Lixiviação de potássio em latossolo amarelo na Amazônia Central brasileira

Abstract

Knowledge of the dynamics of the vertical mobility of nutrients added to fertilizers is essential for the correct management of plant fertility and nutrition, as well as to evaluate possible sources of contamination of soil and groundwater. The present work had the objective of evaluating the potash leaching in a very clayey Yellow Latosol in the Brazilian Central Amazon, under cover of fertilized and non-fertilized oil palm and in the primary forest. For that, the physical-chemical characterization of the studied soil was carried out to determine the parameters of the water retention curve and the performance of columns tests to obtain the breakthrough curves using samples from two depths of the Amazonian soil. From these curves, the solutes transport parameters were determined using the STANMOD computational program. Soil water flow simulations were also performed using the HYDRUS-1D model, where the soil characteristics, boundary conditions and data of effective precipitation and crop evapotranspiration were considered. The results obtained for the water flow were used to estimate the amount of potassium present in the soil solution at depths of 20, 40 and 100 cm. The results showed that potassium showed low interaction with the soil and high leaching potential, reaching the highest concentrations in the fertilized oil palm, mainly after large precipitations, with a cumulative concentration of 148,94 kg K ha-1 at 100 cm depth. In the oil palm non-fertilized, a total leaching of 98,15 kg K ha-1 at 100 cm was estimated. This relatively high amount of K must be derived from the cumulative effect of previous potassium fertilizations and the decomposition of the rich K-litter of the oil palm. In the forest, the leaching of K were the lowest recorded with 33,79 kg K ha-1, possibly due to the decomposition of organic matter in the environment. The reestablishment of K concentration in the soil solution at values similar to the conditions prior to fertilization in the oil palm fertilized occurred about 90 days after the application of the fertilizer, during which time there was a precipitation of 627 mm. This study concluded by the need to extend the study including periods of lower rainfall. The importance of obtaining crop evapotranspiration data and the use of effective precipitation data in water flow simulations in computer programs is emphasized. To optimize the use of fertilizers, it is recommended to observe previous fertilizations, as well as the soil characteristics and rainfall regime of the region. The leaching of K and groundwater contamination, although registered in Brazil only when the intensive application of vinasse in the soil in sugarcane processing plants, also presents a potential risk in wastewater in oil extraction plants of palm oil.