Low external-input agriculture seeks to optimize interactions between species that permit processes at the ecological community level to shift inputs away from nonrenewable or synthetic sources. This goal can be reached through the study of the ecological basis of an array of plant-plant and plant-insect interactions, especially in intercropping systems where particular plant mixtures are of benefit to the entire crop community. These polyculture systems can be managed for nutrient cycling efficiency and pest and disease regulation using knowledge of multi-trophic level interactions and application of recent developments in mutualism and competition theory. A mechanistic model of additive and removal reactions on the environment is proposed as a means of studying species interactions.
