Incorporating Soil and Weather Measurements to Improve Nitrogen Management in the Midwest.

The decomposition of organic nitrogen (N) in the soil can supply between 19 and 100% of corn (Zea mays L.) N needs. The exact amount in dependent on soil characteristics (organic matter, texture, microbial population, etc.) and weather (temperature and precipitation). Fertilizer can supply the amount of N the crops need that the soil does not supply through decomposition. An improved estimate of the ability of the soil to supply N is needed to better estimate the amount of fertilizer needed.

The ability of the anaerobic potentially mineralizable N tests (PMN) alone and in conjunction with soil and weather measurements to predict the economic optimal nitrogen rate (EONR) of corn across the Midwestern Cornbelt was evaluated in this study. The PMN test was altered by testing soils that were sampled early and mid-season, with and without N fertilizer added at planting, and then incubated for 7, 14, and 28-d.

The relationship between PMN alone and EONR was low for all treatment combinations. The addition of initial NH₄⁺ to the model improved the relationship with EONR. Dividing the soils into coarse, fine, and medium textured soils led to further improvements in the model. This presentation will also demonstrate how the inclusion of soil and weather measurements along with PMN affected the ability of the model to predict EONR. Improving estimation of how much N the soil can supply due to the differences in soil and weather may increase accuracy of N fertilizer rate guidelines, improve N use efficiency, and lower environmental impacts.