Effect of the addition of zeolite and vermiculite on the leaching of potassium from the soil

Abstract

This study aimed to investigate the leaching of potassium (K+) from the soil (Oxisol) and to evaluate the efficiency of uptake of this ion with the addition of minerals with high cation exchange capacity (CEC), such as vermiculite and zeolite. Oxisol samples collected in Araraquara (SP) were physically, chemically and mineralogically characterized. The leaching of potassium from the soil was performed using two tests: (1) K+ leaching using columns filled with soil, in the presence of vermiculite or zeolite, and (2) incubating soils with vermiculite and zeolite for 30 days to analyze the interaction between these minerals and the K+ added to the soil in the presence/ absence of Ca2+ (as CaCO3). The soil has clay texture and low acidity, and is poor in nutrients and mineral sources of K+. Tests in soil columns proved that the texture and mineralogy of the soil play an important role in the retention of K+, promoting its rapid transfer from the soluble to the exchangeable phase. The Oxisol released, on average, only 2% of the K+ added to the soil, and this value decreased to 1.6% in the presence of vermiculite and to 1.2% in the presence of zeolite. In the incubation test, it was also noted that the K+ added to the soil is rapidly transferred to the exchangeable phase, and that the retention rate of this cation increases in the soil in the presence of vermiculite and zeolite. However, the presence of calcium in the soil does not favor the retention of K+ by vermiculite - which retains preferably cations of higher valence, such as Ca2+. The same is not true for zeolite, since its exchange sites hold preferably lower valence cations, such as K+. In general, it was found that the addition of minerals with high CEC increases the amount of K+ in the fixed phase, which can serve as a reserve of this ion, and decreases the loss by leaching of this nutrient from the soil.