No. 4.] IRRIGATION. 401 



irrigated area, with only three applications of water, gave a 

 yield two and two-thirds times greater than that obtained 

 on the area which could not be irrigated. As a more recent 

 illustration, which nearly every farmer will recall, we would 

 point to the light hay crop occasioned by the spring and 

 early summer drought of 1800, and again in 1000. In con- 

 trast to this, we can note the large hay crop of the present 

 season (1001), occasioned mainly by the heavy rainfall of 

 Maj r and the early part of June. 



In reference to the second reason why irrigation is val- 

 uable, it may be well to point out, first, that all growing 

 plants are made up largely of water. Green grass or clover 

 contains from 80 to 00 per cent of water. Many of our 

 common fruits, such as strawberries, raspberries, peaches 

 and pears, contain from 80 to 02 per cent of water. The 

 importance of this to the farmer is seen in the fact that 

 when he sells such crops he is mainly disposing of water and 

 a small amount of mineral salts. As one prominent fruit 

 grower puts it, he sells in his fruit many barrels of water 

 with a little flavoring extract in it. The water held in the 

 tissues of the plant, however, represents but a small part of 

 the total amount needed by the plant ; a very large amount 

 is evaporated or transpired through the foliage during the 

 period of growth. 



It has been estimated that a crop of hay at 2 tons per 

 acre, or about G 1 /^ tons of fresh grass, will evaporate during 

 its season of growth about 525 tons of water ; that an 

 average crop of wheat, of 720 pounds of grain and 1,500 

 pounds of straw to the acre, will evaporate about 260 tons 

 of water ; or, in other words, according to these estimates, 

 every ton of green grass evaporates through its foliage 

 during the period of growth about 81 tons of water, and in 

 drying this ton of grass loses about two-thirds of its weight, 

 so that one-third of a ton of hay (667 pounds) utilizes in 

 its growth about 81 tons of water. An inch of rainfall is 

 equal to 113 tons of water per acre. The above figures 

 indicate that the water evaporated by an acre of grass 

 (6!/2 tons) would equal about 4.6 inches. In some cases 

 this amount of water is more than the total rainfall during 



