ENERGY SAVING BY SOIL INSULATION IN GREENHOUSE FREESIA PRODUCTION

This paper describes attempts to find practical methods for mulching in Freesia to prevent evaporation from the soil. If mulching could insulate soil not only for temperature, but also for evaporation, more energy might be saved. Two experi-ments at commercial greenhouses were done to test soil insulation. The first experi-ment aimed to test materials and strategies. This experiment showed that a mulch of styromul bound together with synthetic glue or paper cellulose did not inhibit or harm the crop. In the second experiment soil was insulated using: Biofoam^® (5 mm layer), Styromul (5 mm layer), Biofoam^® glued together with synthetic glue (20 mm layer, Biofoam^® glued together with organic glue (20 mm layer), styromul glued together with synthetic glue (20 mm layer) and an untreated control. Slightly increased evaporation using any mulch layer was measured. However, soil temperature was also higher because of soil heating resulting in higher evaporation of the soil. Net evaporation is calculated to have been decreased by 12% using 20 mm instead of 5 mm mulch, which is expected to result in energy saving of 11.1 MJ.m^-2.yr^-1 on humidity control, which is too low to make up for the cost. Soil insulation decreased temperature fluctuations. Increasing the thickness of the mulch increased temperature insulation, however the effect appeared to decrease rapidly with increasing layer thickness.