In Maine clear and black polyethylene plastic mulches were used in connection with a study of soil temperature effects on potato growth. Neither polyethylene mulch significantly affected potato yields, but both polyethylene mulches gave an increase in soil moisture when used from planting until bloom time. The average daily temperature of the soil was raised 1° F. by black plastic and 3.6° by clear plastic, as compared with bare soil. Cost of the material used is around 4 cents per square yard, or less than $200 for enough material to cover an acre of ground. Plastic covers as mulches-Dryland areas Results of tests conducted at North Platte, Nebr., are indicative of the effects of plastic coverings under the dryland conditions of the central Great Plains. The material used was black, 6-mil, polyethylene plastic sheeting with low water transfer characteristics but fairly permeable to oxygen, nitrogen, and carbon dioxide gases. Preliminary field tests were conducted under dryland conditions with corn and grain sorghum in 1958 and with grain sorghum in 1959. Complete soil cover with plastic greatly reduced total water use by the plants and increased the efficiency of water use (table 6). The complete plastic cover held evaporation losses to a minimum. Total water use in the plastic-covered treatments averaged about 46 percent of the noncovered check plots. It would appear that evaporation losses under dryland conditions in the central Great Plains are approximately 50 percent of the total water use during the cropping season. TABLE 6.-Effect of plastic sheet cover on evaporation losses, total water use, crop yield, and water use efficiency, North Platte, Nebr., 1958-59 Total yield of corn was slightly lower under the plastic cover, whereas the yield of grain sorghum increased 20 percent both years. This increase in sorghum yield may be in part the result from higher temperatures under the black plastic early in the growing season. Water was used more than twice as efficiently by the crops in the plastic-covered plots as in the noncovered plots. Limitations of plastic cover under a wide variety of climatic conditions are not presently known. The possibility of plant disease factors occurring because of the change in microclimate under the cover should not be overlooked. Cost of material used is approximately 12 cents per square foot. This cost limits extensive use except for high-value crops. Laboratory studies at Mandan, N. Dak., were made to determine the effect of the percentage of surface covered with plastic on evapora tion. A marked reduction in evaporation occurred as the percentage of the surface cover was increased. It has been proposed that reduction of evapotranspiration on a regional basis may be difficult, if not impossible, because energy prevented from evaporating soil moisture by waterproofing will increase sensible heat and cause increased evapotranspiration from adjacent cropped areas. This would not be true if the increased reflection by the waterproofing material reflected a larger amount of the sun's energy than was used in evaporation on bare soil. White, pigmented, polyethylene sheeting, 4 mils thick, has a high reflectivity index. Sensible heat convected from the white plastic surfaces to the air was found to be less than 60 percent of the sensible heat convected from soil surfaces, despite the fact that considerable evaporation from the soil surface was taking place. Thus, white-colored polyethylene sheeting can dispose of unwanted energy from the sun by reflection, and regional reduction by evapotranspiration is definitely possible. Unfortunately this particular plastic sheeting decomposes, becomes weakened, and lasts for one, or at the most, two cropping seasons. At present this sheeting costs slightly more than 1 cent per square foot. Large-scale production and distribution could possibly cut this cost in half. Increasing the longevity appears to be the most promising method of decreasing the annual cost of this material. (Black polyethylene plastic has lasted for several years under similar conditions.) Hexadecanol added to soil surface Hexadecanol added to lakes or reservoirs reduces evaporation of water. It may have a similar effect on water stored in soil, but its effect in soil is unknown. Material tested at Fort Collins, Colo., was described as micronized n-hexadecanol. It was a mixture of hexadecanol and octadecanol, long-chain fatty alcohols used in the manufacture of some common detergents. Evaporation of water from soil may be decreased by materials that reduce the surface tension of water and increase the angle of wetting between the liquid and the soil surfaces. Both of these changes reduce the capillary rise of water in soil. Under such conditions evaporation from the surface tends to form a dry layer of soil at the surface, creating a diffusional barrier to loss of water by evaporation. Evaporation of water was reduced by adding hexadecanol to a soil placed in a greenhouse. Mixing the material with soil to a depth of one-fourth inch from the surface was the most effective placement, and mixing the hexadecanol with all the soil in the container was next best of four placements. The amount of water saved by the surface application was 18, 21, and 44 percent for rates of 1, 5, and 25 grams hexadecanol per 3,000 grams soil, respectively. The depth of soil in the container was 6 inches. These values are an average effect for a period of 1 year. The surface application treatment had not changed in effectiveness 1 year after application, but the hexadecanol mixed with the soil was only half as effective after 1 year as at the beginning. The limitations of this material are cost and the decomposition in the soil. The main objective of this research was to determine whether hexadecanol changed certain properties of water in soil enough to reduce evaporation. More effective placements are quite probable, which would lower the rate of application and the rate of decomposition in the soil. Cost of the hexadecanol is nearly 40 cents per pound. In liquid form the hexadecanol costs about one-half as much. In this study the lowest rate of application was 660 pounds per acre. Further research could lower this rate considerably. Hexadecanol is available from various sources, particularly companies manufacturing detergents. Other chemicals tested to reduce evaporation Other materials tested for reduction of evaporation from soils include the chemical dimythylactadecylammonium chloride (hereafter referred to as DDAC). It is sold under the trade name Arquad 2HT. The principal property of DDAC of interest here is its effect on capillary movement of water in soils. Laboratory tests have shown that liquid water movement into a soil properly treated with DDAC is virtually stopped. Treatment of a soil with DDAC changes the treated soil from a water-absorbent to a water-repellent medium. Complete treatment of the soil with DDAC is uneconomical. However, it has been found that partial treatment is quite effective. Since practical conservation of water involves getting the water into the soil as well as minimizing loss once it is there, the effect of DDAC on infiltration was also studied. Since liquid water movement occurs by similar mechanisms in evaporation and infiltration, the result, as would be expected, was reduced infiltration. At present, practical methods of use have not been found because of limitations of the material. A DDAC-treated soil has less dry stability than an untreated soil and is therefore more subject to movement by wind in the field. The treated soil is effective only so long as the soil is air-dry. Since it is uneconomical to treat all the soil, water vapor can be absorbed within the treated soil, thus making it difficult, under field conditions, to keep the treated soil dry. A further limitation is that DDAC treatment not only decreases evaporation but also decreases infiltration. According to the manufacturer, DDAC is a byproduct of the meatpacking industry and is available in large quantities. Very little cost reduction was foreseen as possible in the future. The cost of the material would amount to $25 per acre for a 0.1-percent treatment to the top 2 inches of soil. TRANSPIRATION REDUCTION This is a new field of investigation, and many questions about its effectiveness remain unanswered. Since evaporation from leaf surfaces is a cooling process, there is some question as to detrimental effects on the plant. The control of plant stomatal opening offers possibilities in moisture use efficiency and conservation. Hexadecanol and octadecanol studies on corn The possibility that hexadecanol, which has been effective in reduction of evaporation from water surfaces, might also be used to suppress transpiration by plants was investigated. Hexadecanol and octadecanol (a material similar in properties, cost, and source of supply as hexadecanol) added to a soil in which corn was grown in a greenhouse failed to decrease the amount of water used per unit of dry matter. Both alcohols reduced the yield of corn significantly when they were mixed with the soil at the rate of 25 grams per 3 kilograms of soil. Considerable decomposition of the added alcohols had occurred during nearly 2 months of exposure to the soil. The alcohol could not be recovered from the soil receiving 1-gram treatments per pot. Plastic latex-type spray test Other proposals are to spray plastic latex-type emulsions on growing plants to reduce transpiration losses. Preliminary field trials with grain sorghums were inconclusive. Additional well-planned trials are warranted, using several materials as transpiration depressants and studying the concentration to use; stage of growth to apply; toxicity, if any; persistence of film; action on transpiration; and effect on moisture conservation and its efficient use. AUTOMATION FOR IRRIGATION CONTROL Recent developments by the ARS for better irrigation water control are the automatic and semiautomatic gates. These are constructed of galvanized steel, steel, and copper combined with neoprene and butyl rubber sealing strips. The gates are self-operating and control the delivery of water from irrigation ditches to the land. Costs are not available and the gates are as yet not available commercially. Bondurant, James A. 14(1): 23. 1961. SELECTED REFERENCES Mechanization of surface irrigation. Crops and Soils Automatic gates for surface irri Surface irrigation through auto1962. Bondurant, James A., and Humpherys, A. S. gation. Agr. Res. 10(4): 6-7. 1961. Bondurant, James A., and Humpherys, A. S. matic control. Agr. Engin. 43(1): 20–21, 35. Bowers, S. A., and Hanks, R. J. Effect of DDAC on evaporation and infiltration of soil moisture. Soil Sci. 92: 340–346. 1961. Grossi, Frank X., and Woolsey, John L. Effect of fatty quaternary ammonium salts on physical properties of certain soils. Indus. Engin. and Chem. 47: 2253-2258. 1955. Hoover, J. M., and Davidson, D. T. Organic cationic chemicals as stabilizing agents for Iowa loess. Highway Res. Board Bul. 129: 10–25. 1956. Robins, J. S. Evaporation from agricultural lands. Soil and Water Conserv. Jour. 16(2): 57-60. 1961. Slater, C. S., and Broach, R. V. D. 1960. Plastic ground covers and what they do DRAINAGE The practice of the art of drainage is probably as old as the art of agriculture. The first recorded examples occurred during the time of the Roman Empire. Methods of drainage have not varied greatly in the last 100 years when tile drainage was first introduced. There has been, however, a constant search to improve subsurface and surface drainage facilities, to discover more economical materials, and to discover practical methods and materials to extend the effective life of drains. MOLE CHANNEL LINING Mole drainage is an old practice but has not been very effective, except in a few areas, in the United States. The principal advantage of mole drainage is its low initial cost. At a depth of 30 inches and with drains spaced 20 feet apart, it is estimated that the cost is less |