HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Abstract Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via ISI Web of Science (8) Citing Articles via Google Scholar Google Scholar Articles by Wesley, R. A. Articles by Spurlock, S. R. Search for Related Content PubMed Articles by Wesley, R. A. Articles by Spurlock, S. R. Agricola Articles by Wesley, R. A. Articles by Spurlock, S. R. Related Collections Other Soil Management Other Soil Types Tillage Crop Rotation Systems Other Cropping Systems Economics Production Agriculture

PRODUCTION PAPERS

Deep Tillage and Crop Rotation Effects on Cotton, Soybean, and Grain Sorghum on Clayey Soils

^a USDA-ARS Application and Production Technical Res. Unit, Stoneville, MS 38776
^b Dep. of Agric. Economics, Mississippi State Univ., Mississippi State, MS 39762

Corresponding author (rwesley{at}ars.usda.gov)

	ABSTRACT

TOP ABSTRACT INTRODUCTION Materials and methods Results and discussion Conclusions REFERENCES

 
Deep tillage (subsoiling) of clayey soils in the fall when the profile is dry is a new concept that results in increased yields and net returns from soybean [Glycine max (L). Merr.] grown without irrigation. Crop rotation may also result in increased crop yields. Field studies were conducted on Tunica clay (clayey over loamy, smectitic, nonacid, thermic, Vertic Haplaquept) near Stoneville, MS (33°26' N lat) to determine the individual and combined effects of fall deep tillage and crop rotations on crop yields and net returns. Treatments included monocrop cotton [Gossypium hirsutum (L.)], soybean, and grain sorghum [Sorghum bicolor (L.) Moench], and biennial rotations of cotton with grain sorghum and soybean with grain sorghum grown without irrigation and in either a conventional-till (CT) or deep-till (DT) production system. Yields from all cotton and soybean crop sequences grown in the DT respectively averaged 541 kg ha^-1 and 525 kg ha^-1 greater than comparable cotton (2184 kg ha^-1) and soybean (2983 kg ha^-1) crop sequences grown in the CT. Net returns from monocrop cotton ($552 ha^-1) and soybean ($462 ha^-1) in the DT respectively averaged $392 ha^-1 and $121 ha^-1 more than similar crop sequences in the CT. Rotations increased cotton and soybean yields but not net returns because of the low value of the grain sorghum component. These data indicate that fall deep tillage should be incorporated into monocrop cotton and soybean crop sequences to maximize and stabilize net returns from these crops on Tunica clay.

Abbreviations: CT, conventional-till production system • CV, coefficient of variation • DT, deep-till production system

	INTRODUCTION

TOP ABSTRACT INTRODUCTION Materials and methods Results and discussion Conclusions REFERENCES

 
CLAYEY SOILS occupy approximately 3.9 million ha or about 50% of the total land area of the lower Mississippi River alluvial flood plain (Pettiet, 1974). These soils are characterized by a high percentage of clay, slow internal drainage, and a high water-holding capacity.

The montmorillonitic clays exhibit a high degree of swelling and shrinking as the moisture content of the soil profile cycles between wet and dry. The clay fraction swells and severely restricts water movement into and through the soil profile when these soils approach the maximum water-holding capacity. As water is removed from the soils, the clay fraction shrinks and vertical cracks often form in the profile. When this occurs during the summer growing season, the roots of crops planted on these soils are damaged and often broken as the cracks widen over time.

These shrink–swell clay soils have mainly been planted to nonirrigated monocrop soybean. Soybean yields from this system of production are typically low (1300–1600 kg ha^-1) (Heatherly, 1983, 1988; Heatherly et al., 1990; Wesley and Cooke, 1988) and marginally profitable (Wesley and Cooke, 1988; Wesley et al., 1994a, 1994b, 1995). Cotton, grain sorghum, and rice (Oryza sativa L.) are also adapted to these soils, but they're planted on fewer hectares.

The use of large, heavy field equipment early in the season when the soil is wet may compact soil or reduce its productivity (Phillips and Kirkham, 1962; Gameda et al., 1987; Voorhees, 1985). When soil is compacted, its particles are rearranged such that the total pore space is decreased, whereas bulk density is increased (Singer and Munns, 1987). In most cases, the larger soil pores (macropores) are destroyed by the compactive force exerted on the soil, which results in reduced content and movement of air, water, heat and nutrients in the soil. Compaction also increases soil strength, thereby increasing the resistance to root penetration. When plant roots cannot explore the entire soil structure, plant nutrients become positionally unavailable.

Studies conducted by Akram and Kemper (1979) indicated that soil water content determined the degree of compaction for a given load. They described a positive correlation between soil water content and compaction. Larson et al. (1980) found that the bulk density increased linearly with soil clay content up to a content of 33%. They also determined that medium-textured soils with expanding-type clays compacted the most under high stress.

Deep tillage in the fall when the soil profile is dry disrupts the orientation of these soil blocks and reduces their size. It also increases the volume of loose soil material between these blocks, which improves infiltration by increasing the volume of macropores in the soil. Water moves more quickly through macropores than through the smaller pores in the soil blocks (Ritchie et al., 1972). Higher infiltration rates result in a larger volume of moistened soil following a rainfall event. Excess water is able to drain from the profile, which improves aeration of the soil and allows it to warm more quickly in the spring. Surface runoff and soil erosion are also reduced.

Deep tillage has increased the yields of numerous crops (Barbosa et al., 1989; Mathers et al., 1971), and it has proven to be a practical method for increasing water intake rates and depth-of-profile wetting of slowly permeable clays (Jensen and Sletten, 1965; Music et al., 1981). Recent research on a nonirrigated Tunica clay in Mississippi (Wesley and Smith, 1991) indicated that deep tillage in the fall when the upper profile was dry significantly reduced moisture tension levels during soybean reproductive stages R3 through R6 (Fehr and Caviness, 1977). Soybean yields from DTs averaged 2892 kg ha^-1 and were significantly higher than the 1950 kg ha^-1 yield from the CTs. Economic analyses of results from the same study indicated that net returns from the nonirrigated DT averaged $182 ha^-1 more than the average returns from the nonirrigated CT ($119 ha^-1) and $96 ha^-1 more than the average returns from irrigated CT ($205 ha^-1) (Wesley et al., 1993, 1994b).

Crop rotation is a process that also increases crop yields (Fahad et al., 1982; Baird and Bernard, 1984; Boquet et al., 1986; Dabney et al., 1988). Biennial rotations of two summer crops often improves the yield of both crops. In the midwestern USA, a biennial rotation of corn (Zea mays L.) and soybean produced significant increases in the yields of both crops (Crookston and Kurle, 1989; Meese et al., 1991). A biennial rotation of soybean and grain sorghum has also been used effectively to enhance yields (Dabney et al., 1988; Peterson and Varvel, 1989; Roder et al., 1989a). The cause of the higher yields is related to either increased soil fertility, improved soil physical properties, improved weed control, or reduced incidences of disease, nematode, and insect pests.

Fahad et al. (1982) reported that continuous soybean cropping resulted in less water retention, lower cumulative water infiltration, and decreased soil aggregate stability compared with values measured under corn–soybean and grain sorghum–soybean rotational systems. Baird and Bernard (1984) and Young et al. (1986) claim that crop rotations tend to control plant parasitic nematode populations, whereas Boquet et al. (1986) suggest that the reduction in disease is a vital factor. In corn–wheat (Triticum aestivum L.)–soybean and sorghum–wheat–soybean rotation sequences, crop yields were enhanced and johnsongrass [Sorghum halapense (L.) Pers.] was effectively controlled during the soybean sequence (Litsinger and Moody, 1976). Roder et al. (1989b) found that soybean root densities at most sample depths were greater when the previous crop was grain sorghum rather than soybean.

The objective of this study was to determine the individual and combined effects of fall deep tillage and crop rotations on yields and net returns from nonirrigated monocrop cotton, soybean, grain sorghum, and biennial rotations of cotton with grain sorghum and soybean with grain sorghum grown on the clayey soils of the lower Mississippi River alluvial flood plain. Grain sorghum was selected as the most desirable rotation crop because of its drought tolerance in nonirrigated crop production systems.

	Materials and methods

TOP ABSTRACT INTRODUCTION Materials and methods Results and discussion Conclusions REFERENCES

 
General
Field studies were conducted from 1993 through 1997 on Tunica clay near Stoneville, MS. The surface layer of clay on Tunica clay ranges from 0.5 to 0.75 m thick and overlies a clay loam or silty clay loam subsoil. The soil of the A horizon (upper 0.75 m) at the test site was composed of 1% sand, 36% silt, and 63% clay while 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 1.4 g cm^-3.

The experiment was established in a split-plot design with a randomized complete block arrangement of treatments in four replicates each year. Whole plots were assigned to either a CT or a DT. Subplots consisted of crop sequences of continuous cotton, grain sorghum, and soybean and biennial rotations of cotton with grain sorghum and soybean with grain sorghum (Table 1). Each phase of each sequence was repeated each year, resulting in a total of seven crop sequences annually in each crop production system. Each subplot was 9.1 m wide and 30 m long and contained 12 bedded rows that were spaced 0.75 m apart. The designated crop rotation sequences were first grown in 1992; however, data from that year could not be used because the entire study area had been planted to monocrop soybean in 1991.

Crop rotation sequences used in the study spread field operations over a broader time frame than monocrop systems, and thus allowed timely and more efficient use of equipment. All crops were planted in April and May. Grain sorghum and soybean required minimum production inputs, whereas cotton required extensive inputs and timely application of numerous insecticides. Grain sorghum was harvested early in September, followed by soybean in mid-September. Cotton was harvested with a spindle picker from mid-September through early October.

Crop sequences were randomly assigned to subplots at the beginning of the test period and remained in the same location for the 5-yr study. All winter vegetation was eliminated from the subplots by a broadcast application of either paraquat [1, 1-dimethyl-4, 4-bipyridinium ion] or glyphosate [N-(phosphonomethyl)glycine] before planting each year. Approximately 30 d later, all subplots were smoothed with a row conditioner to prepare a suitable seedbed for planting. A brief summary of the production inputs and costs for each crop is presented below.

Cotton
Each year, cotton was planted at the rate of 11 kg ha^-1 (120000 seed ha^-1). `DES-119' was planted in 1993, 1994, and 1995, and `Suregrow 125' was planted in 1996 and 1997. Weeds were controlled with preemergence applications of metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl) acetamide] and fluometuron {N, N-dimethyl-N-[3-(trifluoromethyl)phenyl]urea}each year. Nitrogen was applied as a urea ammonium nitrate (UAN) solution in split applications beside each row. Nitrogen levels totaled 112, 112, 156, 180, and 200 kg ha ^-1 from 1993 through 1997. Nitrogen levels in 1993 and 1994 were based on recommendations for cotton grown on sandy soils. However, the crop's appearance indicated that the N level was low, probably because of denitrification on the clayey soils. Therefore, N rates were adjusted upward in 1994, 1995, and 1996 to compensate for potential denitrification. Cultivation was used as needed. Postemergence herbicides were used in 1993, 1994, and 1997 for control of johnsongrass. Insecticides were applied each year as needed and as recommended by a crop consultant; applications ranged from as few as three in 1995 to as many as nine in 1993. Cotton was defoliated between 12 and 28 September and harvested between 26 September and 21 October each year. Six rows from each subplot were harvested with a plot picker for determination of seed cotton yields. Lint yields were calculated to be 35% of the harvested seed cotton yield, whereas cottonseed weight was calculated to be 60% of seed cotton yield. Total specified costs for monocrop cotton in the DT ranged from $907 ha^-1 in 1995 to $1237 ha^-1 in 1997 and averaged $1024 ha^-1 over the 5-yr study.

Soybean
Maturity Group V cultivars were planted each year and consisted of `Pioneer 9592' from 1993 through 1995 and `DPL-3588' in 1996 and 1997. Seeding rates were approximately 50 kg ha ^-1 (325000 seed ha^-1). Seed was treated with metalaxyl [N-(2, 6-dimetyl-phenyl)-N-(methoxy-acetyl)-DL-alanine methyl ester] each year. Metolachlor and metribuzin [4-amino-6-(1, 1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one]were applied as a preemergence tank mix each year, and cultivation was used as needed. Postemergence herbicides were applied in 1993, 1994, and 1995 for control of johnsongrass. Harvest dates ranged from 29 September to 5 October each year. Two subsamples, each consisting of five rows, were harvested with a plot combine from each subplot for yield determination. Soybean yields were reported at 130 g kg ^-1 moisture. Total specified production costs for monocrop soybean in the DT ranged from $285 ha^-1 in 1996 to $403 ha^-1 in 1993 and averaged $355 ha^-1 over the 5-yr study.

Sorghum
`Pioneer 8333' grain sorghum was planted each year. Seeding rate was about 7.2 kg ha^-1 (247000 seed ha^-1). Metolachlor plus atrazine [6-chloro-N-ethyl-N¹-(1-methylethyl)-1,3,5-triazine-2,4-diamine] was applied at preemergence each year. All grain sorghum plots were fertilized with UAN at planting and at Growth Stage 2 (Vanderlip and Reeves, 1972), receiving a total of 180 kg ha^-1 N each year. Two applications of dimethoate [phosphorodithioic acid O,O-dimethyl S-(2-(methylamino)-2-oxoethyl) ester] were used each year for control of sorghum midge [Contarina sorghicola (Coquillett)]. Harvest dates ranged from 29 September to 5 October each year. Two subsamples, each consisting of five rows, were harvested with a plot combine from each subplot for yield determinations. Sorghum yields were reported at 140 g kg^-1 moisture. Total specified production costs for monocrop grain sorghum in the DT ranged from $393 ha^-1 in 1996 to $485 ha^-1 in 1993 and averaged $444 ha^-1 over the 5-yr study.

Economic Analyses
Crop enterprise budgets were developed annually for each crop sequence (Spurlock and Laughlin, 1992). Application rates for all of the variable inputs were those recommended and used for crop production in these experiments. Performance rates for all field operations were based on using eight-row equipment with associated power units. Crop prices used in the budgets were the market-year average prices reported by the Mississippi Agricultural Statistics Service (1993)(–1997). Gross income was calculated as the product of crop yield and market-year average price. Variable expenses were the actual prices paid by farmers each year and included the costs of fertilizer, herbicide, insecticides, seed, labor, fuel, repair and maintenance of equipment, and interest on operating capital. Fixed expenses included cost of tractors, self-propelled equipment, and implements. Annual depreciation was calculated using the straight-line method with zero salvage value. Annual interest charges were based on one-half of the original investment times a nominal interest rate on borrowed capital. Total specified expenses included both variable and fixed expenses. No charges were included in any budget for land, management, or general farm overhead. Net returns above specified expenses were calculated annually as the difference between gross income and total specified expenses. Average net returns from each crop sequence were calculated as the mean of the annual net returns over the 5-yr study.

The power complement included one tractor with 67 to 89 kW and one with 104 to 119 kW, one self-propelled combine with a 7.6-m header width, one 4-row cotton picker, and a high-clearance sprayer. The equipment complement included a stalk shredder, subsoiler, disk hipper, row conditioner, planter, liquid fertilizer applicator, cultivator, tractor-mounted sprayer, boll buggy, and a module builder. The farm enterprise size for the study was established to be 225 ha, based on the assumption that the subsoiler unit would be used 100 h each fall. Analysis of variance and LSD values were used each year and across years to determine the significant differences in the yields and net returns among crop production systems and crop sequences (SAS Inst., 1998).

	Results and discussion

TOP ABSTRACT INTRODUCTION Materials and methods Results and discussion Conclusions REFERENCES

 
Weather
Growing-season precipitation exceeded the long-term average each year except 1997. However, the seasonal distribution of precipitation was erratic. In 1994, rainfall received in April, June, August, and September was 196 mm less than the long-term average, whereas record rainfall received within a 10-d period in July exceeded the long-term average by 201 mm. Less than average rainfall was received in August and September of 1994 and 1995. Rainfall received between July and September of 1997 was also less than the long-term average. For the 5-yr study, the monthly maximum air temperature ranged within ±3.3°C of the 30-yr normals.

Agronomic Performance
Cotton
In both the CT and DT, the average yield from monocrop cotton and cotton rotated with grain sorghum averaged the lowest in 1993 and the highest in 1997 (Table 2). The low yields in 1993 were partially attributed to the late planting date (17 May) and less than normal rainfall in June and July. The second lowest yields were produced in 1995 when all cotton plots were replanted on 8 May because of an unacceptable plant population due to excessive rainfall (244 mm) in April. However, rainfall deficits were also recorded in May, August, and September of 1995, and thus adversely affected cotton yields.

In the CT, yields from cotton rotated with grain sorghum were higher than yields from monocrop cotton in all years. This yield increase attributed to rotation effects averaged , respectively, from 1993 through 1997. Over the 5-yr study, yields from the cotton–grain sorghum rotation in the CT averaged greater than yields from monocrop cotton in the CT (1844 kg ha^-1). In the DT, yields from the same crop sequences indicate that the cotton rotation increased yields in 1993, in 1995, , and in 1997. Over the study, yields from cotton rotated with grain sorghum rotation averaged greater than yields from monocrop cotton in the DT (2632 kg ha^-1). However, this yield increase was over and above the higher yield from monocrop cotton in the DT.

Yield data from the DT indicate that fall deep tillage increased the yield of monocrop cotton in all years. These yield increases from 1993 through 1997 averaged , and , respectively. Over the study, yields from monocrop cotton in the DT averaged greater than those in the CT (1844 kg ha^-1). This 788 kg ha^-1 increase attributed to deep tillage was greater than the increase from rotation in the CT (681 kg ha^-1) and DT (187 kg ha^-1). Over the study, yields from monocrop cotton in the DT averaged 107 kg ha^-1 greater than yields from rotated cotton in the CT (2525 kg ha^-1). Yields from rotated cotton in the CT and DT were virtually the same each year, except in 1996 when yields from rotated cotton in the DT exceeded those from the CT by . Over the study, yields from rotated cotton in the DT averaged greater than yields from rotated cotton in the CT (2525 kg ha^-1).

The combined effect of fall deep tillage and crop rotation is indicated by comparing yields from cotton rotation in the DT with yields from monocrop cotton in the CT. Yields from cotton rotation in the DT were greater in all years, exceeding monocrop cotton yields in the CT by an average of from 1993 through 1997. Over the study, the combined effects of deep tillage and rotation increased the average yield from cotton to above yields from moncrop cotton in the CT (1844 kg ha^-1).

Soybean
In the CT and DT, yields from soybean in the monocrop and rotated systems averaged the lowest in 1993 and the highest in 1997 (Table 3). Yields from soybean crop sequences in the DT were greater than those from the CT in all years. Yields from the DT exceeded yields from the CT by an average of , and from 1993 through 1997. These yield increases in the DT occurred in spite of the severe moisture deficits in August and September of 1994 and 1995 during the R5 and R6 stages of seed development. Over the study, yields from soybean crop sequences in the DT averaged greater than yields from crop sequences in the CT (2983 kg ha^-1).

The yield response to fall deep tillage was consistent and similar for monocrop soybean and for soybean rotated with grain sorghum. Yields from monocrop soybean in the DT exceeded those from monocrop soybean in the CT by an average of , and from 1993 through 1997. Yields from rotated soybean in DT exceeded those in the CT by an average of , and from 1993 through 1997. Over the study, yield from monocrop soybean in the DT averaged greater than that in the CT (2798 kg ha^-1) while soybean rotated with grain sorghum in the DT averaged greater than that in the CT (3169 kg ha^-1). As with cotton, the 589 kg ha^-1 yield increase attributed to deep tillage of monocrop soybean was greater than the increase from the rotation in the CT (371 kg ha^-1) and DT (243 kg ha^-1). Over the study, yields from monocrop soybean in the DT averaged 218 kg ha^-1 greater than those from rotated soybean in CT (3169 kg ha^-1).

The combined effect of deep tillage and crop rotation increased soybean yields above monocrop soybean yields in the CT in all years. Yields of rotated soybean in the DT exceeded monocrop CT yields by , and from 1993 through 1997. Over the study, the combined effect of deep tillage and crop rotation in the DT increased the average yield to above the average yield from monocrop soybean in the CT (2798 kg ha^-1).

Sorghum
Yield of monocrop grain sorghum declined in both production systems over time (Table 4). However, the decline was less in the DT. An increased infestation with johnsongrass that became troublesome over time was noted in monocrop grain-sorghum sequences in both the CT and DT. However, the infestation seemed to be less severe in the DT. This could be due to subsoiling in the fall that exposed more rhizomes to the soil surface and allowed better control of this perennial weed, which is closely related to grain sorghum. Johnsongrass is a major problem for grain sorghum production in the midsouthern USA; therefore, grain sorghum is only produced on a rotational basis to allow for johnsongrass control in the nonsorghum crop year.

In the CT, yields from grain sorghum in the cotton rotation exceeded monocrop sorghum yields by in 1994, in 1995, in 1997, and over the study. Rotation of grain sorghum with soybean increased grain sorghum yields by in 1997 and over the study. In the DT, rotations of grain sorghum with cotton and with soybean increased grain sorghum yields above monocrop yields in all years. Yield increases from the cotton rotation ranged from in 1993 to in 1997 and averaged over the study. Similarly, yield increases from the soybean rotation ranged from in 1993 to in 1997 and averaged over the study.

Yields from monocrop sorghum in the DT were greater than those in the CT each year and averaged greater over the study. Yields from sorghum in the cotton and soybean rotations in the DT were also greater than respective rotated yields in the CT each year, except in the cotton rotation in 1994. Over the study, yields from sorghum in the cotton and soybean rotations in the DT respectively averaged and greater than those in the CT.

The combined effects of fall deep tillage and crop rotations resulted in the greatest yield increase above the yield from monocrop grain sorghum in the CT. Over the study, yields from grain sorghum in both the cotton and soybean rotations in the DT respectively averaged and greater than those from monocrop grain sorghum in the CT.

Economic Performance
General
Yield data (Tables 2, 3, and 4) along with the market-year average prices were used to provide a basis for economic evaluations. The market-year average prices for cotton lint for crop years 1993 through 1997 were $1.28, $1.59, $1.61, $1.50, and $1.54 kg^-1 respectively, whereas cottonseed prices were $0.11 kg^-1 in all years. Market-year prices for soybean were $0.2425, $0.2058, $0.2499, $0.2620, and $0.2495 kg^-1 respectively, whereas prices for grain sorghum were $0.0882, $0.0839, $0.1059, $0.1201, and $0.0996 kg^-1, respectively. Gross income, total specified expenses, and net returns above specified expenses were calculated for each crop sequence each year. However, only net returns are presented and discussed.

Cotton
Net returns from cotton crop sequences in the DT averaged higher than those in the CT for all years (Table 5). The low yield in 1993, in conjunction with a low price for cotton lint ($1.28 kg^-1), resulted in a negative net return from monocrop cotton in the CT (-$278 ha^-1) and DT (-$143 ha^-1). Net returns from rotated cotton in both production systems in 1993 were positive because of the higher cotton yields from the rotations. However, these small returns were not sufficient to offset the larger negative returns from monocrop cotton, and thus resulted in negative net returns in both production systems. The average net returns from each production system were positive in all other years because of higher yields and higher crop prices. Over the study, net returns from cotton crop sequences in the DT ($598 ha^-1) averaged $263 ha^-1 more than similar crop sequences in the CT ($335 ha^-1).

Fall deep tillage increased net returns from monocrop cotton in all years. These increases from 1993 through 1997 averaged $135 , $221 , $406 , $735 , and $462 ha^-1 more than returns from monocrop cotton in the CT ($160 ha^-1), and over the study they averaged $392 ha^-1 more. In fact, net returns from monocrop cotton in the DT ($552 ha^-1) averaged $42 ha^-1 more than returns from rotated cotton in the CT ($510 ha^-1).

The combined effect of deep tillage and rotation resulted in net returns that averaged higher than returns from monocrop cotton in the CT for all years. These net returns averaged from 1993 through 1997 and over the study.

Soybean
Net returns from soybean crop sequences in the DT averaged higher than net returns from soybean crop sequences in the CT for all years (Table 6). Net returns from soybean in the DT exceeded those from the CT by , and from 1993 through 1997. When averaged across all years, net returns from soybean crop sequences in the DT were more than those in the CT ($384 ha^-1).

Net returns from monocrop soybean in the DT exceeded those in the CT each year and over the study. These higher returns from the DT averaged , and from 1993 through 1997 and over the study. Net returns from monocrop soybean in the DT averaged $35 ha^-1 more than net returns from the soybean rotation in the CT ($427 ha^-1).

The combined effect of fall deep tillage and crop rotation produced net returns that averaged higher than returns from monocrop soybean in the CT for all years. These returns ranged from more in 1994 to more in 1993. Over the study, the combined effect of deep tillage and rotation increased net returns above the returns from monocrop soybean in CT ($341 ha^-1).

Sorghum
Net returns from grain sorghum grown in crop sequences in the DT averaged higher than returns from similar crop sequences in the CT for all years (Table 7). These increases were small and ranged from in 1994 to in 1997 and averaged $46 ha^-1 over the study.

Net returns from each grain sorghum crop sequence in the DT were greater than returns from comparable crop sequences in the CT for all years except 1994. Over the study, net returns from sorghum grown in the cotton and soybean crop sequences in the DT respectively averaged and more than returns from comparable crop sequences in the CT.

The combined effect of deep tillage and crop rotation is reflected in the higher net returns from grain sorghum in both rotations in the DT relative to monocrop grain sorghum in the CT for all years. Net returns from grain sorghum in the cotton rotation ranged from in 1993 to in 1997 and in 1993 to in 1997 for the soybean rotation. Over the study, net returns from grain sorghum in the cotton and soybean rotations in the DT respectively averaged and more than monocrop grain sorghum in the CT ($39 ha^-1).

Economic Summary
General
Data in Table 8 presents annual net returns, overall net returns, and a measure of stability for each crop sequence in the CT and DT. For example, net returns from cotton and sorghum grown in the cotton–sorghum rotation in the CT respectively averaged $510 (Table 5) and $125 ha^-1 (Table 7). When combined over the study, they averaged $318 ha^-1 with a coefficient of variation (CV) of 58% (Table 8). A summary of these relationships for each cotton and soybean crop sequence in the CT and DT is discussed below.

Soybean
Net returns from monocrop soybean grown in the CT were relatively stable , averaged $341 ha^-1 (Table 8), and were similar to net returns from the soybean–grain sorghum rotation in the CT ($274 ha^-1) and DT ($346 ha^-1). However, variations in returns across years for the soybean–sorghum rotations in the CT and DT were among the lowest. As with cotton, net returns from monocrop soybean in the DT were stable across years , averaged $462 ha^-1, and were greater than net returns from all other soybean crop sequences. Net returns from monocrop soybean in the DT averaged more than returns from monocrop soybean in the CT, more than returns from the soybean rotation in the CT, and more than returns from the soybean rotation in the DT.

	Conclusions

TOP ABSTRACT INTRODUCTION Materials and methods Results and discussion Conclusions REFERENCES

 
Net returns from all crop sequences in the DT were higher and more stable than comparable crop sequences in the CT. Fall deep tillage increased the net returns by $392 ha^-1 for monocrop cotton, $121 ha^-1 for monocrop soybean, $91 ha^-1 for cotton–grain sorghum rotation, $72 ha^-1 for soybean–grain sorghum rotation, and $32 ha^-1 for monocrop grain sorghum. However, net returns from monocrop grain sorghum in both production systems were not sufficient to cover land rental costs (Mississippi Agricultural Statistics Service, 1993–1997).

These data clearly indicate that fall deep tillage should be incorporated into crop sequences on clayey soils to maximize and stabilize net returns from cotton and soybean. Data also show that biennial rotations of cotton and soybean with grain sorghum in the CT and DT increased yields and net returns from the cotton and soybean components in the rotations. However, the average net returns from the cotton and soybean rotation sequences in the CT and the soybean rotation sequence in the DT were significantly lower than returns from either monocrop cotton or monocrop soybean in the DT. This was because of the extremely low net returns from the grain sorghum component grown in alternate years in the rotations. Thus, the recommendation for Midsouth producers would be deep tillage of Tunica clay and similar soils in the fall, with production of monocrop cotton or soybean the following crop production season. Rotations with grain sorghum should be considered only if a significant improvement in price occurs for grain sorghum or after a need develops for rotations, such as disease, weed pressure, or government program limitations.

	ACKNOWLEDGMENTS

 
The authors appreciate the expert technical assistance provided by Ray Adams, John Black, and Debbie Boykin.

Received for publication August 27, 1999.

	REFERENCES

TOP ABSTRACT INTRODUCTION Materials and methods Results and discussion Conclusions REFERENCES

 

• Akram, M., and W.D. Kemper. 1979. Infiltration of soils as affected by the pressure and water content at the time of compaction. Soil Sci. Soc. Am. J. 43:1080–1086.[Abstract/Free Full Text]
• Baird, S.M., and E.C. Bernard. 1984. Nematode populations and community dynamics in soybean–wheat cropping and tillage regimes. J. Nematol. 16:379–386.
• Barbosa, L.R., O. Diaz, and R.G. Barber. 1989. Effects of deep tillage on soil properties, growth, and yield of soya in a compacted Ustochrept in Santa Cruz, Bolivia. Soil Tillage Res. 15:51–63.
• Boquet, D.J., A.B. Coco, and D.E. Summers. 1986. Cropping systems for higher yields. Louisiana Agric. 30:4–7.
• Crookston, R.K., and J.E. Kurle. 1989. Corn residue effect on the yield of corn and soybean grown in rotation. Agron. J. 81:229–232.[Abstract/Free Full Text]
• Dabney, S.M., E.C. McGawley, D.J. Boethel, and D.A. Berger. 1988. Short-term crop rotation systems for soybean production. Agron. J. 80:197–204.[Abstract/Free Full Text]
• Fahad, A.A., L.N. Mielke, A.D. Flowerday, and D. Swartzendruber. 1982. Soil physical properties as affected by soybean and other cropping sequences. Soil Sci. 46:377–381.
• Fehr, W.R., and C.E. Caviness. 1977. Stages of soybean development. Iowa Agric. Exp. Stn. Spec. Rep. 80.
• Gameda, S., G.S.V. Raghavan, E. McKeyes, and R. Theriault. 1987. Subsoil compaction in a clay: I. Cumulative effects. Soil Tillage Res. 10:113–122.
• Heatherly, L.G. 1983. Response of soybean cultivars to irrigation of a clay soil. Agron. J. 75:859–864.[Abstract/Free Full Text]
• Heatherly, L.G. 1988. Planting date, row spacing, and irrigation effects on soybean grown on clay soil. Agron. J. 80:227–231.[Abstract/Free Full Text]
• Heatherly, L.G., R.A. Wesley, and C.D. Elmore. 1990. Corn, sorghum, and soybean response to irrigation in the Mississippi River alluvial plain. Crop Sci. 30:665–672.[Abstract/Free Full Text]
• Jensen, M.E., and W.H. Sletten. 1965. Effects of alfalfa, crop sequence, and tillage practices on intake rate of Pullman silty clay loam and grain yields. USDA Conserv. Res. Rep. 1.
• Larson, W.E., S.C. Gupta, and R.A. Useche. 1980. Compression of agricultural soils from eight soil orders. Soil Sci. Soc. Am. J. 44:450–457.[Abstract/Free Full Text]
• Litsinger, J.A., and K. Moody. 1976. Integrated pest management in multiple cropping systems. p. 293–316. In R.I. Papendick, et al. (ed.) Multiple cropping. ASA Spec. Publ. 27. ASA, CSSA, and SSSA, Madison, WI.
• Mathers, A.C., G.C. Wilson, A.D. Schneider, and P. Scott. 1971. Sugarbeet response to deep tillage, nitrogen, and phosphorus on Pullman clay loam. Agron. J. 63:474–477.[Abstract/Free Full Text]
• Meese, B.G., P.R. Carter, E.S. Oplinger, and J.W. Pendleton. 1991. Corn/soybean rotation effect as influenced by tillage, nitrogen, and hybrid/cultivar. J. Prod. Agric. 4:74–80.
• Mississippi Agricultural Statistics Service. 1993–1997. Mississippi agricultural statistics supplement. Miss. Dep. of Agric. and Commerce, Jackson.
• Music, J.T., D.A. Dusek, and A.D. Schneider. 1981. Deep tillage of irrigated Pullman clay loam—a long-term evaluation. Trans. ASAE 24:1515–1519.
• Peterson, T.A., and G.E. Varvel. 1989. Crop yield as effected by rotation and nitrogen rate. I. Soybean. Agron. J. 81:727–731.
• Pettiet, J.V. 1974. An interpretive evaluation of soils in the Yazoo–Mississippi Delta area for crop production. Mississippi Agric. Forestry Exp. Stn. Bull. 808.
• Phillips, R.E., and D. Kirkham. 1962. Soil compaction in the field and corn growth. Agron. J. 54:29–34.[Abstract/Free Full Text]
• Ritchie, J.T., D.E. Kissel, and E. Burnett. 1972. Water movement in undisturbed swelling clay soils. Soil Sci. Soc. Am. Proc. 36:874–879.
• Roder, W., S.C. Mason, M.D. Clegg, and K.R. Kniep. 1989a. Yield–soil water relationships in sorghum–soybean cropping systems with different fertilizer regimes. Agron. J. 81:470–475.[Abstract/Free Full Text]
• Roder, W., S.C. Mason, M.D. Clegg, and K.R. Kniep. 1989b. Crop root distribution as influenced by grain sorghum–soybean rotation and fertilization. Soil Sci. Soc. Am. J. 53:1464–1470.[Abstract/Free Full Text]
• Singer, M.J., and D.N. Munns. 1987. Soils: An introduction. MacMillan Publ., New York.
• Spurlock, S.R., and D.H. Laughlin. 1992. Mississippi state budget generator user's guide version 3.0. Mississippi State Univ. Dep. of Agric. Economics Tech. Publ. 88.
• Vanderlip, R.L., and H.E. Reeves. 1972. Growth stages of sorghum [Sorghum bicolor (L.) Moench]. Agron. J. 64:13–16.[Abstract/Free Full Text]
• Voorhees, W.B. 1985. Some effects of soil compaction on root growth, nutrient uptake, and yield. p. 58–65. In 15th North Cent. Ext. Ind. Workshop Bull. 279. Potash and Phosphate Institute, Manhattan, KS.
• Wesley, R.A., and F.T. Cooke. 1988. Wheat–soybean double-crop systems on clay soil in the Mississippi Valley area. J. Prod. Agric. 1:166–171.
• Wesley, R.A., L.G. Heatherly, C.D. Elmore, and S.R. Spurlock. 1994a. Net returns from eight irrigated cropping systems on clay soil. J. Prod. Agric. 7:109–115.
• Wesley, R.A., L.G. Heatherly, C.D. Elmore, and S.R. Spurlock. 1995. Net returns from eight nonirrigated cropping systems on clay soil. J. Prod. Agric. 8:514–520.
• Wesley, R.A., and L.A. Smith. 1991. Response of soybean to deep tillage with controlled traffic on clay soil. Trans. ASAE 34:113–119.
• Wesley, R.A., L.A. Smith, and S.R. Spurlock. 1993. Economic analysis of irrigation and deep tillage in soybean production systems on clay soil. Soil Tillage Res. 28:63–78.
• Wesley, R.A., L.A. Smith, and S.R. Spurlock. 1994b. Fall deep tillage of clay: Agronomic and economic benefits to soybeans. Mississippi Agric. and Forestry Exp. Stn. Bull. 1015.
• Young, L.D., E.E. Hartwig, S.C. Anand, and D. Widick. 1986. Response of soybeans and soybean cyst nematodes to cropping sequences. Plant Dis. 70:787–791.

This Article Abstract Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via ISI Web of Science (8) Citing Articles via Google Scholar Google Scholar Articles by Wesley, R. A. Articles by Spurlock, S. R. Search for Related Content PubMed Articles by Wesley, R. A. Articles by Spurlock, S. R. Agricola Articles by Wesley, R. A. Articles by Spurlock, S. R. Related Collections Other Soil Management Other Soil Types Tillage Crop Rotation Systems Other Cropping Systems Economics Production Agriculture