Simulating growth, development, and yield of tillering pearl millet II. Simulation of canopy development

Tillering is an important adaptive feature of pearl millet (Pennisetum amer icanum L.) to the unpredictable growing conditions of dry areas of the semi -arid tropics. Yet, this feature has largely been ignored in the developmen t of simulation models for pearl millet. The objective of this paper is to parameterise and validate a leaf area module for pearl millet, which dynami cally simulates crop leaf area from the leaf area of individual axes throug h simulating inter-axis competition for light, To derive parameters for the model, four cultivars (contrasting in phenology and tillering habit) were grown under well-watered and well-fertilised conditions across a range of p lant densities in three experiments at two locations in India. For selected plants, observations on the number of primary basal titters and on the num ber of visible, fully expanded, and senesced leaves on each axis were made twice a week throughout the growing season. Occurrence of panicle initiatio n (PI) was observed in two experiments only, but data were complemented by published and unpublished data, obtained for comparable cultivars. Paramete rs were obtained for the time from emergence to PI as a function of dayleng th, the leaf initiation rate, the rate of leaf and tiller appearance and th e leaf senescence rate; parameters for leaf size were determined in a previ ous paper. Our parameter estimates compared well with published data and we re, with the exception of time to PI and leaf size, mostly independent of c ultivar, axis and density. Genotypic effects on productive tiller number co uld be attributed to differences in main shoot leaf size. Validation of the leaf area module showed that the module adequately reproduced the effects of density, photoperiod and genotype on the leaf area of individual axes an d on productive tiller number. This was despite the fact that the reduction in leaf area of non-productive tillers was achieved in the module through a reduction in leaf size, whereas the crop reduced leaf area through a redu ction in leaf number. Our results indicate that LAI of a tillering crop can be simulated adequately by simulating LAI from individual leaf area and in corporating the effects of competition for light. (C) 2001 Elsevier Science B.V. All rights reserved.