Nitrogen Mineralization‐Water Relations in Soils

Abstract The relationships between soil N mineralization, soil water content, and matric suction were studied with nine soils of widely differing chemical and physical properties. Highest N mineralization rates occurred between matric suctions of ⅓ to 0.1 bar, in which range 80 to 90% of the total pore space was filled with water. In the range from optimum soil water content (⅓ to 0.1 bar) to 15 bars, a near‐linear relation generally existed between amounts of mineral N accumulated and soil water contents (percent of oven‐dry soil). With increasing dryness, N mineralization continued to decline. Water levels above optimum often reduced mineral N accumulations, presumably because of denitrification. Upon expressing the values for N mineralization ( Y ) and soil water content ( X ) for each soil on a relative basis with respect to maximum N mineralized ( Y = 100) and associated optimum soil water content ( X = 100), the regression of Y on X did not differ among soils. Regression coefficients for common (based on covariance) and total regressions, respectively, were 1.07 and 1.02. Corresponding Y ‐intercepts were −2 and −4. A reasonable approximation of the relationships is expressed by Y = X . Possible application of the findings in predicting N mineralization under fluctuating soil water conditions is discussed.