RAPID CANOPY CLOSURE FOR MAIZE PRODUCTION IN THE NORTHERN US CORN-BELT - RADIATION-USE EFFICIENCY AND GRAIN-YIELD

Slow development of maize (Zea mays L.) canopies in northern areas of the USA may limit light interception and potential productivity. Wheth er radiation-use efficiency (RUE) and grain yield could be increased b y earlier canopy closure was examined with two hybrids contrasting in canopy architecture and potential phytomass production. Early canopy c losure was achieved using a combination of row spacings narrower and p lant population densities (PPD) greater than typically used by local p roducers. Maximum interception of incident PAR (theta(max)) and total PAR intercepted from sowing to theta(max)(IPAR) increased with PPD. Th ermal time to one-half theta(max)(TU0.5) decreased with increasing PPD . Sowing in narrow (38 cm) rows did not affect theta(max), IPAR, or TU 0.5 in the tall hybrid, Pioneer 3790; nor did it affect grain yield, w hich increased with PPD up to 10 plants m(-2). Grain yield of the dwar f hybrid, SX123, was always less than that of Pioneer 3790, due to its low efficiency in converting intercepted PAR into phytomass. Both hyb rids exhibited an optimum rate of canopy development in terms of theta (max), IPAR, and TU0.5 for grain production. Optima for these paramete rs varied across years, but were similar for both hybrids and row spac ings. These results indicate that hybrids adapted to the northern corn belt may yield more grain if sown at PPDs greater than commonly used to promote early canopy closure. Sowing to rows less than 76 cm wide w ill have less impact on grain yield. Productivity of hybrids prone to barrenness or with a low efficiency in converting PAR into phytomass, such as SX123, will not improve with earlier canopy closure.