Lettuce production in southern Quebec, Canada, is the most important vegetable production for the grower of this region. The production is in majority on Histosols. However, the lettuce has a risk of evapotranspiration deficit during the summer, which could be caused by a high spatial heterogeneity of soil water availability, all affecting yields. This problem is accentuated when a mean water application is used; it causes excess and deficit in plant water availability in the field. The objective of this study was to compare site-specific vs. conventional uniform irrigation management for the lettuce.    

One experiment was conducted in summer 2010 on an area of 7ha in southern Quebec. The irrigation schedule was based on a -30 kPa threshold value of soil water potential. The matric potential was measured at three depths in the soil profile with tensiometers installed among zones defined by a soil-depth gradient in the field. Hydraulic properties characterization and mapping of soil water availability for plants were also accomplished to define each zone in the field. Each site-specific irrigation was managed according to the unique value of matric potential generated by the tensiometer of each zone. The conventional irrigation treatment used a mean value of soil water potential generated by all tensiometers of all zones.

The results of the study suggest the importance of the heterogeneity of soil water availability for plants in the field and the date of the plantation for the irrigation scheduling. The site-specific irrigation had a positive effect on the yield of lettuce. The site-specific irrigation strategy becomes really important for the grower to define the irrigation priority when the evapotranspiration is high.