49 



tijue, iiiul thus cfTect a sjiviii<; in lirsl cost over the gasoline plant. 

 The iivera«;;(' steam phiiit iiiuler the coiitlitioiis ohscrveil costs over four 

 times as much for fuel and atteiulance as the averao:e <]:asoline plant. 



In many cases the use of a reservoir holilin<i: from one to three clays' 

 supply of tlu> pump woukl greatly facilitate irri<jation. These res- 

 ervoirs may he constructed l)y thro\vin<; up earth embankments, the 

 inside slope of the end)ankment beinjj: 1 vertical to 2 or 8 liorizontal 

 and tlie outside slope 1 vertical to 1 \ or 2 horizontal, the top of the 

 bank being about 4 feet wide. The l)anks should be constructed 

 as far as possible of water-tight material, such as clay or ''puddle," 

 and should be carried down to a water-tight stratum by means of a 

 carefully tilled ditch, wiiicii will thoroughly bind the bank to the 

 original surface. If the material at hand will not hold water the 

 reservoir must ])e lineil. Concrete, asphalt, antl tar mixtures are used 

 for this purpose. Reservoir embankments, when suitable material 

 for construction is near at liand, should be built for 15 to 25 cents 

 ])er cubic A^ard in the East. To this must be added the cost of lining, 

 if necessary. Cement will ])robably cost 10 to 15 cents ])er scpuire 

 foot laid 4 inches thick, and tar mixtures will be much cheaper. 



RETURNS FROM IRRIGATION. 



In a humid country it is especially hard to get at the probable 

 returns from irrigation, owing to great variations in the distribution 

 of rainfall, the nature of the soil and the subsoil, antl to the effects 

 of severe rains. For example, in a dry j^ear unirrigated crops may 

 be a total failure and irrigated crops be as large as ever, while in a 

 wet year irrigation may prove a positive detriment. An estimate 

 of the real value of irrigation should show the average results obtained 

 during a period sufhciently long to give a fair average of climatic 

 conditions. Only the State experiment stations are in a ])osition 

 to, obtain reliable figures for long periods and to compare directl}' 

 the results of irrigated and unirrigated crops. There is at present 

 little reliable information on tliis question. Still the estimates of 

 various farmers as presented in this report may give a better under- 

 standing of the problem and present a fair idea of the benefits to l)e 

 obtained. 



The average yearly value of truck crops in nine cases was given as 

 SI, 030 per acre, of which value the irrigators estimated that S330 

 was due to irrigation, or an increase of 47 per cent. Other esti- 

 mates run usually 30 to 50 per cent. As the cost of irrigation usually 

 lies between $30 and SI 00 per acre, it is fair to assume an average 

 profit of S200 or more per acre due to irrigation. 



In order to form some idea of the probable benefit of irrigating 

 field crops, many farmers in Pennsylvania were asked the following 



