Irrigation Setpoints in Cranberry from Soil and Photosynthesis Measurements.

There are increasing pressures to improve irrigation management in cranberry to optimize crop yield and to reduce water use. Irrigation guidelines are lacking though, with the few available references (3 references over 70 years) indicating high soil water potential values (-2 to -4 kPa). The objective of this study was therefore to identify appropriate irrigation setpoints for cranberry production in Quebec.  Those setpoints 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.