CALIFORNIA AGRICULTURAL EXPERIMENT STATION Bulletin 701 July, 1947 SEED-BED PREPARATION AND CULTIVATION FOR SUGAR BEETS L. D. DONEEN ~— — Although California growers usually winter-plow sugar- beet seed beds from 8 to 12 inches deep, 4-year tests show that such deep plowing has little effect on growth, yield, sugar content, purity, or on penetration of irrigation water. Plowing is chiefly use- ful in burying weed seeds, in hastening trash decay and in breaking up hard plow pan. Shallow cultivation is useful in killing weed growth. THE COLLEGE OF AGRICULTURE UNIVERSITY OF CALIFORNIA • BERKELEY SEED-BED PREPARATION AND CULTIVATION FOR SUGAR BEETS L D. DONEEN 1 In seed-bed preparation, during the past few decades, there has been a tend- ency to plow the soil deeply and reduce it to a fine state. No doubt, the development of heavy farm machinery and powerful tractors has helped to make this practice extensive. In sugar-beet culture, it is considered essential to have the plow penetrate at least 8 inches— and frequently more. Many sugar-beet producers in California plow 12 inches deep in the late fall or early winter. Then, before planting, they till the land several times with such im- plements as a disk, a harrow (spike, spring- tooth, or both), a roller, a clod smasher, and a float, until the seed bed is finely pulverized and very smooth. The investigations herein reported were conducted to determine whether or not this type of seed bed is necessary for sugar beets, and are a continuation of previous studies on cultivation (Veihmeyer and Hendrickson, 1943). 2 Numerous studies on seed-bed preparation have been conducted in dry-land areas and for cereal crops; much of this work has been concerned with the depth of plowing rather than the elimination of the moldboard plow. Hume (1940) reviews the literature and gives the results he obtained with various depths of plowing. In one of his experiments, disking alone did not reduce the yield of wheat, oats, or legumes, but did reduce the yield of corn. Russell and Keen (1941) compared plowing 8 inches deep with grubbing (cultivating) 4 inches deep, and obtained an increase in yield with wheat, barley, and mangolds from plow- ing. From much of their work on this subject, however, they conclude: "That the primary function of ploughing is weed control, and that it is only advis- able to omit ploughing either if the land is already fairly clean or if the crop will be hoed very early in its development." In the interest of preventing soil erosion, seed-bed preparation for row crops has been studied by Duley and Russel (1941) and by Browning, Norton, and Shedd (1943). According to the former investigators, when the residue remains on the surface and the soil is subtilled (cultivated), the yield of corn is greater than when the residue is plowed under; but according to the latter workers, the reverse is true. The literature reveals few reports on seed-bed preparation or cultivation trials on irrigated lands. It has been shown (Veihmeyer, 1927) that cultivation in the absence of weeds does not in itself save water, because the movement of water by capillarity is too slow to be a factor. Veihmeyer and \ssoc iate Irrigation Agronomist in the Experiment Station. 2 See "Literature Cited" at the end of this bulletin for complete data on citations, which are referred to in the text by author and date. SEED BED PREPARATION AND CULTIVATION FOR SUGAR BEETS 3 Hendrickson (1943) have discussed the principles involved in the cultivation of orchards on irrigated lands. In the following experiments with seed-bed preparation for sugar beets, minimum cultivation for the growing crop was practiced to control weeds. Many investigators over a period of years have carried on and reported results of different frequencies and depths of cultivation with various row crops. A general review would indicate that the main benefit of cultivation is weed control. After thinning of the crop, a cultivation trial was conducted to deter- mine how cultivation affects the production of beets. EXPERIMENTAL PROCEDURE Preparation of the Seed Bed. The following experiments, conducted for a period of four years, consisted of two treatments: (1) the soil was not plowed, but was stirred sufficiently with a spring-tooth harrow or disk to kill all growing weeds before the crop was planted (this operation involved only the surface 2 to 4 inches); (2) the soil was plowed 12 inches deep in the late fall or winter. Before seeding of the sugar beets, the soil was disked, leveled or floated, har- Table 1 PLOTS USED IN EXPERIMENT ON PLOWING FOR SEED-BED PREPARATION FOR SUGAR BEETS Size of Number of Time of plowing Year Location Type of soil plot, feet replications per treatment Previous crop 1934 Davis Yolo fine sandy loam 20x71 8 Tomatoes January 1935 Davis Yolo loam 20x70 16 Oat hayt November Alvarado,* Laguna clay 27 x 1300 8 Tomatoes January Alameda Co. loam 1936 Davis Yolo loam 20x80 8 Oat hay§ January Woodlandf Yolo clay loam 27 x 1136 5 Beans November Hamilton City,* Sacramento 53x600 8 Corn January Glenn Co. silty clay loam 1937 Davis Yolo sandy loam 25x73 11 Barley§ February Land farmed by the Holly Sugar Corporation ; all cultural operations conducted by this company. t Land under control of Spreckels Sugar Company; all cultural operations conducted through this company. t Land not plowed for two years before planting of sugar beets. § Land not plowed for three years before planting of sugar beets. rowed, and rolled to form a rather firm and finely pulverized seed bed. The precaution was taken to utilize land that had not been in sugar-beet produc- tion the previous year, because lifting of the beets during harvest will deeply stir the soil. In all these investigations, the soil had not been plowed for at least one year, and one or more crops had been grown since the last plowing and the beginning of the experiment. 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CO CO CN iH iH . •JS £ o o •4 o -a §1 to « 2 to "3 "a CO V '£ S > § 1 V P P < P^W p bo as H -^ to CO o > eS CO CO CO CO 9 as OS OS OS w* rH tH iH iH SEED BED PREPARATION AND CULTIVATION FOR SUGAR BEETS 5 The sugar beets were planted the latter part of January or in February, according to weather conditions. Except for keeping cultivations to a mini- mum for weed control, the cultural operations after planting were the same as those practiced in the area adjoining the experimental plots. Location of the Experiments. Table 1 gives the location of the various experiments, the size of the plots and the number of times each treatment was repeated (replications), and the crop grown before the experiment was estab- lished. Every other plot was plowed 12 inches deep to form a fine but rather firm seed bed; alternate plots were not plowed. In the discussion, the first will be known as the "plowed" plots. The alternate plots, in which the seed beds were prepared only with a spring-tooth harrow or disk, will be termed "unplowed." Determination of Yields and Sugar Content. When the plots were harvested, the two outside rows and the plants at the ends of the rows were excluded from the yields; these served as guards or buffers between plots and the irri- gation ditch. All other rows were harvested, and the sugar beets were counted and weighed. The sugar content on a fresh weight basis was obtained by direct polarization. The purity was determined by the use of the Abbe refracto- meter (Sidney, 1928) for obtaining the percentage of total solids. The gross yield of sugar per acre was secured by multiplying the yield per acre by the per cent sugar in the beets. All results are reported on an acre basis. RESULTS OF SEED-BED PREPARATION EXPERIMENTS Yield of Beets and Sugar. Table 2 gives the results of a four-year study for the two treatments; namely, the plots that were plowed before seeding and those that were unplowed. The yields show wide variations between location and season. In general, the difference between the two treatments is small. The plots at Davis, in 1934, gave a difference of 2.8 tons per acre in support of plowing. This figure, however, is not significant (at the 5 per cent level). Since the plots at Alvarado, in 1935, were planted late in the spring, a few areas had a thin stand. In addition, some areas in this field were infested with nematodes. Because of these conditions the yields were secured, not on the plots as a whole, but from definitely measured areas within the plots where the stand was uniform and where no damage from nematodes was visible. The difference in mean yield for the treatments, 0.44 ton of sugar beets, is not statistically significant. The variation in the number of beets per acre is small, regardless of treatment, the number of beets left at the time of thinning being the determining factor. The difference in per cent sugar is slight be- tween the plowed and unplowed treatments. The average for the two treat- ments shows 0.33 per cent higher sugar in the beets for the unplowed than for the plowed plots and is not significant. The purity of the beets is about the same for both treatments. The average gross sugar per acre is essentially the same whether the land was plowed or not plowed before seeding of the crop. >3s '^^Ssl 'ft ft M \*ft£& • ^ I if. \ SEED-BED PREPARATION AND CULTIVATION FOR SUGAR BEETS 7 Soil Condition. Figure 1 illustrates the condition of the soil for the 1934 crop at Davis before the soil was prepared for the seed bed. Figure 2 shows the soil plowed to 12 inches for the deeply tilled plots. Figure 3 indicates the dis- tribution of the plots, with alternate ones plowed 12 inches deep and others disked about 2 inches and floated. When there were conditions favorable for rapid drying of the soil, such as a north wind accompanied by low humidity, it was observed throughout these experiments that the surface soil dried earlier in the plowed plots, whereas in the areas not plowed it showed higher moisture for several days. This condition is illustrated in figure 4, a photograph taken at the time the beet seedlings emerged from the soil. The dark areas indi- cate the unplowed plots; the light ones are the plowed plots, with drier soil at the surface. In areas where crusting of the soil is a problem, the moist surface of the shallow-tilled soil provided a period several days longer for the emer- gence of the seedling before crusting occurred. On the unplowed soil, the crust- ing was usually less severe than on the finely pulverized plowed soils. Germination of Beet Seed. On the plots at Davis in 1934 and 1935, the seed- lings were counted before thinning of the beets. In 1934, this count was ob- Fig. 1.— Condition of the soil before the experiment on seed-bed preparation for sugar beets in 1934 at Davis. The previous crop was tomatoes. ^ m Fig. 2. —Soil plowed 12 inches deep for the deeply tilled plots in the seed-bed preparation experiment, 1934, at Davis. Fig. 3.— A partial view of the plowed and unplowed plots in the seed-bed prep- * oration experiment, 1934. The rough land indicates the plowed plots, later cultivated to finely pulverized seed bed. The light areas indicate the un- plowed plots, which have been disked about 2 inches deep, floated, and made ready for seeding the crop. tFig. 4.— The drying of the soil on the plowed and unplowed plots. The light areas are the plowed plots and indicate dry surface soil. The dark areas are the unplowed plots, which were wetter on the surface. CALIFORNIA EXPERIMENT STATION BULLETIN 701 tained for the length of a meter (39.37 inches) per row for 12 rows in every plot; and in 1935, a meter-length count was obtained for 8 rows in every plot. The following tabulation gives the results of the average number of sugar-beet seedlings per meter before thinning for two seed-bed treatments at Davis. Year 1934* 1935f Plowed . 44.0 . . 22.9 . Unplowed . . 45.7 . . 28.7 * Not significant at the 5 per cent level. t Significant at the 1 per cent level. Even though the plowed land had been harrowed and rolled, there was a tendency to deeper planting because the soil was so loose. This looseness was noticeable even when the plowing was done before the fall and winter rains. In the unplowed areas, the seed ball was placed on a firm and compact soil, Table 3 WEIGHTS IN POUNDS PER CUBIC FOOT AND PORE SPACE OF PLOWED AND UNPLOWED SOIL IN SUGAR-BEET EXPERIMENTS, 1936* Soil depth, Wt., lbs. per cu. ft. Pore space, per cent Wt., lbs. per cu. ft. Pore space, per cent inches Plowed Unplowed Plowed Unplowed Plowed Unplowed Plowed Unplowed Woodland February 6 June 19 0-6 6-12 12-18 65.5 71.8 87.4 85.5 91.7 86.1 60.4 56.6 47.2 48.3 44.5 47.9 89.9 94.8 91.1 87.4 96.1 88.6 45.7 42.6 44.9 47.2 41.9 46.4 Hamilton City April 9 May 27 0-6 6-12 12-18 80.5 78.6 86.1 78.0 80.5 84.9 51.3 52.5 47.9 52.8 51.3 48.7 80.5 86.1 84.9 80.5 84.2 85.5 51.3 47.9 48.7 51.3 49.1 48.3 * Soil plowed at Woodland, November, 1935; at Hamilton City, January, 1936. which may have given better germination. Moreover, the time for seedling emergence on the unplowed land was 2 to 4 days less than on the plowed. Only the 1935 plots showed a highly significant difference of germination for the unplowed plots. Growth of Beet Roots Above the Soil Surface. In 1935 a study was made of the development of sugar-beet roots on plowed and unplowed soil. The question arose whether a firm soil, as in the unplowed plots, would cause more of the beet root to grow above ground than in plots plowed 12 inches deep. A row in the center of each plot was taken for this investigation, and the dis- tance from the soil surface to the first leaf scar was measured for every sugar beet in that row. The following tabulation gives the results of the average SEED BED PREPARATION AND CULTIVATION FOR SUGAR BEETS 9 number of sugar beets, and the average distance in inches between the soil surface and the first leaf scar for the two seed-bed treatments. Plowed Number of beets 926 Average distance in inches from soil surface . to first leaf scar 0.35 Unplowed 948 0.39 The difference between treatments is small, only 0.04 inch, which is insig- nificant. These results indicate that the fleshy part of the beet root was not forced to grow above the unstirred portion of the soil. Apparent Specific Gravity of the Soil. The results just given led to the investigation of apparent specific gravities (or densities as weight per cubic foot) of the soil of these two treatments, with results which are reported in table 3 as weight in pounds per cubic foot and per cent pore space. In 1936, Table 4 AVERAGE RATE OF INFILTRATION OF IRRIGATION WATER IN CENTIMETERS FOR A 10-MINUTE PERIOD FOR INDIVIDUAL IRRIGATIONS ON SEED-BED EXPERIMENTS Date of irrigation Plowed Unplowed 1935* June 3 . . June 18 . June 19 . May 28 . . 0.901 0.613 0.359 1.486 0.719 0.766 0.903 0.614 0.455 1936| 1.198 June 24 . July 18.. 0.698 0.789 * Average of 8 plots for each treatment. t Average of 4 plots for each treatment. data were taken from three locations in each of the Woodland plots in the treatment, and at Hamilton City a determination was also made from each plot in the treatment. Weight per cubic foot was obtained at Woodland, February 6, just after the planting of the crop, and was less on the plowed soil for the surface 12 inches. Since the 12-to-18 inch depth of soil was not disturbed by plowing, the slight difference between treatments denotes the natural variation that occurs in soil. By June 19, when the fleshy parts of the roots were enlarging rapidly, the differences in soil weights were very slight between the two treatments. At Hamilton City on April 9, when the roots began to enlarge, and later in the season, on May 27, when the roots were growing rapidly, there were no essential differences in weight per cubic foot of soil between the plowed and the unplowed plots. The pore space is in an inverse relation to the weight of a cubic foot of soil. At the time when the fleshy part of the root was enlarging, the volume weight of the soil 10 CALIFORNIA EXPERIMENT STATION BULLETIN 701 was about the same whether the land was plowed or not plowed in prepara- tion of the seed bed. Water Infiltration. The rate of water infiltration after irrigation of the beets for the two seed-bed preparations was investigated at Davis in 1935 and 1936. The individual plots were rapidly covered with water; and, as it penetrated the soil, readings were made every 10 minutes. Table 4 gives the average rate of water infiltration for each irrigation. On June 3, 1935, the 3 \ P/owed Not P/owed \ V^ Jrr/yaf/on June J frr/paf/'on June /S II ~I?V~ — --J "--»«-——- — ^^ Irr/jaf/on June /9/ i i i i i i t i t i i i i i /O £0 JO 40 50 70 SO 90 /00 //O /£0 /JO M/nutes /40 /50 /60 /70 /SO Fig. 5.— Rate of water infiltration in sugar beets for 10-minute intervals in the seed-bed preparation experiment, 1935. second irrigation was applied for the season. The application on June 19 was on wet soil from the previous day's trial. The only marked difference that occurred was on June 19, when the unplowed plots gave a slightly higher rate of infiltration. The rate of infiltration is plotted at 10-minute intervals in figure 5. In 1936 the infiltration rates were secured from all the irrigations. The first irrigation showed a higher rate for the plowed plots; for the other two, the rate was about the same for the two seed-bed treatments. Judging from the data, plowing will not increase the rate of water infiltra- tion except, possibly, during the first irrigation. Shape of Beet Roots. The shape of the beet roots from the two seed-bed treatments was studied for the first three years of the experiment. Two hun- dred beets were selected at random from the plots in each treatment and were Fig. 6.— The average shape of the sugar beet for 3 trials from the seed-bed preparation experiment. I 5 3 12 CALIFORNIA EXPERIMENT STATION BULLETIN 701 cut lengthwise through the center. With the cut side placed against paper, the outline of each beet was traced. These outlines were systematically measured in the laboratory by taking the total length and 1 1 diameters equally spaced from the lower leaf scar to the tap root 1 inch in diameter. The measurements for the same relative positions were averaged for the total 200 beets, and from these average length and diameter measurements a representative beet was drawn as illustrated in figure 6. The beets harvested at Davis in 1936 were practically identical in shape, regardless of seed-bed treatment. The same was true of the beets grown at Hamilton City that year. Beets from the Woodland plots in 1936 were practically identical; the differences were less than are shown in the figure. From these results it is clear that the shape of the beet is not measurably affected, whether or not the soil is plowed before planting. The individual beet roots weighed from 2 ounces to 12 pounds. Beets of a certain size may differ from one another in shape, although the investigator might mask this difference by averaging all sizes together. In 1934 the beets at Davis were classified by length into 5 sizes. These results (fig. 7) indicate that regardless of size of the beet, the shape is not influenced by seed-bed treatment. Depth of Rooting. According to the experimental evidence, sugar beets root deeply and secure water and nutrients from the lower depths of soil (Doneen, 1942). This fact is illustrated in figure 8, which shows the soil- moisture conditions at Hamilton City, 1936. The extraction of soil moisture indicates the depths of rooting. The flattening of the curve late in the season indicates that all the moisture readily available (Veihmeyer, 1927) to the plant has been used to a depth of 6 feet. Similarly, since nitrate nitrogen has been utilized to this depth (Doneen, 1942), sugar beets may be regarded as deeply rooted. Since they extract all the readily available moisture and nitrate ni- trogen to a depth of at least 6 feet in the deep, fertile soils of the sugar-beet- producing areas of California, cultivation or even plowing cannot be expected to influence greatly the growth and yield of beets which draw their nutrients and water requirements from 6 feet of soil. CULTIVATION AFTER GERMINATION Cultivation Trials. In 1937, investigations were carried on to study the effect of spring cultivation on the yield and sugar content of the sugar beet. In the experiment conducted at the University Farm at Davis, the plowed plots were cultivated 4 times during the spring, whereas the unplowed plots received 2 cultivations for weed control. A similar trial was conducted on plowed land near Woodland on Yolo clay loam, cultivated the same number of times as at Davis (4 versus 2 cultivations). The results (table 5) indicate that Fig. 7.— The average shape of a sugar beet at Davis, classified according to its size, for the seed-bed preparation experiment, 1934: class 1, beets from 4 to 6 inches in length; class 2,6 to 8 inches; class 3,8 to 10 inches; class 4, 10 to 12 inches; and class 5, 12 inches and longer. |^ /st. foot ZZ i^.^v. 3rd. foot /9 ^ _ •5 n L-v \ *" > ^— _ _ \, x. .L.i :_. • — y 20 /5 /O 5 zo J5 10 5 ZO /5 (0 5 O ZO s zz /9 /6 /S /O o o 6 ' tfr foot Legend Sp/7 Mflt'ffure ___ o ""™ C ^ • 1 — i 1 i i i ii N/trote A/zfroyen 1 1 1 May Z7 4 // /8 Z5 Jane /o /7 Ja/y JO /z Jay / Sept SEED BED PREPARATION AND CULTIVATION FOR SUGAR BEETS 15 cultivation is necessary only for weed control. The number of such cultiva- tions will vary with the foulness of the land and the frequency of the spring rains. Weedy land with much spring rain may require 3 to 4 cultivations, whereas land relatively free from weeds may require, in the absence of rain, 1 or, at the most, 2 cultivations for control of weed growth. Table 5 YIELDS AND SUGAR CONTENTS OF SUGAR BEETS GROWN ON LAND RECEIVING CULTIVATION ONLY TO CONTROL WEEDS AND ON LAND WITH MORE FREQUENT CULTIVATIONS Minimum cultivation Frequent practice Location Number cultiva- tions Tons per acre Per cent sugar Pounds fc sugar per acre Number cultiva- tions Tons per acre Per cent sugar Pounds sugar per acre Davis Woodland. 2 2 24.6 8.5 13.8 19.5 6,790 3,318 4 4 25.5 7.8 13.3 20.1 6,782 3,138 Average. . 2 16.55 16.65 5,054 4 16.65 16.7 4,960 DISCUSSION The results show that deep plowing for sugar-beet production is not neces- sary under the conditions of these experiments. All the land used in these experiments had been previously cropped and was relatively free of weed or grass sod and of coarse or fibrous plant residue. This material, however, if not well decayed by spring, will interfere with cultivation by collecting on the cultivator knives and shovels, and by uprooting the young beet seedling. Also trashy material on the surface would interfere in thinning, particularly if mechanical thinning is practiced. Such material as large weeds, woody trash, or unburned high stubble from grain or corn should be plowed under, rather than incorporated into the surface soil, since the latter procedure would lead to interference with cultural operations. If the land is disked after the first fall rains, and again worked lightly before being planted, much of the trashy material will decay by spring and will there- fore not interfere with cultivation and thinning. If the weeds mature and infest the surface soil with their seed, plowing may be practical for burying the seed deeply and thus eliminating some of the weed growth the next year. Under certain other conditions, deep tillage or plowing may be necessary. An example is a plow pan in old grain fields. Such plow pans interfere with the penetration of irrigation water and sometimes cause rotting of the beet root. They should be broken by deep tillage or deeper plowing. The work Fig. 8.— Depth of rooting of the sugar-beets at Hamilton City, 1936, as indi- cated by the use of soil moisture and nitrate nitrogen to a depth of 6 feet. 16 CALIFORNIA EXPERIMENT STATION BULLETIN 701 should be done while the soil is relatively dry; otherwise a deeper plow sole may form with this practice. Even though these exceptions exist, plowing could profitably be eliminated on much of the sugar-beet land in California. SUMMARY A comparison of plowed and unplowed soil for seed-bed preparation for sugar beets was made with seven trials over a period of four years. The results show that nothing is gained by plowing the soil, provided shallow cultivation kills all the weed growth. In this study, the plowed and unplowed plots proved to be substantially the same in the yield, sugar content, purity, and number of beets per acre; the volume weight and pore space of the soil; penetration rates of the irrigation water; and the shape of the beet. The experimental results show that cultivation is necessary only for weed control. ACKNOWLEDGMENT The author wishes to acknowledge the many helpful suggestions offered, and continued interest shown by Professor F. J. Veihmeyer during the course of these experiments. LITERATURE CITED Browning, G. M., R. A. Norton, and C. K. Shedd 1943. Mulch culture in relation to soil and water conservation and corn yields in Iowa. Soil Sci. Soc. Amer. Proc. 8: 424-31. Doneen, L. D. 1942. Some soil -moisture conditions in relation to growth and nutrition of the sugar beet plant. Amer. Soc. Sugar Beet Tech. Proc. 3: 54-62. Duley, F. L., and J. C. Russel 1941. Crop residues for protecting row-crop land against runoff and erosion. Soil Sci. Soc. Amer. Proc. 6: 484-87. Hume, A. N. 1940. Depth of plowing and crop yields. South Dakota Agr. Exp. Sta. Bui. 344: 1-16. Russell, E. W., and B. A. Keen 1941. Studies in soil cultivation. X. The results of a six-year cultivation experiment. Jour. Agr. Sci. 31: 326-47. Sidney, F. Sherwood 1928. Use of the refractometer in the analysis of individual sugar beets. Jour. Agr. Res. 36: 41-52. Veihmeyer, F. J. 1927. Some factors affecting the irrigation requirements of deciduous orchards. Hilgardia 2(6): 125-291. (Out of print.) Veihmeyer, F. J., and A. H. Hendrickson 1943. Essentials of irrigation and cultivation of orchards. California Agr. Ext. Cir. 50: 1-23. Revised edition. 12m-8,'47(A3586)