 45- 45-0 (1980). Nonfertilized continuous cotton (right) and fertilized with 45-45-0 (left) in 1979. Nonfertilized continuous cotton (left) and cotton-sorghum- wheat rotation fertilized with 45-45-0 (right) in 1979. Nonfertilized continuous corn (1981). Corn in a cotton-corn-corn rotation fertilized with 90- 45-0 (1981). 13 Table 13. Influence of farming system and fertilizer practice on wheat yield at Dallas, TX, 1971-1981. System* Grain yield ’ no. (kg/ha) “V 16 cotton-sorghum-wheat, 134-134-0 cotton & sorghum, 67-45-0 wheat 2,962 a** 9 cotton-sorghum-wheat, 45-45-0+ manure cotton 8t sorghum, 67-45-0 wheat 2,889 a 15 cotton-sorghum-wheat, 90-90-0 cotton & sorghum, 67-45-0 wheat 2,887 a 1 1 cotton-sorghum-wheat, 180-180-0 cotton & sorghum, 67-45-0 wheat 2,81 1 ab 14 cotton-wheat-sorghum, 45-0-0 cotton & sorghum, 67-45-0 wheat 2,689 bc 13 cotton-sorghum-wheat, 45-0-0 cotton & sorghum, 67-45-0 wheat 2,660 bcd 7 continuous wheat, 67-45-0 2,596 cd u, 12 cotton-sorghum-wheat, 45-45-0 cotton & sorghum, 67-45-0 wheat 2,487 d 6 continuous wheat, 22-45-0 2,303 e 5 nonfertilized continuous wheat 1,626f 8 nonfertilized cotton-sorghum-wheat 1,019 g ‘For complete system description, refer to Table 1 or the inside back cover. “Means followed by the same letter are not significantly different at the 0.05 level according to Duncan’s multiple range test. rotated system with 67-45-0 applied to wheat (System 12) produced significantly higher yields than the con- tinuous system with 22-45-0 applied to wheat. Rotated wheat and continuous wheat with the same fertilizer rates (Systems 7 and 12) produced comparable yields during the period 1961-1982. Systems 9, 11, 15, and 16 produced similar yields (2,811-2,962 kg/ha; 42-44 bu/ac) during the period 1971- 1981 (Table 13). As in previous years, lowest yields were produced by System 8 (1,019 kg/ha; 15 bu/ac) and the ranking of Systems 5, 6, 8, and 12 was the same as in pre- vious years. The same yield was produced by wheat after cotton (System 14) as by wheat after sorghum (System 13) when 67-45-0 was applied to wheat. Application of phosphorus to sorghum and cotton in a rotation did not increase wheat yield if 67-45-0 was applied to wheat every year (Systems 12 and 13). The data contained in Figure 5 suggest that 67 kg N applied to wheat was not sufficient for maximum yields because an increase in wheat yield was obtained from residual fertilizer applied to cotton and sorghum. The re- gression equation obtained shows that maximum wheat yields could be obtained from systems receiving 130- 130-0 on cotton and sorghum and 67-45-0 on wheat. The information from Table 13 indicates that the yield in- crease was due to residual N. The highest fertilizer rate applied to wheat in these studies was 67-45-0 which was not sufficient for maximum yield. Additional but sepa- rate studies have indicated that in most years optimum wheat yields can be obtained in the Blacklands with ap- plication of 90-45-0. Higher N rates may be required if wheat is grazed and then used for grain production. Long-term trends for four systems involving wheat are depicted in Figure 6. Wheat yields were averaged throughout 5-year increments to reduce environmental variation. Parabolic regression equations were devel- oped using years in the system (X) and wheat yield (Y). The equations and Rzvalues obtained were: System 8: Y = 661 + 47.5X — 1.21X2 , R2 = 0.13; System 5: Y = 173 + 122.4X — 2.56X2, R2 = 0.70; System6: Y = 1223 + 54.7X -— 0.79X2, R2 = 0.45; and System 12: Y = 636 + 99.8X — 1.36X2, R2 = 0.67. Yearly yield increases for the fertilized systems (6 and 12) are assumed to be primarily attri- 14 buted to higher yielding varieties. Also, wheat yield from nonfertilized systems may have increased with im- proved cultivars until fertilizer became limiting because of improved production. Y=1B35+7.95X—0.014X2 Q3000 - :1: a O o o o E5, 8 R2=0f72 g w >- 2000 - F‘ < IIJ g WHEAT 1971-st 1000 4 - - - 0 100 200 300 400 500 FERTILIZER RATE APPLIED TO COTTON AND SORGHUM IN ROTATION (kg/ha of fertilizer with an analysis equivalent to 45-45-0) Figure 5. Wheat yield as affected by fertilizer applied to cotton and sorghum in rotation with wheat. 3000 gig 2500 - 12 2000 — 1500 - 1000 - WHEAT YIELD (KG/HA) 500 - YEAR Figure 6. Relationship between wheat yields and number ofi‘ years in four farming systems (12 is cotton-sorghum-wheat 45-45-0; 6 is continuous wheat 22-45-0; 5 is nonfertilized con- tinuous wheat; and 8 is nonfertilized cotton-sorghum-wheat). Wheat Protein '\ Protein concentration in wheat grain generally in- creased in systems receiving high nitrogen rates on cot- ton and sorghum in rotation (Table 14). One exception was System 7 which was a continuous system receiving 67-45-0 annually. Nonfertilized continuous wheat con- tained protein concentrations as high as some systems receiving N. The 5-year average protein concentration for the treatments ranged from 12.7 for System 12 to 14.2 T‘ for System 11. Protein production was essentially a func- tion of yield because yield differences due to treatment were much greater than protein concentration differ- ences. As with grain yields, Systems 5, 6, 8, and 12 pro- duced the least protein/ha. The least protein was pro- duced by System 8 (117 kg/ha). Systems 9, 11, 15, and 16 produced almost four times as much protein as System 8. The yearly protein concentrations and protein pro- ductions for the period 1978-1982 are presented in Table 15. Protein concentrations and production were less in 1981-1982 than in 1978-1980, regardless of the system. Cotton Yield Four systems involving cotton were in effect from 1948 through 1982, and they all produced significantly differ- ent yields during the period (Table 16). Highest yields (383 kg lint/ha) were produced by the cotton-sorghum- wheat rotation with application of 45-45-0 to cotton (Sys- tem 12). The same system without fertilizer (System 8) produced the next highest yield (344 kg/ha), and these yields were higher than those obtained from continuous cotton with yearly application of 45-45-0 (System 3). Continuous cotton without fertilizer (System 1) pro- duced lower yields than all other systems (268 kg/ha). Application of 45-45-0 to cotton grown in rotation with sorghum and clover (System 10) did not increase yields of cotton over those obtained from the same system with 0-67-0 applied only to clover (Table 17). However, clover did not fix enough N for grain sorghum, which was the second crop after clover. Table 14. Protein concentration in wheat grain and protein pro- duction as influenced by cropping system and fertilizer, 1978- 1982. System* System no. % protein no. kg protein/ha 11 1416a" 15 402a 7 14.11 a 16 399a 9 14.04a 9 394a 15 13.84 ab 11 384 ab 16 13.78 ab 14 344 bc 5 13.48 bc 13 343 bc 14 13.23 cd 7 326c 13 13.10 cde 12 310 cd 6 12.97 cde 6 268 d 8 12.75 de 5 174e 12 12.69e 8 117f _; _A cotton-sorghum-wheat, 180-180-0 cotton & sorghum, 67-45-0 wheat continuous wheat, 67-45-0 cotton-sorghum-wheat, 45-45-0+ manure cotton 8t sorghum, 67-45-0 wheat cotton-sorghum-wheat, 90-90-0 cotton & sorghum, 67-45-0 wheat cotton-sorghum-wheat, 134-134-0 cotton 8t sorghum, 67-45-0 wheat nonfertilized continuous wheat cotton-wheat-sorghum, 45-0-0 cotton 8t sorghum, 67-45-0 wheat cotton-sorghum-wheat, 45-0-0 cotton 8t sorghum, 67-45-0 wheat continuous wheat, 22-45-0 nonfertilized cotton-sorghum-wheat cotton-sorghum-wheat, 45-45-O cotton & sorghum, 67-45-0 wheat _L _L_L _L$L NmmOJ-bmmcnggq *For complete system description, refer to Table 1 or the inside back cover. “Means followed by the same letter are not significantly different at the 0.05 level according to Duncan’s multiple range test. Table 15. Influence of farming system and fertilizer practice on yearly protein concentration in wheat grain and protein production at Dallas, TX, 1978-1982. System* no. 1978 1979 1980 1981 1982 1978 1979 1980 1981 1982 ----------------------------- -- % protein kg protein/ha 5 15.80 14.86 15.17 12.07 9.52 158 189 279 202 42 6 15.31 14.23 13.42 11.17 10.24 250 252 357 292 142 7 16.05 15.48 14.55 11.68 12.81 270 331 442 373 212 8 14.32 13.17 15.30 11.25 9.69 149 119 118 150 50 9 15.56 14.84 15.31 12.58 11.93 361 545 453 388 222 11 15.88 15.71 16.02 13.51 9.69 349 561 476 366 166 12 14.95 12.85 14.16 11.29 10.19 332 293 375 367 184 13 15.88 12.70 14.70 11.53 10.68 311 376 418 410 200 14 15.36 13.71 14.89 12.19 9.99 316 452 381 391 179 A 15 16.01 14.66 15.92 12.84 9.76 365 510 522 450 164 16 15.56 15.30 15.21 13.14 9.65 370 565 491 417 153 5 nonfertilized continuous wheat 6 continuous wheat 22-45-0 7 continuous wheat 67-45-0 8 nonfertilized cotton-sorghum-wheat 9 cotton-sorghum-wheat 45-45-0+manure cotton & sorghum, 67-45-0 wheat 11 cotton-sorghum-wheat 180-180-O cotton 8t sorghum, 67-45-0 wheat "\12 cotton-sorghum-wheat 45-45-0 cotton & sorghum, 67-45-0 wheat 13 cotton-sorghum-wheat 45-0-0 cotton 8t sorghum, 67-45-0 wheat 14 cotton-wheat-sorghum 45-0-0 cotton & sorghum, 67-45-0 wheat 15 cotton-sorghum-wheat 90-90-0 cotton & sorghum, 67-45-0 wheat 16 cotton-sorghum-wheat 134-134-0 cotton & sorghum, 67-45-0 wheat ‘For complete system description, refer to Table 1 or the inside back cover. 15 Table 16. Influence of farming system and fertilizer practice on yield of cotton at Dallas, TX, 1948-1982. System* no. kg lint/ha 12 cotton-sorghum-wheat 45-45-0 383 a“ 8 nonfertilized cotton-sorghum-wheat 344 b 3 continuous cotton 45-45-0 324 c 1 nonfertilized continuous cotton 268 d *For complete system description, refer to Table 1 or the inside back cover. “Means followed by the same letter are not significantly different at the 0.05 level according to Duncans multiple range test. Table 17. Influence of farming system and fertilizer practice on yield of cotton at Dallas, TX, 1952-1970. System* no. kg lint/ha 10 cotton-sorghum-clover 45-45-0 347 a** 11 nonfertilized cotton-sorghum-clover 327 ab 3 continuous cotton 45-45-0 311 b 1 nonfertilized continuous cotton 252 c *For complete system description, refer to Table 1 or the inside back cover. “Means followed by the same letter are not significantly different at the 0.05 level according to Duncans multiple range test. From 1961 to 1982, application of 11,200 kg/ha manure to cotton and sorghum in rotation did not significantly (0.05 level) increase cotton yields more than rotated cot- ton fertilized with 45-45-0 (Table 18). Fertilized and ro- tated cotton (System 12), however, produced higher yields than rotated nonfertilized cotton (System 8). Ro- tated nonfertilized cotton (System 8) produced higher yields than continuous cotton fertilized with 45-45-0 (System 3). During the period from 1961 to 1982, continuous cot- ton receiving 45-0-0 (System 21) produced significantly higher yields than continuous cotton receiving 45-45-0 (System 3). Reasons for the slight decrease in cotton yield due to P application on continuous cotton was not evident from these studies. Phosphorus has induced micronutrient deficiencies in some crops (4). Micronu- trient deficiencies were not visible on any cotton plots during 1977-1982, but plants were not analyzed for micro- nutrient concentration. Phosphorus did not decrease yields of rotated cotton. Table 18. influence of farming system and fertilizer practice on yield of cotton at Dallas, TX, 1961-1982. System* no. kg lint/ha 9 cotton-sorghum-wheat 45-45-O+manure 408 a“ 12 cotton-sorghum-wheat 45-45-0 388 a 8 nonfertilized cotton-sorghum-wheat 352 b 21 continuous cotton 45-0-0 343 b continuous cotton 45-45-0 318 c 1 nonfertilized continuous cotton 263 d ‘For complete system description, refer to Table 1 or the inside back cover. “Means followed by the same letter are not significantly different at the 0.05 level according to Duncan's multiple range test. 16 Analysis of lint yield for the time period 1971-1981 (Table 19) showed that cotton grown in a cotton-sorghum- wheat rotation receiving at least 45 kg N/ha or in a cot@ ton-sorghum-clover rotation produced higher yields than continuous cotton regardless of fertilizer applica- tion. Cotton grown in the rotation cotton-corn-corn (System 18) produced lower yields than cotton grown in a cotton-sorghum-wheat rotation (System 12). Nonfer- tilized continuous cotton produced lower yields than cotton in other systems. Table 19. Influence of farming system and fertilizer practice on yield of cotton at Dallas, TX, 1971-1981. System* no. kg lint/ha 16 cotton-sorghum-wheat134-134-0 396 a* 13 cotton-sorghum-wheat 45-0-0 375 ab 15 cotton-sorghum-wheat 90-90-0 365 bc 11 cotton-sorghum-wheat 180-180-0 365 bc 9 cotton-sorghum-wheat 45-45-0 + manure 363 bc 10 cotton-sorghum-clover 45-45-0 342 cd 14 cotton-wheat-sorghum 45-0-0 341 cd 12 cotton-sorghum-wheat 45-45-0 340 cd 8 nonfertilized cotton-sorghum-wheat 320 de 21 continuous cotton 45-0-0 306 e 18 cotton-corn-corn 45-45-0 304 e 3 continuous cotton 45-45-0 295 e 1 nonfertilized continuous cotton 258 f *For complete system description, refer to Table 1 or the inside back cover. “Means followed by the same letter are not significantly different at the 0.0m level according to Duncan's multiple range test. The data contained in Figure 7 indicate a slight in- crease in lint yield due to increased fertilizer application to cotton grown in a cotton-sorghum-wheat rotation. The polynomial regression equation obtained using fer- tilizer application rate (X) and lint yield (Y) showed 314 kg lint/ha could be produced without fertilizer. Applica- tion of 90-90-0 only increased yields to 371 kg/ha. Al- though the RZ value obtained for the regression equation was statistically significant, it indicated that only 35 per- cent of the variation in yield can be accounted for by ap- plication rate of fertilizer. 500 O Q 400- o <> {II O o E g 0 5 300 O 5 v=a14+o.42x-(s.sax1o‘4)x2 H . ; 200 R2=0.35 F‘ Z . E 100 r ROTATED COTTON 1971-st O | 1 | | O lOO ZOO 300 400 500 FERTILIZER RATE (lcg/ha of fertilizer with an analysis equivalent to 45—45—0)w Figure 7. lnfluence of fertilizer application rate on lint yield from cotton in a cotton-sorghum-wheat rotation. Q Table 20. Influence of farming systems and fertilizer practices on cotton yield at Dallas, TX, 1948-1982. Year System no.* 1 3 8 9 10 11 12 13 14 15 16 18 21 kg lint/ha 1948 283 243 330 249 49 500 528 390 492 50 394 597- 464 723 51 267 383 304 501 52 183 260 226 242 244 251 1953 376 405 387 379 273 448 54 201 253 270 267 245 276 55 285 307 315 298 289 331 56 130 118 155 158 161 150 173 57 228 257 273 291 253 269 261 1958 262 338 419 392 362 323 420 59 297 390 466 242 283 330 327 60 202 286 317 422 304 319 406 61 316 475 546 631 577 504 616 596 534 508 62 491 389 590 694 656 664 771 791 900 638 1963 255 328 357 455 329 402 352 507 500 430 64 260 339 334 372 401 302 392 326 301 271 65 292 402 380 437 393 365 458 423 418 333 66 304 483 530 610 569 408 519 629 409 522 67 193 233 208 289 273 251 258 269 246 253 1968 190 255 293 421 372 358 358 407 463 344 69 140 184 190 221 206 205 195 206 212 167 70 183 229 256 271 264 220 301 269 248 224 71 222 221 238 264 268 267 270 288 266 215 285 191 223 72 354 470 380 497 410 422 435 486 461 465 454 390 436 1973 247 220 304 373 355 467 441 457 335 418 469 327 354 74 163 161 225 158 193 219 182 179 153 169 213 156 191 75 189 220 292 369 371 441 270 431 394 470 406 320 298 76 319 344 331 432 358 392 410 365 320 397 465 337 339 77 292 337 342 388 349 306 394 369 367 363 386 339 296 1978 183 159 152 171 179 144 166 178 158 152 204 151 159 79 340 496 519 575 522 537 521 583 494 530 622 515 454 80 204 214 230 238 216 211 187 230 265 242 262 185 187 81 329 404 510 528 536 606 464 554 544 593 587 434 429 82 323 427 527 588 532 566 564 576 522 589 633 525 482 ‘For complete system description, refer to Table 1 or the inside back cover. Yearly cotton yields for each 0f the systems involving COUOII R00! ROI cotton are provided in Table 20. These data indicate that in addition to cropping system and fertilizer, factors such as weather, insects, and root rot have an influence on cotton yields in the North Texas Blacklands. Black- land prairie soils have high inherent fertility. This is evi- denced by the fact that cotton in a nonfertilized rotation produced 45 kg/ha more lint during years 31 -35 than it did during the first 5 years of the study. Nonfertilized ro- tated cotton produced an average of 388 kg lint/ha dur- ing the last 5 years of the experimental period. All sys- tems produced relatively high yields during years 32-35. Cotton yield could not be predicted by a first or second order regression equation using years as the indepen- .\ dent variable because of low correlation. 17 Cotton root rot, caused by Phymatotrichum omni- vorum, was extremely variable from year to year regard- less of the cropping system (Table 21). Estimation of per- cent of each plot showing root rot symptoms at maturity from 1959 through 1982 indicates that the percent root rot ranged from 0 to 99.7 for nonfertilized continuous cotton (System 1) and ranged from 0 to 51.0 for the non- fertilized rotated cotton (System 8). Statistical analysis of root rot data obtained between 1959 and 1982 showed that cotton grown in a nonfertilized rotation with sor- ghum and wheat (System 8) resulted in significantly less root rot than all other systems except cotton grown in a cotton-sorghum-wheat rotation fertilized with 45-45-0 (System 12 in Table 22). Rotation with sorghum and wheat or sorghum and clover resulted in significantly less root rot than continuous cotton regardless of fer- tilizer rate. Root rot incidence may be slightly increased by fertilizer rate on rotated systems (System 12). Table 21. Influence of farming system and fertilizer practice on cotton root rot incidence at Dallas, TX, 1959-1982. Year System no.’ 1 3 8 9 10 12 °/> Root rot 1959 72.0 47.0 4.3 7.0 1.0 50.0 60 50.3 69.3 20.0 29.7 24.3 16.7 61 20.0 9.3 0 1.7 4.3 1.0 62 63.3 68.3 26.7 33.3 25.0 8.3 63 71.0 66.0 33.3 44.0 40.7 44.0 64 1.3 3.0 1.7 2.7 1.7 0.7 65 28.3 6.3 2.3 4.7 3.0 1.0 66 76.7 49.0 21.7 24.3 50.7 40.3 67 36.7 23.0 12.7 11.0 16.7 5.3 68 75.0 80.7 49.0 52.3 47.0 54.3 69 1.0 0 0.3 0.7 0 0.3 70 12.0 2.0 1.7 1.3 3.3 0 71 99.7 98.3 51.0 58.0 68.3 47.0 72 6.3 3.3 1.7 4.3 1.3 20.0 73 — — — — — — 74 51.0 42.7 6.3 23.0 35.0 17.3 75 82.7 81.3 14.3 50.0 46.7 40.0 76 3.0 26.7 0.7 7.3 18.3 8.0 77 2.0 1.7 O 1.7 3.3 0 78 0 0.3 0 5.7 2.0 1.7 79 34.0 28.7 0.7 10.3 11.7 2.7 80 7.0 3.7 0 5.0 3.0 2.0 81 29.0 18.3 0.7 36.3 13.7 12.0 82 38.7 42.0 0 25.0 15.0 4.0 1 nonfertilized continuous cotton 3 continuous cotton 45-45-0 8 nonfertilized cotton-sorghum-wheat 9 cotton-sorghum-wheat 45-45-0+manure 1O cotton-sorghum-clover 45-45-0 1959-79, no fertilizer on cotton 1980-82 12 cotton-sorghum-wheat 45-45-0 *For complete system description, refer to Table 1 or the inside back cover. Table 22. Influence of farming systems and fertilizer on cotton root rot incidence on Blackland soil at Dallas, TX, 1959-1982. (Arc Sin Transformation for analysis). System* % of plot showing no. root rot symptoms 1 nonfertilized continuous cotton 37.4 a“ 3 continuous cotton 45-45-0 33.9 a 9 cotton-sorghum-wheat45-45-0+manure 19.1 b 10 cotton-sorghum-clover 45-45-0 1959-79 18.9 b no fertilizer on cotton 1980-82 12 cotton-sorghum-wheat 45-45-0 13.6 bc 8 nonfertilized cotton-sorghum-wheat 10.8 c *For complete system description, refer to Table 1 or the inside back cover. “Means followed by the same letter are not significantly different at the 0.05 level according to Duncan’s multiple range test. However, in a 3-year study, Jordan, et al. (17) found that cotton root rot incidence was decreased by the ap- plication of nitrogen and was increased with the applica- tion of phosphorus to Wilson soils. The effects of fer- tilizer on root rot were not consistent on Houston Black clay in their study. Rotated systems with 45-45-0 and ma- nure and cotton-sorghum-clover with 45-45-0 applied t0 cotton resulted in significantly more cotton root rot than nonfertilized cotton-sorghum-wheat rotation. Continu- l8 ous cotton resulted in significantly more root rot than all other systems evaluated. Garrett (8) suggested that mono- culture promotes development of specialized pathogens, such as}? omniuorum, while rotation with taxonomically different plants starves the specialized pathogens. The data from System 8 (cotton-sorghum-wheat rota- tion) in Table 21 suggest that culture of cotton under this system might result in elimination of the symptoms of cotton root rot after a long period of time. Corn Yield Corn grown continuously without fertilizer (System 2) produced an average of 2,065 kg/ha during 1957-1982 (Table 23). This was significantly (0.05 level) lower than the 2,745 kg/ha produced by fertilized continuous corn ‘U (System 17). Corn yields for the period 1964-1982 are presented in Table 24. Corn from the fertilized system of cotton-corn- corn (Systems 18-1 and 18-2) produced higher yields than fertilized continuous corn (System 17). Nonfer- tilized continuous corn produced an average of 1,958 kg/ ha for the 19-year period. Fertilization of continuous corn with 45-45-0 from 1957-1978 and with 90-45-0 from 1979-1982 resulted in 680 kg/ha higher yield than nonfer- tilized continuous corn during the same time period. Table 23. Influence of fertilizer on yield of continuous corn at I\ Dallas, TX, 1957-1982. System* Grain yield no. kg/ha 17 continuous corn 45-45-0 2,745 a** 2 nonfertilized continuous corn 2,065 b *For complete system description, refer to Table 1 or the inside back cover. “Means followed by the same letter are not significantly different at the 0.05 A level according to Duncan’s multiple range test. Table 24. Influence of farming system and fertilizer practice on corn yield at Dallas, TX, 1964-1982. System* Grain yield no. (kg/ha) 18-1 cotton-Qrj-corn 45-45-0 2,922 a** 18-2 cotton-corn-ccfl 45-45-0 2,876 a 17 continuous corn 45-45-0 2,694 b 2 nonfertilized continuous corn 1,958 c ‘For complete system description, refer to Table 1 or the inside back cover. “Means followed by the same letter are not significantly different at the 0.05 level according to Duncan’s multiple range test. Corn produced higher yields when rotated with cotton, but it did not seem to matter whether corn was the first I\_ or second crop after cotton (Table 24). Yields of first year corn after cotton were 2,922 kg/ha, while corn grown the second year after cotton produced 2,876 kg/ha. Both of these were significantly higher than the yield from con- tinuous corn, whether fertilized or not. Nonfertilized continuous corn produced an average of 1,584 kg/ha (Table 25) during the last 5 years of the study (years 23-27). This yield is very close to the 29 bu/ac that Smith, et al. (25) suggested as the equilibrium yield level of nonfertilized corn grown on Blackland soil. Yields were low during the entire study period, but the low yields did not appear to be entirely related to fer- tilizer application rate. Increasing the N application rate from 45 to 90 kg/ha on continuous or rotated corn during the last 4 years of the study did not increase the yield 19 over that obtained during the first 15 years for rotated corn or for the first 22 years for continuous corn (Table 25). There were no definite trends regarding continual in- crease or decrease of corn yield as a function of years for any of the systems. Table 25. influence of farming system and fertilizer on yearly yield of corn at Dallas, TX, 1956-1982. Year System* 2 17 18-1 18-2 ----------------------- -- kg grain/ha 1956 288 57 2,022 2,051 58 2,668 2,737 59 2,760 2,528 60 2,193 2,584 61 2,242 4,029 1962 2,850 3,700 63 1,765 2,555 64 1,666 2,693 3,006 3,155 65 780 985 1,349 1,215 66 3,115 3,797 3,818 3,840 1967 1,541 2,703 3,276 2,661 68 3,096 4,708 5,400 4,376 69 914 1,533 1,152 2,306 70 2,120 2,348 2,597 2,469 71 2,603 3,458 3,040 3,238 1972 2,312 3,000 3,036 3,180 73 2,187 2,638 3,558 3,428 74 2,327 3,293 3,374 3,345 75 2,266 3,257 3,926 3,634 76 2,229 3,627 3,949 3,681 1977 2,122 2,546 2,546 2,312 78 1,666 2,070 2,275 2,070 79 1,344 1,961 2,038 2,051 80 1,206 1,459 1,390 1,549 81 1,430 1,906 2,584 2,384 82 2,275 3,197 3,211 3,742 2 nonfertilized continuous corn 17 continuous corn 45-45-0 18-1 cotton-corn-corn 45-45-0 18-2 cotton-%-gqm 45-45-0 ‘For complete system description, refer to Table 1 or the inside back cover. Soil Properties Organic Carbon Carbon is a major component of soil organic matter. Organic carbon is commonly determined and multiplied by a factor of 1.724 to obtain an estimate of soil organic matter. The carbon content of organic matter is highly variable however, and this factor does not always ap- proximate organic matter. Because of these variations, results from these studies are reported as organic car- bon. Trends of the effects of cropping systems on soil or- ganic carbon content are depicted graphically in Figure 8. Organic carbon decreased with time under Systems 1, 3, 4, 5, 8, 12, and 19. After 32 years, System 1 had the lowest concentration of soil organic carbon for all treat- ments measured. 2.75 2.50 - 2.25 - //Z 2.00 - L75 “H ORGANIC CARBON (z) 1.50 - 1.25 - 1 - - 15 20 25 so YEARS IN SYSTEM O 5 1O 35 Figure 8. Relationship between soil organic carbon percent and years in four different farming systems (9 is cotton- sorghum-wheat 45-45-O + manure; 7 is continuous wheat 67- 45-0; 8 is nonfertilized cotton-sorghum-wheat; and 1 is nonfer- tilized continuous cotton). For System 1 (nonfertilized continuous cotton), the re- lationship between years in system (X) and soil organic carbon percentage (Y) was linear with a negative slope. The equations developed for Systems 1 and 8 (nonfer- tilized cotton-sorAghum-wheat) were Y = 1.81 — 0.011X (R2 = 0.67) and Y = 1.87 — 0.006X (R2 = 0.12), respec- tively (Figure 8). System 9 (cotton-sorghum-wheat, fer- tilizer, and manure) affected soil organic carbon more than any other system measured. The linear increase in organic carbon due to System 9 was described by the equation Y = 1.80 + 0.018X (R2 = 0.92). The increase in organic carbon from this system was due to the 11,200 kg/ha of manure applied yearly to cotton and sorghum because the same system without manure resulted in a decrease in organic carbon. Laws (20) found that about 4,000 kg/ha of residue must be returned to Blackland soil to maintain organic matter levels. These studies showed that organic matter changes were extremely slow in the Blackland soils studied, and it would not be economically feasible to increase soil or- ganic matter. Smith, et al. (25) determined that Black- 20 v0 land soils reached an equilibrium of about 2 percent or- ganic matter (approximately 1.16 percent organic carbon) under continuous nonfertilized corn. All systems mea- sured in these studies were higher, as they contained at least 1.5 percent organic carbon after 32 years. Total Nitrogen Changes in total soil N concentration were similar to those of organic carbon in that total N increased with time under System 9 but decreased under Systems 1, 3, 4, 5, 7, 8, and 12. Typical total N changes with time are depicted in Figure 9. System 9 was the only treatment measured that resulted in increased N. However, treat- ments that received high amounts of N between 1971 and 1981 were not measured. The regression equation ob- tained for System 9 was Y = 0.18 + 0.00094X (R2 = 0.62) (Y = % total N, X = years in system), and for System 1 the regression equation was Y = 0.20 — 0.0015X (R2 = 0.71). The equation for System 1 (nonfertilized continu- ous cotton) resulted in the largest negative slope of all systems measured. This indicates that total N was de- pleted at a faster rate under this system than all other systems measured. The increase in N under System 9 was attributed to manure since the same system without manure (System 12) resulted in less N after 32 years than A initially. About 30 kg/N/ha/yr was removed from soil with non- fertilized grain sorghum treatments (Table 8). This would amount to about 960 kg N/ha over a 32-year period (1948-1979), and should reduce the total soil N concen- tration by 0.043 percent if all N was removed from the top 15 cm of soil and none was returned by N fixation or other processes. The actual reduction in the average N of Systems 8 and 4 was 0.040 percent (Figure 9 and data not shown for System 4). Approximately the same amount 0.25 0.20 - Z TOTAL N (0—15cm) 15 2O 25 3O 35 YEARS IN SYSTEM 1O Figure 9. Relationship between total soil N and number of years U Q in four farming systems (9 is cotton-sorghum-wheat 45-45-0 + ' manure; 7 is continuous wheat 67-45-0; 1 is nonfertilized con- tinuous cotton; and 8 is nonfertilized cotton-sorghum-wheat). of soil N (976 kg/ha) was removed by continuous nonfer- Qtilized wheat during the same period (Table 14). Total N for this system changed from 0.18 percent in 1948 to 0.15 per- cent in 1979. Nitrogen Mineralization Nitrogen mineralization was a function of applied N (Figure 10), but the rate was similar whether the crop- A ping system was continuous sorghum or cotton-sorghum- wheat rotation. Applied N accounted for 88 percent of the variation in N mineralization rate when rotated and continuous treatments were combined. Nitrogen miner- alization rates estimated from the curvilinear equation obtained were 0.47 mg/kg/day with no N applied, to 1.6 mg/kg/day with 1,620 kg N/ha applied over an 11-year period. A 2.0 Q o ROTATED T, o CONTINUOUS o \ I f4” 1.5 - \ n0 5 a 1.0 ~ i=1 N g 0.5g Y=o.4v+1.a9x1o'3x-4.29x1o‘7x2 E t, R2=0.88 z 0.0 1 - - 0 500 1000 1500 2000 N APPLIED (KG/HA/11 YEARS) Figure 10. Soil nitrogen mineralization rate as influenced by N applied to Blackland soil. '5 a 3 50 3. ° 9 l‘: 40 93 srsa Y=aa71x'2-19 R2=0.94 z a, 3O - SYS 12 Y=844X_z‘11 Rz=0.88 ‘t; srsa Y= 217x459 R2=O.76 a 20 - u l2 g 1o - ' m B, A on o m\i_~lk. A - _ i; 0 15 30 45 so '25 90 Z SOIL DEPTH (CM) Figure 11. Relationship between extractable soil phosphorus and soil depth as a result of three farming systems (9 is cotton- sorghum-wheat 45-45-0 + manure; 12 is cotton-sorghum- wheat 45-45-0; and 8 is nonfertilized cotton-sorghum-wheat). 21 Soil Phosphorus Soil P extractable with NaHCO3was greatly increased at the 0-15 cm depth by yearly application of manure (System 9, Figure 11) over the same system without ma- nure (System 12, cotton-sorghum-wheat with 45 kg P2O5/ ha/yr). Extractable soil P was 48, 12, and 5 mg/kg at the 0-15 cm depth for Systems 9, 12, and 8, respectively. Soil phosphorus concentration for all other systems measured (Systems 11 and 16) were similar to that of System 12. As indicated by Figure 11, a small amount of the P applied in System 9 moved to the 15-30 cm depth. Phosphorus concentration at 15-30 cm depth was about 3. times higher under System 9 than under Systems 8 and 12. Exchangeable Potassium Exchangeable soil K is assumed to be available for plant use. Exchangeable K determinations for Systems 1 (nonfertilized continuous cotton) and 9 (cotton-sor- ghum-wheat with fertilizer and manure) in 1981 showed that K levels were still very high in both systems, al- though K had not been applied to System 1 since the in- itiation of the study (Figure 12). System 1 contained about 5,600 kg/ha of available K in the 0-90 cm depth (0-3 ft) after 34 years cropping with cotton. Manure applica- tion (System 9) increased extractable K to about 2.4 and 1.6 milliequivalents (meq)/100 g (1 meq K/100 g = ap- proximately 780 lbs/acre 6 ins.) in the 0-15 and 15-30 cm depth, respectively. Exchangeable K extracted from soil under Systems 8 and 12 was slightly higher (approxi- mately 0.2 meq/ 100 g) than that of System 1 in the 0-30 cm depth but was similar to System 1 at lower depths. These Blackland soils, as well as several other Texas soils, have been found to have an extremely high K sup- plying capacity (6, 12, 13, 21, 22, 26). 2.5 S’ 3 srse 3 F 2.0 - U g, 1 5 _ Y=2.72-o.oe1x+s.oax1o‘4x2 é SYS 1 R2=Q91 g 1.0 - c: Y=1.69—0.012X+3.97X10"5X2 2 0'5 ' 1951 R2=0.92 U >< m 0.0 010 2O 30 4O 5O 60 '70 8O SOIL DEPTH (cm) Figure 12. Exchangeable soil K under two farming systems as influenced by soil depth (9 is cotton-sorghum-wheat 45-45-0 + manure and 1 is nonfertilized continuous cotton). Table 26. Average soil strength values for selected farming systems at Dallas, TX, March 1981. Soil Bottom of furrow Top of bed Bottom of wheel track furrow d th ep System* System System 3 4 9 10 12 3 4 9 10 12 3 4 9 10 12 ins cm bars 2 5.1 10.1 10.5 9.6 12.4 10.5 0.9 1.8 3.4 1.2 1.4 10.8 9.5 10.0 9.8 4 10.2 8.4 8.6 8.0 9.7 8.2 2.8 3.6 5.4 3.9 3.3 8.8 7.9 8.2 9.3 8.2 6 15.2 8.5 8.5 7.5 9.3 7.9 4.9 5.7 5.7 5.7 5.0 8.3 8.3 7.5 9.0 8 20.3 9.4 8.9 7.7 10.3 8.1 5.6 6.0 6.4 6.0 6.1 8.6 8.7 7.8 8.8 7.7 10 25.4 10.2 9.7 7.7 11.8 8.6 6.4 6.4 7.1 7.2 6.7 9.2 9.5 8.1 10.1 7.2 12 30.5 10.8 11.1 8.3 11.8 9.5 6.6 7.3 7.2 8.7 7.2 9.1 9.9 8.3 11.5 8.4 14 35.6 11.5 12.2 8.8 12.5 10.9 7.2 8.6 7.8 9.8 7.6 9.9 11.2 9.3 13.1 10.1 16 40.6 12.2 13.4 9.1 13.7 11.3 7.7 9.5 8.8 11.1 8.4 11.1 12.3 10.5 14.4 11.4 18 45.7 13.0 14.6 9.2 13.9 11.9 8.1 10.6 9.5 12.4 9.4 12.3 13.5 11.4 16.0 12.1 20 50.8 13.7 15.5 9.4 14.5 12.5 9.3 11.8 10.3 13.4 10.6 13.3 14.6 11.6 15.8 12.4 22 55.9 14.0 16.4 9.7 15.5 12.8 10.4 13.2 11.6 14.5 11.3 13.6 15.6 11.8 16.1 13.2 Pr > F Sys 0.0001 3 continuous cotton Depth 0.0001 4 continuous sorghum Sys >< Depth NS 9cotton-sorghum-wheat + manure Loc 0.0001 10 cotton-sorghum-clover Sys >< Loc 0.063 12 cotton-sorghum-wheat Depth >< Loc 0.011 ‘For complete system description, refer to Table 1 or the inside back cover. Soil Strength Root growth is normally reduced and tillage is more difficult in soils with high soil strength values. Gerard, et al. (10) found that soil strength values greater than 25 bars were required to restrict cotton root growth in clay soils. Soil strength values obtained from measurements made in 1981 indicated that soil strength was affected by depth, cropping system, and location of measurement (bed or furrow), but there was no interaction between depth and system (Table 26). Of the treatments mea- sured, Systems 9 and 12 resulted in lower soil strength values than Systems 10 and 4 (Table 27). lt is not clear why substitution of clover (System 10) for wheat in a cot- ton-sorghum-wheat rotation (System 12) would result in higher soil strength values. All soil strength values were lower than 25 bars and would not be expected to decrease crop yields. Yields of sorghum (Table 6) and cotton (Table 19) from Systems 10 and 12 were the same during 1971-1981. Table 27. Influence of farming system on soil strength at Dallas, TX, 1981. System* no. Bars Location Bars 10 11.0a** Furrow 10.9a 4 10.2 ab Trackfurrow 10.6 a 3 9.4 bc Topof bed 7.4b 12 9.0 c 9 8.5 c 10 cotton-sorghum-clover 45-45-0 cotton & sorghum, 0-67-0 clover 4 nonfertilized continuous sorghum 3 continuous cotton 45-45-0 12 cotton-sorghum-wheat 45-45-0 9 cotton-sorghum-wheat 45-45-0 + manure *For complete system description, refer to Table 1 or the inside back cover. “Means followed by the same letter in a column are not significantly different at the 0.05 level according to Duncan's multiple range test. 22 Mean soil strength was 8.5 bars under System 9 and 11.0 bars under System 10. 8.0 u viii Soil strength was significantly lower on tops of beds‘ I I (7.4 bars) than in furrows (average 10.7 bars) as indi- cated in Table 27. There were no differences between strength values obtained in furrows that were normally used as wheel tracks compared to nontrack furrows. Be- cause depth influenced strength, but there was not a sig- nificant system >< depth interaction, soil strength (Y) was plotted as a function of depth (X) (Figure 13). The relationship between depth and strength was parabolic with a positive slope between 0 and 6O cm soil depth. The regression equation developed (Y = 6.76 + 0.027X + O.OO17X2, R2 = 0.29) indicated that soil strength values of about 7 bars could be expected between 0 and 15 cm regardless of cropping system. Soil strength at 55 cm 15 A 1981 O ‘é 1s- 2 5g Y=6.'76+0.02'7X+0.0017X E 11 r=0.54 o E u: 9' P U) i-"l s 7- ° o U) 5 1 i i i i i i i I I O 5 1O 15 20 25 3O 35 4O 45 5O 55 6O son. DEPTH (cu) Figure 13. Strength of Blackland soil as affected by soil depth. was about 13.4 bars for all systems. Average soil strength A values for systems 3, 4, 9, 10, and 12 at three measure- ment locations are given in Table 26. Soil strength at 0-5.1 cm was very low (<3.4 bars) on tops of beds for all sys- tems while strength at the same depth in furrows was about 10 bars. This condition is generally visible to the naked eye at the time of bedding. Bulk Density and Water Infiltration Soil bulk density at 0-15 cm ranged from 1.00 to 1.08 g/cubic centimeter (cc) under Systems 1, 4, 5, and 12 after 34 years of treatment (Table 28), but these differ- ences were not different at the 0.05 level of significance. Water infiltration rate into soil was higher after 34 years under System 4 (continuous sorghum) than it was after 34 years under Systems 1 (continuous cotton), 5 (con- tinuous wheat), or 12 (cotton-sorghum-wheat). Continu- ous grain sorghum grown on a similar soil in South Texas increased water infiltration and was important in salin- ity management (15) and nitrogen requirements of sub- sequent crops (16). Extensive studies were conducted by Laws and Brawand (23) involving cotton (Systems 1, 8, 9, 11, 13, 14, 15, and 18) on soil moisture storage and subsequent cotton pro- duction. They found higher soil moisture content when cotton followed wheat than when cotton followed cot- ton, clover, sorghum, or corn. This would be expected because a longer time is available for moisture accumu- . lation following wheat than the other crops. However, they concluded that cotton yield could not always be explained on the basis of moisture supply. 23 Table 28. Influence of farming system on water infiltration and soil bulk density of Blackland soil at Dallas, TX after 34 years of treatment. System* Bulk density Infiltration no. Crop (g/cc at 0-15 cm) rate (cm/hr) 1 continuous cotton 1.08 0.3 a" 4 continuous grain sorghum 1.06 1.2 b 5 continuous wheat 1.00 0.6 a 12 cotton-sorghum-wheat 1.02 0.4 a *For complete system description, refer to Table 1 or the inside back cover. “Means followed by different letters are significantly different at the 0.05 level according to Duncan’s multiple range test. Acknowledgment Many people were involved in this long-term farming system study. Some of the primary contributors include: Hans Brawand, James Gardenhire, C. J. Gerard, Paul Graff, Carl Gray, Joe Grimes, Frank Grimes, Cindi Gior- dano, Jack Hill, L. R. Hossner, T. C. Longnecker, Derby Laws, Nancy O’Connor, Talmadge Sangster, M. F. Schus- ter, and S. H. Whitehurst. Numerous others provided input into the research in various ways. Their help is also acknowledged. 10. 11. 12. 13. 14. Literature Cited . Allison, L. E. 1965. Organic carbon, p. 1367-1378. In: C. A. Black (ed.). Methods of soil analysis. No. 9. Am. Soc. Agron., Madison, WI. . Brawand, H., and L. R. Hossner. 1976. Nutrient content of sorghum leaves and grain as influenced by long-term crop rotation and fertilizer treatment. Agron. J. 68: 277- 280. . Burleson, C. A., W. R. Cowley, and G. Otey. 1956. Effect of nitrogen fertilization on yield and protein content of grain sorghum in the Lower Rio Grande Valley of Texas. Agron. J. 48: 524-525. . Burleson, C. A., A. D. Dacus, and C. J. Gerard. 1961. The effect of phosphorus fertilization on the zinc nutrition of several irrigated crops. Proc. Soil Sci. Soc. Am. 25: 365- 368. . Chapman, H. D., and P. F. Pratt. 1961. Methods of analysis for soils, plants and water. Univ. Calif. Div. Agri. Sci., Riverside, CA. . Fraps, G. S., and J. F. Fudge. 1927. Chemical composition of soils of Texas. Tex. Agric. Exp. Stn. Bull. 549. . Gallaher, R. N., C. O. Weldon, and F. C. Boswell. 1976. A semiautomatic procedure for total nitrogen in plant and soil samples. Soil Sci. Soc. Am. J. 48: 887-889. . Garrett, S. D. 1970. Pathogenic root-infecting fungi. Cam- bridge Univ. Press, London. . Gerard, C. J., and H. C. Mehta. 1971. Influence of a root crop on physical properties of a medium-textured soil. Agron. J . 63: 889-892. Gerard, C. J., P. Sexton, and G. Shaw. 1982. Physical fac- tors influencing soil strength and root growth. Agron. J. 74: 875-879. Godfrey, C. L. 1964. A summary of the soils of the Black- land Prairies of Texas. Tex. Agric. Exp. Stn. MP 698. Hipp, B. W, and G. W. Thomas. 1968. Method for predict- ing potassium uptake by grain sorghum. Agron. J. 60: 467-469. Hipp, B. W 1969. Potassium fixation and supply by soils with mixed clay minerals. Tex. Agric. Exp. Stn. Bull. 1090. Hipp, B. W, and C. J. Gerard. 1971. Influence of previous crop and nitrogen mineralization on crop response to applied nitrogen. Agron. J. 63: 583-586. 24 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. . Hipp, B. W, and C. J. Gerard. 1973. Influence of cropping system on salt distribution in an irrigated vertisol. Agron. J. 65: 97-99. Hipp, B. W, and C. J. Gerard. 1973. Influence of previous crop on nitrate distribution in a clay soil profile and subsequent response to applied N. Agron. J. 65: 712-714. Jordan, H. V., H. A. Nelson, and J. E. Adams. 1939. Rela- tion of fertilizers, crop residues and tillage to yields of cotton and incidence of root rot. Proc. Soil Sci. Soc. Am. 4: 325-328. Laws, W. D. 1955. The limitation of overseeding winter grains in the blacklands with Huban sweet clover. Tex. Res. Found. Bull. 3. Laws, W. D., and B. J. Simpson. 1959. Grain sorghum in farming systems for the blackland. Tex. Res. Found. Bull. 8. Laws, W D. 1961. Farming systems for soil improvement in the Blacklands. Tex. Res. Found. Bull. 10. Laws, W. D. 1962. Potassium status of eight Texas soils as related to crop yield and plant composition. Soil Sci. 94: 230-234. Laws, W Derby. 1965. Investigation of some potassium relationships of the Blackland Prairie and related soils. Tex. Res. Found. Bull. 23. Laws, W D., and H. Brawand. 1969. The effect of farming systems on soil moisture reserve and cotton production in the Texas Blackland. Tex. Res. Found. Bull. 27. Longnecker, T. C., and W H. Longstaff. 1955. Fertilizing winter grains in the Blacklands. Tex. Res. Found. Bull. 5. Smith, R. M., D. O. Thompson, J. W Collier, and R. J. Her- vey. 1954. Soil organic matter, crop yields, and land use in the Texas Blackland. Soil Sci. 77: 377-388. Thomas, G. W, and B. W Hipp. 1968. Soil factors affect- ing potassium availability. p. 269-291. In." The role of potassium in agriculture. Am. Soc. Agron., Madison, WI. U. S. Salinity Laboratory Staff. 1954. Diagnosis and im- provement of saline and alkali soils. U. S. Dep. Agric. Handb. No. 60. will ‘Q Description of the farming systems and fertilizer treatments used in the long-term cropping system studies at Dallas, TX, 1948-1982. System Fertilizer N-P2O5-K2O Year no. Crops (kg/ha/yr) initiated 1 continuous cotton none 1948 2 continuous corn none 1956 3* continuous cotton 45-45-0 1948 4 continuous grain sorghum none 1948 5 continuous wheat none 1948 6 continuous wheat 17-100-17, 1948-53 (overseeded with Hubam clover) 1948 22-45-0, 1954-82 7 continuous wheat 22-45-0, 1956-58 1956 50-45-0, 1959-62 67-45-0, 1963-82 8 cotton-sorghum-wheat none 1948 9 cotton-sorghum-wheat 45-45-0 and 11,200 kg/ha manure/yr cotton & sorghum, 1956 67-45-0 wheat 10* cotton-sorghum-clover 45-45-0, cotton & sorghum 1952 0-67-O clover, 1952-79 0-67-0 clover, 1980-82 11 cotton-sorghum-clover 0-67-0 clover, 1952-70 1952 cotton-sorghum-wheat 180-180-0 cotton & sorghum 1971 67-45-0 wheat, 1971-81 12* cotton-sorghum-wheat 45-45-0 cotton & sorghum 1948 67-45-0 wheat (plots switched to new location in 1953) 13 cotton-sorghum-wheat 45-0-0 cotton & sorghum 1961 67-45-0 wheat 14 cotton-wheat-sorghum 45-0-0 cotton & sorghum 1961 67-45-0 wheat 15 cotton-sorghum-wheat 90-90-0 cotton & sorghum 1971 67-45-0 wheat 16 cotton-sorghum-wheat 134-134-0 cotton & sorghum 1971 67-45-0 wheat 17 continuous corn 45-45-0, 1957-78 1957 90-45-0, 1979-82 18-1“ cotton-coin-corn 45-45-0, 1964-78 1964 90-45-0, 1979-82 18-2 cotton-corn-coi 45-45-0, 1964-78 1964 90-45-0, 1979-82 19 continuous sorghum 45-45-0 1957 ' 20 continuous sorghum 45-0-0 1960 21 continuous cotton 45-0-0 1971 38 continuous sorghum 134-134-0 1971 39 continuous sorghum 90-90-0 1971 40 continuous sorghum 180-180-0 1971 ‘Systems 3, 10, and 12 received 22 kg KzO/ha/yr, 1948-52. “System 18-1 was first year of corn after cotton; 18-2 was second year of corn after cotton. 8 i Mention of a trademark or a proprietary product does not constitute a guarantee or a warranty of the product by The Texas Agricultural . Experiment Station and does not imply its approval to the exclusion of other products that also may be suitable. All programs and information of The Texas Agricultural Experiment Station are available to everyone without regard to race, color, religion, sex, age, handicap, or national origin. 3M—7-88