Case Study of Groundwater Remediation of Non-Point Source Nitrate
University of Kansas
There are increasing pressures to improve irrigation management in cranberry to optimize crop yield and to reduce water and energy use in Canada, as this crop requires a large amount of water for harvest but also for summer and fall irrigation. Irrigation guidelines are lacking in this crop, with the few available references (3 references over 70 years) indicating high soil water potential values (-2 to -4 kPa). For this crop, because of the specific design of the sub-irrigation systems and of the crop bed configuration, important spatial patterns in irrigation requirements are likely to exist. New wireless real time water potential sensors now exist to identify these irrigation needs and open the route for important water and energy savings by managing local irrigation needs. The objectives of this study were therefore to identify appropriate irrigation set points for cranberry production in Quebec and then, knowing these set points, to identify spatial irrigation patterns on a commercial production site. Those set points were first evaluated using soil physical properties, a hydrological model, field experiments and photosynthesis measurements carried out in a growth chamber. Using unsaturated hydraulic conductivity and water desorption data, an ideal -3.5 to -7.5 kPa range was identified while a minimum value of -8 kPa was determined from a hydrological model combined with field estimation of evapotranspiration. Growth chamber experiments confirmed that the ideal range was in the -3.5 to -8 kPa range, limited at its upper boundary by aeration constraints and at the lower boundary by a low unsaturated hydraulic conductivity. Quebec and Wisconsin?s data for the relationship between yield and soil water potential showed the same trend as that between photosynthesis and water potential. Then, it becomes possible to conclude so far that adequate irrigation setpoints should range between -3.5 to -7 kPa for cranberry production. With respect to the second objective, different real time irrigation sensors were installed and monitored and the data generated were mapped to identify spatial irrigation requirements. The data lead to the conclusion that 1/3 of the production site had sufficient recharge to compensate for irrigation requirement leading to 33 percent saving in water and energy. The identification of appropriate irrigation set points reduce water requirement by 2 to 6 times with respects to evapotranspiration estimate, and to common irrigation practice at the commercial scale.