MODELING GENOTYPIC AND ENVIRONMENTAL-CONTROL OF LEAF-AREA DYNAMICS IN GRAIN-SORGHUM .2. INDIVIDUAL LEAF LEVEL

Development of leaf area on tiller axes of grain sorghum (Sorghum bicolor (L.) Moench) has previously either been ignored or treated with over-simplifications in crop simulation models. This paper describes a framework to simulate total leaf area of tillering sorghums based on the prediction of the appearance and expansion of individual leaves. Data were collated from experiments on grain sorghum hybrids grown at locations ranging in latitude from 39-degrees-11'N to 27-degrees-33'S. A leaf area model was developed which simulated axes within plants independently, such that the production and expansion of individual leaves were simulated on the main culm and each developing tiller. The model simulates total leaf area per plant (TPLA) (without losses due to senescence) using functions to predict: (i) the appearance of successive axes on plants as a function of thermal time from emergence; (ii) a constant rate of mature leaf production per axis per unit of thermal time; (iii) the profile of mature leaf areas for leaves on each axis as a function of total number of leaves produced per axis; and (iv) the leaf area contribution of immature leaves at any time as equivalent to that for a constant number of mature leaves. For seven sorghum hybrids grown at three locations, a general model simulated TPLA over time, accounting for 90% of observed variation with a root mean square deviation of 905 cm2 for observed values of TPLA ranging from 161 cm2 to 10584 cm2.