Characteristics of Micrometeorology under Row Cover Materials made of PVA Flat Yarn in Winter.

We compared the effects of heat retention of the row cover material ‘PVA flat yarn fabric’ with that of PVA non-woven fabric (trade name Tuffbell) from December to January. A tunnel-shaped floating row cover (1 m wide and 30 cm high in the middle) was installed in an open field, and the internal microclimate was measured. PVA flat yarn fabric is made from flat plate-like fibers (6 or 7 mm wide) propped up straight with polyethylene line. Four vacant space rates (22%, 33%, 56%, and 67%) were set up by changing the intervals of the flat yarns, whereupon the following finding became clear.1) On sunny days, the smaller the vacant space rate of the material, the higher the air and soil temperature under the row cover rose in the daytime, although conversely, both dropped at night.2) The difference in air temperature between the inside and outside (row cover-no cover) decreased as the wind velocity increased from 0 m/s to 0.7-0.8 m/s, although the air temperature under the row cover at night rose, when the wind velocity exceeded a certain figure.3) Materials most closely akin to Tuffbell 3800N with respect to the beneficial effects on temperature under the row cover were the PVA flat yarn fabric, the vacant space rates of which were 56% and 67%. The PVA flat yarn fabric was considered to be usable as a substitute for PVA non-woven fabric.4) When the vacant space rate of PVA flat yarn fabric exceeded that of PVA non-woven fabric, an equivalent effect on heat retention was obtained. This may encourage the development of novel materials with good ventilation and the use of PVA flat yarn for the purpose of heat retention.