WEED SUPPRESSION BY LIVE AND DESICCATED HAIRY VETCH (VICIA-VILLOSA)

Hairy vetch was grown as a winter annual cover crop and evaluated for weed suppression when desiccated by paraquat or left alive until natur al senescence in a 3-yr field experiment. Total weed density and bioma ss were variable in the desiccated hairy vetch treatment relative to a bare soil treatment but were consistently lower in the live hairy vet ch treatment relative to the desiccated or bare soil treatments. An av erage of 87% of sites under live hairy vetch compared to 8% of sites u nder desiccated hairy vetch transmitted less than 1% of unobstructed s unlight. The red (660 nm) to far-red (730 nm) ratio of transmitted lig ht was reduced by 70% under live hairy vetch compared to 17% under des iccated hairy vetch. Daily maximum soil temperature and diurnal soil t emperature amplitude were reduced by live hairy vetch > desiccated hai ry vetch > bare soil. Soil moisture content was greater under both liv e and desiccated hairy vetch compared to bare soil during droughty per iods. Changes in light extinction, red to far-red ratio, and diurnal s oil temperature amplitude were sufficient to explain greater weed supp ression by live than desiccated hairy vetch.