Comparison of Weed Biomass and Flora in Four Cover Crops and a Subsequent Lettuce Crop on Three New England Organic Farms

Abstract

Many vegetable growers in the northeastern United States routinely utilize cover crops to suppress weeds as well as conserve and enrich the soil. An exploratory study was conducted to compare weed biomass and species composition in four different cover cropping programs, and in lettuce grown after the cover crops were incorporated into the soil. The treatments were: two plantings of buckwheat followed by winter rye (BW/R), sudangrass followed by winter rye (SG/R), mammoth red clover + oats (C+O), and Italian ryegrass (RG). Cover crops were grown from spring 1988 through spring 1989, then followed by lettuce Some buckwheat plantings suppressed summer weeds effectively, but others failed because of drought. Sudangrass tolerated drought, but grew rapidly and outcompeted weeds only at the most fertile site. Clover established slowly, but suppressed weeds more effectively than rye during fall 1988 and spring 1989. Ryegrass completed its life cycle in early summer 1988 and did not reseed itself effectively. Winter weed species composition differed significantly between treatments Biomass of weeds + cover crop regrowth in lettuce was significantly lower after BW/R and SG/R than after C+O. The lack of summer tillage in C+O, combined with slow clover establishment in 1988, may have allowed greater seed production by crabgrass in C+O than in other treatments. Buckwheat reseeded itself at one site, resulting in substantial cover crop regrowth in the lettuce, while regrowth of other cover crops was negligible. Weed biomass excluding cover crop regrowth was least after BW/R, followed by SG/R, RG and C+O in that order. Lettuce head weight was higher after BW/R than other treatments at one site, but was not significantly affected by treatments at a second site.