Nutrient needs of apple trees

摘要

Essential nutrients need to be in balance, neither too low nor too high. Apple trees need annual supplies of mineral nutrients, either from the environ- ment or in the form of applications by the grower, in order to develop rapidly and produce high yields. Essential elements include the macronutrients carbon, hydrogen, oxygen, mm w nitrogen, phosphorus, potassium, calcium, and magnesium, and the micronutrients sulfur, iron, boron, manganese, copper, zinc, molybdenum, chlorine, and nickel. For optimal growth and fruiting, essential nutrients must be kept in balance. Levels that are too low will negatively impact the tree and fruit quality, while levels that are too high can be toxic to the trees. Nitrogen (N): Nitrogen must be considered according to the variety, tree age, crop load, and tree vigor. Levels should be lower as the trees mature. The aim should be to have relatively high levels early in the season to encourage rapid leaf development, fruit set, and flower bud formation, and lower levels later in the season to favor color development of the fruit and winter hardening of the tree. Phosphorus (P): Phosphorus levels in leaf samples vary by variety. Availability of phosphorus is strongly influenced by soil pH. Low values may be linked to low soil pH levels. High phosphorus values frequently result from an accumulation of phosphorus when growth and leaf expansion are limited by deficiencies of other elements, such as zinc.