ABSTRACT
Interference occurs between plants of the same species, between plants of different species and also between different parts of one plant; e.g. between shoots and fruits of the same plant. The nature and effect of interference is of great interest since it has bearing on almost all processes in the individual plant as well as on the "plant community" or "crop". Interference will frequently occur in the form of "competition". Competition is a physical process. The relationships between crops grown in multiple cropping systems can also be described in economic terms by using a concept of generalized output interrelationships. As plant populations of monocultures are increased, competition will commence earlier and will be more severe. When two species compete, a yield increase of the one species results in a yield decrease of the other species. When the yield decrease is equal to the increase there is "pure competition".
