Explanations for Greater Light Interception in Narrow‐ vs. Wide‐Row

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Abstract
Increased light interception (LI) is considered the main factor responsible for greater seed yield in narrow‐ compared with wide‐row soybean [Glycine max (L.) Merr.] culture. The objectives of this study were to determine the roles of leaf area index (LAI) and light interception efficiency (LIE) in creating greater LI in narrow‐row culture. Light interception efficiency is defined as LI/LAI. Field studies were conducted during 1987 and 1988 at optimal (May) and late (July) planting dates, with cultivars Forrest (Maturity Group V) and Centennial (Maturity Group VI), and at 100‐cm (wide) rows/normal density, 50‐cm (narrow) rows/normal density, and 50‐cm rows/high density. Plots were sampled at the V7, Rl, R3, R5, R6.5, and R6.8 developmental stages. The experiment was conducted at Baton Rouge, LA, on a Mhoon silty clay (fine‐silty, mixed, nonacid, thermic Typic fluvaquent) soil. Greater LI in narrow rows was more pronounced at late compared with optimal plantings and in Forrest, the short‐season cultivar, compared with Centennial, the full‐season cultivar. Results indicated that LAI was the dominant factor responsible for greater LI in narrow rows. Light interception efficiency played an important role in narrow‐row increased LI only when LAI was low and little mutual shading occurred. Selection criteria for cultivar‐genotype performance in narrow‐row culture at late plantings should be based on rapid leaf expansion rates (LER) and high LAI accumulation during vegetative and early reproductive development. Attainment of LAI of 3.5 to 4.0 by R1 should optimize yield. Due to a significant planting date × cultivar × developmental stage interaction for LAI, selection should be done at late rather than optimal planting dates.

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