ROW COVERS MODERATE DIURNAL TEMPERATURE FLUX IN HIGH TUNNELS
Diurnal temperature flux tends to be greater inside high tunnels than outdoors, which may stress plants and reduce yield. We monitored annual and diurnal air temperature flux in a double layered high tunnel for 17 months in 2006-2007, and then tested the ability of translucent polyester row covers to moderate air and soil temperature in the same high tunnel in late winter and early spring of 2010 and 2011. Minimum, average, and maximum soil and air temperatures were recorded hourly in covered and uncovered beds growing Spinacia oleracea (spinach), and Brassica napus var. pabularia (kale). The high tunnel increased diurnal temperature flux from an average of 12°C in summer and 7.8°C in winter to about 15°C year-round. Row covers moderated diurnal temperature flux inside the high tunnel during that late winter and early spring monitoring periods: early morning temperature under row covers was warmer than without row covers; and afternoon temperature was cooler. The high tunnel gave 4.3°C of frost protection and elevated daily minimum air temperature by up to 7.4°C on the coldest monitoring days. Row covers inside the tunnel gave an additional 3.1°C of frost protection and elevated daily minimum air temperature by up to 4.9°C on the coldest monitoring days. Daily minimum air temperature under row covers, Tcov, was a linear function of minimum temperature in uncovered beds, Tin (Tcov=0.85Tin+2.60; R2=0.98), which was a linear function of daily minimum temperature outside the high tunnel, Tout (Tout=0.77Tin+ 3.30; R2=0.98). Row covers had a less pronounced effect on soil temperature, giving only 2.0°C of frost protection, but soil temperature rarely fell below freezing inside high tunnels during the monitoring period. Daily peaks in air and soil temperature, respectively, averaged 1.6 and 1.7°C lower under row covers than in uncovered beds. Crop yields were 35% higher under row covers. The reduced temperature fluctuation and yield increases associated with row cover use holds promise for greater production of cool season greens in high tunnels.
Ward, M.J. and Bomford, M.K. (2013). ROW COVERS MODERATE DIURNAL TEMPERATURE FLUX IN HIGH TUNNELS. Acta Hortic. 987, 59-66
high tunnel, row cover, diurnal temperature flux, frost protection