Effects of treated urban wastewater irrigation on bioenergy sorghum and soil quality

Prolonged drought in arid west Texas has resulted in freshwater scarcities in the Rio Grande basin, forcing growers to abandon agricultural lands. Augmenting freshwater scarcities with marginal quality treated urban wastewater could be an alternative strategy. However, higher salinity in wastewater could be detrimental to crops and soil quality. Therefore, developing information on crops that are salt tolerant and less water-intensive is important to sustain agriculture in this region. Sorghum is both drought and salt-tolerant and could potentially provide revenue due to increasing demand for its lignocellulosic biomass in biofuel industry. This two-year field study evaluated (i) the performance of bioenergy sorghum under wastewater irrigation in terms of its biomass yield potential and biomass quality relative to freshwater irrigation and (ii) wastewater irrigation effects on rootzone soil quality including soil salinity and sodicity. A split-plot experimental design was used with water type (fresh and wastewater) as the main-plot and soil amendments (non-amended and gypsum + sulfur) as the subplot factors. Results show that sorghum biomass yields were not significantly different between fresh and wastewaters in any of the years. Differences in biomass quality were observed overtime but as an indirect consequence of increased soil salinity and/or sodicity after wastewater irrigation. Soil quality changes were apparent with salinity and sodicity increasing over time with irrigation, but this effect was pronounced under wastewater irrigation. Application of gypsum and sulfur was able to significantly reduce soil sodicity, especially in wastewater irrigated plots. The results from this study highlight that treated wastewater can be successfully used to grow bioenergy sorghum in arid regions. However, appropriate soil management practices should be in place to counter the effects of high sodium in wastewater. These results have important implications in diversifying cropping pattern in this region while also help extend freshwater supplies through increased reuse of treated urban wastewater.