Rates and Residual Effects of Potassium Fertilization in a Brazilian Soil

Potassium is, most generally, the second nutrient in terms of plant demand (after N). This nutrient is responsible for several vital mechanisms for plant development and high yields (enzyme activation, translocation and stock of compounds, osmotic regulation, water maintenance, etc). Potassium fertilizers are a must for balanced plant nutrition in the acid soils of tropics, including Brazil. In many areas farmers are cutting back on fertilizer expenses, which could compromise good yields, profit and food safety 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 which may affect the K fertilizer effectiveness in tropical soils (P, lime, phosphogypsum, time of application and locality effect) to evaluate 1) soil K status with time, (2) plant K status with time, and (3) grain yield.

Main 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. These results indicate that we might be able to anticipate suppressing K application (after second crop year cycle and not after third as previously planned) in future. It will be interesting to find out the effect of liming and phosphogypsum application in deciding the K application suppression. This report summarizes data only for the first cropping year, though the project is planned for 6 years. Brazil-56