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Yield Response to Soil Warming: Agronomic 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 parallel electrical heating cables buried 92 cm deep and 183 cm apart. Heat source temperatures ranged from 35 to 38 C during the growing period. Heating increased the average temperature of the soil layer from 0 to I00 cm deep by about 10 C. The average temperature increase of the 0 to 10 cm soil layer was < 3 C. The crops tested were field corn (Zea mays L.), sudangrass (Sorghum vulgare sudanese), sorghumsudangrass hybrid (Sorghum bicolor L.), and tall rescue (Festuca arundinacea).

The yield increases, expressed as percentages of yields obtained on unheated plots, ranged from 19% for tall rescue to about 50% for sudangrass. The yield increases varied widely from year to year for the same crop. 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. A yield decrease occurred only with tall rescue during the summer. Soil heating appears to be most effective when climatic conditions and management factors are limiting. The effects of higher soil temperatures on growth rates were greatest in the early spring.

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.