RADIATION-USE EFFICIENCY IN RELATION TO ROW SPACING FOR LATE-PLANTED SOYBEAN

Greater soybean [Glycine max (L.) Merr.] yield can be achieved at late planting dates by using row spacings narrower than conventional wide rows (76 to 100 cm). Objectives were to determine the relative yield performances of 100-, 50-, and 25-cm row spacings in late-planted soybean and to relate yield differences to changes in yield components, several growth dynamic parameters, and radiation interception. Field studies were conducted at Baton Rouge, LA (30-degrees-N Lat.) from 1989 through 1991 at a late planting date with 'Centennial' soybean (Maturity Group VI) planted on 100-, 50-, and 25-cm row spacings. The test was conducted on a silty clay soil. Highest yield occurred with 50-cm row width. Yield in the 25- vs. 50-cm rows was less, even though light interception (LI) patterns were similar. Growth dynamic analysis revealed that radiation-use efficiency (RUE) during the first half of the seed filling period was significantly lower in 25- vs. 50- or 100-cm rows. Reduced RUE in 25-cm row spacing was related to reduced pod number associated with lower crop growth rate (CGR) from pod initiation to 10 days after seed initiation. Results indicate that factors other than optimal LI (95%) affect yield responses to row width.