SOIL NITROGEN TRANSFORMATIONS AS AFFECTED BY SALINITY

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Abstract
The results presented in this paper reveal that salinity has a major influence on soil N transformations. Studies were conducted to test the effects of Na2SO4, NaCl, and CaCl2, applied at rates that produced electrical conductivities of saturation extracts (ECe) of 5, 10, 15, and 20 dS m−1, on ammonia volatilization, ammonification of urea, and nitrification in three diverse soils. The effects of salinity on ammonia volatilization and nitrification varied depending on the N source, the amounts and types of salts added, and the soils used. In two of the three soils in which ammonia volatilization occurred, increased salinity promoted ammonia loss (up to 3.7-fold increase); however, calcium-reduced NH3 loss of applied urea was observed in one of the two soils. There was no apparent effect of salinity on ammonification of urea in any of the three soils regardless of the type of salts added. Generally, increased salinity progressively decreased nitrification. Appreciable amounts of NO2−-N (up to 6.8 μg g−1 soil; 3.4% of the total N applied) were recovered in salinized soils. The percentage of inhibition of nitrification ranged from 8 to 83%, varying among the soils studied as well as the type of salts added. In most cases, Na2SO4 was less inhibitory to nitrification than the chloride salts. Inhibition of nitrification at ECe values of 20 dS m−1 (NaCl) were as high as 75 and 83% when (NH4)2SO4 and urea were applied to soils, respectively.

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