EFFECT OF DIFFERENT RATES OF K AND Mg ON YIELD AND FRUIT QUALITY OF PINEAPPLE
J.M.P.B. Jayasundara
Horticultural Crop Research and Development Institute, Gannoruwa, Peradeniya.
ABSTRACT
Potassium and magnesium are the major nutrients required for high fruit yields and quality of pineapple. However, majority of pineapple (Ananas comosus L. Merr) growers, who grow pineapple under coconut (Cocos nucifera L.), give less emphasis on nutrient management techniques resulting in gradual decline in yields and quality of fruits with time. K and Mg fertilizer requirements for high and sustainable yields and fruit quality of pineapple grown under coconut were determined in a field experiment conducted over five consecutive crop cycles on a Plinthudult soil at Regional Agricultural Research Station, Makandura. Four K2O levels (75, 150, 300 and 450 kg ha-1) and three MgO levels (25, 50 and 75 kg ha-1) with a zero K2O and MgO treatment were evaluated. Leaf K concentration increased continuously while leaf Mg concentration decreased gradually when fertilizer K level increased. A yield response to applied Mg was observed from mother crop stage up to the end of the study. But a response for combined application of K and Mg fertilizers was observed only from the first ratoon crop stage. The highest fruit yield was recorded when both K2O (300 kg ha-1) and MgO (75 kg ha-1) fertilizers were applied. The most consistent fruit yields were observed when K2O/MgO ratio of applied fertilizer was between 4 and 5. Sugar content of fruits increased with Mg application while acid content decreased with K application. The ratio between total soluble solids and total acid in the fruit juice was higher when K2O/MgO ratio was between 5 and 6. It appears that application of K2O and MgO at 300 and 75 kg ha-1/application, respectively could be recommended for pineapple grown under coconut in these soils to obtain high and sustainable yields.