Growth Dynamics during the Vegetative Period Affects Yield of Narrow‐Row, Late‐Planted Soybean

Narrow‐row culture is recommended for increasing soybean [ Glycine max (L.) Merr.] yield at late plantings in the southeastern USA. Increased pod number resulting from greater light interception (LI) and crop growth rate (CGR) during the early reproductive period [first flowering to seed initiation (R1 to R5)] is mainly responsible for narrow‐row yield increases. However, little is known about rowspacing effects on Ll, CGR, and other growth dynamic parameters during the vegetative period [emergence (E) to R1] and how these parameters affect yield. Our objectives were to determine when LI and CGR differences in narrow vs. wide rows appear during E to R1, to determine if these differences contribute to narrow‐row effects on CGR(R1 to R5), and to determine the roles of leaf area index (LAI) and light interception efficiency (LIE = LI/LAI) in causing narrow‐row LI increases during the vegetative period. Seed of ‘Centennial’ soybean (Maturity Group VI) was planted in mid‐July in 1992 and 1993 at Baton Rouge, LA, on a Commerce silt loam soil (fine‐silty, mixed, nonacid, thermic Aeric Fluvaquent). Experimental design was a randomized complete block in a split‐plot arrangement. Main plots were row spacings of 100, 50, and 25 cm. Split plots were eight sampling dates during E to R5. The CGR(R1 to R5) advantage of narrow‐row culture developed from CGR advantage in the vegetative period, caused by greater LI originating from increased LIE during the first 26 d of the vegetative period. Yield was significantly correlated with CGR during most of the vegetative period. In conclusion, source strength (CGR) during the vegetative period was shown to affect yield at late planting dates.