Long-term impacts of wastewater irrigation on Cuban soils

The disposal of wastewater, known as vinasse, from the sugarcane (Saccharum officinarum L.) industry creates environmental problems. Agriculture can offer a potential solution to these problems by using organic residues as substitutes for chemical fertilizers. This study was conducted in Ultisol profiles from Cuba irrigated with vinasse for 40 yr. The effects of this application on physicochemical and mineralogical properties of soils were investigated. Sods fertilized with traditional inorganic fertilizers were used for comparison. Fertilization with the wastewater caused a decrease of soil pH to a depth of 100 cm. There was an increase, however, in electrical conductivity because of the large concentration of K in the wastewater. The amendment also increased the organic matter content throughout the profile. Vinasse application yielded the intercalation of some compounds in the clay mineral smectite. The formation of organo-mineral complexes produced little change in the particle size distribution, but an increase in the poorly crystalline Fe oxyhydroxides in the upper horizon up to 22%, and the crystallinity of Fe oxyhydroxide in the soil decreased substantially. This was probably due to dissolution and reprecipitation of these oxides by the acid pH of the wastewater. Total and poorly crystalline Mn contents also decreased. The amendment material increased the mobility of metals because of the formation of water-soluble complexes with organic ligands. The results showed that long-term wastewater irrigation could be of agricultural interest due mainly to its organic matter concentration, but micronutrient concentrations in the upper horizons were negatively affected because complexing of metals favored their transport throughout the sod profile, which may eventually lead to deterioration of groundwater quality and micronutrient deficiency.