Soil-Plant-Water Dynamics and Water Productivity Benefits of Subsurface Drip Irrigation

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An innovative five year research program is to be undertaken, aimed at investigating the potential efficacy and benefits of subsurface drip irrigation (SDI) for intensive vegetable production in Eastern Canada. Our hypothesis is that SDI has a superior water use efficiency compared to surface drip and overhead sprinkler irrigation systems, and if properly designed could reduce nutrient leaching below the root zone. There are currently no design criteria on the optimum depth of placement of the drip lines below the soil surface, and the optimum amount of water to be applied, to achieve maximum crop yields, for both mineral and organic soils in Eastern Canada. The research combines field, greenhouse and computer modeling studies. Field studies will be conducted on a mineral soil at the McGill University Horticulture Research Station, and on an organic soil, 100 km south of Montreal, where vegetables are intensively cultivated. Using sweet bell pepper (Capsicum annuum. L) and tomato (S. lycopersicum) as test crops at both sites, drip irrigation lines will be installed at 20 and 30 cm below the soil surface, resulting in two SDI treatments. Drip lines installed on the soil surface will serve as a control. Three soil water replenishment levels (100%, 70% and 50% of field capacity – representing 3 levels of crop water stress) will be applied to the two SDI and the DI treatments, resulting in 9 treatment combinations, which will be statistically replicated. Several parameters including crop yield and marketable harvest, rainfall, evapotranspiration, irrigation applications, and soil moisture will be measured. Pore water samples will be collected from suction lysimeters in the 9 treatment combinations after each fertigation, and analyzed for nitrite, nitrate, and ammonia. This data will inform decisions about the appropriate depth of placement of the SDI lines below the soil surface, for optimum water savings and crop yields, and reduced nutrient leaching on mineral and organic soils. Additionally crop-microclimate parameters (canopy temperature, stomatal conductance, leaf chlorophyll content, and photosynthetically active radiation) will be measured, and used to develop a Crop Water Stress Index (CWSI) for each water stressed condition for both SDI and DI. This data will result in a new technique for irrigation scheduling based on crop indicators, rather than on traditional soil moisture measurements. Furthermore, the CWSI, water savings and crop yield data will enable the development of an innovative crop-water productivity model for Eastern Canada. A greenhouse study with the 2 test crops, coupled with a computer simulation study using HYDRUS-2D, will permit a detailed assessment of soil moisture distribution under the two SDI treatments for both mineral and organic soils. The computer modeling will enable the derivation of SDI design criteria (depth of installation and emitter spacing) for a range of soils and environmental conditions. The research brings new findings on SDI, irrigation of organic soils, CWSI and crop-water productivity modeling to Canada and the scientific and engineering communities. Crop producers, irrigators and water managers who are faced with water scarcity due to competing water demands and climate variability, and rising water costs will benefit from the research findings. The sustainability and competitiveness of the Canadian fruit and vegetable industry, worth $1.5 billion annually, will be further enhanced by adoption of the research results. Five graduate students and several undergraduate students at McGill University will be trained under the project, thereby contributing to the development of highly skilled personnel for the irrigation and agricultural sectors.