Radiation interception and yield response to increased leaflet number in early-maturing soybean genotypes
Early-maturing soybean [Glycine max (L.) Merr.] cultivars require less irrigation than full-season cultivars and may mature before drought periods most often occur in the midsouthern United States. These cultivars require high plant-population densities for radiation interception and acceptable yields, which increase costs. We hypothesized that seven-leaflet genotypes would have greater leaf area per plant, resulting in more radiation interception and higher yield than near-isogenic three-leaflet genotypes at similar populations. Near-isogenic lines from maturity groups 00 to 1.8 were seeded at rates from 4 to 80 m–2. The fraction of photosynthetically active radiation (PAR) intercepted by plots was measured using digital imagery and used to estimate cumulative intercepted PAR (CIPAR). Although seven-leaflet isolines had greater leaf area per leaf than three-leaflet isolines, leaf area per plant was similar between three- and seven-leaflet isolines because the three-leaflet isolines had a slightly greater number of main-stem leaves than seven-leaflet isolines. Generally, seven-leaflet isolines had 10 to 21% greater CIPAR at populations 40 m–2 compared to three-leaflet isolines. At populations 20 m–2, seven-leaflet isolines generally had higher yields than three-leaflet isolines, but yields at these low populations were inherently low and agronomically unacceptable.