Potassium, Nitrogen, and Corn Rootworm Resistance Interactions in Continuous Corn.

Root diseases and pests are known to impair the uptake of nutrients, mainly the less mobile in soils such as P and K. Also, a positive interaction between N and K has been observed in corn and other cereals. However, no research has investigated impacts of rootworm incidence and genetic rootworm resistance on corn responses to N and K fertilization. Therefore, this project addressed these issues in 4-year experiments with continuous corn in north-central Iowa (NI) and southeast Iowa (SE) with NH₄OAc soil K 130 to 170 mg kg^-1(15-cm depth). Replicated treatments at the two sites were the factorial combinations of two corn hybrids (one resistant to glyphosate and European corn borer and an isoline with the addition of rootworm resistance), five N rates (0 to 336 kg ha^-1), and four K rates (0 to 67 kg ha^-1). No insecticide was applied for any hybrid. Root injury by rootworms was much less for the hybrid with the resistant trait at both sites, and neither N nor K fertilization affected root injury. Grain yield and ear-leaf N concentration increased significantly with N fertilization at both sites. There a moderate grain yield response to K at SE but smaller and inconsistent over time at NI. Ear-leaf K concentration was increased with K fertilization but decreased with increasing N rates, with the exception of the resistant hybrid with K fertilization at the SE site. At the SE site, the resistant hybrid with K fertilization yielded more than the susceptible hybrid and the difference became larger as the N rate increased. The N rate to achieve maximum yield and the maximum yield level were higher for the resistant hybrid, and increasing N rates did not decrease K ear-leaf concentrations. We conclude that rootworm resistance did not clearly affect the K rate needed to produce maximum yield, and that at one site it allowed for higher yield and higher response to N fertilization.