Effectiveness of Drainage Systems in Cranberry Production.

Recent work on cranberry irrigation showed that excess water application at fruit setting reduced yields and that optimal soil water potential should be maintained between -4 and -6 kPa. In this project, additional work was conducted to determine the relation between water table depth and soil water potential in the rooting zone in order to design drainage systems maintaining an optimal water table depth. The objectives of this project were 1) to follow the drainage systems of two cranberry fields presenting different designs and 2) to propose design improvements in order to maintain optimal potentials. Based on soil characteristics, rates of water table drop for various drain spacings were predicted using the van Genuchten model (1980). The results revealed drain blocking or clogging for one field. The other field had soil zones presenting strong restrictions to water flow, which could lead to the formation of perched water table. In the absence of these restrictions, water potential was directly linked to water table depth.  Based on simulation data, it is possible to conceive drainage systems bringing back the potential of the rooting zone in the optimal range within a desired period of 24 to 48 h. Simulations of water table level movement revealed that, following a 12 mm precipitation, with the table depth set initially 0.60 m under surface, two draintiles were enough to bring the water table back to an adequate depth of 0.50 m within two days. However, when the water table depth was set initially at the surface, increasing the drain tiles from two to four then six drains reduced the time period to reach that 0.50 m depth from 77 to 54 and 49 h, respectively. Thus, because such depth should be reached within 48 h according to drainage requirements for other species, a minimum of four drains per field should be installed in representative cranberry field. These results are preliminary. Additional experiments will be made, in particular to evaluate the minimum time to reach a 0.50 m depth to the water table depth without affecting cranberry yields.