Side-dressings or foliar fertilizers are used where nutrients in the soil are not sufficient to meet the plant's nutrient requirements. Fertilizer may be applied as a dry side-dressing to the soil, often close to the base of the plant or, in some cases, in the lower leaf axils of mature plants. Care must always be taken to avoid plant damage due to exposure to high osmotic concentrations from dissolving nutrients. The basal white tissue of young and expanding leaves is particularly sensitive to fertilizer burn. If manure is to be used as a postplant source of nutrients, infor mation on nutrient content, possible microbial contamination and the nature of the composting process may be required.
Foliar fertilizer sprays are particularly effective for pineapple plants and application is easily mechanized (Fig. 6.17A-C). The leaves absorb nutrients through the cuticle and nutrients such as nitrogen, potassium, iron, zinc and boron are readily translocated throughout the plant. The morphological structure of the pineapple plant also facilitates receiving foliar sprays and funnelling them to the adventitious roots at the bases of the leaves, while any overflow is channelled to the dense root mat at the base of the plant. Spray volumes used range from about 225 to 2250 l ha-1 (25-250 gallons acre-1). The spray volume applied depends on the age of the crop (size of the canopy), the volume of spray required to cover the plant without injuring the basal white leaf tissue and the chemistry of the soluble fertilizers. Although opinions vary regarding the latest age for effective side-dressings or foliar applications, the usual goal is to meet the entire nutrient requirement prior to natural differentiation or forcing.
Ratoons can be fertilized beginning almost immediately after plant-crop harvest. However, because research on the benefits of ratoon-crop fertilization have been largely inconclusive, ratoon fertilizer programmes are inductively designed according to the local conditions, often with about half the foliar fertilizer used for the plant crop.
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