MANURES IN IRRIGATION WATER -^5 



as deeply as can be done without injury to the roots of trees and 

 vines, and then, if the surface is kept cultivated, it will lie in moist 

 strata and decompose, or be siezed by the searching rootlets. On 

 the other hand, superphosphate, or other really soluble chemical 

 fertilizers, will produce immediate results, and can be most eco- 

 nomically used on light and easily permeable soils, on which falling 

 water sinks and does not flow over the surface. In leachy soils 

 a part of such fertilizers might be carried down beyond the reach 

 of shallow-rooting plants, but there is little danger of this in the 

 case of trees and vines. 



When superphosphate is used on irrigated ground, it is some- 

 times drilled in to prevent its being carried along with the running 

 water. One way is to run a chisel-tooth cultivator ahead of the 

 grain-seed drill and to distribute and drill in the fertilizer as deep 

 as feasible to do without injuring the roots. Spring application of 

 fertilizers are conveniently made by spreading upon the vegetation 

 which is plowed under at that season. 



Manures with Irrigation Water. Distribution of fertilizers by 

 using the flow of irrigation water is described by A. S. Chapman, 

 as follows : 



We shovel sheep manure into the irrigating ditches, allowing each tree to 

 receive about twenty-five pounds at each separate irrigation. Our basins 

 cover the entire surface of the ground. We make no effort to choke such 

 weeds as clover, alfilerilla, and the like; but the irrigator with his hoe de- 

 stroys the obnoxious nightshade, hoarhound, and nettle. 



In the fall of the year we follow with copious liming about three barrels 

 of unslacked lime to the acre applied in the following manner at the head 

 of our irrigating ditch : We plant a box about three feet wide, six feet long, 

 two feet deep, and six inches under the surface of the running water. In it 

 we place a barrel of the lime. It slacks and swells to twice its original bulk. 

 A man stands on this with his hoe and sees that the water carries it off 

 evenly. With an irrigating head such as we use, a man will run into the 

 ditch four barrels a day, or about three barrels to the acre. We have a con- 

 siderable fall, and the water runs very rapidly; but it takes up all the lime, 

 and the water runs white, like milk. 



We now leave the orange orchard till spring, when we plow under weeds, 

 manure and lime. We thus aim to supply our soil with nitrate of lime, 

 potash, and magnesia. Carbonic acid gas is absorbed by the water and 

 attacks the inert plant food in the soil; hard-pan is prevented both by the 

 mechanical effects of the vegetable matter and the lime. 



The basin method of irrigation, to which allusion is made, will 

 be more fully described in the following chapter. 



FERTILIZING MATTERS IN IRRIGATION WATER 



Water used for irrigation may carry in solution injurious sub- 

 stances, as, for example, alkali, as will be noted in the following 

 chapter; or it may carry very valuable fertilizing properties. 

 These facts can only be determined by analysis. Professor Hilgard 

 has found that the water of one creek in Alameda County carries 

 to the land it irrigates about half a grain of potash in each gallon, 



