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Yield Response to Soil Warming: Vegetable Crops¹

Waste heat appears in the form of warm condenser cooling water from power generating plants. It has been proposed to use this water with temperatures ranging from 25 to 40 C for warming soils by pumping it through buried pipes. Experiments were conducted to determine the effect of warming soils in this manner on the growth rates and yields of several crops. The proposed system was simulated with electrical heating cables buried 92 cm deep at a spacing of 183 cm. Heat source temperatures ranged from 35 to 38 C during the growing period. Heating increased the average temperature of the soil layer from O to 100 cm deep by about 10 C. The average temperature increase of the O to 10 cm depth soil layer was µ 3 C. The crops tested were bush beans (Phaseolus vulgaris), lima beans (Phaseolus lunatus), tomatoes (Lycopersicmi esculentum), broccoli (Brassica oleracea), peppers (Capsicum annuum), and strawberries (Fragaria virginiana).

The yield increases, expressed as percentages of yields obtained on unheated plots, ranged from 19% for bush beans to about 100% for broccoli. The greatest advantage gained from soil warming occurred early in the growing season. The advantages decreased as the season progressed. The plants continued to grow fastest on heated plots throughout the growing periods however. Soil warming sustained growth rates of bush beans in the early fall when plants on unheated plots were slowed in growth. A wide variation in yield responses occurred between different years for the same crop and between different crops during the same year. The highest yield increases occurred during years when the yields on unheated plots were lowest. Correlations between yield increases and yields from unheated plots were highly significant.

Key Words: Reject energy • Waste • Soil temperature

² Graduate research assistant, professor of soil science, professor of horticulture, and assistant professor of agricultural and resource economics, respectively. Present address of senior author: Long Island vegetable research farm, 39 Sound Ave., Riverhead, NY 11901.

Received for publication November 25, 1974.