Growers need to take into account the growing system and growing medium when assessing nutrient removal and recycling. With field cultivation, where crop renovation practices after harvest remove most of the leaves and runners, it is assumed that nutrient uptake is the same as nutrient removal. As a result, with crops grown in the field, it is necessary to ensure annual fertilizer supply balances those nutrients available from soil reserves to meet complete crop needs each season.
It is also important to adjust nutrient needs according to production system and yield expectation as there are some major differences between cultivars. This figure shows that some varieties can require twice as much N, P and K as others.
Thus, it is important to base application rates on local trial and practical data to match system requirements and yield and quality characteristics, to the variety being grown.
Crops require good availability of all macronutrients to support critical growth stages.
Nitrogen is required in large quantities at rates of 6 - 7 lb/t of crop yield. Plants require a continuous supply of N for growth and 50% of nitrogen eventually accumulates in the fruit. Excessive amounts in the leaf, and available at later stages, can soften the fruit and delay ripening. Best practice is to ensure regular applications throughout the growing season.
Phosphorus – is important at early stages of crop development to ensure good rooting and leaf growth. Crops take up around 1 - 2 lb P/t of fruit yield. During fruit development, the P concentration in other plant organs decreases, indicating a redistribution of P to the fruits with around 40% of total uptake ending up in the berry.
Potassium is needed in large quantities – at levels above those of nitrogen. Total crop K uptake is around 7 - 9 lb/t of fruit yield. Almost 60% of the potassium is found in the fruit at harvest. Peak K demand is from early fruit formation through to maturity, when uptake is faster than for any other nutrient.
Calcium is required in large quantities. Generally, around 3 lb of calcium is needed for every tonne of fruit. A lot of this calcium is found in the root, the plant leaves and petioles. Transport of calcium into the fruit is limited largely because Ca follows water uptake and is only taken up by transpiring organs thereby mirroring water uptake. Thus regular, season-long supply of calcium to the fruit is critical to maintain fruit quality and in particular firmness and shelf life.
Magnesium, while required in lower amounts than calcium, it is needed to support plant growth and relatively low levels find their way into the harvested fruit. All nutrient uptake figures in this section are given in elemental forms.
While much lower levels of micronutrients are needed all play a role, particularly in supporting plant growth, yield and fruit quality. The micronutrients taken up in greatest quantities are iron and manganese.
Iron and copper are found mostly in the roots and the crown. Boron, manganese and zinc are mainly distributed in the fruit and the leaf. Boron and zinc support the growth of new tissues and poor supply can lead to fruit abortion or malformation. Between 20-30% of the B and Zn taken up by the plant, ends up in the fruit.