Transgenic corn rootworm protection increases grain yield and nitrogen use of maize

Maize (Zea mays L.) hybrids expressing Bacillus thuringiensis (Bt) derived resistance to corn rootworm (Diabrotica spp.) are widely grown. our hypothesis was that Bt hybrids exhibit increased N uptake, resulting in greater grain yield and N use efficiency (NUE) relative to their nonprotected counterparts. In 2008 and 2009, two transgenic corn rootworm resistant (Bt) hybrids with VT3 (YieldGard VT Triple) technology along with their near-isogenic non-Bt roundup ready Corn 2 (RR2) counterparts were evaluated at Champaign, IL, with supplemental N of 0, 67, 134, 201 or 268 kg N ha^-1. Despite minimal corn rootworm feeding pressure on roots, the Bt hybrids produced an average of nearly 1.1 Mg ha^-1 more grain than their rr2 counterparts. In the comparison of DKC61-72 rr2 and DKC61-69 VT3, Bt protection promoted increased grain yield at low N (+1.0 Mg ha^-1; P ≤ 0.01) and a 31% greater response to fertilizer N. With adequate N, grain yields of the comparison DKC63-45 rr2 and DKC63-42 VT3 did not differ; however, the latter maximized its yield with an average of 38% less fertilizer N. Increases in NUE (+80%; P ≤ 0.10) and N uptake efficiency (NUpE) (+31%; P ≤ 0.10) at the N rates required to optimize grain yield of Bt hybrids were detected in 2008, but NUE and NUpE were not significantly different between isolines in 2009. We conclude that transgenic corn rootworm protection has supplemental agronomic benefits, with greater N uptake and NUE in some environments.