Does the Corn Rootworm Resistant Trait Improve N Use Efficiency In Corn?.

The number of acres planted to corn rootworm (Diabrotica spp.) (CRW) resistant corn (Zea mays L.) hybrids have increased in recent years.  The CRW resistant corn hybrids protect yield potential because of reduced stress from CRW larval feeding resulting in larger root systems.  Some agronomists believe higher N rates are needed to achieve the yield potential associated with these hybrids.  However, larger root systems of CRW resistant hybrids could result in greater N use efficiency and perhaps a reduced N fertilizer need compared to non-CRW resistant hybrids. The objective of this study was to determine if corn hybrids, with the CRW resistant gene, vary in their N use efficiency (NUE) and N need compared to non-resistant hybrids. From 2008 through 2010, N fertilizer (0 to 224 kg ha^-1) was applied to each of eight corn hybrids and replicated four times in a completely randomized design. The previous crop was corn. Four of the hybrids had the CRW resistant gene while the other four did not. Two pairs of hybrids were near isolines differing in CRW resistance. Corn rootworm insecticide was applied to the seed in all treatments. Relative yield, partial factor productivity, agronomic N fertilizer efficiency, internal N use efficiency, physiological efficiency, and fertilizer N recovery efficiency were used to evaluate the NUE of CRW resistant compared to non-resistant hybrids. There was no significant difference between resistant and non-resistant hybrids with regard to any measure of NUE. CRW-resistant hybrids had significantly greater yield when no N fertilizer was applied compared to non-resistant hybrids. However, this did not translate into greater maximum yield levels or a different amount of N needed to reach maximum yield. These results suggest that CRW resistance does not improve NUE.