Optimizing water management for sustainable use of agricultural lands and water

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Irrigation is expanding in Southern Manitoba in areas where salinization from poor quality groundwater has been a major problem. Wherever irrigation water is applied to plants, the plants take up the water and leave behind the salts within the root zone leading to salinization. Drainage systems can be used to remove the excess water applied to wash the salts below the rootzone to mitigate salinization. However, conventional drainage systems may also over-drain the field, removing valuable nutrients and water. Controlled drainage can be used to overcome this shortcoming. Previous NSERC funded field-scale research showed that properly designed and managed irrigation and drainage systems can significantly improve yield by 30% in potatoes and 15% in corn. However, major nutrient outflows were observed in tile drainage during spring snowmelt period as well as during high intensity rainfall. Controlled drainage using Drainage Control Structures (DCS) that can hold back the water within the field was shown to lower the nutrient outflow by 90% compared to conventional drainage. The use of DCS was found to be a best management practice to minimize nutrient export from the field. However, this practice may negatively impact soil trafficability due to the high water table in the spring. The proposed research will optimize the operation of controlled drainage to hold back the water and nutrients within the field while allowing improved trafficability. The DCS can also facilitate subirrigation where the irrigation water is applied through the DCS into the subsurface drains. However, the upward flux of subirrigated water may be restricted if the soil beneath the root zone becomes too dry. The data from this research will be used in Hydrus 2D/3D model to simulate different soil types and weather conditions and identify soils suitable for subirrigation. In the short term, the main objectives will be to (1) monitor the water and nutrient movement within the root zone to assess the impact of subirrigation/drainage systems on crop yield and water quality; (2) determine the optimum depth of the water table that will still allow field operations while conserving the water and nutrients within the field; (3) determined the optimum depth of water table that will allow subirrigation during periods of high evapotranspiration. I will use the NSERC Discovery grant to partially support three PhD, five MSc, and twelve BSc students. Farmers will benefit from improved yields and better nutrient retention within the field. In the long term, the objective will be to optimize the integrated water management systems combining subirrigation/controlled drainage systems and develop a protocol for site selection for successful implementation. The long-term goal is to manage the water and nutrients within the field and attain agricultural sustainability at the farm-scale and minimize the nutrient outflow into the rivers and lakes.