THE ART OF IRRIGATION. 



CHAPTER XIX. THE AMOUNT OF WATER REQUIRED. 



(Continued) 



BY T. S. VAN DYKE. 



A patient audience is often a great 

 "^ curse to a speaker for the art of talk- 

 ing without getting anywhere is rapidly 

 cultivated. It is much the same with a 

 writer and this is the hardest of all the 

 hard subjects I ever undertook to explain. 

 It is quite easy to say how much water 

 is -not required, but to say how much is 

 required is quite another thing. 



Suppose the irrigator orders thirty 

 inches, two day's run, six times a year. 

 These order make three hundred and 

 sixty tw T enty-four-hour inches, or practi- 

 cally an inch for a year. This would 

 cover ten acres about a foot and a half 

 deep; making one and a half acre feet, 

 or eighteen acre inches. Suppose we 

 allow the great amount of twenty per 

 cent for waste and a little for error, we 

 then have about fourteen inches going 

 into the ground. This will be fully 

 equal to twenty-eight inches of rain as 

 it generally falls in the growing season. 

 Much of it then comes in heavy dashes 

 with a high percentage of run off and 

 considerable in light showers followed at 

 once by warm, bright sun. An inch of 

 rain will wet ground in good condition 

 about ten inches. As many rains do not 

 exceed an inch a considerable portion of 

 such is lost by evaporation and none of 

 it reaches most of the roots of trees 

 unless quickly followed by more. 



The question then is how much of a 

 crop will twenty-eight inches of rain 

 produce? 



Here we are met with many questions, 

 but two are enough. What kind of 

 crops do you mean and how large a crop 

 do you want? Do you call four, six or 

 eight tons of alfalfa a crop? Then the 

 question comes how much of that suc- 

 cess is due to something beside water? 

 For.it is certain that for very large crops 

 of anything several things beside water 

 are needed. And so we are all at sea 

 again. 



It is certain that government reports 

 and many private reports are sadly astray 

 about the quantity of water required to 

 produce a good crop. Twenty-four inches 



is about the figure reached by govern- 

 ment experts, agricultural colleges and 

 other observers, but most all the data 

 come from rainy countries and too much 

 reliance on general averages seems un- 

 avoidable. The following statements 

 will therefore seem a trifle strong even 

 to those used to California statements, in 

 which we rarely bother ourselves about 

 a cipher or two, provided always they are 

 duly kept to the left of the decimal point. 

 But as there is no state where so many 

 rain records are kept over such small 

 areas and people are so interested in 

 the amount that falls California affords 

 the best field for study of this subject. 

 These statements are true, not for a few 

 places but for thousands, and can be ver- 

 ified in every county south of Tehachipi. 



GOOD CHOP WITH LITTLE WATER. 



Time and again eighteen bushels of 

 wheat and thirty bushels of barley to the 

 acre have been grown on a rainfall of 

 twelve inches. In 1893 a piece of eight 

 acres in San Marcos, San Diego county, 

 yielded sixty bushels of barley on a rain- 

 fall of thirteen and a half inches and 

 the next year, a very dry one with dis- 

 tribution anything but good, the same 

 eight acres yielded fifteen bushels of 

 wheat to the acre. These figures are from 

 the books of the threshing machine and 

 show the number of bushels for which 

 the machine received pay. Taking the 

 weight of the crop and straw this gives 

 about four times the yield generally esti- 

 mated as possible for that amount of 

 water. Yet the rain was all the wetting 

 it ever received. 



Two tons of hay to the acre made of 

 wheat or barley cut in the milk, the best 

 hay in the world where it can be cured 

 in dry air without any danger of rain, 

 are the commonest kind of a crop on 

 this rainfall and if the ground has been 

 summer fallowed the preceding year so 

 as to hold the moisture of that winter 

 and catch the first rains of the year it is 

 planted, on a face well open to receive 



