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Nitrogen Dynamics and Indices to Predict Soil Nitrogen Supply in Humid Temperate Soils

M. St. Luce, J. K. Whalen, N. Ziadi and B. J. Zebarth . 2011. Advances in Agronomy

Abstract

Knowledge of the nitrogen (N) available to crops during the growing season is essential for improving fertilizer-use efficiency and minimizing the adverse impacts of N losses on the environment. In humid temperate regions, soil N supply is dominated by in-season N mineralization because plant-available N (NH4- N and NO3- N) is transformed to nonlabile forms or lost from the soil-plant system during fall and winter. The microbially mediated reactions that generate the soil N supply in agroecosystems are affected by system-specific conditions, including soil properties, agricultural management (crop rotation, tillage system, organic amendments), and most importantly, climate. Potentially mineralizable N (N0) determined from long-term soil incubation is regarded as the standard measure of soil N mineralization potential and may provide a good approximation of the soil N supply. However, this method is time consuming and not practical for routine use. Several chemical methods to estimate the N mineralization potential of soils are discussed in this chapter. The major limitation of chemical methods is that they cannot simulate the microbial-mediated release of plant-available N under field conditions. Consequently, any single chemical method may not be a good predictor of soil N supply. Thus, we suggest a holistic approach to estimate soil N supply in humid temperate regions, which involves (1) the use of a combination of N indices together with weather data and (2) identification and quantification of a specific fraction (s) of organic N that is the dominant contributor (s) to N supply in a particular system