During leaf and shoot development, nitrogen, phosphorus, potassium and zinc concentrations fall. Others, most importantly calcium, increase over this period. As a consequence of these seasonal variations, sampling is normally carried out at standard times. Traditionally this is at 110-125 days post full bloom, during the middle of the growing season. However, deficiencies may already be restricting growth, yield and quality potential by this stage. Thus, analyses at the blossom stage of growth are increasingly being carried out in order to correct nutrient disorders before they arise.
Soil testing can be used to estimate the supply of nutrients available in the soil to support growth. It is particularly important for assessing soil phosphate and potassium levels, as well as pH. Soil testing alone, however, does not provide enough information to ensure accurate nutrition.
Leaf tissue analysis is more commonly used to provide a snapshot of nutrient status at specific stages of growth.
Typical leaf analysis figures for optimum growth for both macro and micronutrients at the post bloom and blossom stage, are given below
While the tables are accepted values for optimum growth, they do not take into account the ability of the tree to recycle nutrients to the fruit. For example, even if tissue levels of Ca are sufficient, fruit may be deficient and suffer from storage quality problems. Analysis of the fruitlet at around 25-30 mm diameter, is increasingly being used to predict nutrient imbalances, which may cause storage problems. This enables correct targeting of fruit or foliar sprays where required.