Organic carbon, nutrient, and salt dynamics in saline soil and switchgrass (Panicum virgatum L.) irrigated with treated municipal wastewater

This study was conducted to evaluate the effects of treated municipal wastewater irrigation on soil organic carbon (SOC), soil macronutrients, Na, Cl, and SO4 dynamics in soil as well as switchgrass (Panicum virgatum L.) shoots under greenhouse conditions. Average SOC concentrations in upper 60cm increased significantly from the prestudy level of 18Mgha(-1) to between 21 and 23Mgha(-1) at the end of the study (2009-2015) under different treatments. Annual average rate of increase for all four depths (upper 60cm) ranged from 0.6 to 0.8Mgha(-1)y(-1). Nutrient concentration in soil samples was positively influenced by fertilizer application. N, P, and K concentrations in soil and switchgrass shoots were significantly positively correlated. On average, Alamo switchgrass cultivar under irrigated conditions removed 28.5 to 35.7gNm(-2), 2.52 to 3.48gPm(-2), and 29.6 to 38.4gKm(-2), and differences between freshwater and wastewater treatments were not significant. This indicated that wastewater irrigation did not result in excessive accumulation of nutrients in switchgrass tissue. Although salt constituents such as Na, Cl, and SO4 concentrations in soil increased over time as a result of wastewater irrigation, their concentration did not increase in switchgrass shoots, indicating a salt exclusion mechanism. The results of this greenhouse study indicated that the use treated municipal wastewater for irrigation can improve SOC contents of salt affected lands and extend the availability of freshwater in arid regions.