INFERENCE BETWEEN MAYWEED CHAMOMILE (ANTHEMIS-COTULA) AND PEA (PISUM-SATIVUM) IS AFFECTED BY FORM OF INTERFERENCE AND SOIL-WATER REGIME

Effects of root-shoot interference, soil water regimes, and soil nitro gen were evaluated to determine aggressivity for pea relative to maywe ed chamomile in the greenhouse using replacement series experiments. I nterference between pea and mayweed chamomile occurred mainly below gr ound, and soil water was more important than soil nitrogen in controll ing the outcome of interference. Pea was a stronger competitor than ma yweed chamomile under all conditions investigated. Leaf area, root wei ght, and shoot weight of mayweed chamomile were reduced 55 to 87% by f ull interference and 27 to 60% by root only interference from pea. Ful l interference from mayweed chamomile for 53 days after planting relea sed the remaining pea from intraspecific interference and it grew 80% larger and produced 100% more pod weight compared to a pea in monocult ure. Low soil water potential (-175 kPa) compared to high water potent ial (-33 kPa) reduced the height, leaf area, and shoot weight of pea i n 1:1 mixtures, but had no effect on mayweed chamomile. Decreasing soi l water increased the aggressivity of mayweed chamomile relative to pe a. Nitrogen added at 20 mg wk-1 compared to no added nitrogen had no e ffect on peas, but more than doubled the size of mayweed chamomile in monoculture and in mixtures with pea. Added nitrogen did not increase the aggressivity of mayweed chamomile relative to pea. Nomenclature: M ayweed chamomile, Anthemis cotula L. #3 ANTCO; peas, Pisum sativum L. 'Alaska 81.'