Soybean maturity group choices for maximizing radiation interception across planting dates in the Midsouth United States

Cumulative interception of photosynthetically active radiation (CIPAR) is a key factor affecting soybean [Glycine max (L.) Merr.] yield. Under well-watered conditions, differences in CIPAR across planting dates, maturity groups (MGs) and row spacing in the US Midsouth could partially explain yield differences. Irrigated experiments were conducted for 2 yr at three locations in Arkansas with four planting dates and 16 cultivars (MG 3–6) using a narrow (0.46–0.48 m) and a twin-row spacing (0.19–0.20 m twin rows on 0.96 m beds) with a seeding density of 35 plants m^–2. The fraction of radiation intercepted (FRI) from emergence to beginning seedfill (or complete canopy closure) was well defined for each row spacing as a sigmoidal relationship with cumulative thermal time. A bilinear relationship between CIPAR and relative yield explained 46% of the yield variation. Relative yield increased with CIPAR, reached a maximum at 687 MJ m^–2 and then declined. Simulations estimated the FRI and CIPAR for a range of planting dates, MG choices, narrow and twin-row spacings, and two locations with 30-yr of historical weather data. Simulations identified scenarios where management of row spacing and MGs avoid low FRI during flowering and at the start of seedfill. Simulations also identified management scenarios that ensure sufficient CIPAR to obtain 95% of maximum yields. Late MGs provided greater CIPAR compared with earlier MGs, but yield decreased at high values of CIPAR emphasizing the importance of understanding mechanisms underlying the yield response to CIPAR across planting dates and MGs.