Transformations of mineral N in a Red-Yellow Podzolic soil under stillage application

Abstract

The transformations of N-NO^-₃ in Red-Yellow Podzolic (RYP) soils from the region of Campos, Rio de Janeiro, Brazil, treated with stillage were followed along two experiments. For the first experiment, pots were incubated with 50 ml of stillage/dm³ of soil (corresponding to 100 m³/ha) or 100/µg of N-NO^-₃/g of soil, separately or in combination with stillage, or K⁺ as K₂SO₄ equivalent to the applied stillage. Corn was grown for a period of 60 days. The amount of N-NO^-₃ and N-NH⁺₄ in the soil, as well as the amount of N in the plants, were determined every fifteen days. For the second experiment, undisturbed samples of soils were incubated with volumes of stillage corresponding to 0, 100, 200, 400 e 800 m³/ha of stillage and addition of 300 µg N-NO^-₃/g of soil, followed weekly by the amounts of N-NO^-₃, N-NH₄, N-NO^-₂ and N-N₂O for 63 days. The two experiments, together combined, suggest that the incorporation of N-NO^-₃ and stillage to the soil causes a fast decrease in the amount of N-NO^-₃, which is mainly due to a reduction process rather than to root absorption. During the first 30 days the amounts of N-NH⁺₄ increased in both experiments. Large amounts of N-N₂O evolved along the first fifteen days, and N-organic slowly accumulated during the first six weeks produced an increase in the disponibility of N-NO^-₃ afterwards. This increase did not correspond to an increase in the N accumulation in the plants.