Application strategies for bananas
Application strategies need to take into account the significant nutrient losses that occur, particularly in tropical plantations, as a result of leaching and volatilization.
The shallow rooted nature of the crop also exacerbates this problem. Most macronutrients and micronutrients can be leached. Phosphorus is an exception, except where over application of water causes surface run-off or leaching from the drip irrigation zone.
Nitrogen volatilization (especially from urea) is a significant problem and losses of up to 50% of the applied nitrogen have been measured. In the tropics, it is assumed that over half of the applied nitrogen and 25% of the potassium and magnesium can be lost. Trials show that 60 – 85% of the total applied nitrogen, potassium, calcium and magnesium fertilizer can be lost on soils with a low CEC. Thus, it is common practice to apply small, but frequent amounts of fertilizer and to use trash wherever possible to supplement applied nutrients and to reduce erosion risks.
Banana plant crops need higher fertilizer rates than ratoon crops. This is because ratoon crops can utilize remobilized nutrients from the mother pseudostem left after harvest of the plant crop (first crop). Applications of compost or leaf litter also help ensure higher nutrient return in ratoon crops which reduces fertilizer rates. Over a 10-week period, the mother pseudostem can supply 40% of the nutrient requirements of the sucker. Thus, it is important that the mother plant is cut as high as possible to allow maximum nutrient recycling to the selected daughter sucker.
In ratoon crops, nitrogen, phosphorus, potassium, sulfur, boron, manganese and copper are highly remobilized and utilized by the current crop. In comparison, magnesium, iron and sink are only moderately remobilized and calcium is not recycled at all and therefore requires regular applications within every crop. It is particularly important to ensure that the daughter sucker is targeted. Especially with micronutrients to ensure vigorous growth of the next generation is not limited.
Basal fertilizers, especially phosphorus and potassium can be incorporated in the soil when establishing the plant crop.
Side-dressed fertilizers are broadcast across the soil surface or banded around the daughter plant.
Fertigation provides nutrients more directly to the limited, active root zone in the banana crop, and is a more efficient and precise way of meeting immediate needs and reducing volatilization and leaching losses. Fertigation systems also ensure better application uniformity for every plant, and allow the right nutrient to be applied at the right time and the right amount for optimum uptake. Under a fertigation system, it is important to maintain correct nutrient ratios to ensure a plant’s needs are properly met throughout the production period.
Foliar application is used to address an immediate nutritional need or where soil conditions restrict availability of specific nutrients. It is also important to target the underside of the leaf as well as the top surface. The use of adjuvants will improve the efficiency of foliar sprays onto the large, waxy banana leaf. Young fruit is quite sensitive to foliar sprays so is important to ensure correct formulations are used to minimize risk of damage.
Fruit applications are rare and often impracticable due to the use of bunch covers, though there is some indication that calcium applied to the bunch can supplement existing reserves and improve fruit storage characteristics.
