Field nitrogen dynamics: Implications for assessing N availability

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Abstract
The amount of organic‐N in a given soil is a result of the cumulative influences of factors affecting additions to and losses from the soil. Many of these factors also influence the rate of N mineralization and, thus, the quantity of available N for plants. Regression techniques were used with data gathered while field testing a soil N availability test for corn (Zea mays L.) to evaluate the influence of various factors on N availability and the rate of N mineralization. Both check plot (no N fertilizer) yields and soil test NO3‐N were related to total Kjeldahl N (TKN), drainage class, and manure application. The estimated rate of N mineralization decreased as TKN increased. Answers to a farmer questionnaire that accompanied samples submitted for soil testing also indicated the importance of soil characteristics and fresh organic residue decomposition to N availability. These findings suggest that soil tests based on TKN or parameters correlated with TKN will not successfully predict N availability for widely different soil types and management practices. The Magdoff Pre‐Sidedress Nitrate Test (PSNT), however, is able to assess the cumulative effects of the variety of factors that govern nitrogen availability in soils.