PRODUCTION AGRICULTURE Economic and Agronomic Assessment of Deep Tillage in Soybean Production on Mississippi River Valley Soils

soil. Planting of the crop over this low density slot is critical. These soils occur in the USA, primarily in the Using deep tillage to alleviate the adverse effects of deleterious soil Coastal Plains, and in other regions to a minor extent physical properties has been tried many times. Consistent economic returns have been reported for in-the-row subsoiling of loamy sand (Buol, 1973). and coarser soils and for deep loamy soils where the subsoil slit bisects In the Mississippi River alluvium region, for example, the water flow channel during rainfall events where there is runoff. yield responses to deep tillage were found for cotton Recent reports of yield responses on clayey soils and silt loams led to (Gossypium hirsutum L.) on deep silt loam or sandy a reassessment of subsoiling of these soils in Arkansas. A randomized loam soils (Spurgeon et al., 1978; Tupper and Spurgeon, complete block design was conducted at four locations with tillage 1981). This response differed from that of nonplastic treatments of conventional shallow, deep chisel, subsoil dry, subsoil soils in that no response was obtained from in-the-row wet, subsoil at 458 to planting direction, and paratill. Plots were harsubsoiling. The best results were obtained from deep vested for grain. Economic analysis was performed using the Missistillage in the fall, which left low-density slits that geometsippi State Budget Generator (MSBG). The machinery complement was commensurate with that found on farms in the region. Net returns rically intersected the low points between old seedling above total specified costs (NRAT) rather than above direct costs rows. The low points concentrate runoff water during were calculated to reflect the decision framework of a producer. A high intensity rainfall events. Thus, it appears that deep profitable yield response was obtained from subsoiling in dry soil on tillage here was promoting infiltration and subsequent deep alluvial clayey and silt loam soils but not on the thin loessial soil water storage in these deep silt or sandy loam soils. silt loams. Net returns to subsoiling wet were not significantly higher More recent studies (Keisling et al., 1998) using a paratill than those to conventional shallow tillage. Tillage with a chisel plow on a bedded system tended to provide consistently as deep as it could be operated (approximately 15 cm) was not a higher cotton yields than conventional tillage practices. substitute for subsoiling because yield responses from deeper tillage were not comparable. The 458 subsoiling in dry soil tended to be No consistent soybean [Glycine max (L.) Merr.] or superior to all other tillage treatments. cotton yield increase from deep tillage on clayey textured soils was reported until 1991 (Wesley and Smith, 1991). Consistent responses were obtained on a Tunica D tillage to loosen soil for the purpose of clay to fall subsoiling when the soil was dry. The clay promoting infiltration, internal water drainage and soil (when subsoiled under these dry conditions) will storage, soil aeration, increased rooting depth, and inbreak into clods that are sometimes as large as 70 by creased rooting density has appeared attractive for 30 cm. These large clods can result in a very rough many years. Many deep tillage studies have been consurface, which some growers want to immediately ducted, but only a low percentage of them have been smooth. Because the soil is very hard, this smoothing reported. The primary reason for this low reporting rate can result in the loss of an economic gain obtained from is the lack of yield response to deep tillage. the subsoiling. The profit potential from subsoiling these Deep tillage responses can be classified according to clayey soils located in the Mississippi River alluvium was soil characteristics. Large, consistent yield responses are comparable to that obtained from irrigation (Wesley et obtained in soils that are deep (i.e., no root restricting al., 1993). naturally occurring horizons in the control layer—the On loamy textured soils that have a naturally octop 70 cm) and have a nonplastic texture (usually loamy curring root and water restrictive horizon in the control sand or coarser) at a 0to 15-cm or 30-cm depth. These layer, yield responses have been found from deep tillage nonplastic soils usually respond to in-the-row subsoiling in the fall when the soil was dry and there was an excess (Batchelor and Keisling, 1982) that provides a continuof soluble salts (Pearce et al., 1999). No other reports of ous low-density slit for roots to penetrate into the subyield responses to deep tillage were found for these soils. The study reported here was initiated with the objectives of (i) quantifying the yield responses on clayey soil M.P. Popp and P.M. Manning, Dep. of Agric. Econ. and Agribusiness, types other than those described in the literature, (ii) 221 Agric. Building, Univ. of Arkansas, Fayetteville, AR 72701; T.C. Keisling, Dep. of Crop, Soil, and Environ. Sci., Univ. of Arkansas, examining the responses on soils with textural and proNortheast Res. and Ext. Cent., P.O. Box 48, Keiser, AR 72351; and file characteristics other than deep clayey soils, and (iii) C.R. Dillon, Dep. of Agric. Econ., 403 Agric. Eng. Building no. 2, Univ. of Kentucky, Lexington, KY 40546-0276. Received 26 July 1999. *Corresponding author ([email protected]). Abbreviations: MSBG, Mississippi State Budget Generator; NRAT, net returns above total specified costs. Published in Agron. J. 93:164–169 (2001).