Transgenic corn response to nitrogen rates under corn rootworm pressure

Recommended N rates for corn (Zea mays L.) typically consider yield, economic, and environmental dimensions, but not optimal protection by Bacillus thuringiensis (Bt) Berliner-based traits against corn rootworm (CRW) (Diabrotica spp.). This research explored N rate effects on CRW trait performance under CRW pressure. The experiment featured a split-plot randomized complete block design with factorial treatment combinations of N rates and hybrids differing in CRW traits. Root mass, N uptake, CRW efficacy, and grain yield data were collected from two locations in 2011. Root mass at growth stage V6 (before CRW injury) increased with N rate and was greater in the Roundup Ready (RR2) hybrid (Monsanto, St. Louis, MO) by 30.6%. Nitrogen uptake was similar between VT Triple (VT3) (Monsanto, St. Louis, MO) and the RR2 hybrids, which exceeded the SmartStax (SSX) (Monsanto, St. Louis, MO: Dow AgroSciences Indianapolis, IN) hybrid by 12.5%. By growth stage V12, CRW injury in the RR2 vs. Bt hybrids reduced N uptake by 42.0%, Beetle emergence was reduced 66 to 91% by Bt hybrids. Yield response to N differed between hybrids at only one site: the CRW-injured RR2 hybrid was unable to utilize increasing N rates while the SSX hybrid did not plateau. Recommended N rates (134–185 kg N per ha^–1) were sufficient to optimize root mass, N uptake, root protection, and yield under a low stress, modest CRW-pressure environment: however, low N resulted in poor performance of these hybrids, suggesting further exploration of N rate effects when N loss or denitrification is present.