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Ionic Effect of Salts on Mineral Nitrogen Release in an Allophanic Soil¹

ABSTRACT

A comparison of the effects of sulfate and chloride salts on N release and microbial activity in Akaka soil showed that only sulfate salts at low concentrations increased CO₂ evolution. The chlorides were more effective than sulfates in effecting NH₄-N release in the soil. The addition of CaCl₂·2H₂O resulted in the greatest NH₄-N release, followed by that of KCl and NaCl. Among sulfates, K₂SO₄ ranked first, followed by Na₂SO₄ and CaSO₄ · 2H₂O. The idea that certain chemical reactions and/or processes are involved in splitting NH₄-N from organo-inorganic complexes of a soil and that NH₄⁺ ions are subsequently exchanged with cations in the surrounding soil solution was further substantiated by results of this investigation. The exchange reaction was noted to depend on the nature and valence of the cation, concentration in the soil solution, length of reaction, and the anionic species associated with the cation. The capacity of the cations for releasing NH₄-N decreased in the order Ca > K > Na for the chloride series.

Unlike the NH₄-N release pattern, sulfates were more effective than chlorides in promoting nitrification. In general, all salts, excepting CaSO₄ · 2H₂O, at higher concentrations curtailed nitrification. The results indicated a real participation of anions in soil N release. Two salts containing the same cation but different anions released different magnitudes of N at an equivalent concentration. Thus, the results of this investigation provide further support for the role of cations in soil N release and, in addition, furnish reasonable evidence of the participation of anionic species. A consideration of the overall values of NH₄- and NO₃-N at various salt concentrations led to the series, CaCl₂ · 2H₂O > KCl > NaCl > K₂SO₄ > Na₂SO₄ > CaSO₄ · 2H₂O, in order of decreasing N release power.

¹ Journal Series no. 1211 of the Hawaii Agr. Exp. Sta. This work is part of the senior author's Ph.D. dissertation, 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) Private 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 May 26, 1970. Accepted for publication January 26, 1971.