Influence of Long-Term Sodic-Water Irrigation, Gypsum, and Organic Amendments on Soil Properties and Nitrogen Mineralization Kinetics under Rice-Wheat System.

Influence of long-term sodic-water (SW) irrigation with or without gypsum and organic amendments [green manure (GM), farmyard manure (FYM), and rice straw (RS)] on soil properties and nitrogen (N) mineralization kinetics was studied after 12 years of rice-wheat cropping in a sandy loam soil in northwest India. Long-term SW irrigation increased soil pH, exchangeable sodium percentage (ESP), and sodium adsorption ratio (SAR) and decreased organic carbon (OC) and total N content. On the other hand, application of gypsum and organic amendments resulted in significant improvement in all these soil properties. Mineralization of soil N ranged from 54 to 111 mg N kg-1 soil in different treatments. Irrigation with SW depressed N mineralization. In SW-irrigated plots, two flushes of N mineralization were observed; the first during 0 to 7 d and the second after 28 d. Amending SW irrigated plots with GM and FYM enhanced mineralization of soil N. Gypsum application along with SW irrigation reduced cumulative N mineralization at 56 days in RS-amended plots but increased it under GM-treated, FYM-treated, or unamended plots. Nitrogen mineralization potential (No) ranged from 62 to 543 mg N kg-1 soil. In the first-order zero-order model (FOZO), the easily decomposable fraction ranged from 5.4 to 42 mg N kg-1 soil. Compared to the first-order single compartment model, the FOZO model could better explain the variations in N mineralization in different treatments. Variations in No were influenced more by changes in pH, SAR, and ESP induced by long-term SW irrigations and amendments rather than by soil OC. [ABSTRACT FROM AUTHOR]