Wastewater and its Residual Effect on Forage Production and the Chemistry of a Degraded Soil

In the face of climate change, forage production is a challenge for human populations sustainability in semiarid areas, due to the decrease in water availability, and increase in soil degradation. Sewage effluents can represent an alternative supply of water and nutrients. However, their excessive use can have negative effects on the environment. The object of the current study was to evaluate the effects of deficit irrigation with treated effluent on productivity and water use efficiency by the forage cactus (Opuntia stricta), and on the chemical properties of a degraded soil. Accordingly, a field experiment was carried out with the cultivation of O. stricta, in combination with two tree species, in degraded soil. Treatments were arranged in randomized blocks with 10 replicates of three stages, based on the annual Opuntia production cycle. Stage 1 (1st cycle): AB0.5 - 0.5 L/plant/week supply water; ET0.5 - treated effluent 0.5 L/plant/week; ET1 - treated effluent 1 L/plant/week. Stage 2 (2nd cycle) all treatments were set at a volume of 0.5 L/plant/week, and in stage 3 (3rd and 4th cycles) treatments were not applied. At the end of each cycle, biometric measurements of the plants and estimates of productivity and water use efficiency were carried out. Soil samples were collected for chemical analysis at the end of the irrigated (2013 – 2015), and non-irrigated (2015 – 2017), periods. The experimental period of irrigation with treated effluent increased soil nutrient content and the percentage of exchangeable Na, After the interruption of irrigation, there was an increase in available P, while basic cations and PST decreased. Highest Opuntia fresh and dry mass productivity was obtained under ET1. The residual effect of the effluent applied in the 1st cycle produced increases in productivity until the 4th cultivation cycle, in addition to greater Opuntia efficiency in water use