Resposta da mandioca à adubação mineral e a métodos de aplicação do potássio em solos de baixa fertilidade

Seven fertility trials were conducted on sites located in two counties in the state of Rio de Janeiro. The purpose of the trials was to determine the effects of N, P and K and method of K application on the yields of Cassava ( Manihot esculenta Grantz). Yield responses at two sites were not statistically significant. At the remaining five sites, phosphorus was the major factor limiting cassava yields. Application of 40 kg/ha of P 2 O 5 increased yields an average of 86%. With the application of an additional 40 kg/ha of P 2 O 5 , the average yield increase was only 8%. Quadratic production functions computed for three sites indicated that 67 kg/ha P 2 O 5 was the most economic level of application and resulted in an average yield of 29,746 kg/ha. State average yields of cassava are approximately 12,000 kg/ha. Yield responses to up to 30 kg/ha of N and up to 40 kg/ha of K 2 O were not statistically significant. Likewise, spliting the application of K had no influence on yields.