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Title: The anaerobic potentially mineralizable nitrogen test as a tool for nitrogen management in the Midwest

item CLARK, JASON - University Of Minnesota
item Veum, Kristen
item FERNANDEZ, FABIAN - University Of Minnesota
item CAMBERATO, JAMES - Purdue University
item CARTER, PAUL - Dupont Pioneer Hi-Bred
item FERGUSON, RICHARD - University Of Nebraska
item FRANZEN, DAVID - North Dakota State University
item Kitchen, Newell
item LABOSKI, CARRIE - University Of Wisconsin
item NAFZIGER, EMERSON - University Of Illinois
item SAWYER, JOHN - Iowa State University
item SHANAHAN, JOHN - Farmer

Submitted to: North Central Extension Industry Soil Fertility Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 11/2/2016
Publication Date: 11/2/2016
Citation: Clark, J., Veum, K.S., Fernandez, F.G., Camberato, J.J., Carter, P.R., Ferguson, R.B., Franzen, D.W., Kitchen, N.R., Laboski, C.A., Nafziger, E.D., Sawyer, J.E., Shanahan, J. 2016. The anaerobic potentially mineralizable nitrogen test as a tool for nitrogen management in the Midwest. North Central Extension Industry Soil Fertility Conference Proceedings, November 2-3, 2016, Des Moines, Iowa. p. 97-110.

Interpretive Summary: Estimation of organic nitrogen that breaks down into inorganic nitrogen (a process called nitrogen mineralization) that plants can take up and use has the potential to improve nitrogen use efficiency. Many have suggested mineralization tests will be helpful for predicting nitrogen uptake, grain yield, and the optimum nitrogen fertilizer rate for corn. This study was conducted from fields across eight Midwestern states to examine how mineralization test length (7-, 14-, and 28-day incubations), time of soil sampling, and nitrogen fertilizer rates impacted crop response and nitrogen use efficiency. There were no identifiable trends between the mineralization tests and time of sampling or addition of nitrogen fertilizer. Mineralization results from soil samples taken before planting were related, but poorly, to the optimal N rate the corn crop needed. When the soil sampling was delayed until the crop was about 6 inches tall and if no nitrogen fertilizer had been applied, a better relationship was found between the mineralization test and plant nitrogen uptake and grain yield. The longer anaerobic incubation times offered little benefit over the shorter, 7-day incubation. In addition, the mineralization tests did not demonstrate much utility as a decision tool for recommending N fertilizer, understanding crop nitrogen uptake, or predicting grain crop yield. The results of this study are beneficial to corn growers and crop advisors that are interested in understanding what tools best help them in making N fertilizer recommendations and maximizing profit while minimizing costs associated with nitrogen loss.

Technical Abstract: The anaerobic potentially mineralizable nitrogen (PMNan) test is a tool that can improve estimations of mineralizable nitrogen (N) and enhance nitrogen use efficiency. This tool may also help improve predictions of N uptake, grain yield, and the economic optimum nitrogen rate (EONR) of corn (Zea mays L.). A 32 site-year study across eight US Midwestern states was conducted to 1) compare the effect of incubation length (7-, 14-, 28-d), soil sampling timing, N fertilizer rate, and their interactions on PMNan, and 2) quantify the predictive power of PMNan values at different soil sampling timings and N fertilizer rates in determining EONR, yield, and plant N uptake for single and split N applications. Soil was sampled from 0-30 cm before planting and N fertilizer application (PPNT) or at the V5 leaf stage where 0 (V50N) or 180 kg-N ha-1 (V5180) were applied at planting. Overall, PMNan ranged from 0.19 to 136 mg-N kg-1 with a mean of 36 mg-N kg-1. There was no consistent pattern in PMNan with time of sampling. The PMNan was larger in nine site-years at PPNT (0.74–125 mg-N kg-1) and ten site-years at V50N, (0.19–136 mg-N kg-1) with no difference in the other eleven site-years. There was also no consistent pattern in response to the addition of N fertilizer. The V5180 PMNAn (0.86–122.47 mg-N kg-1) was lower than the V50N in ten site-years, greater in one site-year, and no different in 19 site-years. The PPNT soil sampling timing had the best correlation to EONR for single (R2=0.023) and split (R2=0.053) N applications. These coefficients of determination are low (similar to many studies) but are significant (P<0.05). The V50N sample timing improved the correlation of plant N uptake and grain yield for split N applications. The 7-d incubation for the V5180N sampling best predicted N uptake (R2=0.09) and yield (R2=0.12) when 180 kg-N ha-1 were applied at planting. On average, all site-years increased in PMNan as laboratory incubation length increased. However, increasing the incubation length beyond 7-d was not justifiable as the maximum increase in R2 values was = 4% across all agronomic variables.