THE IKRIGATION AGE. 



361 



.yields. He is dependent on the natural rainfall and as a 

 rule his crops are poor or good in proportion to the 

 amount of moisture in the soil conserved from previous 

 precipitation. Every acre-inch of water which is re- 

 tained and prevented from passing into the atmosphere 

 may produce an extra bushel 6f grain per acre. There 

 is only water enough to irrigate a part of the fertile, 

 arable land of the west, and so for every acre that is 

 irrigated there will in. time be several acres that must 

 of necessity be farmed dry. How best to conserve the 

 soil moisture over so vast an area, comprising the dry 

 farms of sixteen States and territories, is a question 

 which deserves -the thoughtful consideration of every 

 western farmer. 



TANK IRRIGATION. 



In attempting to give a brief account of our ef- 

 forts in connection with this latest branch of ap- 

 plied irrigation candor compels me to state that our 

 progress has been slow and that while a certain measure 

 of success has been attained, we have also gained in 

 experience through failures. We soon found that in 

 work of this character it would not be wise to rely 

 too much on experiments conducted in the laboratory 

 or under more or less artificial conditions. We wished 

 to find out what became of the water which was spread 

 over cultivated fields and the only practicable way 

 to obtain this information seemed to be to conduct ex- 

 periments in the field. Some mistakes were made be- 

 fore we secured the right kind of vessels to hold soils. 

 The single tanks which were first used were later con- 

 verted into double tanks, water jacketed, in order to 

 facilitate frequent weighings and to maintain a tem- 

 perature substantially equal to that of the adjacent 

 soil. All the tanks now used in California are double, 

 having an annular space of about one inch between 

 the outer and inner, and this space is filled with water. 

 The double tank is placed in the field or orchard with 

 its top a couple of inches above the surface. The equip- 

 ment for weighing consists of a suitable derrick, differ- 

 ential pulley blocks and a scale. Each tank is raised 

 by means of a bale, weighed and again lowered into the 

 watiT of the outer tank.. 



EVAPORATION FROM A WATER SURFACE. 



Mu<ji of the work done in California during the 

 past two years being of a preliminary nature, it was 

 thought best to study first the rate of evaporation from 

 a water surface and the various factors which influence 

 it, and to use the water surface as a standard to which 

 all records pertaining to soil surfaces might be re- 

 ferred. Besides, in irrigation it is customary to flood 

 the surface or to hold the water for a time in checks 

 and basins and a knowledge of the rate of evaporation 

 from such surfaces was necessary in order to compute 

 the loss. The vessels used for this purpose were single 

 tank.* about thirty inches deep, and the amount which 

 evaporated each week was determined by a small hook 

 gage fastened to the edge of the tanks. The tempera- 

 ture of the water was observed and recorded whenever 

 an observation of the evaporation was made. 



The wide range of temperatures in California and 

 the corresponding effect on evaporation induced us to 

 ascertain, if possible, to what extent evaporation is in- 

 fluenced by temperature. Five tanks were placed in 

 an open field at Tulare, in the San Joaquin Valley, 

 last July, and filled with -water, with the idea of main- 

 taining in them temperatures ranging from fifty to 



ninety degrees Fahrenheit. By packing ice and saw- 

 dust around the cold tanks an average of 51.9 was 

 maintained for the first and 61.3 for the second. Oil 

 lamps were kept burning continually at the bottom of 

 each of the hot tanks and average temperatures of 

 80.4 and 88.7 respectively were maintained. The 

 results show that the evaporation from the surface of 

 the hot tanks was seven times as great as from the cold- 

 est tank. , 



Average Temp. Average Weekly Evap. 

 51.9 degrees. 7-12 inches" 



61.3 degrees. 1 1-6 inches. 

 76.8 normal. > 5-8 inches. 



80.4 degrees. 3 inches. 

 88.7 degrees. '4 inches. 



The range of temperature, between 50 and 90 F., 

 is well within practical limits. The temperature of irri- 

 gation water taken from streams of the Sierra is fre- 

 quently as low as 50, while that of the irrigation ditches 

 which furnish water to the cultivated portion of the 

 Imperial Valley in southeastern California has been 

 known to rise to 92. As regards the temperature of the 

 surface of irrigated soils, the range is much greater. 

 Last July the temperature of soil in the orange orchards 

 near Riverside reached 150 F. There is, therefore, in 

 the case of the soils of the citrus regions of California a 

 range of over 110. 



While experiments were being conducted to deter- 

 mine the effect of temperature on evaporation, an effort 

 was made to include the effect of the remaining factors, 

 such as wind, relative humidity. This preliminary work 

 pertaining to evaporation from a water surface is now 

 nearly completed and when the results are compiled they 

 will furnish a guide to the more difficult task of ascer- 

 taining the rate of evaporation from soils. 



EVAPORATION FROM SOIL SURFACES. 



Evaporation from soil surfaces has been determined 

 in connection with the work of growing crops of different 

 kinds in double water- jacketed tanks in the open field. 

 Oats, barley, wheat, alfalfa, corn, beans, sugar beats, 

 potatoes and peanuts have, been grown in this way by 

 using from, six to twelve tanks for each crop and varying 

 the- amounts of water applied to each. 



THE RATE OF EVAPORATION IS DIRECTLY PROPORTIONAL 



TO THE AMOUNT OF MOISTURE IN THE UPPER 



LAYER OF SOIL. 



The fact that a moist soil evaporates more than a 

 dry soil has been known for some time. The chemists 

 of several western experiment stations, in taking samples 

 of soil at different depths, both before and after irriga- 

 tion, have shown this to be the case. It is believed, 

 however, that our experiments carried on in California 

 were the first to demonstrate this fact by actual weigh- 

 ings of soils. 



On June 14, 1904, twelve galvanized iron tanks 

 were filled with soil of average quality and placed in an 

 open field on a level with the surface of the ground. The 

 soil at the start was fairly dry and contained less than 

 8 per cent by weight of moisture. The experiment was 

 carried op in duplicate. Two tanks received no water 

 and the remaining ten received quantities varying from 

 3.8 to 11.3 inches in depth over the surface. The water 

 was applied on the surface and the day following the 

 soil was finely pulverized to correspond to a soil mulch 

 made bythorough cultivation. From the tanks which re- 

 ceived no water an amount equal to one-half an inch in 



