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.

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.

As water for crop production becomes limited and costs of water increase there is a need for more accurate irrigation scheduling. Irrigation scheduling can be improved with reliable and rapid estimates of crop evapotranspiration (ET). The use of three climatebased equations and the soil‐water‐balance equation for estimating sweet corn (Zea mays L. ‘Jubilee’) ET for irrigation scheduling were compared in a 2‐yr field study on a mixed, mesic Cumulic Ultic Hapoxeroll soil. The three climate‐data‐based equations used were the Food and Agriculture Organization of the United Nations (FAO) modified Penman and the FAO and Soil Conservation Service (SCS) Blaney‐Criddle equations. Five irrigation levels ranging from 0 to 100%, with the 100% level intended to refill the root zone to field capacity, were all proportionately irrigated when approximately 50% of the available water was depleted in the 100% level as measured with a neutron meter. A sixth treatment in this randomized complete block experiment was irrigated with the amount of water equivalent to the crop ET estimated by the FAO modified Penman (M PEN) equation, when the crop ET had accumulated to 50% of the available soil water. The crop ET estimated by the soil‐water‐balance equation in 1984 was 481 and 447 mm for the 100% level and for plots irrigated according to the M PEN equation, respectively. In 1985 these ET estimates were 506 and 488 mm, respectively. The crop ET in 1984 was 404, 372, and 374 mm as estimated by the M PEN, FAO, and SCS Blaney‐Criddle equations, while in 1985 these equations estimated 450,448, and 379 mm, respectively. Yield differences were not significant between plots irrigated according to the M PEN equation and the irrigation levels of 50% or more in both years. Calculations indicated that the lower estimates of ET by the FAO and SCS Blaney‐Criddle equations, if used to schedule irrigations, would not be expected to cause yield decreases.

The yield-plant density relationships of 5 bush snap bean cultivars and the effect of rate of N application on the yield-density relationship of a single cultivar were studied in 2 separate experiments. Responses were described by the equation W-θ = α + βρ where W is the pod weight per plant, ρ is the plant population density, and θ, α and β are constants. The θ, α and β values were tested for significant differences among the cultivars and levels of N. In experiment 1, θ = 0.836 was acceptable for all 5 cultivars and in experiment 2, θ = 0.897 was acceptable for the 3 rates of N. Values of θ were similar to those found for bush snap beans by other researchers. Significant differences existed among both α and β values of the cultivars. In the N experiment, α was constant but values of β differed significantly and were inversely related to the level of N. Optimum plant density was dependent on the cultivar and increased with the level of N.

Yields of snap bean pods were increased by irrigation and plant density in 4 field experiments. Highest yields were obtained with the −0.6 bar soil water potential regime which represented removal of 40-45 percent of the available soil water at 30 cm depth. Yields were lowest with the −2.5 bars soil water potential which represented 65-70 percent water removal. An average of 60 percent more water applied to the −0.6 bar than the −2.5 bars treatment increased yields approximately 54 percent. Yields were usually intermediate with the −1.0 bar soil water potential representing 50-55 percent available soil water removal. Two cultivars were used in 2 of the experiments and responded differently to irrigation. Yield of ‘Oregon 1604’ was higher than that of ‘Galamor’ with −0.6 bar soil water potential but was lower than ‘Galamor’ with −2.5 bars. Yield of ‘Oregon 1604’ averaged 27 percent higher in square arrangement than in 91 cm rows and the increase was greater for the high than for the low population density when compared in 1 experiment. Yield was 20 percent higher for high density of 43.0 plants/m2 than for low density of 21.5 plants/m2. Yields of 2 cultivars in 2 experiments averaged 67 percent higher in high density (40-57 plants/m2) than in low density (20-33 plants/m2) plantings. There were no consistent irrigation × density interactions. Usually there was a more rapid depletion of soil water for high density than for low density. Fiber in canned sieve size 5 pods was higher in ‘Oregon 1604’ at −2.5 bars soil water potential than for ‘Galamor’, but at the −0.6 bar soil water potential regime, the amount of fiber was similar in the 2 cultivars. Percent of pod weight attributed to seed and percent fiber were usually highest at −2.5 soil water potential.