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 100 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 fescue 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.
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.
The development potential of soil warming with power plant waste heat is evaluated and major determinants to development are identified by evaluating the economic feasibility of producing selected crops by soil warming. Yield responses to soil warming were identified from a series of test plot experiments. Crop values and soil warming production costs are specific to Willamette Valley, Ore., in 1973. The capital cost of a soil warming installation consisting of 5.08 cm diameter PVC pipes buried 90 cm deep at 183 cm centers with supply lines and pumps was estimated to be $8,213/ha. The annual amortization would be $847 or $l,242/ha at interest rates of 10 and 15%. Additional operating and maintenance costs would result in total annual costs of $927 or $l,407/ha at opportunity costs of 10 and 15%. Only high value crops could be profitably produced using soil warming. The economic potential of the proposed production technique is limited by the high capital cost of the installation. This potential could be improved by decreasing installation costs through the use of wider spacings, by selection of crop cultivars more responsive to soil warming, and by accepting lower interest rates on the invested capital.
The water required to irrigate greenbelts being established around cities in Iran is a major cause of concern in a country with insufficient supplies. Methods of afforestation which do not require irrigation must be found. One such method is to concentrate water, received by a watershed without vegetation, for distribution over a smaller area where plants are growing by making portions of the watershed area impervious to water through application of asphalt. This principle was tested on runoff plots 2 m wide and 10 m long. Runoff from each plot was measured to study its variations as a function of age of asphalt cover and rainfall amount and intensity. The concept was further tested by constructing 2‐m wide terraces along contour lines at 5‐m intervals on a hillside with a slope of about 30%. Tree species, ecologically adapted to the area, were planted on the terraces. Calibrated gypsum blocks were placed at depths of 15, 30, 45, and 60 cm in the terraces and at depths of 10 and 30 cm in the watershed area between the terraces to measure soil water potentials.As the asphalt membrane aged, its efficiency in inducing runoff decreased. The runoff efficiency was nearly 75% initially, but decreased to 25% after 4 years. A regression equation was obtained correlating the runoff efficiency with age of the asphalt membrane. Freezing and thawing of the soil, growth of plants, and shrinking and swelling of clays resulted in the deterioration of the membrane. It remained effective for about 5 years.The runoff from the asphalt‐sprayed microwatersheds resulted in high soil water contents of the terraces, with average potentials of −0.4, −7.7, and −2.5 bars during 1972, 1973, and 1974 where runoff was received, corresponding to −7.7, −23.8, and −21.8 bars on control plots.The technique is being developed as an alternative to the irrigation practices now in use for the establishment of greenbelts. It will result in savings of water, which in some localities could amount to 5,000 m3/ha/year, an amount sufficient to satisfy the needs of 50 people per year.
The feasibility of placing drains at shallow depths and close together to improve drainage conditions on a planosol was evaluated. Field lysimeters were obtained by surrounding soil blocks with vertical sheets of heavy plastic penetrating well into the impermeable subsoil. Perforated plastic tubing placed 22.5 feet (approx. 6.9 m) apart at a depth of 20 inches (approx. 51 cm) provided adequate drainage. Dupuit alfalfa yielded better than 10 T/A dry matter. Manganese levels were below concentrations considered toxic. When a spacing of 45.0 feet (approx. 13.7 m) was used, the alfalfa yields were greatly reduced, and the manganese concentrations were well above levels considered toxic.
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