IMPROVED METHODS FOR PREDICTING INDIVIDUAL LEAF-AREA AND LEAF SENESCENCE IN MAIZE (ZEA-MAYS)

The ability to predict leaf area and leaf area index is crucial in cro p simulation models that predict crop growth and yield. Previous studi es have shown existing methods of predicting leaf area to be inadequat e when applied to a broad range of cultivars with different numbers of leaves. The objectives of the study were to (i) develop generalised m ethods of modelling individual and total plant leaf area, and leaf sen escence, that do not require constants that are specific to environmen ts and/or genotypes, (ii) re-examine the base, optimum, and maximum te mperatures for calculation of thermal time for leaf senescence, and (i ii) assess the method of calculation of individual leaf area from leaf length and leaf width in experimental work. Five cultivars of maize d iffering widely in maturity and adaptation were planted in October 199 4 in south-eastern Queensland, and grown under non-limiting conditions of water and plant nutrient supplies. Additional data for maize plant s with low total leaf number (12-17) grown at Katumani Research Centre , Kenya, were included to extend the range in the total leaf number pe r plant. The equation for the modified (slightly skewed) bell curve co uld be generalised for modelling individual leaf area, as all coeffici ents in it were related to total leaf number. Use of coefficients for individual genotypes can be avoided, and individual and total plant le af area can be calculated from total leaf number. A single, logistic e quation, relying on maximum plant leaf area and thermal time from emer gence, was developed to predict leaf senescence. The base, optimum, an d maximum temperatures for calculation of thermal time for leaf senesc ence were 8, 34, and 40 degrees C, and apply for the whole crop-cycle when used in modelling of leaf senescence. Thus, the modelling of leaf production and senescence is simplified, improved, and generalised. C onsequently, the modelling of leaf area index (LAI) and variables that rely on LAI will be improved. For experimental purposes, we found tha t the calculation of leaf area from leaf length and leaf width remains appropriate, though the relationship differed slightly from previousl y published equations.