Response of soil organic carbon and soil health indicators to treated wastewater irrigation in bioenergy sorghum production on an arid soil

Treated urban wastewater (WW) reuse for crop irrigation is seen as an way to mitigate prolonged drought effects and reduced freshwater (FW) availability for agriculture in arid west Texas. However, the impacts of WW on arid soil health are not clearly understood. This field study evaluated the effects of WW irrigation on soil health indicators including soil organic carbon (SOC), permanganate oxidizable carbon (POXC), mineralizable carbon (MC), and soil protein under bioenergy sorghum production. Water type and gypsum + sulfur application were used as main and subplot factors in a split-plot experimental design with growth year as a repeated measure. Results across time and soil amendments showed that the SOC of WW-irrigated soils (3.26 g kg(-1)) was significantly higher than that of FW-irrigated soils (2.96 g kg(-1)). This signifies the positive impact of WW to contribute to soil carbon with no associated priming effects. Wastewater and soil amendment application by themselves did not affect other soil health indicators, given their soil salinization potential. Irrespective of the water type and amendment application, soil POXC significantly increased from 245 to 262 mg kg(-1) over time, indicating that a labile pool of C was added to the soil. Soil protein concentrations significantly decreased from 1.31 to 1.23 g kg(-1) after 2 years, possibly due to mineralization of organic nitrogen. In conclusion, our results demonstrate that WW application did not adversely affect soil health in the short term. Long-term studies could provide more insight into the sustained effects of WW irrigation on arid soil health.