Water potential; Gas exchange. CO2 efflux. Soil basal respiration

The Brazilian semi-arid region presents irregular rainfall distribution and periods of drought can be observed, which causes shortages of water and food for livestock. The use of reuse water in plantations can reduce this shortage of food for animals. Intercropping planting forage cactus (Opuntia stricta) and Sorghum (Sorghum sudanense) is a reality in the Brazilian semi-arid region, as forage cactus (Opuntia stricta) is already well known and widespread in the region, while sorghum cultivation is gaining prominence. In view of this, the objective of this work was to evaluate the photosynthetic performance and water relations of sorghum (S. sudanense) cultivated in plantation intercropped with forage cactus in different managements with and without the presence of mulch, irrigated with effluent from domestic sewage treated in different irrigation depths, being 80%, 100% and 120% of crop evapotranspiration (ETc) of sorghum (S. sudanense).The work was carried out in the municipality of Pesqueira-PE, at the experimental station for the treatment and reuse of domestic sewage in the district of Mutuca. Were evaluated Leaf gas exchange, water potential, osmotic potential, chlorophyll a fluorescence and photosynthetic pigments in sorghum (S. sudanense). In the soil, the physical, chemical and biological characteristics were evaluated for characterization, being evaluated in relation to time the efflux of CO2, soil basal respiration, gravimetric soil moisture and electrical conductivity. The results of the variance analysis of the gas exchange variables: net photosynthesis (A), transpiration (E) and stomatal conductance (gs) showed significant differences by the Scott-Knnot test, at 5% probability, for the presence of mulch , with no significant difference between the evaluated irrigation depths. For the ratio of internal concentration of CO2 (Ci) and external concentration of CO2 (Ca) and photosynthetic pigments, no significant difference was observed.The water potential and osmotic potential, a significant difference was observed, with a highlight for the treatment with the presence of mulch with 100% of ETc, obtaining the highest values. As for the evaluations of CO2 efflux, soil basal respiration, gravimetric moisture and electrical conductivity, there was a significant difference between the presence and absence of mulch. Gas exchange, water potential, osmotic potential, chlorophyll a fluorescence and microbial analyzes were influenced by the treatments used in this research, with mulch management with the presence of 100% ETc irrigation depth having the highest significant values. He CO2 efflux and soil basal respiration had an increase in their values in relation to the evaluated periods, indicating that the use of mulch and reuse water irrigation depths, provide a propitious environment for the increase of soil microbiota.