Potassium Nutrition of Corn as Affected by the Rootworm Resistance Trait.

Root diseases and pests are known to impair the uptake of relatively immobile nutrients such as K. However, no research has investigated impacts of rootworm incidence and genetic rootworm resistance on corn response to K fertilization. Therefore, this project addressed these issues in nine 3-year experiments with continuous corn at five Iowa locations. Replicated treatments were two hybrids (one resistant to glyphosate and European corn borer and the other an isoline with the addition of rootworm resistance) and five K fertilizer application rates ranging from 0 to 168 kg K ha^-1. No insecticide was applied for any hybrid. Root injury by rootworms was much less for the hybrid with the resistant trait, and K fertilization did not affect root injury. The grain K concentration seldom differed between the hybrids. Grain yield and K removal with grain harvest were significantly greater for the rootworm resistant hybrid in about one-half of the site years, however, and differences were poorly correlated to rootworm incidence. There were inconsistent hybrid differences concerning the K rate that maximized grain yield across the site years, but on average the maximizing K rate was slightly less for the resistant hybrid even though the overall yield level was higher. Potassium concentration and uptake in vegetative tissue was higher for the resistant hybrid mainly with low K supply. The results indicated better K use efficiency of hybrids with rootworm resistance, although higher grain yield determined higher K removal and higher K fertilization rates to maintain desirable soil-test K values over time.