Choice of Right Cover Crop Based on Biomass and Light Transmitted.

Weeds are a major problem in agriculture worldwide.  In organic production systems where, chemical means of weed control is unacceptable, weeds can be limiting factor.  Cover crops can be an efficient means of managing weeds and offer many other benefits to soil and plant productivity in organic production system. To choose a right cover crop it is essential to understand their ability to compete and suppress weeds. Cover crops smother weeds by producing higher biomass and intercepting light that could otherwise be available to weeds. The competitive factor of light interception, cover crop and weed biomass were evaluated in a study conducted in northern Alabama.  Five winter cover crops, rye, crimson clover, canola, Austrian winter peas, and hairy vetch were compared with fallow Control. There was a positive correlation between photosynthetically active radiation (PAR) interception by cover crops and weed suppression. There were significant differences between different cover crops for biomass and percentage light interception. Rye with greater biomass (23.8 Mg ha^-1) suppressed weeds the most (weed biomass of 1.7 Mg ha^-1).  Canola, perhaps due to poor crop stand produced the lowest biomass (3.3 Mg ha^-1) among cover crops and also had the highest weed biomass (4.3 Mg ha^-1).  Weed biomass was the highest (12 Mg ha^-1) in fallow control. The weed biomass was significantly lower in the cover crop plots compared with fallow.  Light interception by cover crops ranged from 24% for canola to 80% in Austrian winter peas.  Thus, light interception by cover crops was positively correlated with their biomass.   Cover crops with greater biomass also had greater weed suppression.  Thus, the effect of cover crops on weed suppression is affected by the biomass which is positively correlated with light interception.