Nitrogen Mineralization Potentials of Soils

Net mineralization of N in 39 widely differing soils was determined over a 30‐week period at 35C, using incubation intervals of 2, 2, 4, 4, 4, 6, and 8 weeks. Mineral N was leached from the soils before the first incubation and following each of seven incubations by means of 0.01 M CaCl 2 and a minus‐N nutrient solution. Soil water contents were adjusted by applying suction (60 cm Hg), and losses of water during incubation under aerobic conditions were negligible. With most soils, cumulative net N mineralized was linearly related to the square root of time, t ½ . The pH of soils changed very little in the course of 30 weeks' incubation. Because of the generally consistent results, the data were employed in calculating the N mineralization potential, N o , of each soil, based on the hypothesis that rate of N mineralization was proportional to the quantity of N comprising the mineralizable substrate. Values of N o ranged from about 20 to over 300 ppm of air‐dry soil. The fraction of total N comprising N o varied widely (5 to 40%) among soils. Mineralization rate constants did not differ significantly among most of the soils. The most reliable estimate of the rate constant, k was .054 ± .009 week ‐1 . The time required to mineralize one‐half of N o , t ½ , was estimated to be 12.8 ± 2.2 weeks. Results suggest that the forms of organic N contributing to N o were similar for most of the soils.