Bananas
Potassium is the nutrient used in the largest quantities by banana plants with potassium uptake exceeding that of nitrogen. Between 180 - 250 kg/ha is removed in the fruit, cull fruit and stems of an average crop, with higher amounts in north Queensland where yield potential is greatest.
Potassium is important in water relations and transport of starch and sugars. It increases the vigour and disease resistance of plants, improves fruit weight and the number of fingers per bunch. In addition, potassium stimulates earlier fruit shooting and shortens the number of days to fruit maturity. Potassium also improves the storage quality of bananas.
However, because of the recognised importance of potassium to banana production, over-application of potassium occurs in some Australian crops where soil fertility is not monitored. This costs money and can result in problems such as soil salinity and interference in magnesium and calcium nutrition. It is important to base fertiliser decisions on expected yield and nutrient removal and to monitor performance with soil and leaf analyses. This will ensure that maximum economic yield is achieved, but problems associated with over-fertilising are avoided.
The greatest demand for potassium occurs during the plant crop of bananas, rather than ratoon crops. Therefore plant crops should be fertilised heavily to provide sufficient nutrients to produce the plant, the fruit of the plant crop and the following sucker.
Potassium applications should be matched to weather conditions, growth rates and expected yield. Fertiliser is usually applied during the warmer months of the year to maximise plant response. Frequent, small dressings are made to minimise leaching losses - four to five applications a year is common in NSW and southern Queensland, and up to 10 in north Queensland.
Fertiliser should not be applied if no rain has fallen since the last application. Where irrigation is available, it is becoming increasingly common to apply nitrogen and potassium fertilisers with the irrigation water.