Predicting economic optimal nitrogen rate with the anaerobic potentially mineralizable nitrogen test

Authors: CLARK, J - South Dakota State University; FERNANDEZ, F - University Of Minnesota; Veum, Kristen; CAMBERATO, J - Purdue University; CARTER, P - Dupont Pioneer Hi-Bred; FERGUSON, R - University Of Nebraska; FRANZEN, D - North Dakota State University; KAISER, D - University Of Minnesota; Kitchen, Newell; LOBOSKI, C - University Of Wisconsin; NAFZIGER, E - University Of Illinois; ROSEN, C - University Of Minnesota; SAWYER, J - Iowa State University; SHANAHAN, J - Fortigen

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/17/2019
Publication Date: 8/30/2019
Citation: Clark, J.D., Fernandez, F.G., Veum, K.S., Camberato, J.J., Carter, P.R., Ferguson, R.B., Franzen, D.W., Kaiser, D.E., Kitchen, N.R., Loboski, C.A., Nafziger, E.D., Rosen, C.J., Sawyer, J.E., Shanahan, J.F. 2019. Predicting economic optimal nitrogen rate with the anaerobic potentially mineralizable nitrogen test. Agronomy Journal. 111(6):3329-3338. https://doi.org/10.2134/agronj2019.03.0224.
DOI: https://doi.org/10.2134/agronj2019.03.0224

Interpretive Summary: Better prediction of the optimal nitrogen fertilizer rates could provide economic and environmental benefits to producers. Laboratory tests have been developed to estimate the amount of organic nitrogen that will be provided by the soil for plants to use during the growing season. This nitrogen is referred to as potential mineralizable nitrogen (PMN) and could be used in making fertilizer decisions to improve nitrogen use efficiency. However, a full understanding of the utility of PMN is still lacking. In this study, PMN was weakly related to the optimum nitrogen fertilization rate for corn when tested across eight US Midwestern states representing a range of climate and soil conditions. This study illustrates that soil texture influences PMN and that several factors need to be considered when using PMN tests to help make nitrogen fertilizer decisions. Ultimately, tests such as PMN may help producers improve crop nitrogen use efficiency, but PMN alone is not a reliable decision tool for determining nitrogen fertilization rates.

Technical Abstract: Estimates of mineralizable N with the anaerobic potentially mineralizable N (PMNan) test could improve predictions for corn (Zea mays L.) economic optimal N rates (EONR). A study across eight U.S. Midwestern states was conducted to quantify the predictability of EONR for single and split N applications by PMNan. Treatment factors included different soil sampling times (pre-plant and V5 development stage), at planting N rates (0 and 180 kg N ha-1), and incubation lengths (7-, 14-, and 28-d) with and without initial measurements of soil NH4+ included with PMNan. Soil was sampled (0-30-cm depth) before planting and N application and at V5 where 0 or 180 kg N ha-1 were applied at planting. Evaluating across all soils, PMNan was a weak predictor of EONR (R2 = 0.08 and RMSE = 67 kg N ha-1), but the predictability improved (15%) when soils were grouped by texture. Using PMNan and initial soil NH4+ as separate explanatory variables improved EONR predictability (11-20%) in fine-textured soils only. Delaying PMNan sampling from pre-plant to V5 regardless of N fertilization improved EONR predictability by 25%, but only in coarse-textured soils. Increasing the incubation length beyond 7-d resulted in modest improvements (R2 increased = 0.18 and RMSE was reduced = 7 kg N ha-1). Alone, PMNan predicted EONR poorly and the improvements from partitioning soils by texture and including initial soil NH4-N were relatively low (R2 = 0.33 and RMSE = 68 kg N ha-1) compared to other tools for N fertilizer recommendations.