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Comparison of Nitrogen and Sulfur Mineralization in Soils¹

ABSTRACT

The relationship between N and S mineralization has not been well understood. In this study, field-moist soil-grass beads mixtures were packed in glass columns and leached with 100 ml of 0.01M KCl and incubated at 20 or 35°C. The leaching procedure was repeated every 2 weeks for a total of 26 weeks. The leachates were analyzed for mineral N and S. Expressed as percentages of soil organic N, the total amounts of N mineralized at 20°C ranged from 1.8 to 6.7 (avg = 3.8%) and, at 35°C, ranged from 8.3 to 26.8 (avg = 16.6%). Expressed as percentages of soil organic S, the total amounts of S mineralized at 20 and 35°C ranged from 3.5 to 13.3 (avg = 7.8%) and from 8.9 to 34.9 (avg = 22.8%), respectively. Results indicate that organic S is depleted faster than organic N.

The cumulative amounts of N and S mineralized in each of the 12 soils studied were linear with time of incubation. The rates (µg/g soil/week) of N and S mineralized at 20°C ranged from 1.7 to 4.2 (avg = 2.9) and from 0.5 to 1.2 (avg = 0.8), respectively. At 35°C, the rates of N and S mineralized ranged from 7.7 to 17.0 (avg = 12.5) and from 1.6 to 3.5 (avg = 2.5). The ratios of N/S mineralized during 26 weeks of incubation at 20 and 35°C ranged from 2.4 to 4.4 (avg = 3.5) and from 3.4 to 6.1 (avg = 5.0). At 35°C, the ratios of N/S mineralized were significantly correlated with soil pH. Rates of S mineralization, however, were significantly, but negatively, correlated with soil pH.

The average Q₁₀ of N mineralization of the soils was 3.0, and that of S mineralization was 1.9. The amounts of N and S mineralized during 26 weeks of inclubation were significantly correlated at 20°C (r = 0.95***) and at 35°C (r = 0.79**).

¹ Journal Paper J-9746 of the Iowa Agriculture & Home Econ. Exp. Stn., Ames, Iowa. Project 2112. Presented before Div. S-4, Soil Sci. Soc. Am., Chicago, Ill., 5 Dec. 1978. This work was supported in part by The Sulphur Institute.

² Professor of Soil Chemistry and Graduate Student, respectively, Dep. of Agronomy, Iowa State Univ., Ames, IA 50011.

Received for publication December 28, 1979. Accepted for publication May 3, 1980.