Biophysical interactions in the alley cropping system in Saskatchewan

Crop production in alley cropping systems and in other mixed-species systems is dependent on the net effects of facilitative and competitive interactions on availability of growth resources (moisture, nutrients, and light) to the crop and trees components of the system. Controlling these interactions can benefit producers through the increased system productivity associated with optimized yields crops and trees. Previous research in the Canadian Prairies has focused on biophysical interactions in shelterbelts. These studies have demonstrated that trees in the shelterbelt system ameliorate soil moisture and temperature by reducing wind speed and trapping snow; this in turn reduces evaporative and heat stress leading to increased yields of intercrops (Marchand and Masse, 2008; Kort et al. 2009). Unlike Eastern Canada and United States (US), there is inadequate information on the on tree-crop interactions under alley cropping systems in the Canadian Prairies. Studies in these areas indicate that nutrient recycling by trees through nitrogen (N)-fixation and litter and root turnover can enhance soil nutrients, especially N thereby reducing fertilizer inputs in the alleyways (Thevathasan and Gordon, 2004). Because of the reduced N inputs and highly efficient capture of nitrate leaching to sub-soils by tree roots, alley cropping systems also hold high promise to reduce N 2 O emissions and groundwater contamination (Doughterty et al. 2009). When plant growth is not limited by water and nutrients, plant biomass production is directly related to the radiant energy up to species-specific saturation points. In the absence of these growth-limiting factors, shading acts as facilitative rather than a competitive effect in agroforestry systems (Jose et al. 2004). Positive ecological interactions discussed here have been demonstrated to increase productivity of food, forage and bioenergy crops in alley cropping systems in Eastern Canada and US, but this has not been done in the Canadian prairies. Thus, it is necessary to assess biophysical interactions in the alley cropping system in this region because impacts of these interactions on plant growth and yield usually depends on many factors including site specific and climatic conditions, age and type of tree species.

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