Impact of potassium fertilization and potassium uptake by plants on soil clay mineral assemblage in South Brazil

Potassium (K) fertilization increases crop productivity, but in some cases, crop productivity is maintained even with inadequate or low K input. In both situations, the soil mineralogy plays a role that should be investigated. The aims of this study were to quantify the potassium concentrations in several soil compartments, determine the amount of K taken up by plants, and consider soil clay mineralogical changes and K dynamics, as response to K fertilization historic and successive crops. A soil field experiment was conducted in south Brazil over a period of 15 years with different K doses, and a second experiment was conducted in a greenhouse with 11 successive plant cycles under two conditions: no K fertilization (K-poor context) and K fertilization of 30 and 90 mg kg(-1) of soil (K-rich context). In the K-poor context, illite was not found in clay fraction and the non-exchangeable K and available K forms were reduced, compromising both the K uptake by plants and the crop yield. In the K-rich context, the low amount of illite was found compared to K-poor context, while relative hydroxy-aluminum interlayered vermiculite (HIV) abundance decreased in detriment of kaolinite. Furthermore, all K compartments (K in plants, available K, structural K, and non-exchangeable K) were restored when high fertilization was applied to the soil. For correct fertilization, the soil mineralogy and fertilization background should be taken into account to obtain high crop production and low K loss in agricultural lands. This will help to maintain soil K reserve, but the successive crops induce ion exhaustion, including K, affecting whole clay mineral assemblage.