Leaf area development in some crop and weed species

ALM D. M., PIKE D. R., HESKETH J. D. and STOLLER E. W. Leafarea develop­ ment in some crop and weed species. BIOTRONICS 17, 29-39, 1988. Leaf expansion is an important factor determining the competitive ability of a crop or weed. Crop models for leaf expansion have been under study and develop­ ment for some time; we report here an exploratory effort to develop a similar information base for weed models. Such models summarise what is known about plant behavior; study of crop: weed competition models may lead to bet­ ter methods for weed control and better predictions of crop yield. Crop and weed plants were grown in growth cabinets to determine the effect of temper­ ature on leaf appearance rate; such information was used to develop species­ specific degree day models for germination, seedling emergence to the first leaf, and the appearance of successive mainstem leaves. Total leaf area was mea­ sured on seedlings with a range of mainstem leaf numbers, in both controlled environment and field conditions. Area per plant vs. accumulated degree days could then be determined from the predicted mainstem leaf number, using the degree day models and derived, allometric relationships between leaf num­ bers and accumulated area. A method for estimating threshold temperatures for leaf expansion was also developed. Limitations to such a simple model for predicting seedling leaf area are discussed, with an indication of improvements needed.