Soybean Response to Different Planting Patterns and Dates 1,3

Soybean [ Glycine max (L.) Merr.] response to narrow rows (less than 50 cm apart) has been inconsistent in the southern United States. However, a more positive response has been documented in the North Central USA. Lack of suitable herbicides for controlling weeds in narrow row soybeans in the South has slowed acceptance of this practice. Development of more effective herbicides has made narrow row soybean production feasible. Earlier planting dates can take advantage of favorable soil moisture conditions. Soybean plantings following wheat [ Triticitm aestivum (L.) em. Thell.] harvest often do not close the crop canopy between rows before flowering when planted in rows 92 cm or more apart. Experiments were conducted in 1978 and 1979 (Vertic Haplaquept soils) to determine the effects of row spacings, broadcast seeding, planting dates, and soybean cultivars on yield and other plant characters. Seed yield was affected by row spacing or methods, planting dates, years, and planting dates x years. Cultivars and the cultivar x planting method interaction were not significant for yield but none of the cultivars used in the study had been selected for narrow row conditions. The 18 and 48 cm row widths produced 15% higher seed yields than the conventional 96 cm row spacing. Mean yields across row spacings (including broadcast planting) and cultivars for the 15 July planting date were less than 50% of the April or May plantings. The cultivar x planting date interaction was large for percent seed protein because the late planted Forrest cultivar was significantly lower in percent protein compared to earlier planted Forrest. Pods per plant were significantly associated with yield in 1979 but not in 1978.