Influence of Salinity on Nitrogen Transformations in Soil

Laboratory experiments were carried out to study the influence of various salinity levels [1 (control), 9 (medium), 17 (high), and 27 dS m–1(strong)] on nitrogen (N) transformations in soil fertilized with urea and ammonium sulfate. Generally, soil salinization affected the normal pathway of N transformations. The results showed that salinity (medium to high) inhibited the second step of nitrification, causing nitrite (NO2 −) accumulation in soil. The inhibition was more severe in cases of high level of salinity. The greatest salinity level caused inhibition of even the first step of nitrification, leaving more ammonium (NH4)-N accumulation in soil. Severity in nitrification inhibition was observed with increase in salinity and rate of N application, which declined with time. Ammonium accumulation with increased salinity caused N losses in the form of ammonia (NH3) volatilization. After 14 days, the NH3 losses were 1.4-, 2-, and 5-fold greater at 9, 17, and 27 dS m–1 than that of the control (1 dS m–1). After 42 days, the losses reached up to 6-fold more than the control at the greatest salinity level. Initially (up to 14 days), NH3 losses were more from urea than from ammonium sulfate, whereas at the later stages (42 days), the losses were almost equal from both the fertilizers. The overall results revealed significant adverse effects of salinity on N transformations in soil.