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 a must 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 good 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 some 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 for the first crop season (soybean and corn second crop) indicated: (1) low response to K in soybean and no response in corn second crop, (2) no effect of lime, time of application, and location, and (3) higher K leaf contents with phosphogypsum application in soybean, but with no effect on yield. Results for the second crop season (soybean) indicated: (1) statistically significant response to K rates for soybean yield and soil K availability, (2) locality effect for soil K availability, and (3) no effect of lime rate and time of K application. This report summarizes data only for the first and second cropping years, though the project is planned for six years. Brazil-56