Changes in potassium pools in Paraná soils under successive cropping and potassium fertilization

Abstract

The changes in soil potassium pools under intense cropping and fertilized with potash fertilizer are still little known to the soils of Paraná State. The effects of potassium fertilization and successive cropping on changes in K pools in different soils of Paraná, Brazil, were investigated in this study. Twelve soil samples, collected from the upper layer 0-0.20 m, were fertilized or not with K and subjected to six successive cropping (i.e., soybean, pearl millet, wheat, common beans, soybean and maize). All the crops were grown for 45 days, and at the end of the second, fourth and sixth cropping, the soil from each pot was sampled to determination of the total K, non-exchangeable K, exchangeable K and solution K. The result showed that the soil potassium pools varied widely. Total K concentration ranged from 547 to 15,563 mg kg -1 (4,714 mg kg -1 , on average). On the average, structural K, non-exchangeable K, exchangeable K and solution K of the soils constituted 84.0, 11.3, 4.6 and 0.1% of the total K, respectively. Soils differ in the ability to supply potassium to the plants in the short to medium term, due to the wide range of parent material and the degree of soil weathering. When the soils were not fertilized with K, the successive cropping of plants resulted in a continuous process of depletion of nonexchangeable K and exchangeable K pools; however, this depletion was less pronounced in soils with higher potential buffer capacity of K. The concentrations of K non-exchangeable and exchangeable K were increased with the addition of potassium fertilizers, indicating the occurrence of K fixation in soil. After the second cropping, the soil exchangeable K levels remained constant with values of 141 and 36 mg kg -1 , respectively, with and without the addition of K fertilizer, reflecting in establishing of a new dynamic equilibrium of K in the soil. Key words: Potassium availability, non-exchangeable K, exchangeable K, potassium supply power, intense cropping ResumoAs alterações nas formas químicas de potássio (K) em solos cultivados e submetidos à fertilização potássica, ainda, são pouco conhecidas para os solos do Estado do Paraná. Neste estudo, os efeitos de cultivos sucessivos e da fertilização potássica nas alterações das formas de K foram estudados em solos com diferentes características físico-químicas do Estado do Paraná. Amostras de 12 solos coletadas da camada de 0-20 cm de profundidade, foram submetidas à adição ou não de fertilizante potássico e a seis cultivos sucessivos de plantas (soja, milheto, trigo, feijão, soja e milho). Em todos os cultivos as plantas foram cultivadas por um período de 40 dias. Após o segundo, quarto e sexto cultivo foram coletadas

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