Rates and Residual Effects of Potassium Fertilization in a Brazilian Soil

Potassium is responsible for several vital mechanisms for plant development (enzyme activation, translocation and stock of compounds, osmotic regulation, water maintenance, etc.) and high yields. Potassium fertilizers are essential for balanced plant nutrition in the acid soils of the tropics, including Brazil. In many areas, farmers are cutting back on fertilizer expenses, which could compromise crop yields, profits, and food security in the future. The main objective of the study is to verify the effects of cutting back K fertilizer rates in some Brazilian soils. The study is also looking at other important factors that may affect the effectiveness of K fertilizer in tropical soils (P, lime, phosphogypsum, time of application, and locality effects) to evaluate their effects on soil K status with time, plant K status with time, and grain yields.

Results of last season (fifth year of the project) showed: 1) phosphogypsum application increased soybean seed weight; 2) residual K from past applications reduced soybean plant height; 3) K applied at seeding time led to higher K leaf content then when 1/3 of K was applied 15 days after emergence; 4) lime application increased grain yield of maize (second crop); 5) lime application in treatments with residual K from previous applications increased maize (second crop) yield and K leaf content, and 6) phosphogypsum application in treatments with residual K from previous application increased K leaf content of maize (second crop).