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Potassium (K) fertilization guidelines often oversimplify, overlooking factors like soil mineralogy and K application methods. This study aimed to evaluate the influence of K fertilizer rates and application methods on crop yields and the forms of K in soils with different textural and mineralogical features. In 2020, two field trials were conducted to evaluate the impact of varying K rates, added through band or broadcast methods, in Planosol and in Ferralsol. Soybean yield was evaluated in both trials, while flooded rice yield was evaluated only in the Planosol. Soil samples collected from the 0–10 and 10–20 cm layers and soil K content was determined using Mehlich-1, nitric acid (HNO3), and sodium tetraphenylborate. In the Ferralsol, K desorption by HNO3 in the 10–20 cm soil layer was 1.4 times higher the in band application (171 mg kg−1) compared to broadcast method (92 mg kg−1). The Mehlich-1 extractor proved insensitive to detecting K rates in the Planosol (91 and 43 mg kg−1 in the 0–10 and 10–20 cm layers, respectively), while it exhibited responsiveness in the Ferralsol, demonstrating positive increases with K rates. Using a proper chemical extractor is crucial for accurate detection and recovery of applied K in the soil. Grain yields were 4.50 Mg ha−1 for soybeans in the Ferralsol and 9.72 and 5.55 Mg ha−1 for rice and soybeans, respectively, in the Planosol. The findings reveal that applied K distributes into preexisting pools, persisting in the applied location, thereby reducing the anthropogenic K gradient with band reapplication. [ABSTRACT FROM AUTHOR]

This study aimed to evaluate the short-term effect of Ca and S addition via single superphosphate (SSP) in each crop and via agricultural gypsum on soybean and wheat yield, and on soil acidity and nutrient availability in two subtropical soils (Acrisol and Ferralsol) under no-tillage. The experiments were established with the application of five rates gypsum (from 0.0 to 8.0 Mg ha−1) applied only at the beginning of the experiment combined with triple superphosphate (TSP) and another treatment without gypsum but with the application of SSP. Soil chemical properties were evaluated five months later, in the 0–5, 5–10, 10–20 and 20–40 cm layers. The application of gypsum linearly increased the available S up to 40 cm depth, and the exchangeable Ca only in the 0–5 cm layer, in both soils. Rates above 4.0 Mg ha−1 of gypsum reduced the exchangeable Mg in the Acrisol (0–10 cm) and Ferralsol (0–5 cm), and the available K in the Acrisol (0–5 cm). The use of SSP was sufficient to raise available S above critical levels in both soils. However, soybean and wheat yields were not affected by gypsum doses or P sources. [ABSTRACT FROM AUTHOR]