Soil Temperature and Tomato Growth Associated with Black Polyethylene and Hairy Vetch Mulches

Abstract

Temperature and root length at selected locations within a raised bed under black polyethylene, hairy vetch (Vicia villosa Roth) residue, or bare soil were measured and correlated with tomato (Lycopersicon esculentum Mill.) growth. Early in the season, before the tomato leaf canopy closed, soil temperature was influenced more by vertical depth in the bed than by horizontal position across the bed. Maximum soil temperatures under black polyethylene averaged 5.7 and 3.4C greater than those under hairy vetch at 5 and 15 cm deep, respectively. More hours at optimum temperatures for root growth (20 to 30C) during the first 4 weeks of the season probably accounted for greater early root and shoot growth and greater early yield of tomatoes grown with black polyethylene than hairy vetch residue or bare soil. After canopy closure, soil temperatures under tomato foliage within the row were reduced by an average of 5.2 and 2.2C at 5 and 15 cm deep, respectively, compared to those on the outer edge of the beds. Most tomato roots were in areas of the bed covered by the tomato canopy where temperatures in all treatments remained in the optimum 20 to 30C range almost continuously. Soil temperature, therefore, did not explain why tomato plants in the hairy vetch treatment had equal or higher total yields than the black polyethylene or unmulched treatments.