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Title: Do soil tests help forecast nitrogen response in first-year corn following alfalfa on fine-textured soils?

Author
item WALKER, Z - University Of Minnesota
item COULTER, J - University Of Minnesota
item RUSSELLE, M - University Of Minnesota
item Venterea, Rodney - Rod
item MALLARINO, A - Iowa State University
item LAUER, J - University Of Wisconsin
item Yost, Matt

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/14/2017
Publication Date: 11/22/2017
Citation: Walker, Z.T., Coulter, J.A., Russelle, M.P., Venterea, R.T., Mallarino, A.P., Lauer, J.G., Yost, M.A. 2017. Do soil tests help forecast nitrogen response in first-year corn following alfalfa on fine-textured soils? Soil Science Society of America Journal. 81(6):1640-1651. doi:10.2136/sssaj2017.06.0183.
DOI: https://doi.org/10.2136/sssaj2017.06.0183

Interpretive Summary: Nitrogen (N) fertilizer is needed to increase grain yield of corn planted after alfalfa termination more frequently on fine-textured soil (soil with high clay content) than other soils, but tools to accurately predict when fertilizer is needed are limited. Two of the most common soil tests used to estimate the need for fertilizer in first-year corn following alfalfa are the pre-sidedress soil nitrate test (PSNT) and the Illinois soil nitrogen test (ISNT). Relationships between PSNT or ISNT concentrations and soil nitrogen mineralization, corn N uptake, and available N were examined in 21 trials in Iowa, Minnesota, and Wisconsin. Results indicated that the PSNT more accurately predicted corn response or non-response to N fertilizer than the ISNT (62 and 52% of trials correctly classified, respectively). Incubation of soil from first-year corn showed that the ISNT explained 30% of the variation in cumulative mineralized soil nitrate-N after 17 weeks compared to 13% by the PSNT. The PSNT positively correlated with aboveground corn N uptake and total available N, and ISNT similarly correlated with potentially mineralizable N. Overall, the PSNT was less related to soil N mineralization, but more related to grain yield response to N fertilizer in first-year corn following alfalfa than the ISNT. Future research should seek to predict the size and mineralization rate of soil N pools following alfalfa termination, especially on fine-textured soil where N response in first-year corn is more frequent than on other soils. Improvements in the ability to predict when first-year corn following alfalfa needs N fertilizer will result in large savings for growers and greatly reduce negative environmental impacts of excessive fertilization.

Technical Abstract: Improved methods of predicting grain yield response to fertilizer N for first-year corn (Zea mays L.) following alfalfa (Medicago sativa L.) on fine-textured soils are needed. Data from 21 site-years in the North Central Region were used to (i) determine how Illinois soil nitrogen test (ISNT) and pre-sidedress soil nitrate test (PSNT) concentrations change during alfalfa-corn rotations; (ii) evaluate the ability of the ISNT and PSNT to predict grain yield response to fertilizer N in first-year corn following alfalfa; and (iii) investigate relationships between the ISNT or PSNT and mineralized and available N. In five long-term trials where alfalfa stand age was evaluated, the ISNT and PSNT changed as alfalfa stands aged, and PSNT concentration increased during first-year corn in three of five trials. The PSNT more accurately predicted corn response to fertilizer N than the ISNT (62 and 52% of site-years correctly classified, respectively). Incubation of soil from first-year corn showed that the ISNT explained 30% of variation in cumulative mineralized soil nitrate-N after 17 wk, compared to 13% with the PSNT. The PSNT was positively correlated with aboveground corn N uptake (ANU) and total available N (TAN), and ISNT similarly correlated with soil potentially mineralizable N (PMN). Overall, the PSNT was less related to soil N mineralization and more related to grain yield response to fertilizer N in first-year corn following alfalfa than the ISNT. Future research should seek to predict the size and mineralization rate of soil N pools following alfalfa termination, especially on fine-textured soil where N response in first-year corn is more frequent than on other soils.