Estimation of Nitrogen (N) and Sulfur (S) Mineralization in Soils Amended with Crop Residues.

Mineralization plays an essential role in supplying available N and S for plants. In order to determine nitrogen and sulfur mineralization, an 8-week aerobic incubation experiment based on the method of Stanford and Smith (1972) was carried out using soils from Absaraka and Walcott. For N mineralization, the soils were amended with three crop residues; corn, soybean, and wheat whereas only corn and wheat residues were used for S mineralization. The cumulative amounts of N mineralization ranged from 0.34 to 2.15 mg kg^-1 in Absaraka soil and from 0.45 to 3.41 mg kg^-1 in Walcott soils. The highest cumulative N mineralized was observed in control soils indicating N immobilization in all residue treated soils. In the case of S, the cumulative S mineralized varied from 29.6 to 38.5 mg kg^-1 and from 3.3 to 5.3 mg kg^-1 in Absaraka and Walcott soils, respectively. Highest cumulative S was found in wheat amended soils at Walcott whereas S immobilization was observed in Absaraka soils. Correlation analysis indicated the negative relationship of C:N ratio with N mineralization (r = -0.42 p ≤ 0.1) and of C:S ratio with S mineralization (r = -0.83; p ≤ 0.05). The N₀ and S₀ values were higher in control soils (except for wheat residues for Walcott) indicating less potential of residue treated soils to mineralize N and S, respectively.