EVAPORATION FROM CRANBERRY

Cranberry is an economically important crop in Central and Northern Wi sconsin. A good understanding of the hydrology of the cranberry system is needed for optimal management of the crop, and for prediction of t he fates of crop production chemicals, A key component of the hydrolog y of a crop-soil-management system is evapotranspiration. We measured the evapotranspiration from a cranberry bed in Central Wisconsin using the energy budget-Bowen ratio method. Gradients of vapor pressure wer e determined by alternately measuring the dewpoint temperature of stre ams of air from 0.5 and 1.0 m above the crop. Temperatures were measur ed at the same two heights using aspirated thermocouples, periodically exchanged between heights with a device described in Appendix A. Evap otranspiration was found to be about 110% of the equilibrium evaporati on rate, appreciably below the Priestley-Taylor empiricism that is kno wn to be applicable to other crops in Wisconsin. Computer simulations reproduced the evapotranspiration rates if all of the radiation leavin g the lower boundary of the canopy was absorbed by the layer of horizo ntal, leafless vines that covered the soil. Thus this vine layer appea rs to play an important role in the energy and water balances of the c rop.