A New Long-term Study: Evaluation of Hybrid, Nitrogen, and Potassium Interactions in Continuous Corn

A long-term experiment was established in 2009 to study continuous corn responses to potassium (K), nitrogen (N), and hybrid rootworm resistance. Previous research suggested a need for this type of study in Southeast Iowa. A long-term trial conducted until 2001 at the Northern Research Farm in a soil testing low in P and K showed that N, P, and K fertilizers greatly increased corn yield but there was an interaction only between N and K. The maximum corn yield level, the relative yield response to N (percent increase for each N addition), and the N rate that maximized yields were highest when K was optimal or higher. In contrast, the relative yield response to N and the N rate that maximized yield were similar for soil-test P levels ranging from very low to very high. Ongoing studies at this research farm and four other farms show that rootworm resistance often increases yield compared with untreated susceptible hybrids. It does not affect the yield response to K consistently, but increases K removal because of the higher yields. Therefore, this new long-term study evaluates possible interactions between corn rootworm resistance, N fertilization, and K fertilization