Water and salt exchange flux and mechanism in a dry saline soil amended with buried straw of varying thicknesses

Abstract

Salt stress severely constrains crop productivity in arid lands of the world. Burying straw at the 40 cm soil depth plus plastic film mulching could mitigate root zone salinity, but little is known about how the thickness of buried straw affects soil water and salt transport. Therefore, a three-year field experiment was conducted from 2010 to 2013 to address this issue, with treatments including: compacted straw thickness of 3 cm (T3), 5 cm (T5), or 7 cm (T7) (corresponding to straw application at rates of 6, 12 and 18 t ha−1, respectively). In addition, a supplementary experiment, which included treatments of no buried straw layer (CK) and 5 cm of compacted straw layer thickness (t5) in the same micro-plot experiment, was carried out from 2014 to 2016 to identify soil pore structure and hydraulic parameters after three years of deep straw burial. Results showed that the initial soil water content increased with increasing thickness but significantly (P < 0.05) decreased in later periods. Soil salinity consistently decreased with increasing straw thickness, and T7 was most effective for improving salt leaching. However, the water and salt regulation under T5 gradually decreased mainly due to the change in saturated water conductivity and porosity among layers. After irrigation, the flux of salt leaching (FL) increased with straw thickness, and the FL under T7 significantly exceeded that under T3 by 105, 89 and 33% and that under T5 by 84, 66 and 33% in 2011, 2012 and 2013, respectively. The salt flux during evaporation under T7 was much higher (P < 0.05) than that under T3 and T5 by 92 and 10% in 2012 and 38, 44% in 2013. At harvest, salt storage within the soil consistently ranked as T3 > T5 > T7. Although T7 had the most pronounced effect on salt mitigation, it was difficult to implement under normal field conditions. Thus, for relatively good water infiltration, salt leaching and inhibition of salt return, straw buried to a thickness of 5 cm is recommended.