Nitrogen fertilizer recommendations in corn (Zea mays L.) that match the economically optimal nitrogen fertilizer rate (EONR) are imperative for profitability and minimizing environmental degradation. However, the amount of soil N available for the crop depends on soil and weather factors, making it difficult to know the EONR from year-to-year and from field-to-field. Our objective was to explore, within the framework of hydrologic soil groups and drainage classifications (HGDC), which site-specific soil and weather properties best estimated corn N needs (i.e., EONR) for two application timings (at-planting and side-dress). Included in this investigation was a validation step using an independent dataset. Forty-nine N response trials conducted across the U.S. Midwest Corn Belt over three growing seasons (2014–2016) were used for recommendation model development, and 181 independent site-years were used for validation. For HGDC models, soil organic matter (SOM), clay content, and evenness of rainfall distribution before side-dress N application were the properties generally most helpful in predicting EONR. Using the validation data, model recommendations were within 34 kg N ha–1 of EONR for 37 and 42% of the sites with a root mean square error (RMSE) of 70 and 68 kg N ha–1 for at-planting and side-dress applications, respectively. Compared to state-specific recommendations, sites needing <100 kg N ha–1 or no N were better estimated with HGDC models. In contrast, for sites where EONR was >150 kg N ha–1, HGDC models underestimated N needs compared to state specific. These results show HGDC groupings could aid in developing tools for N fertilizer recommendations.
Bibliographical noteFunding Information:
This research for developing the models was conducted as part of a public–private collaboration between eight major land-grant universities (Iowa State University, University of Illinois, Purdue University, University of Minnesota, University of Missouri, North Dakota State University, University of Nebraska, and the University of Wisconsin) within the U.S. Corn Belt and Corteva Agriscience (Kitchen et al., 2017). Yield and soil measurements from these plot studies provided the measurements needed to generate N fertilizer recommendation models and N response functions. Soil hydrologic classifications aid in determining corn N fertilizer rates. Economically optimal N rate was best predicted by different soil and weather properties for each hydrologic group. Soil organic matter, clay, and rainfall evenness generally helped in estimating economically optimal N rate. Compared to state N recommendations, developed models were better when economically optimal N rate <100 kg ha−1. Forty-nine corn N response trials were conducted during 2014–2016 in eight midwestern Corn Belt states. In each state, two sites varying in productivity were selected for each growing season, resulting in six sites per state (Missouri had three in 2016). The majority of sites were corn after soybean [Glycine max (L.) Merr.]. Productivity was determined by historical yield and general soil productivity. Research sites were planted at a target population of 86,450 plants ha−1 using Pioneer brand hybrids (Corteva Agriscience) adapted for the selected sites within the region. Descriptions of management for all sites are presented in Kitchen et al. (2017) and Bean et al. (2018a). Fourteen different N application treatments replicated four times were used in a randomized complete block design. Nitrogen treatments comprised of dry-prilled NH4NO3 fertilizer broadcast applied. The “at-planting” fertilizer was applied within 48 h of initial planting, while the side-dress fertilizer was applied between the V8 and V10 leaf stage (Abendroth et al., 2011). At-planting rates ranged from 0 to 315 kg N ha−1 in 45 kg N ha−1 increments. Side-dress rates ranged from 0 to 315 kg N ha−1 in 45 kg N ha−1 increments, but treatments were split applied with 45 kg N ha−1 at planting and the remaining N at the V9 development stage. Additional details about the trial sites, treatments, and measurement have been previously documented (Kitchen et al., 2017). An EONR [corn grain price, US$0.158 kg−1 ($4.00 bu−1), N fertilizer cost, $0.88 kg N−1 ($0.40 lb−1)] was calculated for both the at-planting and split N treatments.
© 2021 The Authors. Agronomy Journal © 2021 American Society of Agronomy