Research indicates that coffee trees grown intensively under full sun have high nutrient requirements. Start fertilising trees six weeks after planting, when the trees have overcome the stress of transplanting. This will ensure the fertiliser does not burn the tree roots. Band the fertiliser within the one metre planting strip and distribute it as evenly as possible. Make sure the fertiliser does not contact the trunk because it can burn the bark and cause ringbarking.
Nitrogen and potassium:
Trials in North Queensland have shown that 100 kg nitrogen and 100 kg of potassium per hectare need to be applied during the first year after planting. Apply them in small amounts every four to six weeks during the year. Potassium is usually applied as muriate of potash and nitrogen as urea. This equates to approximately six grams per plant of urea and six grams per plant of muriate of potash per application at a density of 3,500 plants per hectare.
Take care not to overfertilise with nitrogen in the first year, because shoot growth can get out of balance with root growth. This can lead to leggy plants prone to lodging. Lodging can be a problem if ‘leggy’ plants are planted into the field with inadequate windbreaks or if excessive amounts of nitrogen fertilizer are applied in early seedling growth. This can lead to suckering on the main stem. Water in the nitrogen immediately or apply it through irrigation otherwise you may lose large quantities to the air. In the second year the trees will need 200 kg/ha of both nitrogen and potassium.
Coffee trees require much smaller quantities of phosphorus. If you have already applied superphosphate to the soil before planting (see article on Coffee Site Preparation), then only an additional 35 kg/ha phosphorus (350 kg single superphosphate) needs to be applied during the first year, applied in two spreadings, one before and one after the wet season (November and April). In the second year trees need 20 kg/ha (200 kg single superphosphate).
Overfertilising with phosphorus can cause zinc and iron deficiences.
Experience has shown that the most common nutrient deficiencies seen in young coffee trees are of zinc, iron, copper and magnesium. Correct these by applying 0.5% to 1% foliar sprays of zinc sulphate, iron sulphate, copper sulphate or magnesium sulphate (or a complete foliar fertiliser). Two or three sprays per year will usually correct the deficiency. You can also add 1% urea to the sprays to help increase uptake of the trace elements.
Iron deficiency is usually temporary. Trials have shown that during the rapid growth phase the plant cannot take up iron quickly enough to supply the new growth.
Deficiency symptoms disappear as the growth rate slows.
Coffee trees have shown good response to complete foliar fertilisers such as Wuxal® or Nitrophoska® (10 mi/L). Repeat applications at three week intervals.
Foliar fertilisers are useful for getting an immediate response, and for trees under nutrient stress where roots may have been damaged. However, regular use of foliar fertilisers (except for trace elements) is expensive and should not be necessary. Use them to complement rather than replace ground fertilisers.
Source: James Drinnan and Ted Winston