Relative Impacts of High Tunnels and Internal Row Covers On Soil Temperatures and Soil Growing Degree Days.

High tunnels (HT) are greenhouse-like structures, usually without mechanical heating systems, that are used to extend the in-ground production season of high value crops.  Combinations of HTs and internal row covers are beind tested for the production of warm season crops (tomato and zinnia) over the winter in three HTs at Crystal Springs, Mississippi.  Inside the HTs, 1.6 m tall secondary row covers made of four materials are being tested for their capacity to modify temperatures and crop growth, compared to that seen in uncovered control plots within the HTs.  In the present study, the side and end walls of the HTs, and/or the secondary row covers (COV) are opened or closed manually each day using a protocol based on actual and forecasted air temperatures and precipitation. COV treatments included: none, light weight spun-bonded polypropylene, heavyweight spun-bonded polypropylene, clear polyethylene, and a black, felted landscape fabric.  During winter 2009-2010, soil temperature at 5 cm was recorded in each plot in the HT, plus outside the HT in bare soil (OUT) at fifteen minute increments.  HT influenced soil temperature more than COV, increasing soil growing degree days (SGGD) by more than 100% during the December-January period over OUT.  Differences in soil temperature and SGDD among COV treatments were smaller but sometimes significant, as well.