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Soil Nitrogen and Carbon Mineralization as Affected by Drying-Rewetting Cycles¹

ABSTRACT

The temperature of drying as well as drying-rewetting cycles enhanced N and C mineralization in practically all soils. There was generally greater N release when incubation after drying was included than when omitted. In all unincubated soils, save the Akaka, air-drying caused greater N release than heating at 60C, regardless of the number of drying-rewetting cycles. The organic matter-rich Akaka soil showed increased N mineralization with increased temperature of drying. Mineralization of C was greater in samples incubated after drying-rewetting cycles than those subjected to incubation only. A highly significant correlation existed between rates of N and C mineralization per cycle. Significant correlation was also noted between C/N ratio of the soils and N released during drying and rewetting followed by incubation. It is proposed that in addition to microbial stimulation through drying, heat was directly responsible for the major amount of N and C release in unincubated samples by chemical alteration of otherwise unavailable organic matter and by killing off of organisms. When incubation followed the drying and heating treatment, the direct effect of heat together with increased microbial activity and associated changes during incubation accounted for N and C release.

¹ Published with the approval of the Director of the Hawaii Agr. Exp. Sta. as Journal Series no. 1189. This work is part of the senior author's Ph.D. dissertation submitted to the Univ. of Hawaii. The project was supported in part by the Western Regional Research Project no. W-85.

² Formerly an East-West Center graduate student (now with the I.C.I. (India) Pvt. Ltd., Calcutta), formerly Assistant in Agronomy and Soil Science (now Assistant Soil Chemist, Haryana Agricultural Univ., Hissar, Haryana, India), and Professor of Soil Science, respectively.

Received for publication April 9, 1970. Accepted for publication September 25, 1970.