Depression of ccs in sugarcane after use of liming products: Economic significance and associations with soil chemistry and leaf nutrient composition

Analysis of data from 17 liming experiments across north and south Queensland showed ccs was depressed below control treatments at 65% of sites. Fourteen experiments included lime plus magnesium treatments, while 13 also had application of trace elements. Cane yield responses of 30% or more to liming products were associated with depressed ccs at 47% of sites. Average ccs depression at these responsive sites was 0.68, 0.42 and 0.39 units, in treatments with lime, lime plus magnesium and lime plus magnesium and trace elements, respectively. Economic analysis showed investment in lime for the high response sites in north Queensland was 12% more profitable than not using lime, even though ccs was depressed. Use of lime plus magnesium or lime plus magnesium and trace elements was 19% and 23%, respectively, more profitable than not using ameliorants. Significant associations between depressed ccs and leaf nutrient and soil chemical parameters were demonstrated. Leaf nitrogen was not associated with lower ccs, but the ratio of calcium : magnesium in the index leaf generally provided highest correlations with ccs depression. Ratios of calcium to magnesium, phosphorus, potassium, copper and zinc were useful indices of ccs depression in several experiments. Soil calcium level and ratios of calcium : magnesium and. calcium : potassium in soil also were correlated strongly with depressed ccs, as was soil pH. Strong correlations and the relative consistency in slope for associations between leaf and soil factors and depressed ccs suggest good prospects for development of a hypothesis for interaction between calcium nutrition or the balance of calcium and other nutrients and the sugar accumulation process.