Calibration of soil and leaf analyses for the control of sugar-cane fertilization rates in Southern Queensland

Abstract

Data from a large series of trials over a number of different soil types have been studied to determine the value of leaf and soil analyses for controlling the fertilization of sugar-cane. Statistical data on the correlations obtained are presented.

The response to nitrogen fertilizer could not be assessed from leaf analysis data, but the level of mineral nitrogen in incubated topsoil was well correlated with the amount of fertilizer required. The response to phosphate fertilizer could be assessed through soil, leaf, or juice phosphate analyses, the leaf analysis being the most accurate, with a critical value of 0.18% phosphorus in the dry lamina of the top visible dewlap leaf. The reliability of this assessment depended on the soil calcium/magnesium ratio being normal, and there being no trace element interaction. The response to potassium fertilizer was only poorly correlated with soil potassium. The correlation with leaf potassium was good, and was modified by the response of leaf potassium to potassium fertilizer and by the level of phosphate in the leaf. At 0.174% phosphorus, the critical level for leaf potassium was 1.69%; this fell to 1.44% at 0.22% phosphorus.

Assessment of critical values in leaf tissue was complicated by difficulties in selecting sampling times due to very variable growth rates, and by associated variations in leaf analyses. The levels of calcium and magnesium have not been found to affect the critical levels of potassium.