Wastewater irrigation in orange trees - effects in plants, soil and leachates

摘要

Due to the vast irrigated areas and to the urban development, during the last decades in the Algarve region, the intense aquifer pumping rate and the demand of non-conventional water resources increased. Also the discharge of the effluents on the water basins, rivers, lakes, dams, and seaside attracted public awareness of environmental pollution and the impact on water quality, which is urgent to solve. Its reuse for irrigation represents the last environmental treatment and the effluent removal through the dynamic system Soil-Plant-Atmosphere-Continuum (SPAC). The objective of this work was to estimate advantages and disadvantages of wastewater reuse for agricultural irrigation by means of investigation of the relationships of the system SPAC. For this purpose, the growth of orange-trees (Citrus sinensis, L., Osbeck) was studied and changes in soil profile and leachates were observed when reclaimed water, natural water and fertigation were applied. The wastewater irrigation periods occurred six months per year, between May and October. In order to observe the growth of the orange-trees, the diameter of their trunks was measured two years after plantation. Analyses of soil were made in order to observe the evolution of the pH, organic matter (MO), N, P_2O_5, K_2O, Fe, Mn, Zn, Ca, Mg and Na. Within the leachate, besides salinity, the pH, CO_3~2, HCO_3~-, Na~+, K~+, Mg~(2+), Ca~(2+), Cl~- and NO_3~- were determined. It was concluded that the response to the nutrients, present in reclaimed water, concerning the growth of the trees, was positive. On the other hand were observed the increase of the salinity, within the soil and the leachates, due to the soil natural impermeability.