Row spacing in the early soybean production system

In the southern USA, determinate soybean grown in row spacings (RS) of 50 cm or less generally produce higher yields than that grown in RS of 75 to 100 cm, However, the Early Soybean Production System (ESPS) commonly employs indeterminate cultivars in environments with limited rainfall. This study was conducted to determine whether RS affects seed yield in the ESPS, Twenty-one field experiments were conducted from 1984 to 1997 at sites in Arkansas, Louisiana, and Texas to determine the effect of RS on seed yield in the ESPS. Row spacings of 80 and 40 cm were compared in seven tests; of 75, 50, and 25 cm in six tests: of 75 and 25 cm in one test; of 100, 50, and 25 cm in four tests; and of 100 and 25 cm in three tests. One to five Maturity Group (MG) III and IV indeterminate cultivars were planted in a given test. Based on similarity of treatments and experimental designs, each field test was assigned to one of 10 environmental clusters (EC). Five EC showed a significant (17-36%) yield increase as RS narrowed. Of the other five EC, three had nonsignificant yield increases, one had virtually no yield change, and one had a nonsignificant yield decrease as RS narrowed, Yield was most responsive to RS when the total July and August rainfall ranged from 100 to 270 mm, These results suggest that narrow rows (less than or equal to 40 cm) should be used to optimize yields from ESPS plantings in the midsouthern USA.