Soil sample timing, nitrogen fertilization, and incubation length influence anaerobic potentially mineralizable nitrogen

Authors: CLARK, J - University Of Missouri; Veum, Kristen; FERNANDEZ, F - University Of Minnesota; Kitchen, Newell; 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; LABOSKI, C - University Of Wisconsin; NAFZIGER, E - University Of Illinois; ROSEN, C - University Of Minnesota; SAWYER, J - Iowa State University; SHANAHAN, J - Fortigen

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/4/2020
Publication Date: 4/21/2020
Publication URL: https://handle.nal.usda.gov/10113/7019769
Citation: Clark, J.D., Veum, K.S., Fernandez, F.G., Kitchen, N.R., Camberato, J.J., Carter, P.R., Ferguson, R.B., Franzen, D.W., Kaiser, D.E., Laboski, C.A., Nafziger, E.D., Rosen, C.J., Sawyer, J.E., Shanahan, J.F. 2020. Soil sample timing, nitrogen fertilization, and incubation length influence anaerobic potentially mineralizable nitrogen. Soil Science Society of America Journal. 84(2):627-637. https://doi.org/10.1002/saj2.20050.
DOI: https://doi.org/10.1002/saj2.20050

Interpretive Summary: Laboratory tests have been developed that incubate the soil in order to estimate the amount of organic nitrogen microbes will release during a growing season for plants to use. This nitrogen is referred to as potential mineralizable nitrogen (PMN), and an accurate measurement of this form of nitrogen could improve nitrogen fertilizer decisions for farmers. However, a full understanding of the factors affecting nitrogen mineralization is still lacking. In this study, the role of soil sample timing, nitrogen fertilization rate, and laboratory methodology on PMN was evaluated from 32 sites across eight US Midwestern states representing a range of climate and soil conditions. Sample timing influenced PMN at 50% of the sites, primarily due to the impact of weather on soils. These results demonstrated how weather and soil interact to alter PMN. Similarly, nitrogen fertilization early in the growing season influenced PMN at 37% of the sites, demonstrating that nitrogen fertilization alters mineralization throughout the season. Yet this influence was not the same for all soils. Finally, increased laboratory incubation time always increased PMN. This study illustrates that many factors influence PMN, and these factors need to be considered when using PMN tests to help make nitrogen fertilizer decisions. When accurately utilized, these tests may help producers improve crop nitrogen use efficiency, which in turn will provide environmental benefits.

Technical Abstract: The anaerobic potentially mineralizable N (PMNan) test may improve mineralizable N estimates that inform N fertilizer recommendations and lead to greater corn (Zea mays L.) N use efficiency. An evaluation of PMNan across various climates and soils in the US Midwest has not been conducted. Thirty-two field studies were implemented across eight US Midwestern states to determine the effect of sample timing, N rate, and incubation length on PMNan. Sites were soil sampled (0-30 cm) before pre-plant N application (PP0N) and at the V5 development stage from the pre-plant zero (V50N) and 180 kg-N ha-1 (V5180N) rates and incubated for 7, 14, and 28-d. In sites where soil sample timing affected PMNan (50% of sites), the PMNan at pre-plant was greater than at V5 at sites with less precipitation (< 183 mm) and fewer GDD (< 359) before soil sampling, or soils with larger C:N ratios (> 9.7:1). For sites where N fertilization affected PMNan (37% of sites), PMNan from unfertilized soil was greater than fertilized soil when the soil had greater clay content (> 9.5%) and less total C (< 24.2 g kg-1), SOM (< 3.9 g kg-1), and C:N ratios (< 11.0 g kg-1). Longer incubation lengths increased PMNan at all sites regardless of soil sample timing and N fertilization. Soil and weather conditions influenced the effect that soil sample timing, N fertilization, and incubation length had on PMNan and therefore need to be considered when evaluating PMNan as an estimate of N mineralization to improve N management.