A comparison of determinate and indeterminate soybean lines for double cropping in Virginia
Forty lines, 20 determinate and 20 indeterminate, from four soybean (Glycine max L. Merrill) crosses were evaluated under full-season and double cropping conditions to compare the performance of the two plant types under both cropping systems. The parents and selected lines were in the range of Maturity Groups IV and V. In 1980, the lines were planted 1 July in a replicated test at Warsaw, VA while in 1981 these lines were planted in three replicated tests on 11 June and 8 July at Warsaw and on 12 June at Orange, VA. Both June plantings were considered full-season. Standard cultivars in 1980 included 'Essex', 'Williams', and 'Crawford'. 'Bay' and 'Will' were added in 1981.
Yields were similar in 1980 for both plant types with the determinates yielding 10.1 q/ha and the indeterminates yielding 9.9 q/ha. In 1981, the yields were similar for both types at Orange with the determinates and indeterminates yielding 26.4 and 26.5 respectively. The types were significantly different in the 11 June planting at Warsaw, with yields of 28. 6 and 28. 0 q/ha for the determinate and indeterminate lines, respectively. The opposite was observed for the 8 July planting in which the indeterminates yielded 21.2 q/ha and the determinates yielded 20.8 q/ha.
A comparison of the two determinate and indeterminate lines with the highest yields in both 1981 Warsaw plantings showed that indeterminates were more adaptable to double cropping, though high yielding lines of both types were present. The high yielding indeterminates of the 8 July planting had a tendency to be taller and more erect than the determinates, an attribute desirable for double cropping. Lines that were highest yielding in the 11 June planting were ranked lower in the 8 July planting and vice versa. Spearman' s rank correlation for yield in the two Warsaw plantings had a coefficient of 0. 23, indicating a high degree of specific adaptation to the two environments.
Selection of better adapted lines for double cropping appears feasible. The indeterminate trait appears to make some contributions to this adaptation.