Short-term effects of mechanical weeding on soil and tissue N in snap beans grown in an organic vs. conventional rotations

Owen, J., S. LeBlanc and S.A.E. Fillmore
Oral Presentation. Organic Research Symposium, Guelph, Ontario, January 26, 2007.

Owen, J., S. LeBlanc and S.A.E. Fillmore. 2006. Short-term effect of soil disturbance by mechanical weeding on plant available nutrients in an organic vs. conventional rotations experiment. Poster (PDF, 78kb), Colloquium of Organic Research (COR) 2006. Edinburgh, Scotland. September 18-20, 2006.

Abstract
Mechanical weeding, a common practice in organic crop production, causes frequent soil disturbance. This study, conducted from 2003 to 2005 in an organic vs. conventional rotations experiment in New Brunswick, examined changes in available soil N and in tissue N of snap beans following mechanical weeding events.

The experimental design included continuous snap beans, and a fully phased snap beans/fall rye rotation, to which combinations of yearly applied fertility (chemical fertilizer or compost) and weed control (herbicide or mechanical weeding) were applied. Two mechanical weedings were performed each season. Plant available soil N was monitored by 24-hour burials of ion exchange membranes beginning 12 hours after weeding in both mechanically-weeded and herbicide-treated plots. Ions were eluted from the membranes and analysed. Coinciding with membrane removal from the soil, aerial bean plant parts were collected for total tissue N analysis.

Availability of soil NH4+-N was not affected by weeding treatment. Soil NO3--N availability, however, was consistently less in mechanically weeded plots than in plots treated with herbicide. Weeding method affected tissue N, and interacted significantly with rotation. Scattergrams of treatment means plotted as total tissue N vs available soil N revealed these interactions as distinct groupings.

 

Posted October 2007