Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: April 16, 1996
Publication Date: N/A
Technical Abstract: Weed germination and emergence are not uniform across a field or under a crop canopy. Observations of weed populations within a field would suggest a relationship between the microclimate variables and weed emergence and growth. Soil temperature, soil water content, and available radiation at the soil surface are three microclimate variables that have been associated with weed growth. Variations in soil temperature and soil water content can be estimated from understanding the radiation energy exchanges for bare soil and crop residue-covered soil. These micrometeorological models have been developed and evaluated for a number of different conditions. Crop residue on the soil surface will decrease the amplitude of the soil temperature regime and the rate of soil water evaporation. A weed seed laying on the soil surface will have a greater chance of germinating under residue than on a bare soil surface. However, if the weed seed has a requirement for red light to germinate, then the residue may act as a barrier to light penetration. These components are complicated by the position under the canopy relative to the row and the orientation of the row with respect to the sun's movement throughout the day. These components of the energy balance were combined to describe the probability of a warm season weed seed germinating and growing under a plant canopy. This hypothetical approach begins the development of a model that can be tested in field experiments and shows why some of the variation in weed distribution under canopies occurs. There is little data to evaluate this type of model, however, it can begin to foster interactions among weed ecologists and micrometeorologists in the development of improved weed management strategies.