THE ART OF IRRIGATION. 



CHAPTER XV. IRRIGATING ONLY A PART OF THE GROUND. 



THE PROPER USE OF BASINS. 



BY T. S. VAN DYKE. 



WHEEE the supply is sufficient the 

 whole ground should generally be 

 wet at each application of the water. 

 Especially is this the case in the arid 

 countries, and the shorter the rainfall the 

 greater the necessity for all valuable 

 crops. But in sections generally having 

 enough rain in the growing season, and 

 only occasionally short or not coming at just 

 the right time, such full irrigation is 

 not always necessary and in many cases 

 would be needlessly expensive. The 

 same is the case with many regions where 

 the ground is thoroughly soaked with rain 

 in winter and the subsoil is porous yet so 

 retentive of moisture that it holds almost 

 enough to carry vegetation through and it 

 only needs a little helping out. The 

 former is the case ia most of the country 

 east of the Rocky Mountain slopes and 

 the latter on the greater part of the Pa- 

 cific slope. 



In such cases the principal suffering of 

 plants is for water to transpire or evapo- 

 rate through the leaves, most of the ground 

 being still moist enough to allow the roots 

 to feed. But laboring vegetation must 

 evaporate water from its lungs and skin 

 the same as a laboring man or it cannot do 

 full work, and a crop of high grade prod- 

 uce like fruit may be sadly shortened by 

 the failure to supply water at the right 

 time. But to supply it, it may not be nec- 

 essary to wet the whole ground. 



LIMITED WA.TER SUPPLY. 



Limited irrigation is often required by 

 the nature of the water supply. Perhaps 

 you can get it only in a small stream flow- 

 ing continuously or nearly so and you find 

 a reservoir to store it long enough to give 

 a good irrigating head more costly than 

 your work will justify. This will often be 

 the case where you are dependent on a 

 small spring or a windmill, horse-power 

 or other means of lifting water from a 



well that is fed only by slow seepage 

 and becomes quickly exhausted under a 

 heavy and continuous draft, as is the case 

 with most farm wells. And even under a 

 ditch there may be so many critical times 

 when you cannot get head enough, or for 

 a long enough time, that you may be com- 

 pelled to water only a portion of the 

 ground. 



The objections to this method have been 

 sufficiently detailed in the history of the 

 errors of early irrigators in Chapter IV. of 

 this work. But it is objectionable only 

 when one can just as well do something 

 better. Where it is the best that can be 

 done it generally surpasses no irrigation 

 so far that it is highly respectable. It is 

 available only in those places where con- 

 siderable can be grown without any irri- 

 gation. On pure desert it will rarely do 

 and can never be relied on for anything of 

 much value where the ground, including 

 subsoil, does not in some way get a 

 thorough soaking at least once a year. 

 Otherwise the dry ground around the lim- 

 ited basins or furrows saps the moisture 

 from the watered portion so fast that un- 

 less irrigated every few days the ground 

 around the roots cannot be kept in the 

 proper state of moisture. And at any 

 time a little forgetful ness or lack of care 

 is liable to do damage that cannot be re 

 paired that season. As a rule it should 

 not be used for trees or vines carrying 

 crops of value unless they will live in that 

 place by cultivation alone without any 

 irrigation. If demanded for the life of 

 the tree, basins are generally too unsafe a 

 way of supplying water. 



GOOD JUDGMENT NEEDED. 



The first thing to be done by one who 

 finds he cannot irrigate the whole ground 

 is to learn what kinds of vegetation re- 

 quire the mofet water and what the least, 

 with the intermediate classes, and also 



