Date of Award
Doctor of Philosophy
John E. Sawyer
Improvement in N management to optimize corn N fertilization requirement and minimize NO33--N loss from agricultural fields is an ongoing need for continuous corn (Zea mays L.) and corn-soybean [Glycine max (L.) Merr.] production systems. This is especially important in Iowa as this state has the largest corn production across the U.S.A. The present dissertation includes two projects that evaluated corn response to N application and optimal fertilization rate. The first project evaluated the effect of corn stover harvest (SH) in continuous corn and the interaction with chisel plow and no-tillage systems; and the second project evaluated the effect of a rye cover crop (RCC) in no-till corn-soybean. For the RCC project, an additional in-field experiment was conducted to help understand the N cycling.
Results of the corn SH project showed that across tillage systems and fertilizer N rates, corn grain yield was 7 and 10% greater with 50 and 100% SH compared to no harvest, respectively. Corn grain yield was also 9% greater with chisel plow than with no-tillage. At the economic optimum N rate (EONR), yield was not influenced by SH with chisel plow, but was 6% greater with each SH rate in no-tillage. The EONR was the same with both tillage systems, but decreased by 22 and 45 kg N ha-1 with 50 and 100% SH, respectively. Results indicate, at least on a short term basis, that suggested N fertilization rates should be adjusted when stover is harvested in continuous corn production.
Results of the RCC project showed that the reduced corn grain yield by 6% at the EONR, and increased RCC biomass production resulted in lower corn yield. The EONR was the same with no-RCC and RCC. Soybean yield was not affected by the RCC. The RCC N cycling experiment showed that RCC biomass degradation and N recycling after rye control consistently decreased over time (total of 105 d after control), following an exponential decay. Nitrogen recycling was faster and more N recycled with RCC following soybean than following corn (22 vs. 14 kg N ha-1, respectively), and was influenced by the RCC C:N ratio. This research indicates that corn N fertilization rate should be the same with or without a RCC system, mainly due to the RCC not recycling a large amount of N. Since there was low RCC N uptake, reduced corn yield, and no change in EONR, improvement in the RCC system or management practices are needed for RCC to become viable in a no-till corn-soybean rotation.
Jose L. Pantoja
Pantoja, Jose L., "Effect of corn stover harvest and winter rye cover crop on corn nitrogen fertilization" (2013). Graduate Theses and Dissertations. 13042.