A model for light competition between vegetable crops and weeds

A precise prediction of the yield losses inflicted by weeds is the basis of decisions in weed management. Hitherto. only rough estimates, which neglec t the specific production situation have been available for vegetable crops . In this study a simple simulation model was developed to estimate yield l oss by radiation competition as a function of environmental variables. In t he model, the distribution of incoming photosynthetically active radiation (PAR) in the canopy is calculated using a spatially highly resolved approac h. Growth is calculated as a function of absorbed radiation and its utilisa tion. Newly produced dry matter is allocated to roots and shoots, the latte r comprising vegetative and reproductive organs according to the developmen tal stage. Vegetative shoot dry matter is partitioned according to the main functions of radiation interception (leaves) and structural stability (ste ms and petioles). The resulting leaf area is distributed in the canopy acco rding to the spatial expansion of individual plants. Calibration runs revea led uncertainties predicting the growth of Chenopodium album and a high sen sitivity of crop yield to leaf area development of the weed. Using the area of green leaves (LAI) of C. album as input gave a close correspondence bet ween simulated and observed crop yield loss. Since plant height of C. album is calculated as a function of leaf area, this variable has a multiple eff ect on radiation absorption. A first evaluation with an independent data se t likewise gave an acceptable prediction. To reduce model complexity, a sim plified version is proposed. (C) 2001 Elsevier Science B.V. All rights rese rved.