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Economic analysis of irrigation and deep tillage in soybean production systems on clay soil
Soil& Tillage Research, 28 (1993) 63-78
63
0167-1987/93/$06.00 © 1993 - Elsevier Science Publishers B.V. All rights reserved
Economic analysis of irrigation and deep tillage in soybean production systems on clay soil Richard A. Wesley*,a, Lowrey A. Smitha, Stan R. Spurlockb aUSDA-ARS Field Crops Mechanization, Stoneville, MS 38776, USA bAgricultural Economics Department, Mississippi State University, Mississippi State, MS 39762, USA (Accepted 30 March 1993)
Abstract
A 5-year study ( 1987-1991 ) was conducted on a Tunica clay (clayey over loamy, montmorillonitic, non-acid, thermic Vertic Haplaquept) to determine effects of irrigation and deep tillage on soybean yields and economic returns. Irrigation increased average yield of the conventional check treatment (disked) by 57% (3020 vs. 1924 kg ha - ~). Under irrigation, yields from all deep-tilled treatments and the conventional check treatment were similar and averaged 3066 kg h a - 1. Under non-irrigated conditions, yields from all deep-tilled treatments were similar, averaged 2829 kg ha- ~, and were higher than the conventional check treatment that averaged 1924 kg ha-1. Average yields from the nonirrigated deep-tilled treatments were 92% as high as yields from comparable treatments with irrigation. Irrigation increased the average net returns of the conventional check treatment 75% ($206 vs. $118 h a - 1). Over the 5-year study, average net returns to all irrigated treatments were similar and ranged from $194 to $206 ha- t. Net returns to the non-irrigated deep-tilled treatments averaged 156% higher than returns from the non-irrigated conventional check treatment ($302 vs. $118 ha- 1) and was attributed to the higher yields of the deep-tilled treatments (2829 vs. 1924 kg h a - ~). Net returns to the non-irrigated deep-tilled treatments also averaged 47% higher than returns from the irrigated conventional check treatment ($302 vs. $206 ha-1 ). This difference was attributed to the similarity of yields (2829 vs. 3020 kg ha -~ ) and the sizeable difference in specified costs of production ($335 vs. $481 h a - 1) that favored non-irrigated production of soybean with deep-tillage.
Introduction
Clayey soils occupy approximately 3.7 M ha or about 50% of the land area in the lower Mississippi River alluvial flood plain. Soybean (Glycine m a x (L.) Merr. ) is planted on approximately 2.5 M ha or about 67% of this area. In non-irrigated production systems, soybean yields from these soils are usually low, but with irrigation, sizeable yield increases are possible most years (Heatherly, 1983; Heatherly and Elmore, 1986). Similar results have been reported by other researchers for similar soils with relatively low available water-holding capacity (Boerma and Ashley, 1982; Ramseur et al., 1984). Corresponding author.
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Economic analysis (Salassi et al., 1984) has shown that properly timed irrigation of soybean (furrow or sprinkler) grown on the clayey soils of the mid-southern United States can result in increased returns to land, management, and general farm overhead. However, they reported a yield increase of approximately 1000 kg ha- ~was required to recover the total costs associated with irrigation when based on a seasonal price of $0.2206 per kilogram. Another study in the mid-southern United States (Heatherly et al., 1986 ) investigated the economic effects of furrow irrigation on soybean grown in conventional production systems. Data indicate net returns to soybean grown on clay soil with and without supplemental irrigation averaged $329 and $238 ha-~, respectively or a $91 ha-~ advantage to irrigation. Compaction of soil, whether natural or artificial, alters the soil's condition and affects growth of plants. Compaction adversely affects the content and movement of air, water, heat, and nutrients in the soil (Raney, 1971 ). Early research tended to suggest that an increase in the soil's bulk density would automatically reduce crop yield. Yield of potatoes (Solanum tuberosum) was reduced 22% (Saini and Lantagne, 1974), whereas Phillips and Kirkham (1962) and Morris ( 1975 ) reported reductions in corn (Zea mays L.) yields of 10 and 22%, respectively, owing to compaction. Compaction from machinery traffic reduced wheat (Triticum aestivum L.) growth (Feldman and Domier, 1970) and cotton (Gossypium hirsutum L.) yields (Lowry et al., 1970; Negi et al., 1980). Recent research has demonstrated that for each crop, soil and season, there is an optimum level of compaction for maximum crop yield. Compaction above or below this optimum will result in decreased yield (Soane, 1985 ). As a general rule, responses to tillage and field traffic are variable, but can be explained by a combination of: ( 1 ) site and soil-related factors; (2) plant and crop-related factors; (3) weather and climate-related factors; (4) soil and crop-management factors, including tillage and traffic (Boone, 1988). Predictive equations of the net economic effect of compaction have been developed recently using basic soil mechanics theory, soil survey data, long-term climatic data bases, and field research results (Voorhees, 1987). Kirkegaard et al. (1992) studied the effect of compaction on the growth of pigeonpea (Cajanus cajan) on clay soils in southeast Queensland, Australia. Results of their studies indicated growth restrictions resulting from compaction were primarily related to reduced water uptake resulting from decreased infiltration and storage of water, and restricted root growth. Seasonal conditions, in particular the distribution of rainfall, exerted a strong influence on plant response. Yield reductions resulting from compaction varied from 100% in a very dry season to 0% in a wetter season. The reduced impact of compaction in the wetter season was associated with reduced levels of soil strength during early root growth and a decreased reliance on stored subsoil water for growth.
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Researchers have also attempted to reduce or eliminate effects of compaction on crop growth and yield. Dumas et al. ( 1973 ) developed a controlled traffic system for cotton production systems that increased cotton yields over yields from conventional production systems. In 1980, the concept of deep tillage (subsoiling) in conjunction with controlled traffic systems was investigated and cotton yields were significantly increased (Williford, 1980 ). The historical belief that a loose soil ensures highest crop yields and the economic incentive for more energy-efficient cropping systems has promoted the development of controlled traffic production systems (Taylor, 1983; Lamers et al., 1986). Deep tillage has resulted in increased yields of numerous crops. Deep tillage of a clay loam increased yield of sugarbeet (Beta vulgaris) (Mathers et al., 1971 ), cabbage (Brassica oleracea var. capitata) and soybean (Menzel et al., 1968 ). Deep tillage of a compacted ustochrept soil increased soybean yields 21-24% compared with conventional tillage (disked) and increased the partial gross margins $52-58 ha -1 (Barbosa et al., 1989). Deep tillage has also been shown to be a practical method for increasing water intake rates and depth of profile wetting of slowly permeable structured clays (Music et al., 1981 ). Researchers found that deep tillage of clay soils when the upper profile was dry doubled the average water intake rate during the next crop season when compared with shallow tillage (Jensen and Sletten, 1965 ). Current tillage practices recommended for soybean production on the heavy soils in the mid-southern United States do not include deep tillage or deep disking. The natural shrinking and swelling which causes the soil to crack as it dries is credited for the elimination of the compacted layers caused by machinery traffic. Deep tillage of a Sharkey clay near Stoneville, MS did not increase soybean yields when compared with conventional disking for seedbed preparation (Heatherly, 1981; Barrentine and Tupper, 1983). However, all tillage inputs were applied in late spring when the upper profile of the soil was wet. Excavation and observation of rooting patterns of cotton on Tunica clay when the soil was cracked revealed compacted blocks of soil beneath the plow layer (Smith, 1992). The density of these blocks severely restricted root penetration and confined a majority of the roots to the vicinity of the block surfaces. Therefore, a large portion of the soil nutrients and water stored in the soil blocks were not readily available for plant growth. Deep tillage (subsoiling) in the fall when the soil profile is dry disrupts the orientation of the blocks and reduces their size. The infiltration of water is enhanced because the soil blocks no longer fit together to form a high density continuum when they swell. Loose soil material resulting from the disruption of the soil block arrangement now separates the blocks, and this allows higher rates of internal water movement which results in more water storage during wet periods. Excess water is able to drain from the profile and this improves
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the aeration of the soil and allows the soil to warm up more quickly in the spring for earlier planting. Surface runoff and soil erosion are also reduced. The objectives of this study were to: ( 1 ) determine the effect of irrigation and deep tillage on soybean yield in a controlled traffic production system; and (2) determine the economic returns to irrigation and deep tillage. Materials and methods
General Field studies were conducted from 1987 through 1991 near Stoneville, MS on a Tunica clay soil (clayey over loamy, montmorillonitic, non-acid, thermic Vertic Haplaquept). In general, the clayey layer on Tunica soil ranges from 0.46 to 0.75 m thick and overlies a clay loam or a silty clay loam subsoil. The soil is characterized by a high percentage of clay, 1-2% organic matter, poor internal drainage, a high level of fertility, low bulk density ( 1.5-1.6 g cm-3), and 0.5 to 2.0% slope. The soil compositon of the A horizon (upper 0.75 m) at the test site was composed of 1% sand, 36% silt, and 63% clay; whereas the B horizon was composed of 2% sand, 70% silt, and 28% clay. The field area for this study had a bulk density of approximately 1.6 g cm -3 and a slope of approximately 0.5% and had been continuously cropped in non-irrigated, conventional-tilled soybean. The experiment included four tillage treatments in both an irrigated and non-irrigated environment. The experiment was conducted with irrigation treatments (main plots) and tillage treatments (subplots) in a split-plot arrangement in a randomized complete block design with four replicates each year. Subplots were 16.2 m wide and 28 m long. Traffic lanes were established on 2 m centers and remained in the same location throughout the study period. A production zone was centered between each traffic lane and contained four rows of soybean spaced 0.45 m apart. Therefore, a 0.66 m space was left between the outside rows of adjacent production zones for machinery traffic. Tillage treatments were randomly assigned to the subplots at the beginning of the test period and remained in the same location for the 5-year test period. Tillage treatments included three deep tillage methods and a conventional disked check plot. Treatments are identified as follows: DT1 (triplex subsoiler with 1 shank), DT2 (parabolic subsoiler with 2 shanks), DT3 (parabolic subsoiler with 3 shanks), and C (disked check). The DT1 unit consisted of a straight subsoiler shank with a 0.76 m wide wing attached to the point of elevation to give additional soil fracture. The DT2 unit contained two parabolic shanks spaced 1 m apart, whereas the DT3 unit contained three parabolic shanks spaced 0.5 m apart. All deep-tilled plots were subsoiled to a depth of 0.4-0.5 m each year with the tillage implements centered in each respective production zone. The check plot (C) was prepared in a conventional manner
R.A. Wesley et aL ~Soil & Tillage Research 28 (1993) 63-78
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with a disk-harrow followed by a field cultivator. All tillage inputs were accomplished on 1 October 1986, 19 October 1987, 19 December 1988, 11 October 1989, and 1 October 1990 after soybean harvest. All plots remained as tilled throughout the winter season. Prior to planting soybean each year, all winter vegetation was eliminated either by a broadcast application of paraquat or by tilling with a disk-harrow. All plots were then tilled with a field cultivator followed by a spike-tooth harrow to smooth out the rough areas in the deep-tilled plots. These procedures provided suitable seedbeds for planting soybean. Asgrow 5980 variety was planted all years except 1991. Because of a severe infestation of stem canker (Diaporthephaseolorum var. caulivora) disease in 1990, a resistant variety of soybean (Pioneer 9592 ) was planted in 1991. Planting dates during the study was 19 May 1987, 16 May 1988, 12 May 1989, 8 May 1990, and 13 May 1991. In 1991 soybean were first planted on 24 April. However, because of excessive rainfall after planting that flooded all plots, all soybean was replanted on 13 May 1991. Metolachlor plus metribuzin herbicides were broadcast-applied at planting from 1987 through 1990 for grass and broadleafweed control in all treatment plots. In 1990, a mixture of bentazon and acifluorfen was applied post-emergence. In 1991, a broadcast application ofa metribuzin and chlorimuron mixture was applied pre-emergence, and a mixture of bentazon and acifluorfen post-emergence. All herbicides were applied at the labelled rates and provided adequate weed control. Excellent soybean stands (35 plants m -2) were obtained each year. All machinery traffic was confined to the established traffic lanes. Each year all treatment plots in the irrigated environment were sprinklerirrigated from a lateral-move system whenever soil water potential, as determined by tensiometers located at the 30-cm depth in three replicates of the check plots, averaged between - 0 . 0 5 and - 0 . 0 7 MPa. Previous research with soybean on clay soil indicated this tensiometer placement depth was optimum for maximum yield response (Heatherly, 1984). Tralomethrin was sprayed on 27 August 1987 and thiodicarb on 12 and 26 August 1988 for control of cabbage loopers (Trichoplusia ni). The combine used for harvesting had 2 m wheel spacings, therefore, harvest traffic was also confined to the established traffic lanes. The plot combine's cutter bar was 2 m wide and harvested a complete production zone with each pass. Three production zones were harvested from each subplot for yield determinations. Seed moisture was corrected to 13% dry basis. Harvest occurred between 27 September and 13 October each year. Analysis of variance was used to evaluate the significance of treatment effects on soybean yields. Where significant differences occurred, mean separation was achieved with an LSD 0.05 value calculated with either the whole unit or subunit error terms, or an adjusted error term made up of whole unit and subunit errors (Cochran and Cox, 1957 ).
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Economic analysis Crop enterprise budgets were developed annually for each treatment in the irrigated and non-irrigated environments. Application rates for all the variable inputs were those recommended and used for crop production in this study. Crop prices used in the budgets were the seasonal average prices received for the year as reported by the Mississippi Agricultural Statistics Service, 1987-1991. Gross returns were calculated annually as the product of treatment yields and seasonal average price. Variable costs were the actual prices paid by farmers each year and include the cost of herbicide, seed, labor, fuel, repair and maintenance of equipment, and interest on operating capital. Fixed costs include costs of tractors and other self-propelled equipment, implements, and the irrigation system. Total specified costs include both variable and fixed costs. Net returns per acre were calculated as the difference between gross income and total specified costs. Average net returns were calculated as the mean of the annual net returns over the study period. In constructing the budgets no charges were included for land, management, or overhead. Performance rates on all field operations were based on using eightrow equipment with associated power units. The power complement included one 90-100 drawbar horsepower (DBHP) tractor, one 100-115 DBHP tractor, one 115-150 DBHP tractor, and one 6.1 m header width, self-propelled combine. The equipment complement included a subsoiler unit equipped with either one, two, or three shanks, disk harrow, field cultivator, row conditioner, section harrow, eight-row planter, cultipacker, and a tractor-mounted sprayer. Irrigation costs were based on a 400 m center pivot system capable of irrigating 53 ha from one pivot point. Investment costs include the cost of an engine, well, pump, gearhead, generator, fuel tank and lines, and the pivot system. Total fixed costs consist of annual depreciation, interest on investment, and insurance. Annual depreciation was calculated using the straightline method with zero salvage value. Annual interest charges were based on one half of the original investment times and appropriate interest rate for each year of the study. Insurance was estimated at 1% of the original investment. Operating or direct costs include fuel, oil, labor, and engine repair. Fuel requirements were determined from engineering formulas (Spurlock et al., 1987). Results and discussion
Precipitation received at the test site and supplemental water provided by irrigation during the May-September growing season each year are presented in Table 1. Yields, gross returns, total specified costs of production, and net returns
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Table 1 Total precipiation and supplemental water from irrigation during the May-September period for soybean grown near Stoneville, MS 1987-1991 Crop Year
Rainfall Irrigation Total water
1987
1988
1989
1990
1991
444 307 751
260 369 629
716 115 831
283 198 481
388 206 594
~The long-term (50 year) average rainfall for the region during the May-September period is 475 mm. All values give in the table are in millimetres.
Table 2 Yield of soybean grown in deep tillage-controlled traffic study with and without irrigation near Stoneville, MS 1987-1991 Irrigation treatment
Tillage treatment
Irrigated
Non-irrigated
LSD (0.05)2 Compare treatments within irrigation levels Compare treatments across irrigation levels Compare irrigation levels
DT1 DT2 DT3 C Avg DT1 DT2 DT3 C Avg
Crop year 1987
1988
1989
1990
1991
Avg.
3712 3827 3824 3717 3770 3191 3263 2986 1824 2816
3535 3518 3384 3379 3454 2749 2885 2408 1154 2299
2349 2145 2322 2442 2315 2791 2803 2740 2671 2751
2132 2024 1970 1863 1997 1762 1681 1648 942 1508
3813 3806 3853 3699 3793 3793 3847 3887 3033 3640
3108 3064 3071 3020 3066 2857 2896 2734 1924 2603
305
325
177
309
343
303
431 353
604 548
226 173
336 208
565 498
330 282
~Tillage treatments: DTI, triplex subsoiler with 1 shank; DT2, parabolic subsoiler with 2 shanks; DT3, parabolic subsoiler with 3 shanks; C, disked check plot. 2Significant differences occur at the 0.05 probability level when differences in treatment means equal or exceed the LSD values shown. Values given in kilograms per hectare.
above total specified costs for each treatment in the irrigated and non-irrigated environments are presented in Tables 2-5, respectively. A summary of these data is presented in Table 6. Variable and fixed costs associated with each treatment are shown in Table 7.
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Table 3 Gross returns from soybean grown in deep tillage-controlled traffic study with and without irrigation near Stoneville, MS 1987-1991 Irrigation treatment
Irrigated
Non-irrigated
Tillage treatment 2
DT1 DT2 DT3 C DT1 DT2 DT3 C
Crop year 1987
1988
1989
1990
1991
Avg.
796 821 820 797 684 700 640 391
974 969 932 931 757 795 663 318
509 465 503 529 605 607 594 579
462 438 427 403 382 364 357 204
798 796 806 774 794 805 813 635
708 698 698 687 644 654 613 425
t Gross returns were calculated annually as the product of treatment yields and seasonal average price. Seasonal average prices for soybean for 1987-1991 were $0.2146, $0.2756, $0.2168, $0.2168, and $0.2094 per kilogram respectively. 2Tillage treatments: DTI, triplex subsoiler with 1 shank; DT2, parabolic subsoiler with 2 shanks; DT3, parabolic subsoiler with 3 shanks; C, disked check plot. Values in dollars per hectare. Table 4 Specified costs of production for soybean grown in deep tillage-controlled traffic study with and without irrigation near Stoneville, MS 1987-1991 Irrigation treatment
Irrigated
Non-irrigated
Tillage treatment1
DT1 DT2 DT3 C DT1 DT2 DT3 C
Crop year 1987
1988
1989
1990
1991
Avg.
498 499 500 478 317 318 317 289
493 493 493 471 307 308 306 277
423 423 424 402 268 269 269 245
537 537 538 514 376 377 377 350
563 563 565 539 404 405 406 376
503 503 504 481 334 335 335 307
ITillage treatments: DT1, triplex subsoiler with 1 shank; DT2, parabolic subsoiler with 2 shanks; DT3, parabolic subsoiler with 3 shanks; C, disked check plot, Values in dollars per hectare.
Seed yield Yields from all tillage treatments in the irrigated environment were similar in all years except 1989 (Table 2 ). In 1989, yields from DT2 (2145 kg ha- 1) were lower than the check (2442 kg ha - l ) and DT1 (2349 kg ha -1 ) treatments. Precipitation and supplemental water from the sprinkler irrigation system provided adequate soil moisture in all treatment plots throughout each
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Table 5 Net returns above specified costs for soybean grown in deep tillage-controlled traffic study with and without irrigation near Stoneville, MS 1987-1991 Irrigation treatment
Irrigated
Non-irrigated
Tillage treatment
DT1 DT2 DT3 C DT1 DT2 DT3 C
Crop year 1987
1988
1989
1990
1991
Avg.
298 322 320 319 367 382 323 102
481 476 439 460 450 487 357 41
86 42 79 127 337 338 325 334
-75 -99 - 111 -111 6 -13 -20 -146
235 233 242 235 390 400 407 259
205 195 194 206 310 319 278 118
1Tillage treatments: DT1, triplex subsoiler with 1 shank; DT2, parabolic subsoiler with 2 shanks; DT3, parabolic subsoiler with 3 shanks; C, disked check plot. Values in dollars per hectare. Table 6 Summary of soybean yield, gross income, specified costs and net returns for the conventional check and a deep-tilled treatment in an irrigated and non-irrigated environment on Tunica clay, 1987-1991 Irrigation treatment ~
Tillage treatment 2
Yield (kg ha-~ )
Gross income ($ h a - ' )
Spec. costs ($ h a - ~)
Net return ($ ha-~ )
N1 I N1 I
C C DT2 DT2
1924 3020 2896 3064
425 687 654 698
307 481 335 503
118 206 319 195
qrrigation treatments are NI (non-irrigated) and I (irrigated). 2Tillage treatments are C (conventional disked check) and DT2 (deep tilled with a parabolic subsoiler with two shanks).
production season, thereby over-shadowing any positive effects of deep tillage on soybean yields. In the non-irrigated environment, yields from all deep-tilled treatments were similar all years except 1988 and higher than yields from the check treatment all years except 1989 when all yields were similar (Table 2). In the fall of 1988, deep tillage of the specified plots was delayed because of rain received after harvest. Between harvest date (13 October 1988 ) and the deep tillage operation (19 December 1988), a total of 140 mm was received, and this prevented thorough fracture of the soil profile. Adequate and timely rainfall was also received during the reproductive period of 1989 and thus alleviated all visible evidence of drought stress. Soil moisture tension data recorded for the first 3 years of this experiment indicate the soil moisture tension of all treatments in the irrigated environ-
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Table 7 Average variable costs, fixed expenses, and total costs for soybean grown in deep tillage-controlled traffic study with and without irrigation near Stoneville, MS 1987-1991 Irrigation/tillage Variable costs 2 treatment i Fuel
I-DTI NI-DT1 I-DT2 NI-DT2 I-DT3 NI-DT3 I-C NI-C
Total cost Labor
All other 4
Fixed expense s
Mean 3 Range
Mean Range
Mean Range
Mean Range
45 16 45 16 45 16 41 12
43 40 43 40 43 40 35 31
116 102 116 103 116 102 112 95
204 81 205 81 205 82 198 74
27-52 12-22 27-52 12-22 27-52 12-22 23-48 9-17
37-52 33-48 39-52 33-48 37-52 33-48 29-43 25-40
82-127 79-117 81-128 80-118 83-128 80-118 80-123 72-109
191-215 69-98 192-215 70-98 192-216 70-99 186-208 64-91
503 334 504 335 504 335 481 307
Irrigation treatments are irrigated (I) and non-irrigated (NI). Tillage treatments are: DT 1, triplex subsoiler; DT2, parabolic subsoiler with 2 shanks; DT3, parabolic subsoiler with three shanks; C, disked check plot. 2Variable costs of herbicides for all treatments ranged from $54 to $130 ha-~ with a mean of $95 ha -t. 3Means for all categories represent the 5-year average. 4All other expenses include costs of seed, insecticides, repair and maintenance, interest on operating capital, and hauling costs. SFixed expenses include costs of tractors, self-propelled equipment, implements, and the irrigation system.
ment was maintained at less than 2 bars, whereas in the non-irrigated environment moisture tension in the check treatment was near 12 bars and considerably higher than the moisture tension in the deep-tilled treatments (Wesley and Smith, 1991 ). The higher soil moisture tension in the check treatment was a function of rainfall patterns that resulted in moisture deficits, subsequent plant stress, and depressed yields. There was no visible evidence of drought stress in any of the deep-tilled plots during any year, whereas the non-irrigated check plots exhibited severe wilting in 1987, 1988, and 1990. The low yields in all irrigated treatments and all deep-tilled treatments in the non-irrigated environment in 1990 were attributed to the severe infestation of stem canker in the Asgrow 5980 cultivar. The extremely low yield of the non-irrigated check treatment in 1990 (942 kg h a - ~) was attributed to both stem canker and moisture stress. In 1991, all non-irrigated yields were high owing to timely rainfall received during the reproductive period. Irrigation improved the check plot yield by 22% (666 kg ha-~ ) and deep tillage in the irrigated plots increased yields an additional 4% (125 kg h a - l ) . In the non-irrigated plots, deep tillage improved yield by 27% (809 kg ha -1 ). The 388 m m of precipitation received was sufficient for the non-irrigated plots to produce yields similar to the irrigated plots.
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The relative increase in soybean yield owing to irrigation in production systems with conventional tillage is shown in Fig. 1. Irrigation greatly increased soybean yields all years except 1989 when total available water from precipitation and supplemental irrigation during the growing season exceeded 800 mm. As total water available from precipitation and/or irrigation approached 1000 mm the predicted soybean yield response to irrigation approached zero. The negative response occurs as a result of a water logged profile with insufficient aeration. This type of response was observed in 1989 owing to precipitation events immediately following irrigation. Soybean yield response to deep tillage relative to conventional tillage in non-irrigated production systems is plotted against growing season precipitation in Fig. 2. These data indicate the yield response to deep tillage was greater in the drier growing seasons. Deep tillage in the fall increased soybean yields 150% in 1988 when growing season precipitation was only 260 mm and increased yields 50% when growing season precipitation equaled the longterm average for the region (475 mm). When May-September precipitation approached 700 mm, soybean yield increases were virtually zero. These yield increases resulted from increased water infiltration and storage, internal water o~"
1987
200 i
1988 1~9 199t?
15o -~
100
>-
50
g~
o i
-50
i
i
i
200
0
Total Water
i
400
During
i
600
May - Sept.
i
i
i
800
( p r e c i p . + irrigation,
1000 mm)
Fig. l. Soybean yield response to irrigation in production systems with conventional tillage. 1987 1988 1989 1990 i 4~ • 1991
200
i •
150
100
=
50
=
.
-
.
o
-5C 200 Precipitation
400 During
600
800
May-Sept.
(mm)
1000
Fig. 2. Soybean yield response to deep tillage relative to conventional tillage in non-irrigated production systems.
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0~- 2 0 0 ' t~
150 y = 32.31 - 0042 x
---= 100 "1o ~-
50
g, o -50
i
i
i
200
i
400
i
i
600
i
i
800
i
1000
Total Water During May - Sept. (precip. + irrigation, mm)
Fig. 3. Soybeanyieldresponseto irrigationin productionsystemswith conventionaltillagerelative to non-irrigatedproductionsystemswith deeptillage. movement and drainage, and an overall enhanced soil structure that increased nutrient availability and allowed deeper rooting. The similarity of the yield response of soybean to irrigation during the growing season in production systems with conventional tillage relative to non-irrigated production systems with deep tillage in the fall is shown in Fig. 3. Relative soybean yield increases as a result of irrigation were small, ranged from 17% in 1988 to - 13% in 1989 and averaged only 4% over the 5-year study. Over the 5-year study, yields of soybean from all irrigated treatments were similar. Yields from the deep-tilled treatments in the non-irrigated environment averaged 92% of the yields from comparable treatments in the irrigated environment. The similarity of these yields indicates deep tillage in the fall provided basically the same benefits as irrigation of soybean during the reproductive period. However, yields from the irrigated check treatment averaged 57% higher than the yield of the non-irrigated check treatment. This comparison points out the positive benefits of irrigation to soybean grown in conventional production systems. In the non-irrigated environment, yield data also indicate the average yield from the deep-tilled treatments averaged 47% higher than the average yield of the check treatment. Thus, deep tillage of Tunica clay in the fall when the soil profile was dry significantly enhanced yield potential over that provided by a conventional disk harrow for seedbed preparation. Economic returns
Gross returns (Table 3) from all irrigated treatments were virtually the same each year because all treatment yields were similar each year. However, gross returns across years varied considerably because of year-to-year yield differences and differences in the seasonal average prices. Seasonal prices for
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1987-1991 averaged $0.2146 kg -1, $0.2756 kg -1, $0.2168 kg -1, $0.2168 kg- 1, and $0.2094 kg- 1, respectively. In the non-irrigated environment, gross returns to all deep-tilled treatments were considerably higher than from the check treatment all years except 1989 when yields were similar. Over the 5year experiment, average gross returns to the non-irrigated deep-tilled treatments ($637 ha -~ ) averaged 500/0 higher ($212 ha -1 ) than from the nonirrigated check treatment ($425 ha-1 ) and 91% as high as the average gross returns to all irrigated treatments ($698 h a - l ) . Specified costs of production (Table 4) for all irrigated deep-tilled treatments were very similar each year and averaged $503 ha-1, which was $22 h a - ~higher than the specified costs of production of the irrigated check treatment ($481 ha-a ). In the non-irrigated environment, specified costs of production were considerably less; however, similar relationships were established between treatments. Specified costs for all non-irrigated deep-tilled treatments averaged $28 ha-~ higher than the check treatment ($335 vs. $307 ha-l). Net returns to all irrigated treatments were approximately the same in a given year, but varied from year to year (Table 5 ). The highest net returns were recorded in 1988 and were attributed to a high yield (Table 2 ) and price of $0.2756 kg-1. The lowest net returns were recorded in 1990 and were attributed to the lower than normal yield levels caused by the severe infestation with stem canker disease. Gross income in 1990 combined with average specified costs of production resulted in negative net returns to all irrigated treatments that ranged from - $75 to - $111 h a - 1. In 199 l, exceptionally high yields and gross incomes were recorded. However, the abnormally high specified costs of production were attributed to the costs of replanting and application of pre-emergence and post-emergence herbicides owing to excessive rainfall after planting; thus net returns were reduced considerably. Over the 5-year experiment, the average net returns to all irrigated treatments ranged from $194 to $206 h a - 1 In the non-irrigated environment net returns to all deep-tilled treatments greatly exceeded net returns from the check treatment all years except 1989. These higher returns are directly related to the significantly higher yields of the deep-tilled treatments. In 1989, yields from all treatments were similar and thus resulted in net returns that were virtually identical. In 1990, when yields of all treatments were reduced by stem canker, yields from all deeptilled treatments were sufficient to virtually offset specified costs of production, whereas yields of the check treatment were so low that sizeable negative net returns ( - $146 h a - 1) resulted. Over the 5-year experiment, average net returns above specified costs for all deep-tilled treatments ($302 ha-~ ) were 156% higher than average net returns from the check treatment ($118 h a - ~).
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Economic summary
A comparative summary of the data for the conventional check treatment (C) and the deep-tilled treatment with two subsoiler shanks (DT2) is presented in Table 6. Conventional production practices for soybean in the mid-southern United States include land preparation with a disk harrow, field cultivator, and/or spring-tooth harrow. Soybeans are then planted in the prepared seedbed and grown with or without irrigation during the reproductive period. In most instances soybeans are grown in non-irrigated environments. This production system corresponds to the non-irrigated conventional treatment where the net returns averaged $118 h a - l over the 5-year study. When supplemental irrigation is utilized in conventional production systems, net returns would be typical of the returns from the irrigated conventional treatment that averaged $206 ha -1. These higher returns were a direct result of supplemental irrigation that increased yields 1096 kg ha -l and gross income $262 ha -1, whereas specified costs increased only $174 h a - 1. Thus, in conventional production systems, irrigation increased the average net returns to soybean by 75% ($88 h a - l ) . In non-irrigated production systems on Tunica clay that include deep tillage (subsoiling) in the fall in lieu of supplemental irrigation during the crop's reproductive period, net returns to the deep-tilled treatment averaged $319 h a - 1 and were 170% higher than the net returns from non-irrigated conventional production systems ($118 h a - 1). These highly favorable net returns to deep tillage are attributed to the significantly higher yields of the deep-tilled treatment (2896 vs. 1924 kg h a - 1). The higher yields of the deep-tilled treatment increased gross income $229 ha-1 ($654 vs. $425 ha -1 ) while the specified costs of production with deep tillage increased only $28 ha-1 ($335 vs. $307 h a - 1) The average net returns to the non-irrigated deep-tilled treatment were 55% higher than returns to the irrigated conventional treatment ($319 vs. 206 h a - l ) . Yields and gross income of these treatments were similar. However, the specified costs of production of the irrigated conventional treatment exceeded the cost of the non-irrigated deep-tilled treatment by $146 ha- 1. These higher costs were attributed to the irrigation equipment and associated expenses and significantly reduced the net returns to the irrigated conventional treatment. The average net returns to the non-irrigated deep-tilled treatment also averaged 64% higher than returns to the irrigated deep-tilled treatment ($319 vs. $195 h a - 1). Yields and gross income were similar, however the additional costs associated with irrigation ($168 h a - 1) significantly reduced net returns of the irrigated treatment. Irrigation during the reproductive season failed to increase yields over that attained by deep tillage in the fall.
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Conclusion Production of soybean in a non-irrigated environment with deep tillage in the fall in lieu of supplemental irrigation during the reproductive period: ( 1 ) produced yields similar to those produced in conventional production systems with irrigation; (2) produced significantly higher yields than those produced in conventional production systems without irrigation; (3) produced net returns that greatly exceeded net returns from conventional production systems with and without irrigation. Acknowledgments The authors sincerely appreciate the expert technical assistance provided by Ray Adams and John Black in the conduct of the field experiments, and preparation and economic analysis of the data.
References Barbosa, L.R., Diaz, O. and Barber, R.G., 1989. Effects of deep tillage on soil properties, growth and yield ofsoya in a compacted ustochrept in Santa Cruz, Bolivia. Soil Tillage Res., 15:5163. Barrentine, W.L. and Tupper, G.R., 1983. Tillage and weed control practices in soybeans grown on Sharkey clay soil. Miss. Agric. For. Exp. Stn. Bull., 918, 7 pp. Boerma, H.R. and Ashley, D.A., 1982. Irrigation, row spacing, and genotype effects on late and ultra-late planted soybeans. Agron. J., 74: 995-999. Boone, F.R., 1988. Weather and other environmental factors influencing crop responses to tillage and traffic. Soil Tillage Res., 11: 283-324. Cochran, W.G. and Cox, G.M., 1957. Experimental designs. 2nd Edn., Wiley, New York, 611 PP. Dumas, W.T., Trouse, A.C., Smith, L.A., Kummer, F.A. and Gill, W.R., 1973. Development and evaluation of tillage and other cultural practices in a controlled traffic system for cotton in the southern coastal plains. Transactions ofASAE, 16 (5): 872-880. Feldman, M. and Domier, K., 1970. Wheel traffic effects on soil compaction and growth of wheat. Can. Agric. Eng., 12:8-11. Heatherly, L.G., 1981. Soybean response to tillage of Sharkey clay soil. MS Agric. For. Exp. Sta. Bull. 892. Heatherly, L.G., 1983. Response of soybean cultivars to irrigation of a clay soil. Agron. J., 75: 859-864. Heatherly, L.G., 1984. Soybean response to irrigation of Mississippi River Delta soils. USDAARS Rep. ARS-I 8. US Govt. Print Office, Washington, DC. Heatherly, L.G. and Elmore, C.D., 1986. Irrigation and planting date effects on soybeans grown on clay soil. Agron. J., 78: 576-580.
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Heatherly, L.G., Music, J.A. and Hamill, J.G., 1986. Economic analysis of stale seedbed concept of soybean production on clay soil. Miss. Agric. For. Exp. Stn. Bull. 944, 13 pp. Jensen, M.E. and Sletten, W.H., 1965. Effects of alfalfa, crop sequence and tillage practices on intake rate of Pullman silty clay loam and grain yields. USDA Conserv. Res. Rept. No. 1. Kirkegaard, J.A., So, H.B., Troedson, R.J. and Wallis, E.S., 1992. The effect of compaction on the growth of pigeonpea on clay soils. I. Mechanisms of crop response and seasonal effects on a vertisol in a sub-humid environment. Soil Tillage Res., 24: 107-127. Lamers, J.G., Perdok, U.D., Lumkes, L.M. and Klooster, J.J., 1986. Controlled traffic farming systems in The Netherlands. Soil Tillage Res., 8: 65-76. Lowry, F.E., Taylor, H.M. and Huck, M.G., 1970. Growth rate and yield of cotton as influenced by depth and bulk density of soil pans. Soil Sci. Soc. Am. Proc., 34: 306-309. Mathers, A.C., Wilson, G.C., Schneider, A.D. and Scott, P., 1971. Sugarbeet response to deep tillage, nitrogen and phosphorus on Pullman clay loam. Agron. J., 63: 474-477. Menzel, R.G., Eck, J.P.E. and Wilkins, D.E., 1968. Reduction of Strontium-85 uptake in field crops by deep plowing and sodium carbonate application. Agron. J., 60: 499-502. Morris, D.T., 1975. Interrelationships among soil bulk density, soil moisture and the growth and development of corn. M.Sc. Thesis, Univ. of Guelph, Guelph, Ont., 77 pp. Music, J.T., Dusek, D.A. and Schneider, A.D., 1981. Deep tillage of irrigated Pullman clay loam-a long-term evaluation. Trans. ASAE, 24:1515-1519. Negi, S.C., McKyes, E., Taylor, F., Douglas, E. and Raghavan, G.S.V., 1980. Crop performance as affected by traffic and tillage in a clay soil. Trans. ASAE, 23:1364-1368. Phillips, R.E. and Kirkham, D., 1962. Soil compaction in the field and corn growth. Agron. J., 54: 29-34. Ramseur, E.L., Quisenberry, V.L., Wallace, S.U. and Palmer, J.H., 1984. Yield and yield components of 'Braxton' soybeans as influenced by irrigation and intrarow spacing. Agron. J., 76: 442-446. Raney, W.A., 1971. Compaction as it affects soil conditions. In: K.K. Barnes, W.M. Carleton, H.M. Taylor, R.I. Throckmorton and G.E. Vanden Berg (Editors), Compaction of Agricultural Soils. ASAE, St. Joseph, MI. Saini, G.R. and Lantagne, H.M., 1974. Le tassement du sol. Actualite Agricole, 34:11-13. Salassi, M.E., Musick, J.A., Heatherly, L.G. and Hamill, J.G., 1984. An economic analysis of soybean yield response to irrigation of Mississippi River Delta soils. Miss Agric. For. Exp. Stn. Bull. 928, 16 pp. Smith, L.A., 1992. Response of cotton to deep tillage on Tunica clay. Proc. 1992 Beltwide Cotton Prod. Res. Conf. pp. 505-506. Soane, B.D., 1985. Traction and transport as related to cropping systems. Proc. Int. Conf. Soil Dynamics. Auburn, AL. Vol. 5, pp. 863-935. Spurlock, S.R., Hood, III, E.M., Hamill, J.G. and Thomas J.G., 1987. Cost estimates for nine irrigation systems in the Mississippi Delta. Mississippi State Univ., Agric. Econ. Res. Report No. 175. Taylor, J.H., 1983. Benefits of permanent traffic lanes in a controlled traffic crop production system. Soil Tillage Res., 3: 385-395. Voorhees, W.B., 1987. Assessment of soil susceptibility to compaction using soil and climatic data bases. Soil Tillage Res. 10: 29-38. Wesley, R.A. and Smith, L.A., 1991. Response of soybean to deep tillage with controlled traffic on clay soil. Trans. ASAE, 34:113-118. Williford, J.R., 1980. A controlled-traffic system for crop production. Trans. ASAE, 23: 65-70.
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0167-1987/93/$06.00 © 1993 - Elsevier Science Publishers B.V. All rights reserved
Economic analysis of irrigation and deep tillage in soybean production systems on clay soil Richard A. Wesley*,a, Lowrey A. Smitha, Stan R. Spurlockb aUSDA-ARS Field Crops Mechanization, Stoneville, MS 38776, USA bAgricultural Economics Department, Mississippi State University, Mississippi State, MS 39762, USA (Accepted 30 March 1993)
Abstract
A 5-year study ( 1987-1991 ) was conducted on a Tunica clay (clayey over loamy, montmorillonitic, non-acid, thermic Vertic Haplaquept) to determine effects of irrigation and deep tillage on soybean yields and economic returns. Irrigation increased average yield of the conventional check treatment (disked) by 57% (3020 vs. 1924 kg ha - ~). Under irrigation, yields from all deep-tilled treatments and the conventional check treatment were similar and averaged 3066 kg h a - 1. Under non-irrigated conditions, yields from all deep-tilled treatments were similar, averaged 2829 kg ha- ~, and were higher than the conventional check treatment that averaged 1924 kg ha-1. Average yields from the nonirrigated deep-tilled treatments were 92% as high as yields from comparable treatments with irrigation. Irrigation increased the average net returns of the conventional check treatment 75% ($206 vs. $118 h a - 1). Over the 5-year study, average net returns to all irrigated treatments were similar and ranged from $194 to $206 ha- t. Net returns to the non-irrigated deep-tilled treatments averaged 156% higher than returns from the non-irrigated conventional check treatment ($302 vs. $118 ha- 1) and was attributed to the higher yields of the deep-tilled treatments (2829 vs. 1924 kg h a - ~). Net returns to the non-irrigated deep-tilled treatments also averaged 47% higher than returns from the irrigated conventional check treatment ($302 vs. $206 ha-1 ). This difference was attributed to the similarity of yields (2829 vs. 3020 kg ha -~ ) and the sizeable difference in specified costs of production ($335 vs. $481 h a - 1) that favored non-irrigated production of soybean with deep-tillage.
Introduction
Clayey soils occupy approximately 3.7 M ha or about 50% of the land area in the lower Mississippi River alluvial flood plain. Soybean (Glycine m a x (L.) Merr. ) is planted on approximately 2.5 M ha or about 67% of this area. In non-irrigated production systems, soybean yields from these soils are usually low, but with irrigation, sizeable yield increases are possible most years (Heatherly, 1983; Heatherly and Elmore, 1986). Similar results have been reported by other researchers for similar soils with relatively low available water-holding capacity (Boerma and Ashley, 1982; Ramseur et al., 1984). Corresponding author.
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Economic analysis (Salassi et al., 1984) has shown that properly timed irrigation of soybean (furrow or sprinkler) grown on the clayey soils of the mid-southern United States can result in increased returns to land, management, and general farm overhead. However, they reported a yield increase of approximately 1000 kg ha- ~was required to recover the total costs associated with irrigation when based on a seasonal price of $0.2206 per kilogram. Another study in the mid-southern United States (Heatherly et al., 1986 ) investigated the economic effects of furrow irrigation on soybean grown in conventional production systems. Data indicate net returns to soybean grown on clay soil with and without supplemental irrigation averaged $329 and $238 ha-~, respectively or a $91 ha-~ advantage to irrigation. Compaction of soil, whether natural or artificial, alters the soil's condition and affects growth of plants. Compaction adversely affects the content and movement of air, water, heat, and nutrients in the soil (Raney, 1971 ). Early research tended to suggest that an increase in the soil's bulk density would automatically reduce crop yield. Yield of potatoes (Solanum tuberosum) was reduced 22% (Saini and Lantagne, 1974), whereas Phillips and Kirkham (1962) and Morris ( 1975 ) reported reductions in corn (Zea mays L.) yields of 10 and 22%, respectively, owing to compaction. Compaction from machinery traffic reduced wheat (Triticum aestivum L.) growth (Feldman and Domier, 1970) and cotton (Gossypium hirsutum L.) yields (Lowry et al., 1970; Negi et al., 1980). Recent research has demonstrated that for each crop, soil and season, there is an optimum level of compaction for maximum crop yield. Compaction above or below this optimum will result in decreased yield (Soane, 1985 ). As a general rule, responses to tillage and field traffic are variable, but can be explained by a combination of: ( 1 ) site and soil-related factors; (2) plant and crop-related factors; (3) weather and climate-related factors; (4) soil and crop-management factors, including tillage and traffic (Boone, 1988). Predictive equations of the net economic effect of compaction have been developed recently using basic soil mechanics theory, soil survey data, long-term climatic data bases, and field research results (Voorhees, 1987). Kirkegaard et al. (1992) studied the effect of compaction on the growth of pigeonpea (Cajanus cajan) on clay soils in southeast Queensland, Australia. Results of their studies indicated growth restrictions resulting from compaction were primarily related to reduced water uptake resulting from decreased infiltration and storage of water, and restricted root growth. Seasonal conditions, in particular the distribution of rainfall, exerted a strong influence on plant response. Yield reductions resulting from compaction varied from 100% in a very dry season to 0% in a wetter season. The reduced impact of compaction in the wetter season was associated with reduced levels of soil strength during early root growth and a decreased reliance on stored subsoil water for growth.
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65
Researchers have also attempted to reduce or eliminate effects of compaction on crop growth and yield. Dumas et al. ( 1973 ) developed a controlled traffic system for cotton production systems that increased cotton yields over yields from conventional production systems. In 1980, the concept of deep tillage (subsoiling) in conjunction with controlled traffic systems was investigated and cotton yields were significantly increased (Williford, 1980 ). The historical belief that a loose soil ensures highest crop yields and the economic incentive for more energy-efficient cropping systems has promoted the development of controlled traffic production systems (Taylor, 1983; Lamers et al., 1986). Deep tillage has resulted in increased yields of numerous crops. Deep tillage of a clay loam increased yield of sugarbeet (Beta vulgaris) (Mathers et al., 1971 ), cabbage (Brassica oleracea var. capitata) and soybean (Menzel et al., 1968 ). Deep tillage of a compacted ustochrept soil increased soybean yields 21-24% compared with conventional tillage (disked) and increased the partial gross margins $52-58 ha -1 (Barbosa et al., 1989). Deep tillage has also been shown to be a practical method for increasing water intake rates and depth of profile wetting of slowly permeable structured clays (Music et al., 1981 ). Researchers found that deep tillage of clay soils when the upper profile was dry doubled the average water intake rate during the next crop season when compared with shallow tillage (Jensen and Sletten, 1965 ). Current tillage practices recommended for soybean production on the heavy soils in the mid-southern United States do not include deep tillage or deep disking. The natural shrinking and swelling which causes the soil to crack as it dries is credited for the elimination of the compacted layers caused by machinery traffic. Deep tillage of a Sharkey clay near Stoneville, MS did not increase soybean yields when compared with conventional disking for seedbed preparation (Heatherly, 1981; Barrentine and Tupper, 1983). However, all tillage inputs were applied in late spring when the upper profile of the soil was wet. Excavation and observation of rooting patterns of cotton on Tunica clay when the soil was cracked revealed compacted blocks of soil beneath the plow layer (Smith, 1992). The density of these blocks severely restricted root penetration and confined a majority of the roots to the vicinity of the block surfaces. Therefore, a large portion of the soil nutrients and water stored in the soil blocks were not readily available for plant growth. Deep tillage (subsoiling) in the fall when the soil profile is dry disrupts the orientation of the blocks and reduces their size. The infiltration of water is enhanced because the soil blocks no longer fit together to form a high density continuum when they swell. Loose soil material resulting from the disruption of the soil block arrangement now separates the blocks, and this allows higher rates of internal water movement which results in more water storage during wet periods. Excess water is able to drain from the profile and this improves
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the aeration of the soil and allows the soil to warm up more quickly in the spring for earlier planting. Surface runoff and soil erosion are also reduced. The objectives of this study were to: ( 1 ) determine the effect of irrigation and deep tillage on soybean yield in a controlled traffic production system; and (2) determine the economic returns to irrigation and deep tillage. Materials and methods
General Field studies were conducted from 1987 through 1991 near Stoneville, MS on a Tunica clay soil (clayey over loamy, montmorillonitic, non-acid, thermic Vertic Haplaquept). In general, the clayey layer on Tunica soil ranges from 0.46 to 0.75 m thick and overlies a clay loam or a silty clay loam subsoil. The soil is characterized by a high percentage of clay, 1-2% organic matter, poor internal drainage, a high level of fertility, low bulk density ( 1.5-1.6 g cm-3), and 0.5 to 2.0% slope. The soil compositon of the A horizon (upper 0.75 m) at the test site was composed of 1% sand, 36% silt, and 63% clay; whereas the B horizon was composed of 2% sand, 70% silt, and 28% clay. The field area for this study had a bulk density of approximately 1.6 g cm -3 and a slope of approximately 0.5% and had been continuously cropped in non-irrigated, conventional-tilled soybean. The experiment included four tillage treatments in both an irrigated and non-irrigated environment. The experiment was conducted with irrigation treatments (main plots) and tillage treatments (subplots) in a split-plot arrangement in a randomized complete block design with four replicates each year. Subplots were 16.2 m wide and 28 m long. Traffic lanes were established on 2 m centers and remained in the same location throughout the study period. A production zone was centered between each traffic lane and contained four rows of soybean spaced 0.45 m apart. Therefore, a 0.66 m space was left between the outside rows of adjacent production zones for machinery traffic. Tillage treatments were randomly assigned to the subplots at the beginning of the test period and remained in the same location for the 5-year test period. Tillage treatments included three deep tillage methods and a conventional disked check plot. Treatments are identified as follows: DT1 (triplex subsoiler with 1 shank), DT2 (parabolic subsoiler with 2 shanks), DT3 (parabolic subsoiler with 3 shanks), and C (disked check). The DT1 unit consisted of a straight subsoiler shank with a 0.76 m wide wing attached to the point of elevation to give additional soil fracture. The DT2 unit contained two parabolic shanks spaced 1 m apart, whereas the DT3 unit contained three parabolic shanks spaced 0.5 m apart. All deep-tilled plots were subsoiled to a depth of 0.4-0.5 m each year with the tillage implements centered in each respective production zone. The check plot (C) was prepared in a conventional manner
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67
with a disk-harrow followed by a field cultivator. All tillage inputs were accomplished on 1 October 1986, 19 October 1987, 19 December 1988, 11 October 1989, and 1 October 1990 after soybean harvest. All plots remained as tilled throughout the winter season. Prior to planting soybean each year, all winter vegetation was eliminated either by a broadcast application of paraquat or by tilling with a disk-harrow. All plots were then tilled with a field cultivator followed by a spike-tooth harrow to smooth out the rough areas in the deep-tilled plots. These procedures provided suitable seedbeds for planting soybean. Asgrow 5980 variety was planted all years except 1991. Because of a severe infestation of stem canker (Diaporthephaseolorum var. caulivora) disease in 1990, a resistant variety of soybean (Pioneer 9592 ) was planted in 1991. Planting dates during the study was 19 May 1987, 16 May 1988, 12 May 1989, 8 May 1990, and 13 May 1991. In 1991 soybean were first planted on 24 April. However, because of excessive rainfall after planting that flooded all plots, all soybean was replanted on 13 May 1991. Metolachlor plus metribuzin herbicides were broadcast-applied at planting from 1987 through 1990 for grass and broadleafweed control in all treatment plots. In 1990, a mixture of bentazon and acifluorfen was applied post-emergence. In 1991, a broadcast application ofa metribuzin and chlorimuron mixture was applied pre-emergence, and a mixture of bentazon and acifluorfen post-emergence. All herbicides were applied at the labelled rates and provided adequate weed control. Excellent soybean stands (35 plants m -2) were obtained each year. All machinery traffic was confined to the established traffic lanes. Each year all treatment plots in the irrigated environment were sprinklerirrigated from a lateral-move system whenever soil water potential, as determined by tensiometers located at the 30-cm depth in three replicates of the check plots, averaged between - 0 . 0 5 and - 0 . 0 7 MPa. Previous research with soybean on clay soil indicated this tensiometer placement depth was optimum for maximum yield response (Heatherly, 1984). Tralomethrin was sprayed on 27 August 1987 and thiodicarb on 12 and 26 August 1988 for control of cabbage loopers (Trichoplusia ni). The combine used for harvesting had 2 m wheel spacings, therefore, harvest traffic was also confined to the established traffic lanes. The plot combine's cutter bar was 2 m wide and harvested a complete production zone with each pass. Three production zones were harvested from each subplot for yield determinations. Seed moisture was corrected to 13% dry basis. Harvest occurred between 27 September and 13 October each year. Analysis of variance was used to evaluate the significance of treatment effects on soybean yields. Where significant differences occurred, mean separation was achieved with an LSD 0.05 value calculated with either the whole unit or subunit error terms, or an adjusted error term made up of whole unit and subunit errors (Cochran and Cox, 1957 ).
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Economic analysis Crop enterprise budgets were developed annually for each treatment in the irrigated and non-irrigated environments. Application rates for all the variable inputs were those recommended and used for crop production in this study. Crop prices used in the budgets were the seasonal average prices received for the year as reported by the Mississippi Agricultural Statistics Service, 1987-1991. Gross returns were calculated annually as the product of treatment yields and seasonal average price. Variable costs were the actual prices paid by farmers each year and include the cost of herbicide, seed, labor, fuel, repair and maintenance of equipment, and interest on operating capital. Fixed costs include costs of tractors and other self-propelled equipment, implements, and the irrigation system. Total specified costs include both variable and fixed costs. Net returns per acre were calculated as the difference between gross income and total specified costs. Average net returns were calculated as the mean of the annual net returns over the study period. In constructing the budgets no charges were included for land, management, or overhead. Performance rates on all field operations were based on using eightrow equipment with associated power units. The power complement included one 90-100 drawbar horsepower (DBHP) tractor, one 100-115 DBHP tractor, one 115-150 DBHP tractor, and one 6.1 m header width, self-propelled combine. The equipment complement included a subsoiler unit equipped with either one, two, or three shanks, disk harrow, field cultivator, row conditioner, section harrow, eight-row planter, cultipacker, and a tractor-mounted sprayer. Irrigation costs were based on a 400 m center pivot system capable of irrigating 53 ha from one pivot point. Investment costs include the cost of an engine, well, pump, gearhead, generator, fuel tank and lines, and the pivot system. Total fixed costs consist of annual depreciation, interest on investment, and insurance. Annual depreciation was calculated using the straightline method with zero salvage value. Annual interest charges were based on one half of the original investment times and appropriate interest rate for each year of the study. Insurance was estimated at 1% of the original investment. Operating or direct costs include fuel, oil, labor, and engine repair. Fuel requirements were determined from engineering formulas (Spurlock et al., 1987). Results and discussion
Precipitation received at the test site and supplemental water provided by irrigation during the May-September growing season each year are presented in Table 1. Yields, gross returns, total specified costs of production, and net returns
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Table 1 Total precipiation and supplemental water from irrigation during the May-September period for soybean grown near Stoneville, MS 1987-1991 Crop Year
Rainfall Irrigation Total water
1987
1988
1989
1990
1991
444 307 751
260 369 629
716 115 831
283 198 481
388 206 594
~The long-term (50 year) average rainfall for the region during the May-September period is 475 mm. All values give in the table are in millimetres.
Table 2 Yield of soybean grown in deep tillage-controlled traffic study with and without irrigation near Stoneville, MS 1987-1991 Irrigation treatment
Tillage treatment
Irrigated
Non-irrigated
LSD (0.05)2 Compare treatments within irrigation levels Compare treatments across irrigation levels Compare irrigation levels
DT1 DT2 DT3 C Avg DT1 DT2 DT3 C Avg
Crop year 1987
1988
1989
1990
1991
Avg.
3712 3827 3824 3717 3770 3191 3263 2986 1824 2816
3535 3518 3384 3379 3454 2749 2885 2408 1154 2299
2349 2145 2322 2442 2315 2791 2803 2740 2671 2751
2132 2024 1970 1863 1997 1762 1681 1648 942 1508
3813 3806 3853 3699 3793 3793 3847 3887 3033 3640
3108 3064 3071 3020 3066 2857 2896 2734 1924 2603
305
325
177
309
343
303
431 353
604 548
226 173
336 208
565 498
330 282
~Tillage treatments: DTI, triplex subsoiler with 1 shank; DT2, parabolic subsoiler with 2 shanks; DT3, parabolic subsoiler with 3 shanks; C, disked check plot. 2Significant differences occur at the 0.05 probability level when differences in treatment means equal or exceed the LSD values shown. Values given in kilograms per hectare.
above total specified costs for each treatment in the irrigated and non-irrigated environments are presented in Tables 2-5, respectively. A summary of these data is presented in Table 6. Variable and fixed costs associated with each treatment are shown in Table 7.
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Table 3 Gross returns from soybean grown in deep tillage-controlled traffic study with and without irrigation near Stoneville, MS 1987-1991 Irrigation treatment
Irrigated
Non-irrigated
Tillage treatment 2
DT1 DT2 DT3 C DT1 DT2 DT3 C
Crop year 1987
1988
1989
1990
1991
Avg.
796 821 820 797 684 700 640 391
974 969 932 931 757 795 663 318
509 465 503 529 605 607 594 579
462 438 427 403 382 364 357 204
798 796 806 774 794 805 813 635
708 698 698 687 644 654 613 425
t Gross returns were calculated annually as the product of treatment yields and seasonal average price. Seasonal average prices for soybean for 1987-1991 were $0.2146, $0.2756, $0.2168, $0.2168, and $0.2094 per kilogram respectively. 2Tillage treatments: DTI, triplex subsoiler with 1 shank; DT2, parabolic subsoiler with 2 shanks; DT3, parabolic subsoiler with 3 shanks; C, disked check plot. Values in dollars per hectare. Table 4 Specified costs of production for soybean grown in deep tillage-controlled traffic study with and without irrigation near Stoneville, MS 1987-1991 Irrigation treatment
Irrigated
Non-irrigated
Tillage treatment1
DT1 DT2 DT3 C DT1 DT2 DT3 C
Crop year 1987
1988
1989
1990
1991
Avg.
498 499 500 478 317 318 317 289
493 493 493 471 307 308 306 277
423 423 424 402 268 269 269 245
537 537 538 514 376 377 377 350
563 563 565 539 404 405 406 376
503 503 504 481 334 335 335 307
ITillage treatments: DT1, triplex subsoiler with 1 shank; DT2, parabolic subsoiler with 2 shanks; DT3, parabolic subsoiler with 3 shanks; C, disked check plot, Values in dollars per hectare.
Seed yield Yields from all tillage treatments in the irrigated environment were similar in all years except 1989 (Table 2 ). In 1989, yields from DT2 (2145 kg ha- 1) were lower than the check (2442 kg ha - l ) and DT1 (2349 kg ha -1 ) treatments. Precipitation and supplemental water from the sprinkler irrigation system provided adequate soil moisture in all treatment plots throughout each
R.A. Wesley et al. / Soil & Tillage Research 28 (1993) 63- 78
71
Table 5 Net returns above specified costs for soybean grown in deep tillage-controlled traffic study with and without irrigation near Stoneville, MS 1987-1991 Irrigation treatment
Irrigated
Non-irrigated
Tillage treatment
DT1 DT2 DT3 C DT1 DT2 DT3 C
Crop year 1987
1988
1989
1990
1991
Avg.
298 322 320 319 367 382 323 102
481 476 439 460 450 487 357 41
86 42 79 127 337 338 325 334
-75 -99 - 111 -111 6 -13 -20 -146
235 233 242 235 390 400 407 259
205 195 194 206 310 319 278 118
1Tillage treatments: DT1, triplex subsoiler with 1 shank; DT2, parabolic subsoiler with 2 shanks; DT3, parabolic subsoiler with 3 shanks; C, disked check plot. Values in dollars per hectare. Table 6 Summary of soybean yield, gross income, specified costs and net returns for the conventional check and a deep-tilled treatment in an irrigated and non-irrigated environment on Tunica clay, 1987-1991 Irrigation treatment ~
Tillage treatment 2
Yield (kg ha-~ )
Gross income ($ h a - ' )
Spec. costs ($ h a - ~)
Net return ($ ha-~ )
N1 I N1 I
C C DT2 DT2
1924 3020 2896 3064
425 687 654 698
307 481 335 503
118 206 319 195
qrrigation treatments are NI (non-irrigated) and I (irrigated). 2Tillage treatments are C (conventional disked check) and DT2 (deep tilled with a parabolic subsoiler with two shanks).
production season, thereby over-shadowing any positive effects of deep tillage on soybean yields. In the non-irrigated environment, yields from all deep-tilled treatments were similar all years except 1988 and higher than yields from the check treatment all years except 1989 when all yields were similar (Table 2). In the fall of 1988, deep tillage of the specified plots was delayed because of rain received after harvest. Between harvest date (13 October 1988 ) and the deep tillage operation (19 December 1988), a total of 140 mm was received, and this prevented thorough fracture of the soil profile. Adequate and timely rainfall was also received during the reproductive period of 1989 and thus alleviated all visible evidence of drought stress. Soil moisture tension data recorded for the first 3 years of this experiment indicate the soil moisture tension of all treatments in the irrigated environ-
72
R.A. Wesley et al. ~Soil & Tillage Research 28 (1993) 63-78
Table 7 Average variable costs, fixed expenses, and total costs for soybean grown in deep tillage-controlled traffic study with and without irrigation near Stoneville, MS 1987-1991 Irrigation/tillage Variable costs 2 treatment i Fuel
I-DTI NI-DT1 I-DT2 NI-DT2 I-DT3 NI-DT3 I-C NI-C
Total cost Labor
All other 4
Fixed expense s
Mean 3 Range
Mean Range
Mean Range
Mean Range
45 16 45 16 45 16 41 12
43 40 43 40 43 40 35 31
116 102 116 103 116 102 112 95
204 81 205 81 205 82 198 74
27-52 12-22 27-52 12-22 27-52 12-22 23-48 9-17
37-52 33-48 39-52 33-48 37-52 33-48 29-43 25-40
82-127 79-117 81-128 80-118 83-128 80-118 80-123 72-109
191-215 69-98 192-215 70-98 192-216 70-99 186-208 64-91
503 334 504 335 504 335 481 307
Irrigation treatments are irrigated (I) and non-irrigated (NI). Tillage treatments are: DT 1, triplex subsoiler; DT2, parabolic subsoiler with 2 shanks; DT3, parabolic subsoiler with three shanks; C, disked check plot. 2Variable costs of herbicides for all treatments ranged from $54 to $130 ha-~ with a mean of $95 ha -t. 3Means for all categories represent the 5-year average. 4All other expenses include costs of seed, insecticides, repair and maintenance, interest on operating capital, and hauling costs. SFixed expenses include costs of tractors, self-propelled equipment, implements, and the irrigation system.
ment was maintained at less than 2 bars, whereas in the non-irrigated environment moisture tension in the check treatment was near 12 bars and considerably higher than the moisture tension in the deep-tilled treatments (Wesley and Smith, 1991 ). The higher soil moisture tension in the check treatment was a function of rainfall patterns that resulted in moisture deficits, subsequent plant stress, and depressed yields. There was no visible evidence of drought stress in any of the deep-tilled plots during any year, whereas the non-irrigated check plots exhibited severe wilting in 1987, 1988, and 1990. The low yields in all irrigated treatments and all deep-tilled treatments in the non-irrigated environment in 1990 were attributed to the severe infestation of stem canker in the Asgrow 5980 cultivar. The extremely low yield of the non-irrigated check treatment in 1990 (942 kg h a - ~) was attributed to both stem canker and moisture stress. In 1991, all non-irrigated yields were high owing to timely rainfall received during the reproductive period. Irrigation improved the check plot yield by 22% (666 kg ha-~ ) and deep tillage in the irrigated plots increased yields an additional 4% (125 kg h a - l ) . In the non-irrigated plots, deep tillage improved yield by 27% (809 kg ha -1 ). The 388 m m of precipitation received was sufficient for the non-irrigated plots to produce yields similar to the irrigated plots.
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R.A. Wesley et al. / Soil & Tillage Research 28 (1993) 63- 78
The relative increase in soybean yield owing to irrigation in production systems with conventional tillage is shown in Fig. 1. Irrigation greatly increased soybean yields all years except 1989 when total available water from precipitation and supplemental irrigation during the growing season exceeded 800 mm. As total water available from precipitation and/or irrigation approached 1000 mm the predicted soybean yield response to irrigation approached zero. The negative response occurs as a result of a water logged profile with insufficient aeration. This type of response was observed in 1989 owing to precipitation events immediately following irrigation. Soybean yield response to deep tillage relative to conventional tillage in non-irrigated production systems is plotted against growing season precipitation in Fig. 2. These data indicate the yield response to deep tillage was greater in the drier growing seasons. Deep tillage in the fall increased soybean yields 150% in 1988 when growing season precipitation was only 260 mm and increased yields 50% when growing season precipitation equaled the longterm average for the region (475 mm). When May-September precipitation approached 700 mm, soybean yield increases were virtually zero. These yield increases resulted from increased water infiltration and storage, internal water o~"
1987
200 i
1988 1~9 199t?
15o -~
100
>-
50
g~
o i
-50
i
i
i
200
0
Total Water
i
400
During
i
600
May - Sept.
i
i
i
800
( p r e c i p . + irrigation,
1000 mm)
Fig. l. Soybean yield response to irrigation in production systems with conventional tillage. 1987 1988 1989 1990 i 4~ • 1991
200
i •
150
100
=
50
=
.
-
.
o
-5C 200 Precipitation
400 During
600
800
May-Sept.
(mm)
1000
Fig. 2. Soybean yield response to deep tillage relative to conventional tillage in non-irrigated production systems.
74
R.A. Wesley et al. / Soil & Tillage Research 28 (1993) 63- 78
0~- 2 0 0 ' t~
150 y = 32.31 - 0042 x
---= 100 "1o ~-
50
g, o -50
i
i
i
200
i
400
i
i
600
i
i
800
i
1000
Total Water During May - Sept. (precip. + irrigation, mm)
Fig. 3. Soybeanyieldresponseto irrigationin productionsystemswith conventionaltillagerelative to non-irrigatedproductionsystemswith deeptillage. movement and drainage, and an overall enhanced soil structure that increased nutrient availability and allowed deeper rooting. The similarity of the yield response of soybean to irrigation during the growing season in production systems with conventional tillage relative to non-irrigated production systems with deep tillage in the fall is shown in Fig. 3. Relative soybean yield increases as a result of irrigation were small, ranged from 17% in 1988 to - 13% in 1989 and averaged only 4% over the 5-year study. Over the 5-year study, yields of soybean from all irrigated treatments were similar. Yields from the deep-tilled treatments in the non-irrigated environment averaged 92% of the yields from comparable treatments in the irrigated environment. The similarity of these yields indicates deep tillage in the fall provided basically the same benefits as irrigation of soybean during the reproductive period. However, yields from the irrigated check treatment averaged 57% higher than the yield of the non-irrigated check treatment. This comparison points out the positive benefits of irrigation to soybean grown in conventional production systems. In the non-irrigated environment, yield data also indicate the average yield from the deep-tilled treatments averaged 47% higher than the average yield of the check treatment. Thus, deep tillage of Tunica clay in the fall when the soil profile was dry significantly enhanced yield potential over that provided by a conventional disk harrow for seedbed preparation. Economic returns
Gross returns (Table 3) from all irrigated treatments were virtually the same each year because all treatment yields were similar each year. However, gross returns across years varied considerably because of year-to-year yield differences and differences in the seasonal average prices. Seasonal prices for
R.A. Wesley et al. / Soil & Tillage Research 28 (1993) 63- 78
75
1987-1991 averaged $0.2146 kg -1, $0.2756 kg -1, $0.2168 kg -1, $0.2168 kg- 1, and $0.2094 kg- 1, respectively. In the non-irrigated environment, gross returns to all deep-tilled treatments were considerably higher than from the check treatment all years except 1989 when yields were similar. Over the 5year experiment, average gross returns to the non-irrigated deep-tilled treatments ($637 ha -~ ) averaged 500/0 higher ($212 ha -1 ) than from the nonirrigated check treatment ($425 ha-1 ) and 91% as high as the average gross returns to all irrigated treatments ($698 h a - l ) . Specified costs of production (Table 4) for all irrigated deep-tilled treatments were very similar each year and averaged $503 ha-1, which was $22 h a - ~higher than the specified costs of production of the irrigated check treatment ($481 ha-a ). In the non-irrigated environment, specified costs of production were considerably less; however, similar relationships were established between treatments. Specified costs for all non-irrigated deep-tilled treatments averaged $28 ha-~ higher than the check treatment ($335 vs. $307 ha-l). Net returns to all irrigated treatments were approximately the same in a given year, but varied from year to year (Table 5 ). The highest net returns were recorded in 1988 and were attributed to a high yield (Table 2 ) and price of $0.2756 kg-1. The lowest net returns were recorded in 1990 and were attributed to the lower than normal yield levels caused by the severe infestation with stem canker disease. Gross income in 1990 combined with average specified costs of production resulted in negative net returns to all irrigated treatments that ranged from - $75 to - $111 h a - 1. In 199 l, exceptionally high yields and gross incomes were recorded. However, the abnormally high specified costs of production were attributed to the costs of replanting and application of pre-emergence and post-emergence herbicides owing to excessive rainfall after planting; thus net returns were reduced considerably. Over the 5-year experiment, the average net returns to all irrigated treatments ranged from $194 to $206 h a - 1 In the non-irrigated environment net returns to all deep-tilled treatments greatly exceeded net returns from the check treatment all years except 1989. These higher returns are directly related to the significantly higher yields of the deep-tilled treatments. In 1989, yields from all treatments were similar and thus resulted in net returns that were virtually identical. In 1990, when yields of all treatments were reduced by stem canker, yields from all deeptilled treatments were sufficient to virtually offset specified costs of production, whereas yields of the check treatment were so low that sizeable negative net returns ( - $146 h a - 1) resulted. Over the 5-year experiment, average net returns above specified costs for all deep-tilled treatments ($302 ha-~ ) were 156% higher than average net returns from the check treatment ($118 h a - ~).
76
R.A. Wesley et al. / Soil dk Tillage Research 28 (1993) 63-78
Economic summary
A comparative summary of the data for the conventional check treatment (C) and the deep-tilled treatment with two subsoiler shanks (DT2) is presented in Table 6. Conventional production practices for soybean in the mid-southern United States include land preparation with a disk harrow, field cultivator, and/or spring-tooth harrow. Soybeans are then planted in the prepared seedbed and grown with or without irrigation during the reproductive period. In most instances soybeans are grown in non-irrigated environments. This production system corresponds to the non-irrigated conventional treatment where the net returns averaged $118 h a - l over the 5-year study. When supplemental irrigation is utilized in conventional production systems, net returns would be typical of the returns from the irrigated conventional treatment that averaged $206 ha -1. These higher returns were a direct result of supplemental irrigation that increased yields 1096 kg ha -l and gross income $262 ha -1, whereas specified costs increased only $174 h a - 1. Thus, in conventional production systems, irrigation increased the average net returns to soybean by 75% ($88 h a - l ) . In non-irrigated production systems on Tunica clay that include deep tillage (subsoiling) in the fall in lieu of supplemental irrigation during the crop's reproductive period, net returns to the deep-tilled treatment averaged $319 h a - 1 and were 170% higher than the net returns from non-irrigated conventional production systems ($118 h a - 1). These highly favorable net returns to deep tillage are attributed to the significantly higher yields of the deep-tilled treatment (2896 vs. 1924 kg h a - 1). The higher yields of the deep-tilled treatment increased gross income $229 ha-1 ($654 vs. $425 ha -1 ) while the specified costs of production with deep tillage increased only $28 ha-1 ($335 vs. $307 h a - 1) The average net returns to the non-irrigated deep-tilled treatment were 55% higher than returns to the irrigated conventional treatment ($319 vs. 206 h a - l ) . Yields and gross income of these treatments were similar. However, the specified costs of production of the irrigated conventional treatment exceeded the cost of the non-irrigated deep-tilled treatment by $146 ha- 1. These higher costs were attributed to the irrigation equipment and associated expenses and significantly reduced the net returns to the irrigated conventional treatment. The average net returns to the non-irrigated deep-tilled treatment also averaged 64% higher than returns to the irrigated deep-tilled treatment ($319 vs. $195 h a - 1). Yields and gross income were similar, however the additional costs associated with irrigation ($168 h a - 1) significantly reduced net returns of the irrigated treatment. Irrigation during the reproductive season failed to increase yields over that attained by deep tillage in the fall.
R.A. Wesley et al. / Soil & Tillage Research 28 (1993) 63-78
77
Conclusion Production of soybean in a non-irrigated environment with deep tillage in the fall in lieu of supplemental irrigation during the reproductive period: ( 1 ) produced yields similar to those produced in conventional production systems with irrigation; (2) produced significantly higher yields than those produced in conventional production systems without irrigation; (3) produced net returns that greatly exceeded net returns from conventional production systems with and without irrigation. Acknowledgments The authors sincerely appreciate the expert technical assistance provided by Ray Adams and John Black in the conduct of the field experiments, and preparation and economic analysis of the data.
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Heatherly, L.G., Music, J.A. and Hamill, J.G., 1986. Economic analysis of stale seedbed concept of soybean production on clay soil. Miss. Agric. For. Exp. Stn. Bull. 944, 13 pp. Jensen, M.E. and Sletten, W.H., 1965. Effects of alfalfa, crop sequence and tillage practices on intake rate of Pullman silty clay loam and grain yields. USDA Conserv. Res. Rept. No. 1. Kirkegaard, J.A., So, H.B., Troedson, R.J. and Wallis, E.S., 1992. The effect of compaction on the growth of pigeonpea on clay soils. I. Mechanisms of crop response and seasonal effects on a vertisol in a sub-humid environment. Soil Tillage Res., 24: 107-127. Lamers, J.G., Perdok, U.D., Lumkes, L.M. and Klooster, J.J., 1986. Controlled traffic farming systems in The Netherlands. Soil Tillage Res., 8: 65-76. Lowry, F.E., Taylor, H.M. and Huck, M.G., 1970. Growth rate and yield of cotton as influenced by depth and bulk density of soil pans. Soil Sci. Soc. Am. Proc., 34: 306-309. Mathers, A.C., Wilson, G.C., Schneider, A.D. and Scott, P., 1971. Sugarbeet response to deep tillage, nitrogen and phosphorus on Pullman clay loam. Agron. J., 63: 474-477. Menzel, R.G., Eck, J.P.E. and Wilkins, D.E., 1968. Reduction of Strontium-85 uptake in field crops by deep plowing and sodium carbonate application. Agron. J., 60: 499-502. Morris, D.T., 1975. Interrelationships among soil bulk density, soil moisture and the growth and development of corn. M.Sc. Thesis, Univ. of Guelph, Guelph, Ont., 77 pp. Music, J.T., Dusek, D.A. and Schneider, A.D., 1981. Deep tillage of irrigated Pullman clay loam-a long-term evaluation. Trans. ASAE, 24:1515-1519. Negi, S.C., McKyes, E., Taylor, F., Douglas, E. and Raghavan, G.S.V., 1980. Crop performance as affected by traffic and tillage in a clay soil. Trans. ASAE, 23:1364-1368. Phillips, R.E. and Kirkham, D., 1962. Soil compaction in the field and corn growth. Agron. J., 54: 29-34. Ramseur, E.L., Quisenberry, V.L., Wallace, S.U. and Palmer, J.H., 1984. Yield and yield components of 'Braxton' soybeans as influenced by irrigation and intrarow spacing. Agron. J., 76: 442-446. Raney, W.A., 1971. Compaction as it affects soil conditions. In: K.K. Barnes, W.M. Carleton, H.M. Taylor, R.I. Throckmorton and G.E. Vanden Berg (Editors), Compaction of Agricultural Soils. ASAE, St. Joseph, MI. Saini, G.R. and Lantagne, H.M., 1974. Le tassement du sol. Actualite Agricole, 34:11-13. Salassi, M.E., Musick, J.A., Heatherly, L.G. and Hamill, J.G., 1984. An economic analysis of soybean yield response to irrigation of Mississippi River Delta soils. Miss Agric. For. Exp. Stn. Bull. 928, 16 pp. Smith, L.A., 1992. Response of cotton to deep tillage on Tunica clay. Proc. 1992 Beltwide Cotton Prod. Res. Conf. pp. 505-506. Soane, B.D., 1985. Traction and transport as related to cropping systems. Proc. Int. Conf. Soil Dynamics. Auburn, AL. Vol. 5, pp. 863-935. Spurlock, S.R., Hood, III, E.M., Hamill, J.G. and Thomas J.G., 1987. Cost estimates for nine irrigation systems in the Mississippi Delta. Mississippi State Univ., Agric. Econ. Res. Report No. 175. Taylor, J.H., 1983. Benefits of permanent traffic lanes in a controlled traffic crop production system. Soil Tillage Res., 3: 385-395. Voorhees, W.B., 1987. Assessment of soil susceptibility to compaction using soil and climatic data bases. Soil Tillage Res. 10: 29-38. Wesley, R.A. and Smith, L.A., 1991. Response of soybean to deep tillage with controlled traffic on clay soil. Trans. ASAE, 34:113-118. Williford, J.R., 1980. A controlled-traffic system for crop production. Trans. ASAE, 23: 65-70.