Microbial biomass carbon and some soil properties as influenced by long-term sodic-water irrigation, gypsum, and organic amendments

Abstract

Long-term sodic-water irrigation may adversely affect the quality of soil organic carbon along with some soil properties. The extent to which the adverse effects can be ameliorated through the use of gypsum and amendments needs to be known. Soil properties and microbial biomass carbon (MBC) were studied after 14 years of sodic water (SW) irrigation and application of different levels of gypsum, farmyard manure (FYM), green manure (GM), and wheat straw (WS) to a sandy loam soil. Irrigation with SW increased pH, electrical conductivity, sodium adsorption ratio, exchangeable sodium percentage (ESP), and bulk density, and decreased final infiltration rate of soil. Application of gypsum and organic amendments reversed these trends. Decrease in MBC due to SW irrigation was from 132.5 to 44.6 mg/kg soil in the 0–75 mm soil layer and from 49.0 to 17.3 mg/kg soil in the 75–150 mm soil layer. Application of gypsum and organic amendments significantly increased MBC; GM and FYM were more effective than WS. Changes in soil ESP explained 85 and 75% variation in MBC in the unamended and organically amended SW treatments, respectively. Soil pH as additional variable improved the predictability of MBC to 96% and 77%. Irrigation with SW reduced yield of rice plus wheat by 5 t/ha. Application of gypsum and organic amendments significantly increased the rice and wheat yield; it was significantly correlated with MBC (r = 0.56**, n = 60). It confirms that MBC rather than organic C is a more sensitive indicator of environmental stresses in soils caused by long-term sodic water irrigation.