Influence of phosphorus, potassium and magnesium on sugarcane yield

Increase K fertilization significantly lowered the Mg in the leaf and significantly increased K leaf content at sixth month and at harvest. Increased K application also decreased juice Mg. Dolomite application (47 kg Mg/ha) at KOP2 (zero K and 200 P/ha) significantly increased the cane tonnage (TC/ha). Increased K fertilization at all P levels and at MO (zero Mg) significantly increased the tonnage. Analysis of variance showed a significant interaction between Mg and KP treatment. The highest tonnage of 56.3 TC/ha was obtained from the K1P2M1 (200 kg K/ha; 200 kg P/ha; and 80 kg Mg/ha). Correlation analysis showed a highly significant relationship between P content of the juice and piculs sugar per ton cane (PS/TC). Application of either 80 kg Mg/ha or dolomite produced a marked increase in mean P concentration of the juice. This substantiates the idea that Mg enhances P availability or uptake. Although positive correlation between Mg in the juice and PS/TC was absent, there is some indication of improvement of PS/TC with Mg fertilization. The highest PS/TC of 1.74 was observed in the K2P1M1 (400 kg K/ha; 100 kg P/ha; and 80 kg M g/ha) treatment. Analysis of variance on piculs sugar per hectare showed a significant interaction between Mg and KP treatment. The highest sugar yield of 94.3 PS/ha was observed in the K2P1M1 treatment. Eighty kilograms (M1) Mg/ha slightly increased the mean PS/ha. Higher amounts of Mg were not able to increase the sugar yield. Increased K fertilization of 400 kg K/ha (K2) at P2 (200 kg P/ha) and at MO (zero Mg) significantly increased the sugar yield. The most profitable treatment (ROI=11.13) is P2KODol (200 kg P/ha; zero K; and dolomite). Dolomite would be more profitable to use than MgSO4 as a Mg source. In the Mg fractionation study, five out of the nine soils studied contained less than 120 ppm. the optimum level suggested by Nartea (1972)