3-1321 $51?“ - - ater ManagementStudies L! Rfim€ Rolling Plains The Texas Agricultural Experiment Station, Neville P. Clarke, Director, College Station, Texas, The Texas ASM University System ‘D CONTENTS 2 SUMMARY 3 INTRODUCTION 3 CROP WATER REQUIREMENT 4 COTTON 9 GRAIN SORGHUM 12 SMALL GRAINS q 14 POTATOES 16 SWEET CORN 19 LITERATURE CITED SUMMARY Water management studies were conducted with cotton, grain sorghum, wheat, potatoes, and sweet corn from 1976 through 1978.“ These studies demonstrated that water is the dominant factor influencing yields in the Rolling Plains. Yields of cotton, grain sorghum, potatoes, and sweet corn were a linear function of applied water and water use. Moisture need and average rainfall patterns at Chillicothe and Iowa Park showed that Q irrigation often is not needed for production of 3O to 5O bushels of l wheat per acre. Water Management Studies In the Rolling Plains C. J. GERARD, D. G. BORDOVSKY, AND L. E. CLARK* Crop production in the Rolling Plains is dependent upon the effective utilization of rainfall and, sometimes, supplemental irrigation. Although irrigation is practiced on only a small percentage of the area in the Rolling Plains, the amount is significant. For example, in the Knox county area about 1,000 to 1,300 acres of irrigated potatoes and about another 50,000 acres of irrigated field crops are grown. The Wichita Falls Irrigation District is an area growing irrigated crops such as cotton, Coastal bermudagrass, pecans, and vegetables. The irrigated acreage probably will always be small compared to that in dryland and rangeland agriculture because water production from the shallow reservoirs in the Rolling Plains is often limited; however, the water is often of excellent quality for irrigation of agricultural crops and relatively inexpensive to pump. Because of the relatively low pumping costs, there seems to be poten- tial for considerably more irrigation. Potential projects for improving the water quality in the Red River Basin could further improve and increase the potential for irrigation along the rivers in this section of Texas. It is important, therefore, that the response of different crops to irrigation and rainfall in the Rolling Plains be better understood and defined. Efficient use of water is dependent upon an under- standing of the role of soil properties on the available water and nutrient reservoirs of different soils, the permeability of soil to water and plant roots, and the available water-holding capacities of these soils. Kramer, Biddulph, and Nakayama (7) stated that the most important feature of annual crop root systems is their rapid extension into previously unoccupied soil. It is this ontinuous invasion of new soil mass that enables plants to grow for days or weeks without rain or irrigation. The role of soil properties on adaptability and management requirements for different crops in South Texas was E ‘ *Respectively, professor, The Texas Agricultural Experiment Station, Vernon; research engineer, The Texas Agricultural Experiment Station, Munday; and associate professor, The Texas Agricultural Experiment Station, Vernon. recently described by Gerard, Hipp, and Reeves (3). Effective storage and utilization of rainfall in the soil reservoir exploited by plant roots are dependent upon climatic conditions and on soil and crop management practices. Management studies were conducted at differ- ent locations to determine the response of important crops in the Rolling Plains to water. Such studies are essential to a better understanding of the interactions of crops with soils, climate, and management, which is necessary for efficient water use for crop production. CROP WATER REQUIREMENT Water is one of the most important factors influenc- ing crop yields. Water use or evapotranspiration by plants is dependent upon climatic conditions, available soil moisture, and stage of plant growth. If a crop is grown under climatic conditions which create high evaporative demands, the consumptive use of water by the crop is high. High temperatures, high light intensities (solar radiation), low humidity, and high wind speeds create ‘an environment of high evaporative demand or high water use. In contrast, low tempera- tures, low light intensities, high humidity, and low wind speeds create an environment of low evaporative de- mands or water needs. Cotton and grain sorghum are grown under conditions of high evaporative demand during the spring and summer, while small grains are grown under conditions of low evaporative demand during the fall and winter. Thus, water use by crops is influenced by variations in climatic conditions within and between years. Soil conditions such as available soil moisture, soil fertility, and compaction can also influence the water use of crops. Management practices such as tillage can influence soil conditions and thus the water use by crops. Water use by plants is low during the early vegeta- tive growth period but increases rapidly as the vegeta- tive growth or leaf area index (LAI) increases. Leaf area index is the leaf area divided by the land area. Leaf area 3 indices during early stages of plant growth will be close t0 zero, but as plants increase in size and vegetative growth, LAI values can be several times greater than one. Generally water use by crops reaches a maximum during the reproductive stage of plant growth when vegetative growth and LAI are high. At maturity, when the vegetation dies and LAI decreases, the water use by plants decreases and eventually becomes only evapora- tion from the soil. Water use by crops is thus influenced by several factors and their ever-changing interaction with each other. Research over a number of years is needed to obtain an average measure of the influence of these factors and their interaction on water use. The critical stages of plant growth with respect to water are often considered the period just prior to, during, and just after the reproductive stage. Stress or deficiencies during these stages of plant growth can cause substantial yield reductions. In the Rolling Plains water is often deficient and the dominant factor which limits crop production. However, significant rainfall during the critical stages of growth can often cause plants which have been subjected to prolonged stress to produce high yields. This is due to the ability of plants to recover from severe stress and become productive when moisture conditions become favorable. Applying supple- mental irrigations during these critical stages of growth is an efficient way of utilizing water for increased yields. Some plants have the ability to recover from stress or are more drouth tolerant than others. In fact some plants under stress can become almost dormant. For example, stress conditions created by lack of available moisture, high temperature, or both, will sometimes cause cotton to cease fruiting (cutout). However, cotton which has cutout due to stress has often shown the ability, when conditions become favorable, to initiate fruiting again, thereby producing a second crop The precise conditions causing this have not been defined. Water management studies under field conditions which can monitor the roles of different factors and their interactions are needed for better understanding of the response of different crops to rainfall and supplemental irrigation in the Rolling Plains. The roles of these factors and their interactions on water needs and requirements of different crops are complex. However, the findings generated from the studies reported here should con- tribute to the more efficient use of water, rainfall, and supplemental irrigation for crop production in the Rol- ling Plains. COTTON Summary Cotton yields were a linear function of applied water and water use. Three irrigations of about 2. 75 to 3 inches per irrigation during the blooming and fruiting period increased cotton yields from about 300 to 900 pounds per acre. Cotton produced about 5O pounds per inch of water. Results in 1976 and 1977 indicated that about 16 and 2O inches of water were used to produce 4 about 750 and 1,000 pounds of lint cotton per acre, respectively. These studies demonstrated that the criti- cal stage of plant growth is the blooming and fruiting period and that some varieties such as Lockett 77 and Tamcot SP-37 are more efficient than others in the use of water. Methods and Materials A moisture level-variety-fertility experiment was conducted with cotton on the Abilene clay loam soil at Chillicothe in 1976. Because fertility did not influence yields in 1976, the study was changed to a moisture level-variety-chiseling study in 1977. Four moisture levels (Table 1) were randomized in a Latin square. Cotton was planted in 40-inch rows, and each moisture level treatment was 24 rows wide and 75 feet long. Moisture level treatments consisted of none, one, two, and three irrigations with approximately 2. 75 to 3 inches of water applied per irrigation. The moisture level treatments were split to include two varieties, Lockett 77 and Lankart 611. Variety plots were 12 rows wide. In 1976, treatments of 0, 40, and 80 pounds of nitrogen per acre (N/A) were subplots of varieties. Nitrogen treatments were four rows wide. In 1977, varieties were split to include non-chiseled and chiseled treatments. Plots for these treatments were six rows wide. Cotton varieties Lankart 611 and Lockett 77 were planted on May 20, 1976, and June 2, 1977. Chiseled treatments in 1977 consisted of ripping the middle of rows 12 inches deep on Iuly 11. Water was metered onto plots using gated pipe. Soil moisture at different depths to 12 inches below the surface was determined at different times during the growing season using a neutron probe. Soil moisture in the surface 12 inches of soil was determined gravimet- rically. Water use by cotton on different treatments was determined. Blooming as influenced by moisture levels and varieties was determined on selected 10-foot increments of row by counting blooms daily. Plant height, leaf area TABLE 1. DESCRIPTION OF MOISTURE LEVEL-VARIETY EX- PERIMENT CONDUCTED ON ABILENE CLAY LOAM SOIL IN 1976 AND 1977 ' Moisture Available soil level Description moisture at No. of treatmentsab time of irrigation“ irrigations A Non-irrigated 0 B Irrigation at first bloom 25-30% 1 C Irrigation at first bloom plus One irrigation“ 25-30% 2 D Irrigation at first bloom plus 2 irrigations” 25-30% 3 ‘Moisture levels were 24, 40-inch rows wide. Percentages refer to available soil moisture in effective root zone (top 2 feet of soil). bVarieties were 12, 40-inch rows wide. °Intervals between Ist and 2nd and 3rd irrigation were 20 and 15 days, respectively. 9‘ Q indices, and fruit shedding of cotton as influenced by varieties and moisture levels as a function of time were evaluated. Yields, as influenced by treatments, were evaluated by machine harvesting two center rows (140 feet) of each plot in November. Lint percentages were determined, and yields were converted to lint cotton per acre. Fiber qualities as influenced by treatments and varieties were measured. The data were statistically analyzed, and relationships between yield and water applied plus rainfall during blooming and fruiting period and water use were calculated. Results Blooming and Leaf Area Index Data Average blooming of varieties as a function of time in 1976 is shown in Figure 1. Irrigation had little or almost no influence on blooming. However, Lockett 77 had about 10 percent more blooms than Lankart 611. High temperatures for an extended period of time or related high stress caused early cut-off of fruiting in 1976 (Figure 2). Blooming as a function of time, varieties, and irrigation treatments in 1977 on Abilene clay loam soil is represented in Figures 3 and 4. The blooming of non- irrigated Tamcot SP-37 was taken from a 16-row border 200 x é 15o /O <2 / l» é 8 k4.) I00 X —x— LOCKETT 2 -o- LANKART 8 i5 a 5O Z9 O 2O '15 3O 5 l0 l5 2O JULY AUG. Figure 1. Average blooming as a function 0f time by Lankart 611 and Loclcett 77, 1976. — °- TEMPERATURE —X— BLOOMING - IRRIGATED COTTON — O - BLOOMING — NON —lRRlGATED COTTON ‘ O X BLOOMS/TEN FEET w a \. a /1o O .\X 8/15 area adjacent to irrigation treatments (Figure 3). Bloom- ing by non-irrigated Lockett 77 and Tamcot SP-37 was considerably higher than that of Lankart 611. Lockett 77 40o $300 i g . LOCKETT > x LANKART 2200 o SP a7 o o i $ .00 {s W o x n/ _ ° 1o so 1o 3o 1o so JULY AUG sm Figure 3. Influence of varieties when not irrigated 0n accumulative blooming as function of time on Abilene clay loam, 1977. 40o Z300 o LOCKETT o g o LANKART 0/ E i0 z z /° }2oo Z o Q Q 10o ° 1o 3o 1o so 1o 3o JULY AUG sew Figure 4. Influence of three irrigations on accumulative blooming by two varieties on Abilene clay loam, 1977. I00 TEMPERATURE - °F 95 Figure 2. Blooming and temperature data for non-irrigated and irrigated cotton in 1976. a /2o 5 irrigated three times (Figure 4) in 1977 had higher blooming than non-irrigated cotton (Figure 3) and con- siderably higher accumulative blooming than irrigated Lankart 611 (Figure 4). Leaf area indices of non-irrigated Lankart 611, Lockett 77, and Tamcot SP-37 on Abilene clay loam in 1977 are presented in Figure 5. Cotton production by non-irrigated Lockett 77, Lankart 611, and Tamcot SP- 37 averaged 376, 435, and 463 pounds of lint cotton per acre, respectively. In 1977, hot, dry conditions during September and October caused cotton bolls to be more open than usual, resulting in considerable lint loss. Lockett 77 was one of the more susceptible varieties, and estimated lint losses by this variety ranged from 15 to 3O percent. Leaf area indices of Tamcot SP-37, although it yielded very well, were considerably lower than those of the other two varieties in 1977. These results suggest that certain varieties may use water more efficiently than other varieties. Relationships between yield and LAI for Lankart 611 and Lockett 77 for 1976 and 1977 are reported in Figures 6 and 7, respectively. These relationships, in addition to yield data which will be discussed later, indicate that Lockett 77 is more efficient in the use of water than Lankart 611. Yield Data Yields, as influenced by irrigation treatments, varieties, and N in 1976 are reported in Table 2. Results from irrigation treatments, varieties, and chiseling in 1977 are reported in Table 3. In 1976 moisture levels and varieties significantly influenced yields and pounds of cotton produced per inch of water, but nitrogen did not increase cotton yield on the Abilene clay loam. In 1968, Mulkey (9) reported a response to 2O to 4O pounds of N/A by cotton on Miles fine sandy loam soil. Lockett 77 was a more efficient user of water than Lankart 611. Years modified the effects of treatments and varieties (Table 3). This was due to lint losses on the ground by Lockett 77 which was not irrigated and that irrigated once. This was discussed previously. However, (Table 3) Lockett 77 irrigated two and three times during bloom- - LANKART x 3 o LOCKETT 3 0 SP 37 E < P 3 2 < /D O LL 4 L“. o 1 X I o 1o 3o 1o 3o 1o 3o JULY AUG SEPT Figure 5. Influence of varieties when not irrigated on leaf area indices as a function of time on Abilene clay loam, 1977. 6 aoo T Ml 5 ( g e00 ' 40o Q 9- 91 + 221x 5’ a- 0.90 o mo 3n 0 I977 ° 1 2 a 4 s LEAF AREA mosx O Figure 6. Relationship between average leaf area index during bloom- ing and fruiting period and yield of Lockett 77 in Rolling Plains, 1976 and 1977. 8CD 5' i 600 :> i? 1 2 a | 4% Y= 272 + 120x 9 R= 0.79 E >' O 1976 0 1977 200 ° 1 2 3 4 s LEAF AREA INDEX Figure 7. Relationship between average leaf area index during bloom- ing and fruiting period and yield of Lankart 611 in Rolling Plains, 1976 and 1977. a ing and fruiting periods was a more efficient user of water than similarly treated Lankart 611. Relationships between yields of lint cotton per acre on Abilene clay loam soil in 1976 and 1977 and water applied plus rainfall during the blooming and fruiting period and water use are reported in Figures 8 and 9, respectively. Yields ranged from about 300 pounds per acre by dryland cotton to about 9OO pounds per acre by (v cotton irrigated three times during blooming and fruit- ing period. These data emphasize that the critical demand period by cotton as has been reported for South Texas (3) (4) is the blooming and fruiting period. The importance of the need for water during this stage of 1 growth is indicated by the relationship between yield and water use in inches per day during the blooming and TABLE 2. YIELDS OF LINT COTTON AS INFLUENCED BY MOISTURE LEVELS, VARIETIES, AND N ON ABILENE CLAY LOAM SOIL, 1976 g Moisture Lankart 611“ Lockett 77 Overall h‘ t lfvel t a Nitrogen, Nitrogen, average rea men S pounds/acre pounds/acre 0 40 80 Average lb/in 0 40 80 Average lb/in H2O H2O ACYO A 342 355 341 346 45 385 379 365 376 49 361 B 414 439 446 433 40 495 482 530 502 46 468 C 620 571 585 592 46 756 724 713 731 57 662 D 761 y 785 782 776 51 890 927 876 898 59 837 Average 534 538 539 537 46 632 629 616 627 53 “Moisture level treatments and varieties significantly influenced yields at 1% level. TABLE 3. YIELD OF LINT COTTON AS INFLUENCED BY MOISTURE LEVEL, VARIETIES, AND TILLAGE IN 1977 Lint cotton/acre lb/in of H2O 1 Number of Lankart 611 Lockett 77 Lankart 611 Lockett 77 Irrigations Not chiseled Chiseled Not chiseled Chiseled 0 422 448 376 373 47 41 1 499 527 500 532 40 4O 2 689 684 708 762 46 49 3 738 771 794 888 43 48 Average 587 608 595 639 44 45 Treatments significantly influenced yields at the indicated probability levels: Moisture levels —— 0.01. Tillage treatments — 0.05. h Tillage-moisture level and tillage variety interactions -- 0.10. 1000 1000 LU 5 i 800 z f5‘ aoo 9 1 l- 8 5 h 600 t C g t» 60o “- z ° 'Y‘- 23o + so.4x :. U’) g 400 R ' 0'95 5 'Y‘- ,-s1.a + s|.4x A § o 1976 8 4°° R“ 0'91 o 1977 5 0 Q 2 o 1976 200 0 I977 ‘ 200 ° s 1o l5 2o 0 _ WATER APPLIED + RAINFALL- INCHES 5 10 I5 20 I Figure 8. Relationship between water applied plus rainfall during WATER USE-INCHES -'- blooming and fruiting period and cotton yields in the Rolling Plains, Figure 9. Relationship between yield and water use by cotton in the 1976 and 1977. Rolling Plains, 1976 and 1977. 7 fruiting period (Figure 10). The relationship between yields and water applied plus rainfall and water use are linear and highly significant. Obviously water is the dominant factor which determines cotton yields in the Rolling Plains. Production of lint cotton per inch of water averaged 51 pounds (Figure 9). Accumulative potential evapotranspiration and av- erage accumulative water use by cotton irrigated two and three times in 1976 are shown in Figure 11. Before blooming, actual evapotranspiration was low and consid- erably less than potential evapotranspiration. However, after blooming, cotton irrigated two and three times used about 0.9 and 1.05 times potential evapo- transpiration, respectively (Figure 11). Evapotranspira- tion was estimated according to ]ensen’s method (6) and from climatic data obtained from the Texas Agricultural Experiment Station at Munday, Texas. These data emphasize that (a) water is the dominant factor which influences cotton yields, (b) the blooming and fruiting period is the critical stage of plant growth, and (c) some varieties such as Lockett 77 and Tamcot SP- 37 are more efficient users of water than varieties such as Lankart 611. 3C0 U] a: u s 600 Z O l- F" 8 E 40o Y=93.7+288i.2X I R=O.95 U‘! D Z 5 2 O o Figure 10. Relationship between water use in inches/day during the blooming and fruiting period and cotton yields, 1976 and 1977. O O Q-QS 0.10 0.15 0.20 0.25 O-BO MOISTURE USE-INCHES/DAY 20 3 /X I g l5 x '- 1‘; / a. _ - T X’. O H.1- / o/ g 1o X/x / < XX/ /o 5 ,/" ° 5 o s g x / Figure 11. Average accumulative moisture /0 use by cotton irrigated two and three times O and potential evapotranspiration (ETp) as o iii determined from climatic data, 1976. yrs 9/25 7/5 1/15 1/25 a/s 8/15 a/zs c») 5 N. "F GRAIN SORGHUM Summary Sorghum yields were a linear function of applied water and water use. Irrigation with 10 to 14 inches, 3 t0 5 inches per irrigation, during the reproductive stages of plant growth increased yields from about 3,000 to 6,600 pounds per acre. The average production of grain sor- ghum was about 304 pounds per inch of water used. An average of 24 inches of water was required to produce about 6,600 pounds of grains sorghum per acre. Grain sorghum planted two rows per bed produced about 4 percent higher yield than single-row grain sorghum. Methods and Materials Studies to determine the water use requirements and water use efficiency of grain sorghum were con- ducted at the Munday Station during 1976, 1977, and 1978. The soil is a Miles fine sandy loam. The treatments were arranged in a split-plot design with main plots irrigation treatments and subplots row configurations. Planting dates in 1976, 1977, and 1978 were May 10, May 21, and May 24, respectively. Plots were sixteen 40-inch rows wide by 125 feet long. Plots received 125 N/A and 80 pounds of P205 per acre each year. Irrigation water was applied with gated pipe and sprinklers in 1976 and with sprinklers in 1977 and 1978. Water was metered onto all plots. Plant populations were approximately the same regardless of row configuration and moisture level. Treatments were irrigated when varying amounts of soil moisture were depleted and/or by growth stage. Moisture depletions were based on the estimated crop water use. Treatments are described in Tables 4 and 5. Crop water use was estimated using ]ensen’s (6) method of determining potential evapotranspiration. The water use was then estimated by adjusting the potential evapotranspiration with the percentage of ground covered by the crop canopy. Adjustments were also made for rainfall. In 1978 on August 2 and 3, more than 8 inches of rainfall was received. The rainfall figures for the large rain were adjusted by treatments to correct for estimated runoff on August 2 and 3. Soil moisture data were determined by gravimetric sampling of the surface foot and by neutron scattering at TABLE 4. IRRIGATION TREATMENTS FOR GRAIN SORGHUM, 1976, MUN DAY, TEXAS Relative Irrigation Number irrigation level of level description irrigations Wet Irrigated when Va of available soil moisture depleted from top 2 feet; applied 1 inch water with sprinkler 11 Medium (sprinkler) Irrigated when 1/2 of available soil moisture depleted from top 2 feet; applied 1.5 inches water with sprinklers 7 Dry (sprinkler) Irrigated when 2/3 of available soil moisture depleted from top 2 feet; applied 2.0 inches water with sprinklers 5 Medium (furrow) Irrigated when 1/2 of available soil moisture depleted from top 2 feet; applied 2.0 inches with gated pipe 7 Dry (furrow) Irrigated when 2/3 of available soil moisture depleted from top 2 feet; applied 2.5 inches with gated pipe 5 Non-irrigated Received only rainfall during growing season TABLE 5. IRRIGATION TREATMENTS FOR GRAIN SORCI-IUM, 1977 AND I978, MUNDAY, TEXAS Relative I Irrigation Number irrigation level of level description irrigations 1977 1978 Wet Applied 100% of water use when estimated water use was 1.0 inch 14 10 Medium Applied 75% of water use when estimated water use was 2.0 inches Dry A Applied 50% of water use during each of following stages 3 4 a) emergence through vegetative b) vegetative through early boot-bloom c) early boot-bloom through soft dough Very dry Applied 100% of water use at early boot-bloom, not to exceed 3.0 inches 2 Non-irrigated Received only rainfall during growing season 0 0 other depths to 5 feet. Water use estimates using soil moisture depletion are subject to errors due to unac- countable losses due t0 runoff and subsurface drainage or percolation. In most instances there was no runoff from plots in these studies. However, on the above occasion of unusually heavy rainfall on August 2 and 3, it was necessary to make an estimate of runoff. Most of the studies reported in this publication were conducted on the Miles fine sandy loam, Abilene clay loam and related type soils. These soils have compacted on slowly permeable subsoils or hardpans at soil depth of about 10-15 inches Because of the physical properties of these soils, deep percolation was considered negligible. In the Rolling Plains in 1977 (Knox County) Wendt et al. (9) reported that deep percolation was negligible on a Miles loamy fine sand. Row configurations were single and double rows per bed. Double rows were planted 10 inches apart. Both configurations were seeded to produce approximately X6 the same plant population per acre. The desired plant l) density was six plants per foot of bed. Sprinkler irrigated plots had sprinkler spacings of 40 feet in 1976 and 30 feet in 1977 and 1978. Yield and plant growth data were collected from the second, third, and fourth rows from the plot centers. Results Yield data from 1976, 1977, and 1978 are given in Tables 6 and 7. Yields were highly correlated with available water from irrigation and rainfall. Total water use and water use efficiencies from irrigation treatments in 1976, 1977, and 1978 are given in Tables 8, 9, and 10, These findings would suggest that depletion technique respectively‘ would give reliable estimates of soil moisture use on many soils in the Rolling Plains. Errors on water use estimates using depletion technique by crops over the entire season would probably be small. Summer rainfall significantly influenced sorghum yields, especially yields of non-irrigated sorghum in 1976 and 1978. In 1976 (Figure 12) frequent precipitation p" occurred from boot through bloom stages. Dryland yields in 1976 averaged 3,300 pounds per acre (Table 6). In 1977 non-irrigated sorghum produced only 1,600 pounds per acre because less rainfall was received TABLE 6. GRAIN SORGHUM YIELD, 1976, MUNDAY, TEXAS 321231116“ Yleld’ pounds/acre during the reproductive stages of plant growth. The 1978 level Single Double Mean* crop year was characterized by low rainfall until after the Wet 6556 6615 6566a sorghurn’s normal blooming date‘ (Figure 12). However, Medium (Sprinkler) 6664 6247 623065 over.8 inches of rainfall was received on August 2 and 3, Dry (gprinklef) 6010 6315 6180ab causing non-irrigated sorghum to produce a late crop of Medium (furrow) 5989 6496 6152ab 4,200 pounds per acre. Test weights of non-irrigated Dry (furrow) 5816 6350 6032b grain were less in 1978. \ NOR-irrigated 3208 2353b 3292c Yields were a linear function of applied water Mean* 56078. (Figure 13). The contrasting rainfall conditions during the 3 years complicated the relationship shown in Figure 13. Dryland grain sorghum ranged from about 1,600 *Means not followed by the same letter are significantly different at the 5% probability level. TABLE 7. GRAIN SORGHUM YIELD, 1977 AND 1978, MUNDAY, TEXAS _ 1977 Yield 1978 Yield Belatwe pounds/acre pounds/acre irrigation level Single Double Mean* Single Double Mean* Wet 5546 5813 5680a 5584 5842 5713a Medium 5027 5463 5245a 5638 5831 5735a Dry 4427 4382 4405b 5003 5590 52973.1) Very dry 342s 2975 3202c 4356 4644 4500bc Non-irrigated 1715 1417 1566d 3975 4417 4196c M ean* 4029 40 12 _ 491 1d 5265e *Means not followed by the same letter are significantly different at the 5% probability level for each year, respectively. TABLE 8. GRAIN SORGHUM WATER USE AND WATER USE EFFICIENCY, 1976, MUNDAY, TEXAS Irrigation Water use, Water use efficiency, Relative water inches pounds/inch irrigation applied, 5a level inches Single Double Single Double Wet 12.9 23.3 22.8 286 291 Medium (sprinkler) 12.1 22.6 22.2 268 282 Dry (sprinkler) l 10.5 21.5 21.0 280 301 Medium (furrow) 14.0 23.8 24.3 251 268 Dry (furrow) 12.0 22.5 22.8 259 279 ‘ Non-irrigated 0 10.8 11.2 297 303 10 TABLE 9. GRAIN SORGHUM WATER USE FOR 1977 AND 1978, MUNDAY, TEXAS Irrigation Belatil/e wafer Water use, inches irrigation applied, level inches Single Double 1977 Wet 14.9 22.2 22.8 Medium 9. 8 19.1 19.3 Dry 6.0 16.2 16.0 Very dry 3.0 13.6 13.2 Non-irrigated 0 11.1 11.1 1978 Wet 12.1 21.4 21.9 Medium 10.0 21.2 20.9 Dry 8.0 20.9 21.0 Very dry 6.0 17.2 17.0 Non-irrigated 0 14.6 15.5 TABLE 10. GRAIN SORGHUM WATER USE EFFICIENCY FOR 1977 AND 1978, MUNDAY, TEXAS Water use efficiency, pounds/inch Relative irrigation 1977 1978 level Single Double Single Double Wet 250 255 261 267 Medium 263 283 266 279 Dry 274 275 239 266 Very dry 252 222 253 273 Non-irrigated 155 130 272 285 pounds in 1977 to 4,200 pounds per acre in 1978. The average dryland production was about 3,000 pounds per acre. On the average, irrigation increased yields from 3,000 to about 6,600 pounds per acre. The average production per inch of applied water was about 240 pounds per acre (Figure 13). It appears that maximum yields for Rolling Plains climatic conditions are obtained when 10 to 14 inches of supplemental irrigation water are applied during the growing season. Water should be applied during the critical growth periods for maximum effectiveness. Relationship between yield and water use (Figure 14) indicated that despite summer rainfall water is the dominant factor which influences yields. In 1977, a dry year, the relationship between yield and water use indicated that about 5 inches of water was needed before any yield was produced. However, (Tables 8 and 10) the average sorghum produced per inch of water was 281, 237, and 266 pounds in 1976, 1977, and 1978, respec- tively. The lower average production per inch of water in 1977 was due to low production by dryland sorghum. Dryland single and double row sorghum in 1977 pro- duced only 155 and 130 pounds per inch of water, respectively. In 1976 double rows per bed consistently out A yielded single rows per bed with an average increase of 5 percent. In 1977 double rows were best on the more 4 1976 lz-BLOOM a F"! 1 o . l |. I 4 1977 ‘ BLOOM a "2" , RAINFALI. - INCHES oll J1 l __|ILL|-l~| IO 2O 3O 4O 5O 6O 7O 80 9O TOO ITO I20 DAYS AFTER PLANTING Figure 12. The rainfall pattern and amounts with respect to days after planting for sorghum in 1976, 1977 and 1978. The range in time 0f 1/2 bloom stage of variously irrigated sorghum is indicated. aooo § g 6000 } D Z 3 2 , 4000 E’. Ill " 'Y“=1797 + 22o.4x . = 0.93 8 o SINGLE ROW e DOUBLE now o 5 TO T5 2O 25 APPLIED WATER + RAINFALL Figure 13. Relationship between yields of sorghum and applied water plus rainfall during period of 40 to 120 days after planting. heavily irrigated treatments, while in 1978 double rows were again higher yielding by 7 percent. Double rows per bed can give yield increases in some years, but the magnitude of this increase in the Rolling Plains appears to be small. 11 aooo o smote now 6000 o DOUBLE now E 3 \ 8 Z 5 ‘°°° O E A " Y. 303.7X - nan 2000 r = 0.95 o s 1o 1s 2o 2s WATER USE - INCHES Figure 14. Relationship between yields of sorghum and water use. An advantage of double rows per bed over single rows per bed is the shading effect 0n weeds. Observa- tions indicate that mid- t0 late-season weed growth was considerably less 0n plots with double rows per bed. SMALL GRAINS Summary The water use-wheat yield relationship in 1977 showed that about 15 inches of Water is required for production of a 50-bushel crop. Available moisture needed, during April and May, to produce a 40- to 50- bushel per acre crop of wheat is about 0.20 to 0.25 inch per day. Rainfall from September through May which could influence wheat yields averages about 17 and 22 inches at Chillicothe and Iowa Park, respectively. These data emphasize that irrigation often is not needed for the production of 30 to 50 bushels of wheat per acre. Methods and Materials Moisture use by dryland and irrigated wheat follow- ing different cropping and fertility treatments was evalu- ated for 1976, 1977, and 1978 crop years. The dryland and irrigated wheat experiments at Chillicothe were in randomized block design consisting of four replications. Response of wheat in 1976 and 1977 to irrigation was small or insignificant. In 1978 the wheat in that experi- ment was not irrigated. Studies were conducted with wheat and barley at Iowa Park in 1977 and 1978. The roles of furrow and flat irrigation on yield and water use and salinity were compared. Because of timely rains, the crops were not irrigated in 1977. The wheat was planted in December and November in 1976 and 1977, respectively. Because of lack of September and October rainfall the fields were pre-irrigated in October 1977 and wheat and barley planted in November 1977. The small grain crops were irrigated on April 14 and 28, 1978. Moisture use by wheat and barley was evaluated at Chillicothe and Iowa Park for crop years 1977 and 1978. The surface foot of soil was gravimetrically determined. 12 Soil moisture at depths of 1 to 4 feet was determined at 6-inch intervals by neutron scattering technique. Yields of wheat and barley were obtained by harvesting a strip in each plot with a self-propelled combine. Yields were converted to bushels per acre, and yields and test weights as influenced by treatment were measured. The relationship between total moisture use and small grain yields at Chillicothe and Iowa Park was calculated. The estimated relationship between mois- ture use in inches per day during April and May (considered as critical to yield) and yield was determined for wheat. Barley yields were converted to 60 pounds per bushel for these calculations. LAI measurements of wheat obtained with Lambda leaf area meter were made in 1977 and 1978. The relationship between maximum LAI and yields of wheat was calculated. Results Wheat yields in the Rolling Plains are often limited by factors other than moisture. For example, experimen- tal results in 1975-76 and 1976-77 at Chillicothe indi- cated that irrigation did not markedly influence wheat yields (unpublished data). However, the 1977-78 small grain crop year was characterized by a deficient supply of water at planting time in 1977 and in the early spring of 1978. Because moisture was deficient, it was possible to determine the relationship between yield and water use from results obtained at Chillicothe and Iowa Park (Figure 15). Yields were a highly significant linear function of water in the range of 7 to 15 inches. This relationship indicated that about 7 inches of water was required before the small grain produced any crop. Every inch of water above 7 inches produced 6 bushels (Figure 15). The relationship between yields in bushel per acre and moisture use in inches per day by small grain at Chillicothe and Iowa Park in 1976-77 and 1977-78 in April and May was highly significant and linear. The available moisture needed during April and May for a 40- to 50-bushel-per-acre wheat crop is about 0.20 to 0.25 inch per day (Figure 16). The relationship between maximum LAI during this critical stage and wheat yields is also linear and highly significant (Figure 17). About 15 inches of water is required to produce a 50-bushel crop of wheat in the Rolling Plains (Figure 15). Data from the experiment stations at Chillicothe and Iowa Park (Table 11) indicate that average rainfall from September through May which could influence wheat yields was about 17 and 22 inches, respectively. These data emphasize why irrigation is often not needed in the Rolling Plains for production of 30 to 50 bushels of wheat per acre. This is particularly true of the area in the‘ Rolling Plains where more than 15 inches occur during the wheat production season. However, in 1977-78 rainfall for the period from September through May at Chillicothe and Iowa Park averaged only 10.5 inches. At Chillicothe about 3.50 inches of this rainfall occurred J- after May 18. The result was that non-irrigated wheat produced only 10 to 20 bushels per acre in 1977-78. 5O 40 LU 8 U so Q Y=-40.7+6.0X 3 R=0-96 an | a -l H] F 20 IO 0 O 5 IO l5 20 WATER USE-INCHES Figure 15. Relationship between yields of small grain in bushels/acre and water use in 1977-78. 0 so ° 40 30 H] 5 i 0 3 2o ?=—4.4>+220.s Q | R=O-9b Q —l a» >- 10 0 00s 0.10 0.15 0.20 0.25 MOI STUR E USE- lNCHis/DAY Figure 1 6. Relationship between yields of small grain in bushels/acre ‘ and water usein inches/day in 1976-77 and 1977-78. l. Finally, these data suggest why irrigation water is often not needed in the production of small grain in the Rolling Plains. The knowledge that rainfall is often adequate to produce maximum small grain yields in the Wichita Valley could be used t0 reduce soil salinity on soils with so O 40 g; 30 Z U < \ 3 T a 2O 1| a >- 10 ?=-2.43+1s.4 2:096 0 0 1 2 3 4 LEAF AREA INDEX Figure 17. Relationship between yields of wheat in bushels/acre in 1976-77 and 1977-78 and maximum leaf area indices (LAI) during critical growth stages of April and May. TABLE ll. AVERAGE MONTHLY RAINFALL AT EXPERIMENT STATIONS AT CHILLICOTHE, IOWA PARK, AND MUNDAY Chillicothe, Iowa Park, Munday, Months inches“ inchesb inches“ Ianuary 0. 78 1.11 0.95 February 0.91 1.41 1.13 March 1.35 1.89 1.23 April 2. 23 2. 78 2.43 May 3.83 4.50 3.76 ]une 3.09 3.11 2.85 Iuly 2.16 2.43 2.33 August 2. 05 2. 5O 2. 05 September ‘ 2. 99 3. 45 2. 93 October 2. 81 3. 36 2. 52 November 1. l9 1.52 1.29 December 1. 00 1.58 - 1.17 TOTAL 24. 39 29. 64 24. 64 “72-year average b5l-year average °30-year average. moderate to high salinity. Soil salinity created by irrigating with saline water could be reduced by (a) planting salt tolerant barley and (b) following the barley crop with a fallow period until the next spring. The amount of salts leached below the effective root zone by this practice would be influenced by September and October rainfall (Table ll) and the condition or permea- bility of the soil at the time of these rains. 13 POTATOES Summary Potato production was a linear function of applied water and water use. Yields of large potatoes (> 3.0 inches) were a hyperbolic function of water use. Fre- quent irrigations and maintenance of low soil moisture suction were needed to produce large potatoes and high yields. Red LaSoda was more efficient in water use than Norchip, producing more large potatoes and higher yields. Red LaSoda produced 250 hundredweights per acre (cwt/acre) with 17 to 18 inches of water. Methods and Materials Irish potato production in the Texas Rolling Plains is concentrated in the Knox County area with 1,000 to 1,300 acres in production yearly. The majority of the crop is sold as fresh market or chippers. Data were not available on water use requirements of potatoes in the Texas Bolling Plains prior to 1976 (1). A study was set up at the Texas AiSzM Vegetable Research Station in 1976 to determine the water use requirements and the yield and growth characteristics of potatoes grown under different water regimes. Valid data were collected from these studies in 1976 and 1978. The variety Red LaSoda was used in 1976; Red LaSoda and Norchip were used in 1978. Plots were sixteen 40-inch rows wide by 125 feet“ long. Irrigation was with gated pipe or sprinklers in 1976 and with sprinklers only in 1978. The plots were planted with a plot planter to a desired “in row” spacing of 9-10 inches. Seed piece size was approximately 11/2 to 2 ounces each. Final plant spacing was approximately 15 inches in 1976 and 10 inches in 1978. Crop water use was estimated using ]ensen’s (7) method of determining the potential evapotranspiration. The potential evapotranspiration was adjusted using the percentage of ground covered by the crop canopy and the rainfall between irrigations. Depending upon treat- ments (Tables 12 and 13), potatoes were irrigated on the basis of soil moisture conditions or estimated evapotrans- piration. Plots received 100 to 120 pounds P205 and 150 pounds N/A each year. All plots were treated with disulfoton (DiSyston) at 3 pounds active ingredient per acre. Yield data were collected from two 33-foot row sections in each plot. TABLE 12. IRRIGATION TREATMENTS FOR POTATOES, 1976, MUNDAY, TEXAS Relative Irrigation Number irrigation level of level description irrigations Very wet Irrigated when tensiometer readings at 6 and 12 inches averaged .15 s ) atmosphere suction; applied .75 inches water with sprinklers 12 Wet Irrigated when 33% of available soil moisture was depleted from 2- foot root zone; applied 1.00 inch water with sprinklers 6 Medium (sprinkler) Irrigated when 50% of available soil moisture was depleted from 2- foot root zone; applied 1.50 inches water with sprinklers 4 Medium (furrow) Irrigated when 50% of available soil moisture depleted from 2-foot root zone; applied 2.00 inches with gated pipe 4 Dry (sprinkler) Irrigated when 67% of available soil moisture depleted from 2-foot root zone; applied 2.00 inches with sprinklers 3 Dry (furrow) Irrigated when 67% available soil moisture depleted from 2-foot root zone; applied 2.50 inches with gated pipe 3 Non-irrigated Received only rainfall during growing season TABLE 13. IRRIGATION TREATMENTS FOR‘ POTATOES, 1978, MUNDAY, TEXAS Relative Irrigation Number irrigation level of level description irrigations Very wet Irrigated when tensiometer readings at 6 and 12 inches average .15 atmosphere suction; applied .75 inch water with sprinklers 16 Wet Irrigated every 7 days; applied 100% of estimated evapotranspiration 7 Medium Irrigated every 7 days; applied 75% of estimated evapotranspiration Dry Irrigated every 10-11 days; applied 75% of estimated evapotranspira- tion 6 Very dry Irrigated every 10-11 days; applied 50% of estimated evapotranspira- Non-irrigated Received only rainfall during growing season 14 tion 6 0 Soil moisture readings were obtained by gravimet- ric sampling of the surface foot and by neutron scattering at other depths to 5 feet. Irrigation treatments varied between years; howev- er, two treatments were identical each year allowing comparison of treatments over years. Results Potatoes, variety Red LaSoda in 1976 and 1978 and Norchip in 1978, were grown under varying irrigation schedules to determine their water use requirements in the Texas Rolling Plains. Yields and water use efficiency of Red LaSoda and Norchip in 1976 and 1978 are shown in Tables 14, 15, and 16. Yield was linearly correlated with applied water regardless of year or variety (Figures 1s and 19). The yield increases from added irrigation water are the result of an increased percentage of tubers in the “greater than 3.0 inch diameter” category (Tables 17 and 18). As treatments became drier, the majority of weight shifted to the smaller size categories. The Red LaSodas produced under dryland in 1978 had almost 75 percent of the yield in the “less than 1% inch diameter” category, while only 15 percent of the wettest treatment was less than 17/3 inch diameter (Table 19). The dramatic effect of a slight change in water availability and use on potato yields is shown in Figure 20. The yields of tubers over 3.0 inches in diameter are hyperbolic functions of water use. Short delays in applying an irrigation can thus result in rather large yield decreases, especially late in the growing season when water requirements are high. Similar effects would TABLE 14. POTATO YIELD OF RED LASODA, WATER USE, AND WATER USE EFFICIENCY, MUNDAY, TEXAS, 1976 Irrigation Total Water Relative Yield Yield, total water water use irrigation #1 potatoes, marketable, applied, use, efliciencyf‘ level cwt/acrel cwt/acre inches inchesz cwt/inch Very wet 228.8c 244.90 8.7 14.6 16.8a Wet 185.3bc 195.0bc 6. 4 12.9 15.1%! Medium (sprinkler) 163.5b 173.5b 6.0 11.5 15. 1a Medium (furrow) 173.6b 181.Ib 7.0 13.6 133a Dry (sprinkler) 171.9b 180.7b 6.3 11.3 16. 1a Dry (furrow) 147.8b 156.9b 6.7 13.4 11.7a Non-irrigated 83. 4a 94. 3a 0 7. 1 13. 3a R1 Includes only those potatoes greater than 17/8 inches in diameter. “Includes irrigation water applied, rainfall, used stored soil moisture, and drainage. aCalculated using total marketable yield and total water use. Values followed by the same letter do not differ significantly at the 5% level. TABLE 15. POTATO VARIETY RED LASODA YIELD, WATER USE, AND WATER USE EFFICIENCY, MUNDAY, TEXAS, 1978 Irrigation Total Water Relative Yield Yield, total water water use irrigation #1 potatoes, marketable, applied, use, efficiency, level cwt/acre cwt/acre inches inches cwt/inch Very Wet 247.2a 2795a 13.8 ‘ 18.2 15.4 Wet 156.9b 196.5b 10.7 15.3 12.8 Medium 136.9bc 1851b 8. 2 13.0 14.2 Dry 89.7cd 1388c 7.8 13.1 10.6 Very dry 71.4d 124.10 5.6 10.8 11.5 Non-irrigated 8.7e 34.6d 0 6.0 5.8 A TABLE 16. POTATO VARIETY NORCHIP, YIELD, WATER USE, AND WATER USE EFFICIENCY, MUNDAY, TEXAS, 1978 Irrigation Total Water Relative Yield Yield, total water water use ‘jrigation #1 potatoes, marketable, applied, use, efficiency, .evel cwt/acre cwt/acre inches inches cwt/inch Very wet 143.9a 198.5a 13.8 17.6 11.3 Wet 81.5b 158.9b 10.7 15.1 10.5 Medium 79.4b 141.1bc 8.2 12.5 11.3 Dry 50.5bc 114.6cd 7.8 12.7 9.0 Very dry 32.9bc 94.4d 5.6 10.5 9.0 Non-irrigated 7.8c 43.2e 0 6.0 14.4 15 25o LASODA 20° o 197s 0 1978 =—s0.s +17.7x\ r I 0.92 < } 150 3 U | O —J a >- 100 0 NQRCHIP Y =-40.7 +13.4X 5o r= 0.9a ° s 10 1s 20 WATER USE-- INCHES Figure 18. Relationship between yield in hundredweights/acre of N0. 1 Red La Soda and Norchip and water use. result from a poor job of applying or distributing irrigation water. Stress or climatic conditions (years) can cause marked differences in the response to water (Figure 20). The variety Red LaSoda produced more large potatoes in 1976 with less water than in 1978. The variety Norchip (Figure 20) is much less elticient in producing large potatoes than the Red LaSoda, explaining why Red LaSoda uses water more ePficiently than the variety Norchip. A comparison of the tuber production by Red LaSoda and Norchip in Tables 17 and 18 shows that the total numbers of tubers of Red LaSoda and Norchip under the dilTerent treatments I. 20° - LASODA -197b ?= 13.1617)‘ R = 0.91 0 LASODA- 197s Y =0.O3e'49X 150 a = 0.96 LU E U fi 5 10o 0 NORCHlP-1978 I \ o Y - 0.007s ~47)‘ g R - 0.93 >- s0 r/ 0 5 1O 15 2O WATER USE - INCHES Figure 20. Relationship between yields in hundredweights/acre of large potatoes (B 3.0” diameter) and water use. 16 LASODA 25o o 197s *. . 197s Y=_(>4.5 + wax g r= 0.82 e NQRCHIP 200 Y=-72.1+11.1X r= 0.93 fiiso l- 3 U | D d ; 100 so n 0 5 1O 15 2O WATER USE — INCHES Figure 19. Relation between total yields in hundredweights/acre 0f Red LaSoda and Norchip and water use. were almost identical, but the LaSoda had considerably more 3.0 inch-diameter tubers than Norchip. The water use efficiency of the Red LaSoda is * considerably higher than that of Norchip even though total water use was slightly higher for Red LaSoda in 1978. The greater water use efficiency is due to the higher yields produced by Red LaSoda. A comparison of furrow and sprinkler irrigation treatments for Red LaSoda in 1976 indicated no signifi- cant yield or water use eiliciency differences between methods of applications. Even so, it is worthy to note DE PTH - FEET V‘ §> 9° 1° —- 9 9 o o O o o w o P o —- .—- N N u- m ow o u: ROOT DENSITY - INCHES/CUBIC INCH l Figure 21. Bed cross section showing rooting density by frequently irrigated Red La Soda potatoes, 1976. P F f TABLE 17. NUMBER OF RED LASODA TUBERS HARVESTED, MUNDAY, TEXAS, 1978 Number of tubers Relative Number of tubers greater than 17/8" Number of tubers Total number irrigation greater than 3.0" but less than less than 17/8" of tubers level per acre 3.0" per acre per acre per acre Very wet 29,502 42, 174 23,562 95,238 Wet 12,870 41,184 27,324 81,378 Medium 9,702 37,026 32,076 78,804 Dry 3, 960 29, 502 39, 402 72, 864 Very dry 2,772 25,334 36,828 64,944 Non-irrigated 0 3, 762 20, 790 24 , 552 TABLE 18. NUMBER OF NORCHIP TUBERS HARVESTED, MUNDAY, TEXAS, 1978 Number of tubers Relative Number of tubers greater than 17/8" Number of tubers Total number irrigation greater than 3.0" but less than less than 1%" of tubers level per acre 3.0" per acre per acre per acre Very wet 5,940 47,718 36,234 89,892 Wet 2,376 33,264 59,202 94,842 Medium 2,772 32,274 48,312 83,358 Dry 396 23, 364 46, 728 70, 488 Very dry 198 16,236 52,074 68,508 Non-irrigated 0 3,960 31,482 35,442 TABLE 19. PERCENTAGE OF TUBER WEIGHT BY GRADE SIZE, MUNDAY, TEXAS, 1978 ‘ % by weight BelatlYe % by weight greater than % by weight lfflgatlofl greater than 17/8" but less than level 3.0" less than 3.0" 1%" Very wet LaSoda 46.6 41.9 15,5 Wet 27.2 52.6 20.2 Medium 21.5 52.4 25,1 Dry 11.9 52.7 35,4 Very dry 8.2 49.4 42,4 N on-irrigated 0. 8 24. 3 74, 9 Very wet Norchip 10.8 61.7 27,5 Wet 5.4 46.6 48.0 Medium 6.9 . 49.4 43.7 Dry 1.0 48.0 56,0 Very dry 0.8 84.0 65.2 Non-irrigated 0,0 1&1 81,9 I that the treatments watered with sprinklers had a higher r water use efficiency than their treatment counterparts which were watered with gated pipe. This is generally expected. The 1978 Red LaSoda data (Table l5) indicate that ‘irrigation intervals of greater than 7 days can cause ,¢@ significant yield reduction. However, decreasing the water applied by 25 percent and keeping a 7-day irrigation interval only decreased yields slightly. This shows that the timing and the amount of water applied are very critical in potato production. Potatoes on this soil have a shallow root system (Figure 21). This is somewhat typical of some vegetable crops. However, the rooting density shown in Figure 21 may have been created in part by a compacted layer at the 10- to 15-inch soil depth. This means potatoes exploited a shallow reservoir on this soil. For high yields the shallow reservoir required frequent replenishment by irrigation or rainfall. 17 l" "£4 i TEXAS A&M UNIVERSITY llllllll I ll Illllll Illlll Illlllllll ALI-IIBEIB Ecllfil? SWEET CORN m? Summary Sweet corn yields were a linear function of applied 12000 water and water use in 1977. However, rainfall was adequate to produce maximum yields in 1978. In the eastern part of the Rolling Plains it is expected that May and ]une rainfall often will minimize the effect of I°°°° irrigation on vegetable crops with short growing seasons such as sweet corn. a Methods and Materials é 8°°° A drip irrigation system was used to study the g response of sweet corn to different levels of drip ‘I: irrigation in 1977 and 1978. Levels of drip irrigation Q 6000 which were based on different levels of potential evapo- > transpiration are indicated in Table 20. Potential evapo- transpiration in inches was estimated as 0.6 to 0.7 Class 4000 q, 3928 + mox A Weather Bureau pan. Pan evaporation was measured R= 0.97 at the Texas Agricultural Experiment Station at Iowa Park. Drip irrigation levels were applied between bed and furrow with Submatic emitters spaced 2 feet apart. 2°°° Plots were four rows wide and 5O feet in length; each treatment was replicated three times. The amounts of water applied to different treatments were automatically . -. controlled with pressure regulators and timers which o 2 4 6 8 controlled cut-off solenoids. Moisture use by sweet corn on different treatments was determined by neutron scattering techniques and gravimetric sampling. Salinity of soil was determined initially and after harvesting of sweet corn in 1977 and 1978. Yield of sweet corn was evaluated by harvesting and counting ears. The relation- ships between yield and water applied and water use were determined in 1977. In 1977 and 1978, attempts were made to grow crops of squash and sweet pepper, respectively. Problems with germination of squash and early growth of peppers were encountered. Results Yields of sweet corn in 1977 (Table 20) were excellent, and a linear function of applied water and water use as shown in Figures 22 and 23. An attempt to grow a second crop in 1977 (squash) was unsuccessful because the latter did not germinate. Dry weather in late spring and summer resulted in detrimental salt accumulations in this soil (Yahola fine sandy loam). The level of salinity was high enough to prevent germination on all treatments, including the dry treatments. Actual- ly, the sweet corn on all plots, including the dry TABLE 20. YIELDS AND WATER USE DATA BY SWEET CORN AS INFLUENCED BY DRIP IRRIGATION, 1977 Treatment-level of potential 7 Yield, Water use, Ears/in evapotranspiration ears/acre inches of H20 0* 4,300 8.8 490 50%* 6,600 11.3 580 100%* 10,400 11.9 875 150%* 12,500 13.6 920 I Sign 0.01 *All treatments were irrigated after planting in 1977. 18 WATER APPLIED — INCHES Figure 22. Relationship between yield of sweet corn in ears/acre and applied water in 1977. i S iF- -n:m + I74IX a- 0.94 new - EARS/ACRE 3 5 IO I5 WATER USE- INCHES Figure 23. Relationship between water use and sweet corn yields under drip irrigation treatments, 1977. treatment, had to be irrigated at planting time. The average soil salinity by depth prior to initiation of the experiment and after irrigation in 1977 and salinity conditions at different depths and treatments after sweet corn in 1977 are shown in Table 21. In 1978 (Table 22) timely rains minimized the response of sweet corn to irrigation. Variability between 1* A plots was greater in 1978 than 1977. In 1978 an attempt t0 grow a second crop of peppers was unsuccessful. Soil salinity data in Table 23 indicate that the salinity levels .were not high enough prior to the sweet corn crop in TABLE 21. AVERAGE SOIL SALINITY AT DIFFERENT DEPTHS PRIOR TO AND AFTER IRRIGATION AND GROWTH OF CORN CROP, 1977 Soil Salinity level of drip irrigation (PE)" Depth Prior to 0 50% 100% 150% inches irrigation ----------- -— mmhos/cmb ----------- -- 0-6 1.8 6.5 6.1 11.5 7.9 6-12 2.1 4.0 4.6 5.7 5.1 12-24 2.0 3.1 5.3 5.2 4.0 24-36 1.9 3.5 4.3 4.7 4.1 36-48 2.6 - - - - 48-60 3.3 - - - - “Estimated level of potential evapotranspiration. bConductivity of solution extracted from saturated soil paste. TABLE 22. YIELDS AND WATER USE DATA BY SWEET CORN AS INFLUENCED BY DRIP IRRIGATION, 1978 Treatment level of potential Yield Water use, Ears/in evapotranspiration ears/acre’ inches of H20 0 ' 8800 7.3 1200 50% 10500 11.1 950 100% 9700 13.1 740 150% 11350 16.2 690 “Yields were not significantly influenced by treatments in 1978. TABLE 23. SOIL SALINITY AS INFLUENCED BY DRIP IRRIGA- TION TREATMENT, 1978 - Level of potential evapotranspiration Depth, 0% 50% 100% 150% inches mmhos/cm* 4/11 8/11 4/11 8/11 4/11 8/11 4/11 8/11 0-6 1.8 1.1 2.5 2.6 2.7 2.6 2.0 1.8 6-12 1.7 1.7 2.0 4.3 2.0 5.2 2.0 3.0 12-24 2.5 3.3 2.7 5.6 2.5 * 4.5 3.2 3.7 24-36 2.4 2.8 2.7 4.7 2.7 2.7 3.4 4.2 36-48 2.6 2.4 3.2 3.9 2.9 3.4 3.2 3.6 48-60 2.7 3.0 3.0 3.4 2.9 3.0 3.1 3.9 *Conductivity of solution extracted from saturated soil paste. April and just after planting of the pepper crop in August to cause the crop failure. Residual herbicide from the sweet corn crop was believed responsible for loss of the pepper crop. Shape of row, amount of water applied at each irrigation, and subsurface drip irrigation rather than surface drip irrigation might reduce salinity of the soil surface. Further studies are needed to determine the roles of these management practices on yields and soil productivity. This method of irrigation would probably be excellent for vegetable and pecan production. How- ever, use of drip irrigation with the salty water from Lake Kemp will require that a leaching fraction be applied to keep the soil salinity in the effective root zone below hazardous levels. LITERATURE CITED 1. Bordovsky, D. G., C. I. Gerard and B. D. Kingston. 1977. Water use of potatoes in the Texas Rolling Plains. PR: 3433C 14 p. 2. Clark, L. E., C. I. Gerard and C. G. Obenhaus. 1979. Growth and fruiting response of short season cotton cultivars under stress. Agron. Abst. p100. 3. Gerard, C. I., B. W. Hipp and S. A. Reeves. 1977. Yield, growth, management requirements of selected crops as influenced by soil properties. Tex. Agri. Expt. Sta. B-1172. 23p. 4. Gerard, C. I. and L. N. Namken. 1966. Influence of soil texture and rainfall on response of cotton to moisture regime. Agron. Iournal 58:39-42. 5. Gerard, C. I. and L. E. Clark. 1978. Effects of water management and soil physical properties on cotton production in the Rolling Plains. TAES MP - 1382C. 26p. 6. Iensen, M. E., I. L. Wright and B. I. Pratt. 1971. Estimating soil moisture depletion from climate, crop and soil data. Trans. ASAE . 14: 954-959. 7. Kramer, P. I., O. Biddulph and F. S. Nakayama. 1967. Water absorption, conduction and transpiration. In Agron. Monogr. 11: 320-329pp. Irrigation of Agricultural Lands (Edited by R. M. Hagan and others). 8. Mulkey, I. R. 1968p Agronomic research in Texas Rolling Plains. TAES. Consolidated PR. 2616-2626. p.13-15. 9. Wendt, C. W., A. B. Onken, O. C. Wilke, R. Hargrove, W. Bausch and L. Barner. 1977. Effect of irrigation systems on the water requirements of sweet corn. Soil Sci. Amer. Proc. 41:785- 788. 19 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 ex- clusion of other products that also may be suitable. All programs and information of The Texas Agricultural Experiment Station are available without regard to race, ethnic origin, religion, sex, and age. The Texas Agricultural Experiment Station, Neville P. Clarke, Director, College Station, Texas 3M-9-80