Yield Response to Soil Warming: Vegetable Crops¹

Abstract

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.

Root‐zone temperature and nitrogen affect the yield and secondary metabolite concentration of fall‐ and spring‐grown, high‐density leaf lettuce

“…For leaf biomass specifically, the presence of root‐zone heating increased shoot fresh weight in both years, an outcome consistent with previous reports 36, 41, 42. However, the effect was greatest in 2009 and corresponded to the potential impact of soil heating given ambient temperatures.…”

Canopy Cover and Root-zone Heating Effects on Fall- and Spring-grown Leaf Lettuce Yield in Ohio

“…The influence of air-or water-mediated active root-zone heating is most often studied in growth chambers or greenhouses (Economakis, 1997;Elwell et al, 1985;Li et al, 1994;Shedlosky and White, 1987). Fewer recent studies (Bumgarner et al, 2012;Hunter et al, 2010) have capitalized on earlier reports (e.g., Cameron Brown and Gray, 1957;Canham, 1952;Rykbost et al, 1975) and considered the impacts of direct soil heating in differently engineered low-and high-tunnel systems, especially in temperate climates.…”

Soil Heating and Secondary Plant Covers Influence Growth and Yield of Winter High Tunnel Spinach

“…The use of heating cables significantly increased soil temperature in all trials but had its greatest effect when temperatures were lowest late in the Fall and early in the Winter. Others have also reported that heating cables increase soil temperature (Bumgarner et al, 2011(Bumgarner et al, , 2012Hunter, 2010;Rykbost et al, 1975). Heating cables allowed spinach roots to be exposed to soil temperatures within 7 to 23°C range which are optimal for spinach root growth.…”

“…The addition of soil heating cables generally leads to an increase in the total yield for early spring grown tomatoes, bush beans, peppers, broccoli, and lettuce (Bumgarner et al, 2011;Hunter et al, 2012;Rykbost et al, 1975) and results in increased yield for winter-grown lettuce (Bumgarner et al, 2011(Bumgarner et al, , 2012Hunter, 2010). Additional heat increased total plant biomass and nutrient uptake by maintaining root zone temperatures above freezing and closer to optimal root temperature.…”