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

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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.
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  • Western Regional Research (W-85)

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