A phytomer-based simulation model for growth in competitive weed-crop systems

A computer model for simulating the dynamics of vegetative phenology and vertical distribution of leaf area in competitive weed-crop systems was developed. The model was based on (1) a temperature function for leaf appearance rate (2) a function for individual leaf expansion based on leaf appearance (3) a function for elongation of individual internodes based on individual leaf expansion and (4) vertical stratification of leaf area based on the sum of subtending internode lengths. The degree day requirement for leaf appearance was determined for a number of crop and weed species. Leaf appearance in nearly all crops and weeds required more degree days in the field than in growth cabinets.A logistic equation for single leaf expansion was derived, substituting the phyllochron (schedule of leaf appearance events) for real time. This equation requires the initial and potential final areas, and the duration of expansion (in phyllochrons) as parameters.A light absorption model, adapted from existing hedgerow and leaf angle class models, was used to simulate competition for light within the area of influence of a weed--the ground area over which the crop is affected by a weed. This model was added to the leaf expansion model for calculations of photosynthesis by horizontal layers. In the model, photosynthate of individual leaves is interpolated from strata values based on leaf height.An experiment was performed to test a model developed by Charles-Edwards (1986) for predicting the vertical distribution of nitrogen in a canopy. The organic leaf nitrogen in Amaranthus retroflexus (L.) (redroot pigweed) was found to be proportional to the fraction of full sun received by the leaf and the light saturated photosynthetic carbon exchange rate was found to be proportional to a photosynthetically active component of the leaf organic nitrogen, validating the model. The residual or non-photosynthetically active component of leaf organic nitrogen, however, was found to be higher in fertilized than unfertilized plants, suggesting that unfertilized plants were actually more photosynthetically efficient per unit nitrogen. The leaf area index of the fertilized plants, however, was 50% greater.Another experiment was performed to quantify the change in the vertical distribution of leaf area in both a single weed, Abutilon theophrasti Medic., (velvetleaf), and the crop, Glycine max (L.) Merr. (soybean) cv. Elgin, caused by interspecific competition. Competition was found to cause an upward shift in the leaf area of velvetleaf (compared to an open-grown velvetleaf control with 1 m to the nearest neighbor) while the leaf area distribution of the soybean crop was unaffected (compared to the row crop control).U of I OnlyETDs are only available to UIUC Users without author permissio