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

Abstract

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.