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 long-term 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 K2O. 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 K2O 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.