LABORATORY ESTIMATION OF NUTRIENT LOSSES BY LEACHING ON AN OXISOL FROM BRAZIL

Nutrient leaching losses were estimated in a laboratory experiment on an Oxisol soil used in slash-and-burn agriculture in Brazil. Soils wer e packed in columns to field bulk densities. Treatments included addit ions of ash from the burning of the slash, fine roots separated from u ncultivated soil, and untreated soil. Leachates were analysed for Ca, Mg, K, organic and inorganic P, and mineral N. Leaching losses were no greater where ash or roots were added than in the control. Estimated annual losses of nutrients were 70-100, 0.5, 28, 13, and 60 kg ha(-1), of N, P, Ca, Mg, and K, respectively. Organic P (Po) and ammonium wer e the dominant forms of P and mineral N in the leachates. The adsorpti on selectivity of the soil for basic cations followed the order: K < C a < Mg. The most significant differences in the soil columns occurred in the 0- to 5-cm depth, where exchangeable Ca, Mg, the sum of cations , and pH values were higher, particularly in the treatment amended wit h ash.