Effect of previous crop and herbicides on weed growth and wheat yield

Abstract

Field experiments were established in 1998, 1999 and 2000 at the Lethbridge Research Centre to examine the effect of preceding annual crops and accompanying recommended herbicides on weed infestations in following winter and spring wheat (Triticum aestivum L.). Seven crops and fallow were established in year 1 with and without herbicides for weed control. In year 2, spring and winter wheat were grown without herbicides and with minimal fertilizer inputs to measure the effect of the previous crop and herbicides on weed and crop growth, available N and P, and available soil moisture. Lentil (Lens culinaris Medic) as a previous crop provided an environment that promoted wheat growth but not weed growth. In contrast, mustard (Brassica juncea L.) as a previous crop inhibited spring and winter wheat growth, but did not inhibit total weed biomass production in year 2. The beneficial effects of lentil and the detrimental effects of mustard were partially explained by available soil moisture and soil N for the second crop but additional factors, such as allelopathic chemicals or changes in soil biology, must be involved to cause the large differences in weed and wheat growth that were observed in year 2. The lack of herbicides with some crops led to dense weed populations in year 2. In addition, N, P, moisture utilization, and possible additional changes in soil biology or chemistry caused by uncontrolled weeds affected wheat yield after lentil and fallow. Key words: Available soil moisture, available soil nitrogen, crop rotation, lentil, mustard, weed density