Annual additions of potassium to the soil increased apple yield in Brazil

Potassium (K) is a very important nutrient for apples (Malus domestica) because it affects fruit quality and storage as well as yield. The amount of K to be applied varies with many plant and soil parameters, including cultivar, soil type. crop load, and climate. This study was carried out to assess the effect of longterm annual soil additions of K on fruit yield of a Fuji orchard grown in an Oxisol (Hapludox) previously well fertilized, under subtropical climate, in Southern Brazil. The trees (1234/ha), grafted on MM 106 rootstock, were planted in 1987. Potassium chloride was added annually to the soil surface, at rates of 0, 37, 75, 150, and 300 kg ha(-1) of KO. Addition of K increased fruit yield in 4 of 6 years, even when soil exchangeable K was still high. Maximum annual productivity varied from 73 to 120 t ha(-1). To obtain maximum yields 196 to 225 kg ha(-1) of KO were required, but only about 70 kg(-1) ha(-1) year(-1) of K2O was required to maintain the initial K value in the plow layer. Addition of K increased the concentration of K+ in the soil, leaves and fruits, reduced calcium (Ca) concentration in leaves and fruits. but had no effect on fruit quality and storability. Thus, application of K to Fuji orchards in Southern Brazil can maintain soil levels higher than those actually recommended for annual crops, without reducing fruit quality or storage life.