Economics of fall tillage for early and conventional soybean plantings in the midsouthern USA.

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 degrees 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.