J B-I I02 August 1970 Summcizry Six years’ research in the Trans-Pecos area with “variable row spacing” (VRS), new irrigated cotton row-spacing patterns, is reported. The new system consists of alternate close and wide spaced rows, with narrow irrigation furrows between the close row spacings only. The wide spac- ings serve as dry beds for tractor wheel traffic. The purpose of using the new patterns is to reduce the costs of producing cotton through conservation of water and by other management savings. Studies on both level and sloping irrigation systems are reported. The results show conclusively that yields on regular row spacings currently are b-eing obtained with considerably greater production input than is required by the crop with its present yield potential. The new spacings offer the possibility for substantial cost reductions through application of less water per acre, more efficient utilization of this water by the crop, better weed control with less cultivation, and earlier maturity. Other potential advantages include elimination of the need for thinning stands, reductions in soil compaction and less damage from Verticillium wilt (V. albo atrum) where this disease is a problem. Contents Summary .......................................................................... ._ 2 Introduction .................................................................... -. 3 Description of Irrigated Areas ..................................... .. 3 Quality of Irrigation l/Vaters ....................................... .. 3 Nature and Scope of the Row Spacing Studies ...... .. 4 Evaluation of the 26—54-inch VRS System ................. .- 5 Level/Irrigation ......................................................... .. 5 Yields and Varieties ........................................... .. 6 Water Use and Evaporation ............................. .. 6 Weed Control and Cultivation ....................... .- 7 Plant Growth and Plant Population ............... .. 7 Earliness of Maturity ......................................... .- 7 Water Use Efficiency ......................................... .. 7 Other Management Considerations ............... -. 8 Sloping Irrigation ..................................................... -. 9 Yields, Water and Plant Growth ..................... ..l0 Some varieties were found to be better ada to the new planting arrangement than others. differences appeared to be more genetic than l» nomic. Desirable characteristics were short com growth and ability to set kfruit under higher- normal soil moisture stress. i‘ The VRS system constitutes a less radical parture from regular row spacings than narrow 1 or broadcast type plantings; it permits use (iii u. equipment already on farms; and it requires 1 minor alterations inirrigation and other manage 1 practices. The chief obstacle to adoption of the new remains the inability of commercial spindle mach to harvest open-boll cottons on these new spa’ patterns. Stripping of storm resistant strains sh be no problem. a One other disadvantage is the possibility gradual salt accumulation due to inadequate leac where saline waters are applied and rainfall is Certainly more precise soil and water manag would be required if the new VRS patterns adopted. =a Water Management and Maturity ............. ._i Control of Water and Weeds ....................... Boll Characteristics and Fiber Properties ...... Lint Percent ..................................................... _.; Boll Weight ..................................................... __ Fiber Length ................................................... __ Fiber Strength and Fineness __________________________ j, Evaluation of Other VRS Systems ___________________________ _ Sloping Irrigation __________________________________ ____________ __ Yields _________________________________________________________________ __ Earliness ____________________________________________________________ __ ~ Level Irrigation ____________________________________________________ l Important Factors To Be Considered __________________ __ Dangers of Salt Accumulation _________________________________ __; Acknowledgment _________________________________________________________ __ " Literature Cited __________________________________________________________ iERlCAN COTTON FARMER is currently engaged '» struggle for survival. He is beset by con- } ing costs of labor, equipment, repairs, chem- i other supplies 0n the one hand, and by the {jof synthetic fibers 0n the other. Thus, his , costs continue to increase without corre- i increases in returns for fiber and seed i; on growers in the irrigated areas of far West d New Mexico are particularly hard hit. with all the high costs of full irrigation, ‘ unable to increase yields per acre due pri- I climatic limitations—high altitude and a ' growing season. Their only apparent re- w the immediate future lies in their ability v reduce production costs. Some researchers inced this can only be accomplished, to the ecessary, by radical changes in management 0 I the exception of various skip-row patterns, A these areas has traditionally been grown in _ spaced 38 or 40-inch rows. These regular y {I118 are desirable for ease o-f mechanization I some serious economic disadvantages. They themselves easily to either water conserva- fbweed control. Water use is excessive, and 'on losses are high because the entire soil g.- wetted with each irrigation. Consequently, ‘ency of water use by the crop is low in these ’ regions where water is costly and supplies L ed. In addition, adequate weed co-ntrol in '1 is difficult even with frequent cultivation Ff se of herbicides. With normal seasonal appli- i.» 3 to 6 acre feet of water per acre, the crop f es excessive vegetative growth at the expense ‘t g which, in turn, delays maturity and lowers lity of late-maturing bolls. urgent need to reduce production costs and rve water has stimulated renewed studies of , cotton row-spacing patterns (4, 5, 6). A new 1 variable row spacing (VRS), was initiated at i as A8cM University Agricultural Research at El Paso in 1964 and has been intensively for the past 5 years. This publication reports _ ely, associate agronomist, Texas A8cM University Agri- YResearch Station at El Paso; former agronomist in exas A8cM University Agricultural Research Station at Cstant professor in charge, Texas A&M Universty Agri- ‘Research Station at Pecos; and research coordinator, i 0s area, Texas A8cM Universtiy Agricultural Research E1 Paso. riable Row Spacing of Irrigated Cotton D. E. LONGENECKER, E. L. THAxToN, ]R., j. j. HEFNER AND P. J. LYERLY these studies in detail. Many aspects of plant, soil and water management are involved. These Variable Row Spacing systems show considerable promise for reducing both costs of production and water require- ments. However, the various management factors involved should be thoroughly understood and care- fully evaluated before these VRS systems are recom- mended or adopted. Such things as irrigation system design, water quality, soil permeability, cotton varieties to be grown, or the contemplated harvest method may or may not be compatible with these new row patterns. DESCRIPTION OF IRRIGATED AREAS The Trans-Pecos region is the only part of Texas where cotton is grown under full irrigation. Annual rainfall is too slight and uncertain to be of any real value for crop production. Irrigated agriculture, therefore, is limited to those areas where either surface or ground waters are available for irrigation. The major area using surface waters is the Rio Grande Valley above and below El Paso. These soils are alluvial and calcareous but without caliche horizons in the profile. They vary texturally from loamy sands to clays with predominantly mo-ntmorillonite colloid. Irrigation system designs are level, with comp-ara- tively short runs. By far the larger portion of the Trans-Pecos irrigated acreage consists of upland soils, also calcare- ous, with definite horizons of caliche (carbonates or gypsum) within the profile. The major areas of these soils are at Pecos, Ft. Stockton, Coyanosa, Van Horn and Dell City. These soils are mainly silt loams or clay loams with illitic colloid. Nearly all farming is on sloping irrigation systems, surface irrigated by pump waters. Irrigation runs are long, and efficiency of water use is poor on the more permeable soils. QUALITY OF IRRIGATION WATERS The row spacing studies reported herein were conducted at three locations—the Pecos and Dell City pump irrigated areas and the El Paso Valley. Quality of waters varies considerably within each area depend- ing upon many factors. In the El Paso Valley, most of the app-lied water in average years is from the Rio Grande River. This is supplemented with pump water when river supplies are deficient. Table 1 gives results of many water analyses made during the last l5 years, reported as high, low and average values for each of the three areas. High total salt content is the most adverse quality factor of these waters. Sodium percentages of the El Paso and Pecos waters 3 TABLE 1. THE RIO GRANDE RIVER AT EL PASO QUALITY OF WATERS USED FOR IRRIGATION IN THE PECOS AND DELL CITY PUMP AREAS, IN THE EL PASO VALLEY AND Milliequivalents per liter Total 1 salt, Sodium Calcium Magnesium Potassium Chloride Sulfate Bicarbonate S ppm N0 Ca Mg K Cl S04 HCOa PECOS PUMP AREA High 5533 53.0 20.3 27.3 3.1 33.5 29.3 2.1 Low 2175 20.0 7.9 12.7 0.6 21.4 15.6 1.8 4 Average‘ 2793 21.8 9.3 16.1 0.7 28.5 16.7 1.9 4 DELL CITY PUMP AREA High 6365 57.6 16.9 36.4 0.8 65.6 4.5 y * Low 904 3.5 8.2 9.5 0.3 7.0 12.1 3.2 f 1 Average2 1462 61 9.9 11.9 0.3 9 8 3.0 3.9 * s EL PASO VALLEY—PUMP WATER High 4807 35.0 23.1 11.2 2.1 56.9 11.6 2.8 Low 970 9.4 2.4 3.5 0.4 8.8 5.2 3.1 ‘ Average3 1756 15.8 6.2 5.3 0.6 17.6 5.8 3.8 ‘.- EL PASO VALLEY——RIO GRANDE RIVER WATER River 1368 11.8 6.9 2.4 0.1 6.6 11.3 3.3 5/5/1956 River 1110 10.6 6.7 2.4 0.2 6.3 9.6 3.2 ‘f 6/8/1962 ‘Average of 96 wells. zAverage of 32 wells. 3Average of 65 wells. are high but not dangerously so. Waters of the Dell City area are comparatively high in calcium and magnesium with low sodium percentages. NATURE AND SCOPE OF THE ROW SPACING STUDIES A basic assumption underlying the row spacing studies was that the cotton plant, being naturally drouth tolerant, should be able to produce satisfactory yields with only a portion of the water usually applied if this water could be applied in a more efficient manner. A single field study was conducted at the El Paso station in 1964 to test this assumption. The test included five variables-row spacing, irrigation rates, irrigation frequencies, cotton varieties and plant populations. A semi-randomized block arrangement was utilized with the two row spacings and two varieties split for two frequencies of summer water application. The varieties were seeded in four- row plots, with the center two harvested fo-r yield and other data. Alternate 40-foot plots across the 700-foot field length were thinned in late spring to three plants per foot. The intervening plots were left unthinned with six to twelve plants per foot. Summer irrigation frequencies were every l2 and 18 days during June, July and August. A normal irrigation on level soils is about 4 inches per acre, and this amount, measured by sparling meter and calibrated siphons, was applied to the 40-inch single row beds (Figure l, number l) at each irrigation. Only half this amount (2 inches per irriga- tion) was applied to the alternate 26—54-inch row 4 -----u-o" - - - - - - - - --~ro"---- --_--4¢>"----- if ----v'------ ' ----3:r_--_- “-311”- ' ___33_'____ -_3°|l_-- I --- 3011-.- --J.6'-'-- ” ".151- .5. Q9. %gp".. Figure 1. Row spacing patterns studied in field tests from) to 1969: (1) Regular 40-inch single rows; (2) regular double rows; (3), (4), (5), (6) various spacing patterns c0 with (1) or (2) on level or sloping systems. re l, number 5). The reason was three- luce the amount of water applied, to water to the narrow furrows for more ization and to avoid wetting the wide Otter weed control. This procedure con- i spacings with irrigation rates, but this ble if test size was t0 be held within _ proportions. ent tests in following years utilized similar g designs but were enlarged to include tr cotton varieties. Irrigation rates and lso were adjusted for differences in soil ; system design (sloping or level systems). g» . rate tests comparing the alternate 26-54- ing with regular 38 or 40-inch rows were 1964 to 1967, 5 at the El Paso Station, fty and 1 at Pecos. The Dell City and .1 re on sloping systems with longer irriga- (ll spacings also were investigated. From 1,, four tests at the Pecos station comp-aring _t row spacings were completed. The _~ with single tests at the El Paso station 1969 comparing an alternate 30—50-inch with regular 38-inch rows. ‘erential summer irrigation rates did not ant irrigations. All tests received uni- Lt irrigations of 12 inches per acre (level 12-15 inches per acre (sloping systems). sparling meters and gated pipe or cali- l RELATIVE TO FIVE FIELD TESTS COMPARING TWO v I ater at the two experiment stations was brated sipho-ns. At off-station sites (Dell City) co- operators closely approximated the specified irrigation rates and frequencies. Soil fertility was not included as a variable in any of the tests. Test areas were uniformly fertilized with nitrogen either prior to planting or as side dressing after emergence. Phos- phate was applied to some tests where needed. In the various tests, data were obtained on many or all of the following: yields, earliness, water use efficiency, boll characteristics and fiber properties. In addition, observations were made of plant growth, fruiting characteristics, weed control and disease inci- dence. A 3-year detailed soil sampling study of salt movement and distribution in the root. zone as related to water quality and irrigatio-n rates and frequencies was completed also and is reported in a separate publi- cation Due to the inability of spindle machines to harvest certain of these row spacings, most of the harvesting was done by hand in October and at the end of the season. EVALUATION OF THE 26-54-INCH VRS SYSTEM Level Irrigation From 1964 through 1967, five field tests compar- ing an alternate 26—54-inch row spacing with regular 38 or 40-inch rows (Figure l, numbers l or 2) on level systems were completed, all at the El Paso Research Station. The 1964 test design has been described. One test in 1965, two in 1966 and one in 1967 com- pleted this series. Three of these, 1965 through 1967, were on the same sandy loam soil, with irrigation ROW SPACINGS ON LEVEL IRRIGATION SYSTEMS IN THE EL PASO VALLEY, Summer Summer Total irrigation irrigation water rates frequencies applied Planting Plant Cotton Row date population varieties spacings Inches/acre Days Inches/acre‘ 4/23 Three per foot Acala 1517D 26—-54" 2 12 26.0 and Stoneville 7A 18 20.0 unthinned 40" 4 12 46.0 18 34.0 4/20 Same Acala 1517D 26-54" 1.5 10 25.5 Stoneville 7A 2O 21.5 Blightmaster 38" 3 10 39.0 2O 30.5 4/18 Same Acala 1517C 26-54" 1.5 14 26.0 Stoneville 7A 21 23.5 Hopicala 38" 3 14 35.5 D.P.L. 5540 21 30.5 4/18 Same Same as 26-54" 1.5 14 26.0 , above 21 22.0 38" 3 14 36.0 21 28.0 4/21 Same Acala 1517c 26-54" 1.5 14 24.2 Stoneville 7A 21 20.8 Hopicala 38" 3 14 38.0 Calif. SJ-l 21 31.0 1h preplant irrigation plus effective rainfall. treatments relocated in identical positions to facilitate long term soil salinity studies. Table 2 contains pertinent agronomic data relative to these tests. Yields and Varieties Average lint yields from the five tests are reported in Table 3. In some tests and under some conditions, most of the varieties yielded as well on the 26—54-inch row spacing as on regular 38 or 40-inch rows. Yields of Stoneville 7A were consistently higher with variable row spacing, whereasthose of Acala 1517 (Ci or D) were more variable but yielded, on the average, about the same on both sp-acings. A statistically significant difference in yield among varieties, evident in all tests, appeared to be strongly related to varietal growth and fruiting characteristics. Varieties with shorter, more compact growth habits appeared to be better suited to the 26—54-inch spacing than did taller varieties with more rangy growth habits. Varieties having short compact growth associated with the ability to set and hold a heavy TABLE 3. PASO VALLEY, 1964-1967 AVERAGE LINT YIELDS (POUNDS PER ACRE) IN FIVE TESTS COMPARING TWO ROW SPACINGS ON LEVEL IRRIGATION IN fruit load (Stoneville 7A), appeared especially i‘ to the new sp-acing arrangement. Other desi characteristics were good drouth tolerance an ability to set ample fruit under conditions of h plant populations. Of the four Acalas studied, cala appeared best suited to the variable row The other three seemed to require more wat optimum growth and yields and were more sen to factors which could affect fruiting and shed (shading, higher plant popiilations, over or u irrigation and so forth.) - ‘LY- Water Use and Evaporation i‘ These comparable yields were obtained 0 VRS system with considerable reduction in‘. amounts of water applied (Table 2). The a? appears t0 lie in more efficient utilization of by the crop as well as reduction in losses to eva tion. By midsummer (Figure 2) the narrow 2 water furrows were almost completely shaded. August and September (Figure 2) shading of Regular 38 or 48" rows 26-54" variable row spacing Seven irrigations Five irrigations i i. Seven irrigations Five irrigations Cotton Variety V ' variety Thin No thin Thin No thin average Thin No thin Thin No thin a I _ I964——CLAY LOAM sort i. I Acala I5I7D I028 II45 II53 I269 II49 952 II80 I IOI4 I207 "I Stoneville 7A I228 I327 I3I2 I326 I298 I266 I394 I392 I632 Average II28 I236 I232 I297 II09 I287 I203 I4I9 LSD between individual means: .O5—88 lb; .OI—-I I2 lb 211 I965—SANDY LOAM SOlLl Acala I5I7D 929 977 65I 75I 827 735 8I6 826 9I3 T} Stoneville 7A II7I II53 858 925 I027 I052 II28 996 II4I P} Blightmaster 976 I 067 70I 848 898 894 864 700 8I 2 Average I025 I066 737 84I 894 936 84I 955 — LSD between individual means: .O5—I04 lb; .OI——I32 lb I966——SANDY LOAM SOlLl Acala I5I7C 697 677 824 753 738 622 66I 677 670 c‘ Stoneville 7A 965 960 880 987 948 930 924 I060 956 Hopicala 7I7 7I5 88I 8I5 782 740 7I4 8I2 872 Deltapine 5540 898 909 923 86I 898 762 765 956 88I Average 8I9 8I5 877 854 765 766 876 845 A1 LSD between individual means: .05—89 lb; .OI—I I7 lb St H I966-—CLAY LOAM SOIL D: Acala I5I7C - 776 906 840 I 957 870 776 963 950 I024 l Stoneville 7A 927 965’ I080 I092 IOI 6 987 I062 I I09 I I07 Hopicala 782 890 983 II00 939 III5 II3I III4 II63 Deltapine 5540 687 805 994 II23 902 943 I023 I046 I027 A1 Average 793 89I 974 I 068 955 I 045 I055 I 080 St LSD between individual means; .O5—I20 lb; .OI——I58 lb H1 D I967—-SANDY LOAM SOIL‘ A: Acala I5I7C 892 747 738 67I 762 7I9 757 590 547 Stoneville 7A 802 833 850 947 858 II08 II29 9I2 847 Hopicala 798 7I3 936 954 850 699 745 609 63I Calif. SJ-I 686 593 7I8 72I 679 8I8 807 68I 64I Average 794 72I 8I0 823 836 859 698 666 LSD between individual means: ‘These tests relocated in identical positions (1965-67) for soil salinity study. 6 .O5—-IO8 lb; .OI—-I43 lb |>o;Q? I. eas was complete whereas considerable areas soil in the regular row spacings were still o the sun. Although no evaporation measure- made, shading undoubtedly reduced evapo- s substantially. her factor probably contributing to the ields with less water on the VRS arrangement I distribution within the soil profile. With _- inch rows and normal irrigations, the entire 'le was re-wetted with each summer irrigation. VRS pattern only a portion o-f the profile, the major root area, was re-wetted. This fied by soil cores taken for salt distribution ntrol and Cultivation j ' control ‘was less of a problem in the 26-54- spacings because the tops of the wide ‘beds ‘ dry during the summer and because the ;as were more completely shaded. In some iof preemergence herbicides effectively con- a ual weeds in the VRS plots, and occasional '7, ow sweeps was the only cultivation required. “ulation in the centers of the 54-inch beds i: weed control. Periodic cultivations were control weeds in regular spaced rows, even _bicides had been applied. "wth and Plant Population g} sistent characteristic of all varieties grown _" S pattern was shorter plant height as com- fIFLthOE grown on regular 38 or 40-inch rows. ‘be attributed to application of less summer ' irrigation and greater crowding of plants iction of root systems. Results show that to 1 , 1966-1967 (THREE TESTS) obtain comparable yields of most varieties where growth is restricted, higher plant populations are desirable. In most tests, unthinned VRS plots yielded as much or more cotton than plots thinned to three plants per foo-t of row. Elimination of the need for thinning stands would be an additional cost saving. Earliness of Maturity Closely related to the shorter growth and reduced rates of water application on the VRS spacings were significant improvements in earliness of maturity. Earliness is highly desirable in areas with limited growing seasons so long as reductions in yields or fiber quality can be avoided. Table 4 gives earliness data from three tests, based on the percentage of the seed cotton harvested at the first of two pickings. In all three tests, percent first picking on the 26—54-inch row spacings was increased substantially over that on the regular row spacings. Increases occurred with all varieties. Average increase attribut- able to variable row spacing was about 15 percent in each test. This considerable improvement in earliness should have economic significance since it was obtained without reductions in yield for the most part. Earlier maturity is also usually associated with improvements in overall fiber quality. This will be discussed in a later section. Water Use Efficiency Water use efficiency in irrigated cotton produc- tion is defined as the pounds of lint produced per inch of applied water plus effective rainfall. Table 5 reports efficiency data obtained from the 1966 and 1967 tests. I RLINESS (PERCENT FIRST HARVEST) OF FOUR COTTON VARIETIES IN TWO ROW SPACINGS ON LEVEL IRRIGATION IN THE EL =7 Regular 38" rows 26-54" variable row spacing Seven irrigations Five irrigations Seven irrigations Five irrigations Thin No thin Thin No thin Thin No thin Thin No thin I966—SANDY LOAM SOIL 44.9 42.4 44.3 33.2 43.0 44.6 54.5 52.0 36.2 33.9 34.6 32.6 53.0 55.9 52.7 47.9 ‘_ 37.3 34.7 42.6 41.6 60.6 64.2 59.9 56.3 40 25.0 26.3 32.6 24.2 55.0 54.6 42.3 33.3 l 35.3 34.4 33.5 34.1 52.9 54.3 52.3 43.7 1966—CLAY LOAM $011 44.2 44.4 56.2 53.0 43.5 43.0 52.2 53.6 33.3 33.2 50.5 49.9 53.0 51.6 74.4 69.0 ,- 41.7 39.6 53.6 56.3 56.7 51.2 63.3 65.2 40 15.9 13.4 30.4 29.1 39.1 34.7 43.7 45.3 35.0 4 - 35.1 47.7 43.4 49.3 46.4 53.5 53.4 i i967--SANDY LOAM SOIL 59.1 47.3 61.3 64.5 71.3 63.3 66.0 76.3 44.2 50.0 53.7 59.2 53.6 59.0 69.4 30.9 56.6 59.0 67.3 66.5 31.0 73 2 79.0 32.5 43.9 41.9 52.3 53.0 66.3 66.9 63.3 70.9 52.2 49.7 59.0 62.0 69.3 63.1 69.5 77.3 The VRS system gave more efficient use of water than regular 38-inch rows in each of the three tests. Greater increases in efficiency occurred with less fre- quent irrigation. Some possible reasons for this- narrow furrows, shading of wetted areas, partial profile wetting-have already been mentioned. A further explanation may lie in a possible “skip-row effect”1 in yields in the new system. The wide beds permitted ample light o-n one side of each row all summer. The effect o~f this light on fruiting resulted in most of the fruit being produced on short lateral ‘branches o-n the bed side of the plants. Skipping rows to obtain this effect is common practice in the Mississippi delta and the Southwest. With the VRS system, any such effect was obtained without skipping any rows. ‘Increased yields of outside rows attributed to additional light, root space and so forth. Qther Management Considerations A continuing difficulty with the narrow 26-i furrows on level systems was control of irriga water. Greater care was needed in water applica to insure that the reduced rates were applied as formly as possible without overflowing the furr Careful p-re-leveling of fields was essential for effic water distribution. This problem prompted f studies of 3()—5O-incl1 row spacings, reported he A previously overloo-ked advantage was the i bility of eliminating soil compaction due to tra wheels in moist furrows. With the VRS system, u wide front axles, all wheels could be kept 0-n the A dry beds. This was done in most tests; however, paction effects were not investigated. This as merits study and consideration as does the fact s. t Figure 2. Cotton planted " ternate 26—-54-lnch row s, pattern at various stag growth; (left, top to bottom) and July; (right, top to a August and September. absence of weeds despite 1 mum cultivation. ' ould get into the fields sooner following s. At times this can be very important. g er advantage stemmed from the finding er plant populations were both desirable "ntial for best yields in the VRS system. ions on incidence and severity of V erticilliizvn A, e two tests on fine-textured soil showed that tion was consistently higher and more severe plots than on unthinned plots. Thicker ive been recognized for many years as a good trol measure. The necessity for thinning on row spacings has largely prevented growers ing advantage of this knowledge. With parieties, stands as thick as 10-12 plants per foot were satisfactory on the VRS spacing. These higher plant populations could definitely aid in con- trol of Verticillium wilt on the heavier so-ils. Sloping Irrigation Sloping‘ irrigation systems of the Pecos and Dell (lity areas are characterized by long irrigation runs on readily permeable soils. Slopes vary from less than 0.2 percent to more than 0.6 percent. Surface application of pump waters on these systems is highly inefficient. Distribution of water is poor, with the upper portions of fields often over-irrigated. Tail- water runoff is excessive, and much water is wasted. Because most of these pump waters are saline, cotton TABLE 5. 1966-1967 [THREE TESTS) WATER USE EFFICIENCY‘ OF FOUR COTTON VARIETIES IN TWO ROW SPACINGS ON LEVEL IRRIGATION IN THE EL PASO VA I Regular 38" rows 26-54" variable row spacing Seven irrigations Five irrigations Seven irrigations Five irrigations Cotton variety Thin No thin Thin No thin Thin No thin Thin No 1966—-SANDY LOAM SOIL Acala 1517c 19.6 19.1 27.0 24.7 23.9 25.4f-Y 28.8 i Stoneville 7A 25.8 25.8 28.9 30.0 36.2 35.2” 43.1 41 Hopicala 21.5 21.4 28.9 29.1 28.1 27.8 36.6 _ -‘ Deltapine 5540 25.3 25.6 30.3 28.2 29.3 29.4 40.7 3 Average 23.0 23.0 28.8 28.0 29.4 29.4 37.3 3 1966—CLAY LOAM SOIL Acala 1517C 21.6 25.2 30.0 34.2 29.8 37.0 43.2 Stoneville 7A 25.7 26.8 38.6 39.0 38.0 40.8 50.4 t. Hopicala 21.7 24.7 35.1 39.3 42.9 43.5 50.6 5 Deltapine 5540 19.1 22.4 35.5 40.1 36.3 39.3 47.5 -‘ Average 22 0 24.8 34.8 38.1 36.7 40.1 47.9 4 1967——SANDY LOAM SOIL Acala 1517C 23.5 19.7 23.8 21.6 29.6 31.2 28.4 2 Stoneville 7A 21.1 21.9 27.4 30.5 45.7 46.6 44.0 4 Hopicala 21.0 18.8 30.2 30.8 28.8 30.7 29.3 3, Calif. SJ-l 18.1 15.6 23.2 23.3 33.7 33.3 32.8 3 Average 20.9 19.0 26.1 26.5 34.4 35.4 33.6 3 ‘Pounds of lint produced per inch of water applied, plus effective rainfall. has traditionally been lister planted in the furrows. Cost of pumping water for these systems is high and constitutes a major portion of overall production costs. Yields, Water and Plant Growth Yield results of five field tests comparing the alternate 26—54-inch row spacing with regular ‘IO-inch rows are reported in Table 6. Four tests were at Dell City and one at Pecos. The Dell City tests (two each in 1966 and 1967) were located near the top and near the bottom of IAOO-foot runs on approximately a 0.3-percent slope to study possible growth and yield differences due t0 location within a field. Because of high soil permeability, the upper tests received more water than the lower tests at each irrigation at any given rate or frequency of surface water appli- cation. A normal irrigation on these long sloping runs on permeable soils is about 6 inches per acre. This amount was applied to the regular llO-inch rows at each summer irrigation. The 26—54-inch row spacings received only half this amount. Tail-water runoff occurred as a normal p-art of each irrigation, but the amounts were not measured. Table 7 gives pertinent data regarding the five tests. The yield data (Table 6) show that in three tests (Pecos, 1965; Dell City, 1966) lint yields were gen- erally lower with variable row spacing than with regular llO-inch rows. The reason appeared to be related to the water needs of the VRS cotton in early summer. The water applied in June and early July was inadequate for good plant growth, and cotton in the VRS plots was stressed for moisture at a time when 10 vegetative growth needed to be encouraged. resulted in less total growth and consequent tions in yield. In the 1967 tests on the same field, one additi irrigation on a 14-day interval was applied to the I plots in June. This effectively prevented moi stress, and the cotton made more vegetative o; before fruiting began. Yields of VRS cotton strongly related to p-lant size. Thus, with only 3 in additional water, applied at a critical time, VRS y' were increased 200 to 300 pounds of lint per acre 1 1966. This emphasizes the importance of irriga“ timing in row spacing studies. When less wat_ applied per irrigation, timing 0f this water bee more critical. Water Management and Maturity With early summer water stress eliminated, y of all varieties in the 1967 VRS plots were higher those on regular 40-inch rows. This can be attrii partly to excessive vegetative growth and delayed t, ing of cotton in the regular row spacings. Ma the late bolls in these plots did not mature a frost (Figure Rate and frequency of water a . cation have a controlling effect on growth, fru and maturity of cotton in areas of limited grol season (1). A proper balance between vege I growth and fruiting, obtained through correct i. tion, is essential for highest yields. Highest yiel the entire series were with Hop-icala in the 26-54- row spacing in 1967. This variety showed. the_ combination of good growth, heavy fruiting and I maturity under the conditions of these Dell City V _ presents earliness data from the four tests the tests near the lower ends of the irrigation runs. A y based on percent seed cotton at first This obviously was due to differences in the amounts iesults were quite similar to those on level of water received by the crop at the two locations. _ El Paso. Maturity of all varieties in all High soil permeability acted to reduce field irrigation i proved on the VRS system, with greatest efficiency considerably. Cotton in those parts of the earliness obtained with less frequent sum- field getting more water was taller and later maturing. 0n. Overall, the VRS plots yielded l0 Thinning of stands to three plants per foot had little ire cotton at first harvest in 1966, and effect upon earliness in any of these tests, however. imore in 1967. Earlier maturity often means ‘l yields in these areas of limited growing Conn-Q] of wafer and weeds éiis occurred in the 1967 tests. Cotton in lots matured completely before frost (Figure ,1 . that on regular row spacings was caught i‘ freeze in a relatively immature stage of Water use efficiency was not calculated in these tests on sloping runs because tail-water runoff was not measured. Water use by the crop was definitely more efficient in the VRS plots, however-at least in the 1967 tests. In these two tests, higher yields were U: of the tests in the field also had some obtained on Variable Row Spacing although the total ' earliness. Tests closest to the point of amounts of water applied (Table 7) were considerably ation were somewhat later maturing than less than on 40-inch rows. 1 TIVERAGE LINT YIELDS (POUNDS PER ACRE) IN FIVE TESTS COMPARING TWO ROW SPACINGS ON SLOPING IRRIGATION AT DELL ,CO5, 1965—1967 Regular 40" rows 26—54" variable row spacings Seven irrigations Five irrigations Seven irrigations Five irrigations ii --—-—i-- Variety i e Variety Thin No thin Thin No thin average Thin No thin Thin No thin average 1965—-PECOS-—SILTY CLAY LOAM SOIL 1041 949 1036 921 987 934 929 826 875 891 1259 1176 1217 1187 1210 995 1071 1036 1136 1059 948 894 970 932 936 959 987 824 927 924 1083 1006 1074 1013 963 996 895 979 LSD between individual means: .05—132 lb; .01—-174 lb I966—DELL CITY-—SILT LOAM SOILI 777 959 1107 1083 981 705 821 706 784 754 . Lf 803 1015 1071 974 966 759 858 756 785 789 1042 1138 1190 1175 1136 858 923 826 908 879 760 767 823 760 777 660 707 692 719 694 845 970 1048 998 745 827 745 799 LSD between individual means: .05—-92 lb; .01—122 lb 1966—DELL CITY—-SILT LOAM SOIL’ 896 933 916 1025 942 837 883 762 874 839 . Lf 937 1019 876 915 937 856 877 755 757 811 1063 1165 981 1052 1065 961 971 895 918 936 818 787 652 694 738 749 710 755 747 740 928 976 856 921 851 860 792 824 LSD between individual means: .05——86 lb; .01—114 lb 1967—DELL ClTY—-SILT LOAM SOILI 888 959 1153 1173 1043 1091 1197 1084 1146 1129 624 613 1022 1045 826 1040 1156 1118 1140 1113 906 970 1177 1249 1075 1244 1362 1257 1324 1297 656 742 1036 1078 878 1031 1029 944 964 992 768 821 1097 1136 1101 1186 1101 1143 LSD between individual means: .05—110 lb; .01——145 lb 1967—DELL CITY-—SILT LOAM SOIL’ 887 ., 1045 1040 1066 1009 1068 1112 1001 985 1041 614 '3‘ “683 935 1039 818 940 997 965 990 973 863 ‘ 972 1072 1132 1010 1193 1236 1149 1139 1179 749 827 954 917 862 887 954 902 912 914 778 882 1000 1038 1022 1075 1004 1006 LSD between individual means: .05—95 lb; .01—125 lb of l/4-mile irrigation run. on of l/i-mile irrigation run. I 11 TABLE 7. DATA RELA”TIVE TO FIVE FIELD TESTS COMPARING TWO ROW SPACINGS ON SLOPING IRRIGATION SYSTEMS AT DELL CITY 1 PECOS, 1965-1967 I Summer Summer Total‘ irrigation irrigation wat rates frequencies appli Soil Planting Plant Cotton Row i-i- Year type date population varieties spacings Inches/acre Days Inches/ I I965 Silty 4/20 Three per foot Acala I5I7D 26—54" 3 10 39. clay and Stoneville 7A 20 33. Ioam unthinned Blightmaster 40" 6 10 60. f 2O 48. I966 Silt 4/26 Same Stoneville 7A 26-54" 3 14 40. loqm Deltapine Smooth Leaf 21 34. 1161516616 40" 6 14 61. Del Cerro 21 49. 1966 Silt 4/26 Sdme StoneviIIe 7A 26-54" 3 14 ‘40. Ioam Deltapine Smooth Leaf 21 34. H6p1¢6|6 4o" 6 14 61. Del Cerro 21 49. 1967 Silt 5/5 Same Acala 1517C 26-54" 3 14 45.5 loam Stoneville 7A 14-21 39. Hopicala 40" 6 I4 63.5 Calif. SJ-I 14-21 51. _ 1967 Silt 5/5 Same A6616 1517c 26-54" 3 14 45. Ioam Stoneville 7A 14-21 39. Hopicala 40" 6 14 63. 14-21 Calif. SJ-I ‘Includes I2 to I5—-inch preplant irrigation plus effective rainfall. TABLE 8. EARLINESS (PERCENT FIRST HARVEST) OF FOUR COTTON VARIETIES IN TWO ROW SPACINGS ON SLOPING IRRIGATION AT CITY, I966-1967 51.1 Cotton — A variety Thin No thin Thin No thin Thin No thin Thin No DELL CITY, I966—-S|LT LOAM SOIL‘ Stoneville 7A 39.3 39.9 44.2 46.1 48.4 46.9 53.4 5 Deltapine Sm. Lf. 38.9 38.7 41.3 42.6 46.6 47.3 50.2 5 Hopicala 48.8 48.4 63.3 65.4 64.7 68.2 66.5 7, Del Cerro 38.2 37.6 40.3 40.8 45.5 47.7 49.1 I__ Average 41.3 41.1 47.3 48.7 51.3 52.5 54.8 5 DELL CITY, I966—SILT LOAM SOIL’ , StoneviIIe 7A 41.1 5 42.7 46.2 46.9 51.7 50.3 56.6 -'l Deltapine Sm. Lf. 40.4 40.7 44.2 43.6 49.9 50.4 53.7 »_ Hopicala 51.6 52.9 64.4 65.5 59.6 58.7 67.8 7 Del Cerro 40.6 41.1 43.3 45.2 54.6 52.2 58.3 5 Average 43.4 44.3 49.5 50.3 53.9 52.9 59.1 6 DELL CITY, 1967-—SILT LOAM SOIL‘ Acala 1517C 52.1 52.5 63.2 63.7 70.0 76.8 80.7 8 Stoneville 7A 48.8 46.8 61.5 65.8 64.3 69.7 75.0 7 ' Hopicala 58.2 57.3 69.9 71.4 76.7 84.2 85.6 9 Calif. SJ-1 63.9 66.1 65.6 64.8 64.1 70.0 72.9 7_ Average 55.7 55.7 65.0 66.4 68.8 75.2 78.5 8 DELL CITY, I967—SILT LOAM SO|L2 _, Acala 1517C 58.6 54.6 74.9 74.9 85.8 84.6 82.2 8’ StoneviIIe 7A 50.8 46.8 69.2 70.7 82.2 82.2 82.4 8 Hopicala 62.2 61.8 74.2 78.0 86.2 87.7 88.1 9 Calif. SJ-I 61.1 58.3 72.0 74.1 77.6 73.3 77.3 7 Average 58.2 55.4 72.6 82.9 I . Regular 40" rows Seven irrigations Five irrigations 74.4 26-54" variable row spacing Seven irrigations 81.9 Five irrigations, 82.5 iUpper third of l/4-mile sloping irrigation run. ‘Lower third of l/4-mile sloping irrigation run. 12 I’ \iD 3. Stoneville 7A cotton in 40-inch rows (top) and h VRS spacing (bot- Dell City, November l0, ilReguIar rows caught by _n partially open stage; h cotton fully open. “date May 5. e effect of the new row spacing on weed con- not easy to evaluate. Cotton on 40-inch rows tivated regularly. The VRS plots, which re- special equipment adjustment, were no-t. rainfall in these areas also co-ntributed t0 Q eed growth than in the El Paso Valley. How- , ater control presented no problems, and the of the VRS plots were not wetted during 'ons. It appears likely that proper cultivation ‘fly intervals should be able to effectively con- ual weeds on this system without the need ‘icides. loll Characteristics and Fiber Properties all tests on both level and sloping systems, » ples were taken for evaluation of certain boll r properties and for conversion of seed cotton p‘: t0 lint yields. In 1966, a study was made on L: tests at El Pastoito determine the effects of cing and management on these properties. it ples were carefully selected from all plots in ts in early October. These were ginned and in the fiber laboratory at the El Paso Station. ij9—l4 report some results of this study. Lint Percent Lint p-ercents of seed cotton samples from the VRS plots (Table 9) were appreciably higher than those of regular 38-inch rows. Increases, noted with all varieties at both irrigation frequencies, averaged about 1.5 percent. The effect of plant population on lint percents was negligible. Similar results were obtained fro-m other of these tests at other locations in other years. Boll Weight Data on weights o-f seed cotton per boll (Table l0) show that bolls on the VRS plots were slightly smaller than tho-se on regular row spacings. This was generally true of all varieties at both irrigation fre- quencies. These two factors, smaller bolls with higher lint percents, thus appear to be largely self-com- pensating with regards to yields of lint. Thinning to three plants per foot usually resulted in larger bolls regardless of row spacing or irrigation manage- ment. Also noted was the production o-f somewhat larger bolls on the finer-textured clay loam so-il. l3 TABLE 9. LINT PERCENTS OF SEED COTTON FROM FOUR COTTON VARIETIES IN TWO ROW SPACINGS ON LEVEL IRRIGATION AT EL P 1966 . Regular 38" rows 26-54" variable row spacing Seven irrigations Five irrigations Seven irrigations Five irrigations Cotton variety Thin No thin Thin No thin Thin No thin Thin No“ SANDY LOAM SOIL AcaIa 1517C 36.9 37.0 35.9 38.1 37.0 37.9 38.7 3 Hopicala 37.6 38.1 38.2 38.9 40.0 39.5 39.4 3 Stoneville 7A 37.2 36.7 38.0 37.7 39.9 39.3 40.3 3 Deltapine 5540 39.1 38.3 38.5 38.5 41.6 40.4 41.4 4 Average 37.7 37.5 37.6 38.3 39.6 39.3 39.9 3 CLAY LOAM SOIL p‘ AcaIa 1517C 35.9 34.2 35.3 34.7 36.6 36.0 35.9 é 3 Hopicala 37.5 36.8 36.8 36.6 38.2 38.4 38.0 3 StoneviIIe 7A 38.6 38.9 37.3 35.4 37.9 37.7 39.6 3 Deltapine 5540 37.7 37.3 38.0 36.9 40.3 40.0 40.9 3 Average 37.4 36.8 36.8 35.9 38.2 38.0 38.6 3 Fiber Length Tables ll and l2 report the digital fibrograph 50 percent and 2.5-percent span values, respectively. The former corresponds closely to mean length and the latter to classers’ staple length in inches. Row spacing, irrigation frequency and plant population had little effect on mean length on the clay loam soil (Table ll). On the sandy soil, mean length of fiber from the VRS plots averaged slightly shorter than that from regular 38-inch rows. These same effects can be noted in the 2.5-percent span data in Table l2. This slight reduction in length, more noticeable on sandier soils, was observed in other tests and appeared to be characteristic of all varieties on the 26—-54-inch spacing. Such small differences might or might not be detected by cotton classers. Fiber Strength and Fineness Fiber strength (Stelometer T1) values and fiber fineness (micronaire) values for the two 1966 tests are TABLE 10. AT EL PASO, 1966 5 reported in Tables l3 and l4, respectively. I. spacing appeared not to affect fiber strength to extent. Fiber from thinned stands generally w bit stronger than from unthinned stands regar of row spacing. Within any given variety, fineness serves - measure of fiber maturity. (higher micronaire) fiber of all varieties in the plots. This was also noted in other tests. Micro , . of all varieties also was substantially higher on sandy soil than o-n the clay loam soil. Most of the above noted differences in boll g acteristics and fiber properties (higher lint per smaller bolls, shorter staple, higher micronaire) at utable to variable row spacing can be explain the basis of the somewhat greater mo-isture stre the VRS cotton throughout the summer. All of effects except shorter staple can be considered l? able. WEIGHTS OF SEED COTTON PER BOLL (GRAMS) FROM FOUR COTTON VARIETIES IN TWO ROW SPACINGS ON LEVEL IRRIGAA Regular 38" rows 26-54" variable row spacing Seven irrigations Five irrigations Seven irrigations Five irrigation ;_- Cotton variety' Thin No thin Thin No thin Thin No thin Thin N? SANDY LOAM SOIL AcaIa 1517C 6.85 6.45 6.00 5.80 6.45 5.60 6.10 5 ~ Hopicala 6.55 5.80 6.18 6.17 6.35 5.52 6.38 7 Stoneville 7A 5.58 4.80 5.52 4.92 5.58 4.67 5.17 4 Deltapine 5540 5.32 4.60 5.23 4.78 5.10 4.82 4.95 4 Average 6.07 5.41 5.73 5.42 5.87 5.15 5.64 5 CLAY LOAM SOIL AcaIa 1517C 7.17 6.59 6.88 6.17 6.59 6.46 7.15 Hopicala 7.36 6.90 7.48 6.65 7.25 6.52 7.31 Stoneville 7A 5.47 5.24 5.50 5.21 5.33 5.38 5.34 Deltapine 5540 5.74 5.24 5.92 5.19 6.09 5.49 5.68 Average 6.43 5.99 6.44 5.80 6.31 5.96 6.37 14 In both tests (Table there was a trend toward somewhat more ma ~_ O~ JIGITAL FIBROGRAPH 50-PERCENT SPAN LENGTH‘ OF FIBER FROM FOUR COTTON VARIETIES IN TWO ROW SPACINGS ON LEVEL . 4T EL PASO, 1966 Regular 38" rows 26-54" variable row spacing Seven irrigaTions ‘closely To classers' mean lengTh in inches. Five irrigaTions Seven irrigaTions Five irrigaTions Thin No Thin Thin No Thin Thin No Thin Thin No Thin SANDY LOAM SOIL 0.55 0.54 0.55 0.55 0.53 0.52 0.52 0.53 0.54 0.53 0.53 0.54 0.51 0.51 0.51 0.51 0.52 0.51 0.52 0.52 0.47 0.48 0.49 0.49 0.48 0.50 0.49 0.48 0.46 0.46 0.47 0.46 0.52 0.52 0.52 0.52 0.49 0.49 0.50 0.50 CLAY LOAM SOIL 0.54 0.56 0.54 0.55 0.54 ‘0.56 0.53 0.55 ' 0.55 0.55 0.54 0.56 0.55 0.55 0.53 0.53 0.50 0.51 0.50 0.51 0.50 0.53 0.48 0.50 0.48 0.47 0.48 0.48 0.48 0.47 0.48 0.49 0.52 0.52 0.52 0.52 0.52 0.53 0.51 0.52 FIGITAL FIBROGRAPH 2.5-PERCENT SPAN LENGTH‘ OF FIBER FROM FOUR COTTON VARIETIES IN TWO ROW SPACINGS ON TION AT_EL PASO, 1966 Regular 38" rows Seven irrigaTions Five irrigaTions 26-54" variable row spacing Seven irrigaTions Five irrigaTions Thin No Thin Thin No Thin Thin No Thin Thin No Thin SANDY LOAM SOIL 1.25 1.24 1.23 1.22 1.23 1.22 1.20 1.23 1.21 1.17 1.16 1.17 1.15 1.14 1.14 1.16 1.19 1.17 1.18 1.19 1.11 1.12 1.14 1.13 1.17 1.20 1.16 1.16 1.10 1.12 1.13 1.11 1.20 1.19 1.18 1.18 1.15 1.15 1.15 1.16 CLAY LOAM SOIL 1.24 1.27 1.24 1.27 1.22 1.25 1.22 1.23 1.20 1.18 1.19 1.20 1.18 1.18 1.16 1.16 1.17 1.18 1.18 1.20 1.16 1.20 1.16 1.14 1.19 1.16 1.16 1.17 1.18 1.17 1.13 1.16 1.20 1.20 1.19 1.21 1.19 1.20 1.17 1.17 1;‘ 1966 "Iosely To classers’ sTaple IengTh in inches. RENGTH (STELOMETER T1 VALUES)‘ OF FIBER FROM FOUR COTTON VARIETIES IN TWO ROW SPACINGS ON LEVEL IRRIGATION Regular 38" rows Seven irrigaTions Five irrigaTions 26-54" variable row spacing Seven irrigaTions indicate stronger fiber. Five irrigaTions Thin No Thin Thin No Thin Thin No Thin Thin No Thin SANDY LOAM SOIL 2.23 2.13 2.41 2.36 2.35 2.26 2.35 2.29 2.28 2.31 2.45 2.48 2.42 2.36 2.42 2.31 , 1.94 1.81 1.96 1.86 1.88 1.83 1.84 1.88 2.16 2.02 2.13 2.02 2.13 1.94 2.12 2.04 2.15 2.06 2.24 2.18 2.19 2.10 2.18 2.13 CLAY LOAM SOIL 2.35 2.35 2.46 2.38 2.32 2.36 2.55 2.39 2.48 2.41 2.51 2.44 2.38 2.32 2.44 2.41 1.94 1.80 1.94 1.91 1.83 1.84 1.94 1.96 2.03 2.04 2.13 1.96 2.03 2.04 2.17 2.15 2.20 2.15 2.26 2.17 2.14 2.14 2.27 2.23 15 TABLE 14. FINENESiS [MICRONAIREP OF FIBER FROM FOUR COTTON VARIETIES IN TWO ROW SPACINGS ON LEVEL IRRIGATION AT EL P 1966 Regular 38" rows 26-54" variable row spacing Seven irrigations Five irrigations Seven irrigationsq Five irrigations Cotton variety Thin No thin Thin No thin Thin No thin Thin No SANDY LOAM SOIL .; Acala 1517C 4.17 4.18 3.98 4.17 4.18 4.24 l: 4.14 4 Hopicala 4.48 4.45 4.68 4.67 4.62 4.52 4.53 4 StoneviIIe 7A 5.15 4.92 5.10 5.05 5.23 5.10 5.27 5 Deltapine 5540 3.90 3.60 3.90 3.80 4.33 4.20 4.03 4 Average 4.42 4.29 4.41 4.42 4.59 4.51 4.49 4 CLAY LOAM SOIL z AcaIa 1517C 3.87 3.90 3.80 3.95 3.87 3.80 4.02 4 Hopicala 4.25 4.00 4.15 4.27 4.40 4.17 4.62 4 Stoneville 7A 4.37 4.42 4.50 4.50 4.67 4.77 4.70 5 Deltapine 5540 3.40 3.32 3.52 3.42 3.82 3.70 3.77 4* Average 3.97 3.91 3.99 4.03 4.19 4.11 4.28 47 ‘Higher values indicate coarser or more mature fiber. EVALUATION OF OTHER VRS SYSTEMS The alternate 26—54-inch row spacing of the pre- vious tests was rather arbitrarily selected for study because it provided a narrow furrow for water appli- cation, a wide bed for light and for tractor wheel traffic and the same number of rows per acre as solid 40-inch plantings. There was a good possibility, however, that other row spacings might prove more satisfactory from the crop yield or management stand- points. Accordingly, two other spacing arrangements were subsequently chosen for study on sloping systems at Pecos and a third on level systems at El Paso. Sloping Irrigation Because control of irrigation water presented no problem in furrow irrigation down sloping systems, two additional row spacings were included in the studies at Pecos in 1966. These were an alternate 32—48-inch row spacing (Figure 1, number 3) and an alternate 20—-60-inch spacing (Figure l, number 6). Water furrows were between the 32-inch and 20-inch rows only. Field design was similar to that of previous tests, with the four row spacings split for two fre- quencies of water application. As before, two rates of water were applied—a normal 6-inch summer irriga- tion on regular 40-inch rows, and 3 inches per irriga- tion on the other three row spacings. All plots received a measured 12-inch preplant irrigation. To avoid increasing the size of the tests, only two cotton varieties were included. Alternate 40-foot plots down the slope were thinned to three plants per foot, with intervening plots left unthinned. One test was com- pleted in 1966, two more in 1967 and a fourth in 1968. Table l5 gives average lint yields from the four tests. Yields: Lint yields, although varying somewhat among tests and varieties, were essentially as high with 16 the 32—48-inch and 26—54-inch VRS systems as regular 40-inch rows. As in previous tests, these I parable yields were obtained with a minimu iv cultivation and only half the summer water ap to the regular row spacing. Highest yields of series were obtained with Hopicala on the 32—48- spacing in 1968. Lowest yields also were with t cala on 20—60-inch spacing in 1967. Only in 1966 ' the 40-inch rows outyield all other row spacings. With one exception (Northern Star in 1966) l I yields consistently were obtained with the 20-60- spacing. This spacing apparently resulted in exc crowding of plants with too much restriction of i root and to-p growth for best yields. - Pecos area soils, although mineralogically n to those at Dell City, have a finer texture and ~ -. water holding capacity. Soil moisture was not. main factor limiting yields in these tests at P since little or no additional lint was obtained A more frequent irrigation in any of the tests or on of the four row spacings. Plant population also little influence on lint yields. Varietal characte ' appeared to be a major factor affecting growth, ing and yields. Some of these have already discussed. Earliness: Earliness was determined on the twoi in 1967 (Table 16). Each of the three VRS sy produced a substantially higher percentage of cotton at first harvest than cotton on 40-inch rows. ‘ in previous tests, this effect was probably re more to the amounts of summer water applied t0 row-spacing arrangement. Cotton on 40-inch (6-inch irrigations) grew taller and began f later than that on the three VRS spacings (r irrigations). As at Dell City, cotton on the lower of the irrigation run was shorter and earlier mat I a reflection of the amounts of water received irrigation. Boll samples (data not reported) sh 1.. ‘. lNT YIELDS (POUNDS PER ACRE) or TWO COTTON VARIETIES IN FOUR ROW SPACINGS ON st OPING IRRIGATION AT PECOS, 1 yield potential. half of sloping 1,000-foot irrigation run. _. flom half of sloping 1,000-foot irrigation run. “Qocing got 6-inch summer irrigations; other spacings got 3-inch irrigations. _l o bale-per-acre cotton in alternate 26-54-inch row being hand-harvested at Dell City, November 15, pitan peak, Guadalupe Mountains, is in background. l gller bolls with higher gin turnout in all as compared with those of 40-inch rows. frizing the research o-n sloping systems, it at present yields on regular 40-inch row being obtained with considerably greater f input than is required by the crop with ' This study shows that TESTS) Seven irrigations Five irrigations Row Seven irrigations Five irrigations Row spacing spacing Thin No thin Thin No thin average Thin No thin Thin No thin average HOPICALA 1966 NORTHERN STAR 1154 1142 1204 1229 1182 1098 1099 1168 1162 1132 1055 1055 960 938 1002 1015 978 993 1014 1000 1127 1159 1061 1025 1093 1112 1160 1024 1005 1075 995 973 980 970 979 1008 1071 1019 1008 1026 1083 1082 1051 1040 1064 1058 1077 1051 1047 1058 LSD between individual means: .05—66 lb; .01——88 lb HOPICALA 19671 STONEVILLE 7A 1014 961 1143 1017 1034 1121 1204 1192 1220 1184 1140 1136 1185 1097 1139 1298 1331 1164 1168 1240 1091 1006 1102 1160 1090 1252 1248 1174 1259 1233 975 936 983 980 968 1066 1157 1135 1140 1124 1055 1010 1103 1063 1058 1184 1235 1166 1197 1195 LSD between individual means: .05——89 lb; .01——1 18 lb HOPICALA 1967* STONEVILLE 7A 1123 1143 990 1068 1081 1263 1291 1193 1220 1242 1053 1102 1084 1073 1078 1224 1272 1262 1270 1257 1060 1028 974 1050 1028 1300 1358 1184 1151 1248 978 882 845 935 910 1091 1023 1065 1007 1046 1053 1039 973 1031 1024 1219 1236 1176 1162 1198 LSD between individual means: .05——1 00 lb; .01——1 32 lb HOPICALA 1968 STONEVILLE 508 1242 1151 1220 1200 1203 950 966 898 947 940 1302 1272 1373 1369 1329 947 930 944 1041 965 1250 1143 1156 1137 1171 1023 930 926 952 958 1121 1078 1141 1091 1108 945 963 882 895 921 1229 1161 1222 1199 1203 966 947 912 959 946 LSD between individual means: .05——89 lb; .01—1 18 lb equal or higher yields can be obtained with the 26- 54-inch or 32—48-inch spacings with appreciably less water than currently is being app-lied (Figure 4). Add to this savings in labor and pumping costs associated with water application, the possibility of better wee-d control with less cultivation and the assurance of earlier harvest of fiber of more uniformly good quality. This is with present cotton varieties. New varieties more specifically adapted to the VRS systems, if developed, might further increase yields. Satisfactory economic studies cannot be made until sound farm management systems involving all aspects of the new spacings are worked out. This must await the solution of the machine harvest problem, the chief obstacle preventing farmer acceptance on these sloping soils with open boll varieties. However, there is little doubt that the potential exists for substantial savings in production costs. Level Irrigation Previous studies with the alternate 26—54-inch row spacing on level soils had disclosed that adequate control of irrigation water was difficult with the narrow 26-inch furrows. Accordingly, tests were con- ducted at the El Paso Station in 1968 and 1969 com- 17 TABLE 16. EARLINESS (PERCENT FIRST HARVEST) OF TWO COTTON VARIETIES IN FOUR ROW SPACINGS ON SLOPING IRRIGATION AT ' 1967 . Hopicala Stoneville 7A R°w_ Seven irrigations Five irrigations Row Seven irrigations Five irrigations spacing spacing -, (inches) Thin No thin Thin No thin average Thin No thin Thin No thin a UPPER TEST‘ 40-40“ 26.2 28.5 20.7 24.3 24.9 28.5 31.0 ' 311.9 34.3 32-48 42.0 40.4 43.4 42.4 42.0 46.2 53.3 35.5 40.8 26-54 46.2 48.9 45.4 43.5 46.0 40.0 51.2 44.0 45.3 20—60 37.7 36.3 39.2 38.9 38.0 37.6 45.1 38.0 42.5 Average 38.0 38.5 37.2 37.3 37.7 38.1 45.1 37.3 40.7 LOWER TEST’ “'1 4 40-403 40.4 40.6 37.7 35.6 38.6 45.6 45.0 42.9 41.2 32-48 51.3 51.4 62.4 56.7 55.4 55.4 54.2 60.3 59.2 26-54 55.2 55.2 59.8 58.3 57.1 57.9 58.5 55.6 61.9 20-60 46.9 41.3 63.3 59.1 52.6 51.0 55.6 62.6 67.5 Average 48.4 47.1 55.8 52.4 50.9 52.5 53.3 55.3 57.4 ‘Located on upper half of sloping LOGO-foot irrigation run. zLocated on lower half of sloping 1,000-foot irrigation run. 3The 40-40-inch spacing got 6-inch summer irrigations; other spacings got 3-inch irrigations. paring an alternate 3()—5()-inch row spacing (Figure 1, number 4) with regular 38-inch rows (Figure l, number 2). Field design, fertilization, irrigation rates and plant populations were similar to those of the 1965- 67 El Paso tests. Four cotton varieties were included at three summer irrigation frequencies-every 14, 21 and 28 days during the summer. The 1968 test was on a productive alluvial loam soil; the 1969 test was on sandy loam of lower productivity. Heavy July rains disrupted irrigation schedules in 1968. As a result, the 14-day frequency got five summer irrigations while the 21 and 28-day frequen- cies both go-t only three irrigations. Table 17 gives irrigation rates, dates applied and effective rainfall for this test. Table 18 gives average lint yields of the four varieties in the 1968 and 1969 tests. Due to poorer than average stands in 1969, all plots in this final test were left unthinned. Performance of the two Acala varieties in the 1968 test was exceptionally good on both row spacings. Hop-icala consistently produced highest yields. These were as good, or better, on the 30—50-inch plots as on regular 38-inch rows. Overall comparison of the two row sp-acings showed a slight advantage for the 30-50- inch spacing with 14-day summer irrigation and a similar slight disadvantage with less frequent irriga- tion. The unexpected heavy rains in July, together with the reduced water applications in late summer, appeared to favor the Acalas. Plant height of all varieties was shorter on the VRS plots. Head-high growth with 14-day irrigation on 38-inch rows reduced yields somewhat. This was reflected in higher yields of cotton on the thinned plots. Percentage of the crop harvested at first picking (earliness) again favored the VRS system (data not shown). Increases averaged about 15 percent. Water use efficiency also was better with the 30—50-inch spacing, since similar yields were produced with less 18 water. Although a preplant herbicide was apt to the entire test, cultivation of all plots was nec for weed control because of the July rains. Control of irrigation water was much better the 30—50-inch spacing than with the previous 2 inch arrangement. spacing should not be a problem if furrows are open and bed centers kept high. ' Yields of all plots in the 1969 test were seri affected by unusually rapid early growth of nut - (Cyperus spp.) infesting the test area. The main ' of this perennial was to smother early cotton "i? growth. Damage was worse on the VRS plots be no adequate cultivation equipment was avail This final test, tho-ugh not a fair comparison of two row spacings, is included to emp-hasize that w particularly certain perennials, can significantly r cotton yields on VRS plantings if permitted t0) out of control. TABLE 17. WATER APPLICATION RATES, DATES OF APPLIC AND EFFECTIVE RAINFALL‘ FOR THE 1968 VRS TEST ON LEVEL GATION AT EL PASO. (REPORTED AS INCHES PER ACRE) 14-day irrigation 21-day irrigation 28-day irrigl Regular Regular Re 30-50" 38" 30-50" 38" 30-50" 3 rows rows rows rows rows -' Date spacing spacing spacing spacing spacing s 3/24 12 12 12 12 12 1 5/31 1.5 3 1.5 3 1.5 6/14 1.5 3 6/21 1.5 3 6/28 1.5 3 2 7/3 to 7/6‘ 6.2 6.2 6.2 6.2 6.2 7/26 1.5 3 8/1‘ 1.3 1.3 1.3 1.3 1.3 8/15 1.5 3 1.5 3 1.5 Total 27.1 34.6 24.1 28.6 24.6 Water control on the 30-50 2 ‘Rainfall more than 1 inch during any single shower peril i‘ "- Z\ :_’.‘L'>_ >‘_.z~>:: 1>>QT awn r-rwflh In nut -_l hi! p“ T EL PASO, 1968-1969 '1 VERAGE LINT YIELDS (POUNDS PER ACRE) OF FOUR VARIETIES IN TWO TESTS COMPARING TWO ROW SPACINGS ON LEVEL LSD between individual means: 14-day 21-day 28-day irrigation irrigation irrigation Thin No thin Thin No thin Thin No thin 1968 REGULAR 38" ROW SPACING 1398 1347 1525 1515 i493 i462 1354 1221 i429 i343 i453 1369 973 873 i227 i206 1191 1069 917 813 1090 1193 1176 1112 1160 1065 1318 1314 1328 1253 ALTERNATE 30-50" ROW SPACING 1635 1552 1429 1303 1505 1560 1330 1189 1448 1399 1195 1230 1141 1134 1196 1136 1045 1122 1086 985 1170 1077 933 1046 1293 1215 1311 1229 1169 1239 LSD between individual means: .05—-188 lb; .01-—249 lb 1969 REGULAR 38" ROW SPACING 975 870 844 908 938 813 904 1045 898 865 1042 850 913 974 851 ALTERNATE 30-50" ROW SPACING 869 700 832 756 708 714 851 935 944 813 778 750 822 780 810 .05-——72 lb; .0i—96 lb q ANT FACTORS TO BE CONSIDERED regoing studies have shown that adoption ‘ an regular cotton row spacing patterns fsrtunities for reducing production costs ater savings and other alterations in man- l ctices. However, changes in row spacing uld not be made until their effect on over- _ y, ent of the operation, from gro-und break- cutting, has been carefully evaluated. i’ en a major management change is con- jflit is wiser to convert the entire operation gessary adjustments in equipment can be ' ore changing row spacings, the following {jSuch a change should be considered: e cotton varieties now grown compatible thew system, or would variety changes be . Changing varieties is a serious step unless n that they will produce well and that the arketable in that area. 'ng is a precision operation. Could present i‘ adapted to the new pattern so as to give ,3 stands? This operation should be verified l if possible. herbicides, if needed, be applied and in- v satisfactorily with available equipment? Could cultivation, fertilization and insect control equipment be adjusted to the new system? Is the irrigation method now in use sufficiently flexible to irrigate the new spacing efficiently at reduced water application rates? Level systems require more precise leveling for water contro-l when furrow width and depth are decreased. Could harvesting be satisfactorily accomplished without excessive ground losses? This is a major problem with open boll varieties and, like planting, should be given prior consideration. Are water quality and soil permeability good, or is there a danger of salt accumulation if water appli- cation rates are reduced? This aspect is clarified in the following section. DANGERS OF SALT ACCUMULATION Adequate control of soluble salts in the soil is essential to continued good crop production in irri- gated areas Soluble salts applied in irrigation waters must be continuously or periodically leached downward below the bottom of the root zone to prevent gradual accumulation and eventual crop dam- age. Where irrigation waters are saline or rainfall inadequate to aid in the leaching process, water appli- 19 cation rates musthbe increased to provide the necessary leaching. Reduced water application rates in these VRS systems present the danger of gradual salt accumula- tion. This was borne out by a study of salt movement and distribution in conjunction with the above study. Tests at El Paso and Pecos were relocated in identical positions during a 3-year period. Hundreds of soil samples were analyzed for soluble salts and exchange- able cations Results verify that salts will accumu- late under these VRS patterns if irrigation waters are saline and if these patterns are maintained in the same fields for several years. Accumulation would be more rapid under low rainfall conditions and with sharp reductions in the amounts of water per irrigation. Danger of accumulation would be considerably less in higher rainfall areas or where good quality waters are used. Where salt accumulation is likely to occur, periodic rotation with other crops such as alfalfa, small grains or sorghum should help restore soils to their normal salinity levels. ACKNOWLEDGMENT The excellent cooperation of the Lynch brothers of C 8c L Ranch, Dell City, in supervising irrigation, 20 fertilization, cultivation and insect control on“ spacing tests on their land in 1966 and 1967 is gratefully acknowledged. LITERATURE CITED 1. Longenecker, D. E., E. L. Thaxton, Jr. and P. J. Cotton production in far West Texas with empha irrigation and fertilization. I TAES Bull. 1001. 24 1963. 2. Longenecker, D. E., E. L. Thaxton, Jr. and P. J. _ Salt concentrations in soils furrow-irrigated with waters. TAES Misc. Pub. 939. 12 pages, 1970. f‘ 3. Lyerly, Paul J. and D. E. Longenecker. Salinity con‘ irrigation agriculture. TAES Bull. 876, 20 pages,‘ revised 1959, 1962. i 4. Newman, J. S. Yields and fiber properties of cotton "*4 in solid and skip-row systems under minimal soil m levels. TAES Misc. Pub. 843, 16 pages, 1967. 5. WVanjura, D. F. and E. B. Hudspeth, Jr. Broadcast p —a method of producing cotton on the high plains. Prog. Rept. 2295, 4 pages, 1964. ' 6. Wilkes, L. H. and Price Hobgood. Broadcast and A row cotton in the Brazos River valley. TAES Prog.“ 2428, 4 pages, 1966. _