Tuesday, November 14, 2006 - 1:45 PM

Determination of optimum soybean planting date, maturity group, and seeding rate for the upper midsouthern United States.

Eric R. Walker, Clifford H. Koger, Alemu Mengistu, and Nacer Bellaloui. USDA-ARS-CG&PRU, 605 Airways Blvd., Jackson, TN 38301

Non-irrigated conditions and late-season droughts and high temperatures are obstacles that many soybean producers in the upper midsouthern United States face annually.  The effects of these factors may be minimized with the adoption of the early soybean production system (ESPS), which matches the growth and development of early-maturing cultivars with seasonal rainfall patterns within the frost-free period, increasing and stabilizing yields with little or no increase in input costs.  Also, some producers may be planting at higher seeding rates than necessary and may reduce input costs with reduced seeding rates without lowering yields.  Therefore, field studies were conducted to determine optimum soybean planting dates and seeding rates for maturity groups (MG) III-V in the upper midsouthern United States.  Two cultivars from each MG were planted at recommended and reduced seeding rates (81,000 and 64,800 sd/ha for MG III; 64,800 and 48,600 sd/ha for MG IV and V) on dates ranging from May 4 to August 10, 2005.  MG V cultivars planted on May 4 yielded 6050 kg/ha, while all other MG III-V cultivars planted from May 4 through June 7 produced 5040-5650 kg/ha. Yields from June 23 through July 20 plantings decreased to 2350-3900 kg/ha, while August plantings produced less than 940 kg/ha.  However, recommended and reduced seeding rates produced equal yields.  In a separate field study, MG III, IV, and V soybean were planted at 32,400-97,200 sd/ha on April 18, May 12, and June 23.  MG V soybean produced 4500 kg/ha compared to 4170 and 3630 kg/ha for MG IV and III soybean, respectively, and soybean planted at 32,400 sd/ha produced yields equal to higher seeding rates within each MG.  These data suggest that mid-April to mid-June plantings of MG III-V soybean planted at reduced seeding rates will optimize soybean production in the upper midsouthern United States.