Kochia can be a 'killer' on spring wheat
And, according to Jeremy and Marshall, allelopathy is significant for weed-crop ecology in three respects: (1) as a factor affecting changes in weed composition, (2) as a source of weed interference with crop growth and yield, and (3) as a possible tool in reducing crop losses from weeds. If the allelochemicals produced by certain seeds that affect crops can be identified, then scientists may be able to neutralize their effects or lessen their severity. If that is possible, then weeds that are a nuisance in agriculture could be controlled in a more natural manner.
Allelopathic potential has been suggested for only about 90 species of weeds and only one allelopathic effect has been proven to exist. So, the work of Brimhall and Overcast seems pretty significant at this point. Little did I know that plants can demonstrate two different types of allelopathy: (1) true allelopathy involves one plant releasing exudates that immediately affect another plant; (2) functional allelopathy occurs when exudates released by one plant affect another as the result of transformation by microflora. I also didn’t know that true allelochemicals can be released by a plant in many ways. Volatilization occurs when plants release allelochemicals in gaseous form through their leaves. Other plants are affected when the absorb these chemicals from the air. Leaching occurs when plants store allelochemicals in their leaves. When their leaves fall to the ground and decompose, they release these chemicals into the soil. Exudation, which is probably the most common method, occurs when plants release allelochemicals directly into the soil through their roots. Functional allelopathy usually arises from decomposition of the exudates of plants or parts of the plants themselves by microflora. The products of the decomposition affect other plants.
Anyway, back to the studies of Jeremy and Marshall: kochia (Kochia scoparia), wild oat (Avena fatua), and wild buckwheat (Polygonum convolvulus) were tested on spring wheat (Triticum aestivum). In one of their studies, the three weed plants were grown in sterilized and unsterilized soil. These same pots were then used to grow spring wheat. Wild buckwheat (Polygonum convolvulus) and wild oat (Avena fatua) plants grown in both sterilized and unsterilized soil demonstrated no significant allelopathic affect on the emergence, rate of growth, final height, or average vegetative dry weight of spring wheat plants. These young scientists concluded that root exudates of wild buckwheat and wild oat plants have no significant effect on the early growth of spring wheat. Significance was found, however, in some of the experiments involving kochia (Kochia scoparia) plants. Kochia plants grown in unsterilized soil affected the total emergence of spring wheat such that it was significantly less than the respective control group. Kochia grown in sterilized soil also affected the total emergence of spring wheat negatively, but to a lesser extent. The average vegetative dry weight of spring wheat plants was significantly reduced by root exudates of kochia grown in sterilized soil but not in unsterilized soil.