From adamf@vtaix.cc.vt.eduSat Nov 26 11:51:02 1994 Date: Sat, 26 Nov 1994 09:11:56 -0500 From: Adam Finkelstein To: london@sunsite.unc.edu Subject: Legume Green Manure Effects on Bean/Wild Mustard Interference* Plant Systems Division Plant Pat -------------------- Legume Green Manure Effects on Bean/Wild Mustard Interference* Plant Systems Division Plant Pathology/Weed Science Program University of Maine Proposal #9300546 Matt Liebman $120,000 Herbicides are the most heavily used class of pesticide to U.S. cropland. Despite current empahsis on chemical weed control, several factors have recently led to a reappraisal of herbicide use. These factors include contamination of ground and surface water, increased numbers of herbicide-resistant weeds, increased costs of discovering and registering new herbicides, and concern over possible negative effects of routine herbicide use on human health. New alternatives to chemical weed management need to be developed so that farmers have effective options for controlling weeds in an environmentally sound and profitable manner. This project will aid the development of successful strategies for reducing reliance on chemical weed control through improved understanding of weed ecology and mechanisms of crop- weed interactions. The project will focus on management of wild mustard in dry bean cropping systems. More than 670,000 hectares (1.6 million acres) of dry beans are grown in the U.S., and the crop ranks ninth nationally for total herbicide use. Wild mustard has been identified as one of the most troublesome and economically damaging weeds in northern bean production regions, including North Dakota, Minnesota, Michigan, and Maine. Despite the fact that beans are legumes, with the ability to fix atmospheric nitrogen in root nodules, the short season varieties grown in northern states are usually unable to fix enough nitrogen for high yields. Consequently, synthetic nitrogen fertilizer is commonly applied to dry bean crops in Maine and elsewhere. With funds obtained from NRICGP, a field experiment will be conducted at the University of Maine's Sustainable Agricultural Research Farm (Stillwater, ME) that will identify how mustard might be controlled in beans with little or no herbicide through a shift in fertilization practices from conventional use of synthetic nitrogen(N) fertilizer to use of legume green manure (i.e., a leguminous crop planted specifically to enhance soil productivity and yields of subsequent crops). Data from previous experimental work at the University of Maine strongly indicate that slow release sources of inorganic N, such as decomposing residues of clover, can starve weeds of N during the early portion of the growing season and reduce their interference ability against crops. In the experiment funded by this grant, emphasis will be placed on detailed study of how temporal patterns of soil inorganic N availability, crop and weed growth dynamics, and crop-weed interference interactions are effected by using legume green manure vs. synthetic fertilizer N sources. By helping to clarify the ecological mechanism(s) responsible for weed control in legume-based cropping systems, these experiments will aid the development of environmentally sound production systems in other regions and countries. *Strengthening Award