THE IRRIGATION AGR. 131 



acres which have been enumerated above. Now, were this supposi- 

 tion true, and all of these acres were brought together in one solid 

 square, it would have but 500 miles on a side. But to cover such an 

 area as this with '2 inches of water once in 10 days would require more 

 than three Nile rivers flowing at maximum flood a river 50 feet deep, 

 1,156 miles wide, running three miles an hour. 



Such statements as these must make it clear that to whatever ex- 

 tent irrigation may, in the future, be developed there must always 

 remain a many times greater extent of land whose moisture must be 

 conserved rather than supplemented and hence that methods of con- 

 serving soil moisture must always take rank of first importance among 

 agricultural operations. There is perhaps no country in the world 

 which can furnish more forceful illustrations of the extent to which 

 tillage may take the place of irrigation; of the effectiveness of soil 

 mulches in conserving moisture; and of the ability of vegetation to 

 spread its roots widely and deeply in a comparatively dry soil for its 

 water supply than portions of California and the state of Washington. 



Twenty years ago, when the soils of these states were more nearly 

 in their virgin condition than they are today, wheat was extensively 

 grown by ' 'dry farming" and good and even large, yields per acre 

 were realized and yet, in the San Joaquin valley, the mean annual 

 rainfall ranges from 5 inches in the far south to 12 inches in the north, 

 and this amount all falling between Nov. 1 arid May 1. In 1879 the 

 average yield of wheat per acre was 6 to 13 bushels in the south and 

 from 13 to '20 bushels in the north; the average for over 1,800,000 acres 

 being 16.1 bushels. To one accustomed to the disastrous results which 

 follow droughts of two or three weeks in humid climates it is hard to 

 realize how it is possible for a wheat crop to be carried from the first 

 of May to full maturity without a drop of rain and without irrigation; 

 and yet in the last of July, 1895, as we traveled southward and ap- 

 proached Merced from the north a very sandy belt was passed which 

 was white and glistening in the sun, and which drifted as badly as 

 much of apparently similar land in Wisconsin, and yet on these coarse 

 sands wheat was being harvested which would give larger yields than 

 would be expected on such lands in Wisconsin with a summer rainfall 

 of not less than ten inches. But here the crop had stood and matured 

 from early May until the end of July without irrigation and without 

 rain. 



If we consider the "dry farming" sections of the state of Wash- 

 ington, where most of the wheat grown has been the spring varieties, 

 sown in April, and sometimes as late as May, and harvested in August 

 or early in September, we shall have the growing season more nearly 

 the same as that in the corresponding latitudes of the humid parts of 

 the United States. Here, too, the rainfall in amount is very nearly 

 the same as that of the district to the south for the corresponding 

 period of time, but the rains begin a month earlier and continue a 



