Contribution of non-exchangeable potassium forms and its accumulation in corn plants/Contribuicao de formas nao-trocaveis de potassio para seu acumulo em plantas de milho

The state of Paraiba, Brazil, has soils from well- to poorly-developed, in which potassium (K) is found in different levels, forms and, consequently, with varying availability to plants. The objective of this study was to evaluate the contribution of non-exchangeable K forms to corn plants in 12 soils from Paraiba state, along four successive cycles. The experimental design was completely randomized block with three replicates and the 24 treatments consisted of the combination between two K levels (0 and 100 mg [dm.sup.-3]) and 12 soils. Before and after each cycle, subsamples of 0.2 [dm.sup.3] were collected in each pot for the determination of non-exchangeable K (Kne), exchangeable K (Ke) and soluble K (Ks). For each cycle, dry matter production, dry matter K content and plant K content (absorbed K) were determined. In the studied soils, the amounts of absorbed K after successive cycles were higher than the amounts of exchangeable K released, which shows the contribution of non-exchangeable K forms to corn nutrition.