Effects of corn row width and defoliation timing and intensity on canopy light interception

Yield losses due to defoliation may be reduced in corn (Zea mays L.) grown at narrow compared to wider row widths. However, the physiological mechanisms behind this response are unclear. A 2-yr experiment was conducted with two hybrids, row widths (38 and 76 cm), and a combination of defoliation timings–intensities: Undefoliated control, V7–100%, V14–50%, V14–100%, R2–50%, and R2–100%. Intercepted photosynthetically active radiation (IPAR, MJ m−2) was measured after defoliation at V8, VT, R2, and R5. Post-defoliation reductions in IPAR were always associated with yield losses after V14–100% and R2–100% defoliations. Conversely, V7–100%, V14–50%, and R2–50% defoliations were not always associated with yield penalties, as a result of a leaf area recovery that allowed plants to reach 72 to 85% IPAR around VT/R1. Changes in grain yields were independent from changes in IPAR-V8 following V7–100% defoliations, and IPAR at or after VT following V14–100% and R2–100% defoliations. We found no interactions between rows and IPAR-VT, IPAR-R2 or IPAR-R5 for V7–100%, V14–50%, and R2–50% defoliations, implying that the change in grain yield per unit change in IPAR was the same for both rows at each IPAR stage. No evidence of two (IPAR-VT × IPAR-R2) and three-way interactions (IPAR-VT × IPAR-R2 × IPAR-R5) among IPAR stages was found. A simple model explaining >35% of the yield variability in defoliated corn stands, independently of row width, using IPAR between VT and R5 as predictors was fitted. Greater yields associated with narrow rows in corn-defoliated stands may be related to better resource allocation but was not related to greater intercepted radiation in our study.