Non-Peer ReviewedA three-year field study was conducted in the Dark Brown and Black Soil Zones of Saskatchewan to assess the effects of trifluralin (Treflan ), metribuzin (Sencor), MCPB (Tropotox), and sethoxydim (Poast) on growth and symbiotic nitrogen fixation of field pea (Pisum sativum cv. Trapper) and lentil (Lens culinaris cv. Eston). Herbicides were applied at Saskatchewan recommended field rates and twice the recommended field rates. Treflan, Sencor, and Poast did not adversely affect plant growth or nitrogen fixation potential of field pea and lentil when applied at recommended field rates. Similarly, application of MCPB at the recommended rate did not adversely affect field pea under normal growing conditions. In some instances, herbicide application at the recommended rate was observed to have a stimulatory effect on growth and nitrogen fixation. In contrast, at application rates in excess of those currently recommended in Saskatchewan, or when plants were severely stressed by unfavorable growing conditions such as poor soil
moisture, plant growth, yield, nodulation, and nitrogen fixation were adversely effected by herbicides. These effects were not consistent nor were they predictable. MCPB is not registered for use in lentil and,
when applied in this crop, often resulted in reduced nitrogen fixation and seed yield. In all cases, data suggest that reductions in the nitrogen fixation potential were due to indirect effects of herbicide application on plant growth rather than to direct effects on nodulation and nitrogenase activity
