Modification of the biophysical water function to predict the change in soil mineral nitrogen concentration resulting from concurrent mineralization and denitrification

Uncertainty in soil N supply is an important limitation in making crop fertilizer N recommendations. This study modified a biophysical water function developed to predict net soil N mineralization, making it possible to consider how both N mineralization and denitrification processes affect the rate of soil mineral N accumulation. Data were from a published experiment measuring changes in soil mineral N concentration in five soils of varying texture (loamy sand to clay loam) incubated for 3 mo with or without addition of red clover residue and at two levels of compaction. The biophysical water function was effective in fitting the relationship between scaled change in the rate of soil mineral N accumulation ( Delta SMN) and scaled water-filled pore space (WFPS sub(S)) across soils and treatments provided that WFPS sub(S) = 1 was set to the water content at which the transition from mineralization to denitrification occurs. The water content at WFPS sub(S) = 1 varied with soil type, but not residue addition or compaction treatments, and was closely related to clay content. The k sub(D) parameter, which controls the denitrification term of the function, was influenced by soil type, whereas legume residue application had no significant effect on the k sub(D) parameter despite a twofold increase in net N mineralization. The modified biophysical water function holds promise for improving estimates of soil N supply because it can predict changes in Delta SMN in response to N mineralization and denitrification processes across a wide range of soil water contents.Original Abstract: Le fait qu'on ne sache pas exactement combien de N est present dans le sol constitue un important facteur limitatif quand vient le temps de formuler des recommandations sur l'usage d'engrais azotes en agriculture. Les auteurs ont modifie une fonction biophysique de l'eau mise au point pour predire la mineralisation nette du N dans le sol afin qu'elle tienne compte de la maniere dont la mineralisation et la denitrification affectent la vitesse a laquelle le N mineral s'accumule dans le sol. Les donnees emanaient d'une experience publiee mesurant l'evolution de la teneur en N mineral dans cinq sols de texture differente (du sable loameux au loam argileux) qu'on avait incube pendant trois mois avec ou sans residus de trefle rouge et a deux degres de compactage. La fonction biophysique de l'eau permet d'ajuster efficacement les liens entre le changement progressif du taux d'accumulation du