Abstract
Intense cropping of plants in pots was used to assess the contribution of non-exchangeable K to plant uptake in different soils of Parana State, Brazil. Surface samples from nine soil types were fertilized or not with K fertilizer and subjected to six successive cropping (i.e., soybean, pearl millet, wheat, common beans, soybean and maize) under greenhouse conditions. The crops were grown in 8-L pots for 45 days, and at the end of the sixth cropping, the soil was sampled to determination non-exchangeable and exchangeable K. Shoot dry matter yield, K taken up, non-exchangeable pool contribution to K nutrition of plants were also determined. Soils differ in the ability to K supply to the plants in the short to medium term, due to the wide range of parent material and exchangeable K and non-exchangeable K pools. When the soils were not fertilized with K, the successive cropping of plants resulted in a continuous process of depletion of non-exchangeable K and exchangeable K pools; however, this depletion was less pronounced in soils with higher potential buffer capacity of K. Concentrations of non-exchangeable K and exchangeable K were increased with the addition of K fertilizers, indicating the occurrence of K fixation in soil. Non-exchangeable K contribution to K nutrition of plants during the six croppings ranged from 50 to 73% and from 1 to 18%, respectively, without and with K fertilizer addition. These data report the importance of non-exchangeable K pools in the supply of this nutrient to plants in agricultural production systems.
Highlights
Potassium (K) is a macronutrient needed in large amounts by plants
When solution and exchangeable K are reduced to low levels by plant uptake and/or leaching, non-exchangeable K can be released from clay interlayers (BRITZKE et al, 2012; ROSOLEM; VICENTINI; STEINER, 2012; SIMONSSON; HILLIER; ÖBORN, 2009)
The results presented here for the exchangeable K and nonexchangeable K in the soils (Figure 4) confirm the results reported by Bortoluzzi et al (2005), Fraga et al (2009) and Rosolem, Vicentini and Steiner (2012)
Summary
Potassium (K) is a macronutrient needed in large amounts by plants. Soil K includes the solution K, exchangeable K, non-exchangeable K and structural K, and these pools are in equilibrium, following a gradient in which its availability decreases (SPARKS; HUANG, 1985). In tropical soils with predominance of low activity clay minerals as kaolinite and sesquioxides, the solution and exchangeable K are the most important pools of this nutrient in the soil and known as the readily available K pool to plants (SHAIKH et al, 2007). The available K pool is relatively low (0.1 to 2% of total K) and corresponds to crop demand during only a few years of intense cropping and the release of K from nonexchangeable sources can contribute significantly to plant K nutrition in some soils (ROSOLEM; VICENTINI; STEINER, 2012; SIMONSSON et al, 2007). When solution and exchangeable K are reduced to low levels by plant uptake and/or leaching, non-exchangeable K can be released from clay interlayers (BRITZKE et al, 2012; ROSOLEM; VICENTINI; STEINER, 2012; SIMONSSON; HILLIER; ÖBORN, 2009). For sustainable crop production, the available K must be continually replenished through non-exchangeable and mineral K reserves
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