GROWTH ANALYSIS AND GROWTH SIMULATION OF SOYBEANS IN COMPETITION WITH VELVETLEAF AND JIMSONWEED
Abstract
Field studies were conducted in three years to evaluate the effects of velvetleaf (Abutilon theophrasti Medic.) and jimsonweed (Datura stramonium L.) densities and planting dates on the growth and yield of soybeans {Glycine max (L.) Merr. 'Amsoy 71'}. Velvetleaf densities ranging from 2.5 to 40 plants/m('2) caused reductions in the dry weight of soybean leaves, stems, roots, pods and seeds, and in the leaf area index, pod number, and seed yield when velvetleaf and soybean plants emerged at the same time. Jimsonweed densities of 1.5 and 2 plants/m('2) did not reduce any of these soybean growth parameters, but densities ranging from 3 to 16 plants/m('2) were sufficient to reduce soybean growth by maturity. For both velvetleaf and jimsonweed, the magnitude of reduction in soybean growth, and the time at which this reduction was first observed, was highly dependent on weed density. A highly significant interaction was observed in which growth reductions caused by velvetleaf and jimsonweed were greater when soil moisture was limited and when environmental conditions favored rapid weed canopy development. No density of velvetleaf or jimsonweed reduced soybean growth or yield when weed emergence followed soybean emergence by 21 and 23 days. In conjunction with field studies, a model to predict soybean growth based on simulated carbon flow within the plant was refined and tested for sensitivity to weed induced alterations in the soybean microenvironment. The model was calibrated based upon data obtained in the first year's growth analysis studies. Subsequent simulation of weed free soybean growth corresponded closely to field data in two years and in response to varying environmental conditions. The simulation of soybean growth based on estimates of solar radiation reduction caused by varying densities of velvetleaf and jimsonweed also was accurate in comparison to data obtained in the field studies.
Degree
Ph.D.
Subject Area
Agronomy
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