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PRODUCTION PAPERS

Economics of Fall Tillage for Early and Conventional Soybean Plantings in the Midsouthern USA

^a USDA-ARS, Crop Genet. and Production Res. Unit, P.O. Box 343, Stoneville, MS 38776
^b Dep. of Agric. Econ., Mississippi State, MS 39762

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

Received for publication January 24, 2000.

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION AND CONCLUSIONS REFERENCES

 
Conventional soybean [Glycine max (L.) Merr.] production in the midsouthern USA has involved planting Maturity Group (MG) V and later cultivars in May and later months in a seedbed that has been shallow-tilled in the fall or spring just before planting. Moisture deficits that frequently occur from April through September reduce yield of soybean cultivars used in this traditional production system. Field experiments using MG IV ‘DP 3478’ and MG V ‘Hutcheson’ were conducted at Stoneville, MS (33°26' N lat) on Sharkey clay (very fine, smectitic, thermic chromic Epiaquert) in 1995, 1996, and 1998. The objective was to compare yields and economic returns from April and May or later plantings of MG IV and V soybean cultivars grown without irrigation on clay soil following shallow (ST) and deep (DT) fall tillage. Net returns were calculated as the difference between income and all direct and indirect costs, excluding those for land, management, and general farm overhead. Costs for the DT treatment were $22 to $27 ha^-1 greater than those for ST. Yields and net returns resulting from DT were greater than those from ST in 1 yr. Yields and net returns from April plantings were greater than those from May or later plantings in 2 of the 3 yr. These results indicate that April plantings will result in greater yields and net returns over the long term, but increased profits from DT are infrequent.

Abbreviations: DOP, date of planting • DT, deep fall tillage • FT, fall tillage • MG, maturity group • ST, shallow fall tillage

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION AND CONCLUSIONS REFERENCES

 
CONVENTIONAL SOYBEAN PRODUCTION in the midsouthern USA utilizes MG V and later cultivars planted in May and later months in a seedbed that had been harrowed (disk or spring tooth) in the fall and left stale or untilled before planting (Heatherly and Elmore, 1983; Heatherly, 1999c) or harrowed in the spring just before planting. Use of this system resulted in an average yield of 1500 kg ha^-1 during the 1970 through 1991 period in Mississippi (MCLRS, 1980, 1985; MASS, 1991, 1995; Anonymous, 1995).

The frequency and severity of moisture deficits at Stoneville, MS (33°26'N lat) typically increase from April through September (Boykin et al., 1995). Van Bavel (1959) calculated that the number of drought days (number of days in a period when potential evapotranspiration exceeds capacity of soil to supply that amount of water) in the middle Mississippi River valley was near zero in April and May but climbed to 13, 14, and 15 d mo^-1 in June, July, and August, respectively. The effect of the drought days in July and August was compounded by previous months with a high incidence of drought. Cultivars planted in May or later typically flowered, set pods, and filled seeds during the hottest and driest portion of the growing season (Reicosky and Heatherly, 1990) when moisture deficits were greatest (Boykin et al., 1995) and soil water normally was depleted. Thus, they were susceptible to yield limitations imposed by drought. Results from research revealed that May and June plantings of these cultivars were high-risk enterprises (Heatherly, 1999a).

Planting early maturing cultivars (relative to latitude; MG IV and V at Stoneville, MS) in April vs. May and later allows their critical reproductive development to coincide with periods of adequate soil moisture and greater rainfall, thus partially avoiding drought stress. Recent reports indicate that a system involving seedbed preparation tillage in the fall; killing emerged weeds with a preplant, foliar-applied herbicide; and planting early maturing cultivars into a stale, untilled seedbed in April will result in improved yield and profit potential for soybean in the lower Mississippi River valley region (Heatherly, 1999b).

Kane and Grabau (1992) reported that MG II vs. traditional MG III, IV, and V soybean cultivars planted in late April or early May at Kentucky locations (36°40' to 38°07'N lat) produced the highest average yields. Sweeney et al. (1995) showed that MG I soybean cultivars planted in April offer a viable alternative to traditional varieties of MG III, IV, and V planted in June in Kansas (37°20'N lat) dryland systems. Bowers (1995) conducted 3 yr (1986–1988) of nonirrigated studies at two northeast Texas locations (Blossom, 33°33'N lat and Hooks, 33°38'N lat) and found that MG III and IV cultivars planted in April yielded more than traditional MG V to VIII cultivars planted in May. Heatherly and Spurlock (1999) conducted a 5-yr study at Stoneville and found that yields of MG IV and V cultivars planted in April and not irrigated yielded more than nonirrigated May plantings and that net return from this system was higher. After 3 yr of research at St. Joseph, LA (31°50'N lat), Boquet (1998) concluded that consistent high yields produced by MG IV cultivars in a short-season system reduced risk of low yields or crop failure associated with the traditional system. Thus, it appears that higher yields can be obtained more consistently in the lower Mississippi River valley region by planting early maturing cultivars earlier in the spring than has been done. The reasons for higher yields associated with this practice probably vary among locations; however, they must include drought avoidance and probably avoidance of above-optimum temperatures during reproductive phases. The advantage of earlier-than-normal planting is not realized at more northerly latitudes, as shown by Logan et al. (1998) at three Tennessee locations and by Steele and Grabau (1997) and Kane et al. (1997) at a Kentucky location. Reasons for this may be associated with low temperatures in April and lack of summer drought to the degree that it occurs in the lower Mississippi Valley region.

Clay soils occupy more than 3.7 million ha, or about 50% of the land area in the lower Mississippi River alluvial flood plain in the midsouthern USA. Of these clay soils, Sharkey is the dominant series and comprises about 1.2 million ha in the Mississippi River flood plain regions of Arkansas, Kentucky, Louisiana, Mississippi, Missouri, and Tennessee (Pettry and Switzer, 1996). Soybean is planted on the majority of the cropped clay soils, and most of this soybean hectarage is not irrigated. Thus, low yield potential, high-risk dryland production is the normal system (Heatherly, 1999a; Williams, 1999). Profitable production systems are needed for these nonirrigated sites.

If spring tillage is conducted, it almost always delays planting, and on poorly drained clay soils, that delay frequently becomes extended to weeks because of inconveniently timed spring rains. Heatherly (1981) measured almost identical yields among treatments in studies on Sharkey clay where deep tillage (0.45-m depth) performed in the spring (Mar., Apr., or May) was compared with shallow, disk-harrow spring tillage preceding soybean planting in May or later. Wesley and Smith (1991) performed deep tillage on a Tunica silty clay (clayey over loamy, smectitic, nonacid, thermic Vertic Haplaquept) in the fall following soybean harvest when the soil profile was dry as a result of soil water depletion in the growing season. They measured large, significant yield increases from soybean planted in May during years when drought occurred during the growing season and determined that net return was greatly increased from this practice (Wesley et al., 1994). The increased production was associated with increased moisture content in the soil, presumably because of greater infiltration and storage resulting from the deep tillage. This work has been used to promote the deep tillage of all dry clay soils in the fall.

Deep tillage of dry Sharkey clay soils in the fall has not been investigated as a production practice to be used with April planting. The objective of this work was to compare yields and economic returns from April and May or later plantings of MG IV and V soybean cultivars grown without irrigation on clay soil following shallow (ST) and deep (DT) fall tillage. Economic analysis of 3 yr of results was conducted to assess and compare the profitability of the two tillage systems in April vs. later plantings.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION AND CONCLUSIONS REFERENCES

 
Field studies were conducted in 1995, 1996, and 1998 on Sharkey clay at the Delta Research and Extension Center, Stoneville, MS (33°26'N lat). Each year, four adjacent nonirrigated experiments were conducted to encompass two dates of planting (DOP; DOP1, April; DOP2, May or June) of MG IV and V soybean cultivars following two fall tillage (FT) treatments (ST and DT). All experiments were conducted in a randomized complete block design with four replicates. All experimental units remained in the same location for the duration of the research. Effective deep tillage could not be done in the fall of 1996 because of wet soil resulting from 200 mm of rain that fell from 10 August through 30 September. Thus, results are not included from a 1997 experiment maintained on the same site.

On 28 Sept. 1994, 2 Oct. 1995, and 4 Oct. 1997, appropriate areas were either deep-tilled with an implement having curved tines spaced 1 m apart or shallow-tilled using a disk harrow and/or spring-tooth cultivator. All tillage operations were started immediately following harvest of soybean when soil was dry. Rainfall preceding deep tillage was 11 and 29 mm, respectively, in August and September 1994; 36 and 41 mm, respectively, in August and September 1995; and 71 and 56 mm, respectively, in August (before 15 Aug.) and September 1997. The deep tillage was done approximately 0.4 to 0.45 m deep and was followed by soil surface smoothing with a disk harrow and spring-tooth cultivator. Number of preplant tillage operations, implements used, and associated costs for ST and DT are shown in Table 1. Weather data in Table 2 were collected about 0.8 km from the experimental site by the Midsouth Agricultural Weather Service Center of the National Oceanic and Atmospheric Association in 1995 and by Delta Research and Extension Center personnel in 1996–1998.

Row spacing was 0.5 m and seeding rate was 16 seed m^-1 of row, or about 50 kg ha^-1 seed. Plots were 30.5 m long and 4 m (eight rows) wide. Plantings were made into a stale seedbed (Heatherly, 1999c) following application of glyphosate [N-(phosphonomethyl)glycine] to kill weed vegetation. After planting, weeds were managed every year with pre-emergent broadleaf and grass herbicides applied at labeled rates. In some years, broadleaf weeds emerged after planting and were controlled with postemergent herbicides that were applied at labeled rates and with appropriate adjuvants. Postemergent grass control was not needed in any year. In all cases, weeds were managed so that weed competition was not a factor limiting crop production.

All production inputs within each year were recorded for all experiments. Estimates of costs and returns were developed for each annual cycle of each experimental unit using the Mississippi State Budget Generator (Spurlock and Laughlin, 1992). Total specified expenses were calculated using actual inputs for each treatment in each year of the experiment and included all direct and fixed costs but excluded costs for land, management, and general farm overhead, which were assumed to be the same for all treatment combinations. Direct expenses included costs for pesticides, seed, and labor; costs for fuel, repair, and maintenance of machinery; cost of hauling harvested seed; and interest on operating capital. Fixed expenses were ownership costs for tractors, self-propelled harvesters, implements, and sprayers. Costs of variable inputs and machinery were based on prices paid by Mississippi farmers each year; i.e., machinery costs varied with year. Cost estimates of field operations were based on using 16-row equipment. 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 an appropriate interest rate for each year of the study.

Income from each experimental unit was calculated by multiplying the market-year average price for Mississippi ($0.248, $0.269, and $0.222 kg^-1 for 1995, 1996, and 1998, respectively) by the experimental yield. Yearly prices (MASS, 1999) were used instead of an average long-term price to reflect the effect of market forces on income for each individual year. Net returns above total specified expenses were determined for each experimental unit each year. Average price for the 1994–1998 period in Mississippi was $0.240 kg^-1, which can be substituted for the yearly prices that were used in this presentation.

Soybean plant height at maturity was recorded for each plot just before harvest to determine the possible effect of tillage system on plant stature. A field combine modified for small plots was used to harvest the four center rows of each plot. Soybean seed were harvested from 28 Aug. to 28 Sept. 1995, 13 Sept. to 7 Oct. 1996, and 27 Aug. to 5 Oct. 1998. Yields were adjusted to 130 g moisture kg^-1 seed.

Analysis of variance [PROC MIXED (SAS Inst., 1996)] was used to evaluate the significance of effects on plant height, seed yield, and net returns. Analyses across years treated year as a fixed effect to determine interactions involving year. Analyses for individual years treated FT and DOP as fixed effects and cultivar as random. Mean separation was achieved with an LSD_0.05.

	RESULTS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION AND CONCLUSIONS REFERENCES

 
Weather
In 1995, average maximum air temperatures were 2°C or more above normal in April, May, and August (Table 2). Moisture deficits (rainfall minus pan evaporation) in 1995 were above normal in May and August but below normal in July. The 15 July to 31 August period received only 25 mm of rain. Average maximum air temperatures in 1996 were near normal for most months. The months of June through August (reproductive period of both cultivars—Table 3) had near- or below-normal moisture deficits. In 1998, the May through August period was generally hotter than normal, and moisture deficits were above normal in all months except July. The 15 July to 31 August period received only 18 mm of rain. Thus, all years had periods of low rainfall and high temperatures that resulted in drought stress conditions during some portion of the soybean reproductive phase.

Costs
Costs within a planting date each year were essentially the same, except for those related to FT. Preplant tillage expenses and total expenses (excluding costs for land, management, and general farm overhead) for the ST and DT treatments within year and planting date are presented in Table 1. Costs associated with DT ranged from $22 to $27 ha^-1 more than for ST. Differences in total cost between planting dates within a year were the result of greater weed control costs for the later planting. Differences in total cost among respective planting dates across years resulted from different weed control practices that were required to address each year's specific weed management requirements.

Plant Height
In 1995, DT resulted in an average plant height of 63 cm vs. an average of 56 cm for plants in ST (data not shown). Plants in DOP2 were 10 cm taller than those in DOP1, and DP 3478 plants averaged 17 cm taller than those of Hutcheson. In 1996, when the earlier planting was 30 April and the later planting was 15 May, DT resulted in only slightly taller plants than did ST (68 vs. 64 cm). Plants in DOP2 were 13 cm taller than those in DOP1, and DP 3478 plants averaged 16 cm taller than those of Hutcheson. In 1998, the 62-cm average height of DT plants was greater than the 51-cm average height of ST plants. Plants in DOP2 were 33 cm taller than plants in DOP1 while average height of DP 3478 plants was 16 cm greater than that of Hutcheson. Thus, in years when early planting occurred in early April, DT resulted in taller plants. Lodging greater than a few plants leaning did not occur in any year.

Seed Yield and Net Return
General
Analysis of variance revealed that interactions between year and all other factors were significant. Therefore, results are presented on an individual year basis.

1995
Average yields of 2180 and 2310 kg ha^-1 from ST and DT, respectively, were not significantly different (Table 4). Average yield of 2540 kg ha^-1 from DOP1 was greater than the 1950 kg ha^-1 average yield from DOP2, and average yield from DP 3478 was greater than that from Hutcheson. Interactions among the three factors were not significant for yield.

1998
Yield and net return were significantly affected by the FT x DOP and DOP x cultivar interactions (Tables 4 and 5). In DOP1, average yield following DT was 640 kg ha^-1 greater than the average yield following ST, and average net return from DT was $102 ha^-1 greater than average net return from ST. In DOP2, average yield and net return from DT (1520 kg ha^-1 and $4 ha^-1) were not significantly greater than those from ST (1140 kg ha^-1 and $-42 ha^-1). DP 3478 outyielded Hutcheson in DOP1 but not in DOP2. Average net return from DP 3478 was greater than that from Hutcheson in DOP1 while the opposite was true in DOP2. In DOP1, the 2550 kg ha^-1 yield from DT DP 3478 was the highest of any treatment combination. All net returns from DOP2 treatment combinations were negative.

	DISCUSSION AND CONCLUSIONS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION AND CONCLUSIONS REFERENCES

 
Levels of yield and net return achieved from deep tillage of the clay soil in this nonirrigated study did not approach those from irrigated plantings of soybean at this location (Heatherly and Spurlock, 1999). Also, these yield and net-return responses achieved as a result of DT of Sharkey clay are not of the magnitude of those achieved on Tunica silty clay by Wesley and Smith (1991) and Wesley et al. (1994). Presumably, the improved soil moisture status resulting from deep tillage that was measured by Wesley and Smith (1991) was not as effective for soybean grown on Sharkey clay in this study even though moisture deficits were experienced in all years. Rainfall amounts between DT dates and DOP1 dates in 1995, 1996, and 1998 were 900, 720, and 735 mm, respectively. These amounts were distributed over the approximate 6-mo period between FT and DOP1 dates in a manner that would have allowed a fully recharged soil profile at the beginning of each growing season.

The additional costs associated with deep tillage and subsequent seedbed preparation operations in this study were in the range of $22 to $27 ha^-1. Using the 1994–1998 average price of $0.24 kg^-1, yield increases of 90 to 110 kg ha^-1 would be required to break even. At a soybean price of $0.20 kg^-1, a yield increase of 110 to 135 kg ha^-1 would be necessary to break even. Thus, with low commodity prices, significant profitability from deep tillage of these clay soils in the fall will require larger yield increases than those obtained in this study. The significant yield increase obtained from the April planting in one year of this study provides a more positive outlook for increased profits if prices are higher than those used here. Thus, the use of DT on this soil should be based on expected commodity price because economical yield increases were not consistently achieved.

If equipment for deep tillage is on hand (fixed cost incurred), the occasional response of early planted cultivars to DT indicates that, over the long term, net return will be increased from DT. If equipment is not on hand, these results do not support the large capitalization required to obtain the necessary equipment. This practice should not be used for May and later plantings or to replace existing irrigation capability.

These results do not address the long-term effects of deep tillage of clay soil. The term of this study may not be long enough to determine if the effect of deep tillage of the clay soils is cumulative. The 1998 results can lead to this conclusion, but they may also just be the response to a unique set of weather conditions or to the earliest DOP1 date of the 3 yr. These results further confirm the importance of April planting of soybean cropped on nonirrigated clay hectarage in the midsouthern USA, regardless of FT input. Yields and net returns from the system used in this study were equal to or greater than those from the later plantings. Deep tillage in the fall complemented this system only in one year. Thus, the advantage of using deep tillage was not as consistent or pronounced as was the advantage (2 out of 3 yr) of using the early planting component.

	ACKNOWLEDGMENTS

 
The authors appreciate the expert technical assistance provided by Lawrence Ginn, Sandra Mosley, John Black, and Debbie Boykin; resources provided by the Delta Research and Extension Center; and supplemental funding provided by the United Soybean Board and the Mississippi Soybean Promotion Board.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION AND CONCLUSIONS REFERENCES

 

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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 HighWire Citing Articles via ISI Web of Science (5) Citing Articles via Google Scholar Google Scholar Articles by Heatherly, L. G. Articles by Spurlock, S. R. Search for Related Content PubMed Articles by Heatherly, L. G. Articles by Spurlock, S. R. Agricola Articles by Heatherly, L. G. Articles by Spurlock, S. R. Related Collections Tillage Soybean Economics Production Agriculture