With the intention of understanding the dynamics of some of the constituents of vinasse, and to evaluate the risks of groundwater pollution due to sugarcane irrigation with this wastewater, a study was carried out from October 1984 to June 1985 in Piracicaba, São Paulo State, Brazil. Vinasse was sprinkled at a rate of 800 m3/ha by a hydraulic big gun. This applied 804.76 kg/ha of potassium and 305.86 kg/ha of nitrogen. The leaching of K and NO3. was measured by the use of tensiometers and tension lysimeters installed at various depths. It was concluded that the methodology is acceptable as a procedure for field research. Potassium and nitrate did not leach as expected. After 6 months, only 0.34 kg/ha of potassium and 0.41 kg/ha of nitrate had leached to below 120 cm. The roles of soil and plants were very important in preventing groundwater pollution. The soil retained part of the applied potassium, and the sugar-cane plants absorbed a large part of the N and K applied to the soil.

The effects of irrigation with vinasse (distillery effluent) on microbial populations in experimental squares of sugar-cane plantation were studied. The soil was a haplortox, with a sandy clay loam texture. The plantation was at Usina Costa Pinto, São Paulo State. A substantial and temporary increase was observed in the populations of bacteria and fungi. The actinomycetes were inhibited during the initial period. The major chemical compound known to be present in the vinasse is simple carbohydrate, although other complex organic compounds may be present. The behaviour of the cellulolytic micro-organisms was analysed, as a tentative attempt to select a biological indicator. Nitrifying micro-organisms were inhibited during the second stage of the decomposition of the waste. The great microbiological transformations resulting from the irrigation of soil with vinasse did not cause, as expected, a significant elevation in the soil pH.