THE IRRIGA Tl ON A Gt\ 133 



Washington, falling, so nauch of it, before the growing season, to en- 

 sure the maturity of such large crops under so clear a sky and in spite 

 of so long and continuous a period of drought, while iu western Kan- 

 sas 25 to 33 per cent more rainfall, well distributed through the grow- 

 ing season, produces less than one-half the yield per acre. The yield 

 is certainly less than one-half, besause the averages used for Kansas 

 are too large for the western section of the state, whose rainfall has 

 been brought into comparison. 



While we are a long way from possessing the needful data for the 

 solution of this problem, some of the factors are evident enough and 

 may be stated here. In ihe first place, the rains of the sections of 

 California and of Washington under consideration fall in the cooler 

 portion of the year, when the air is more nearly saturated and when 

 the wind velocities are small, while the sun is much of the time 

 obscured by clouds. All these conditions conspire to permit a large 

 per cent of the water which falls upon the ground to enter it deeply, 

 without being lost by evaporation, while a deep, retentive soil serves 

 to prevent loss by drainage. 



In western Kansas on the other hand, where the rain falls largely 

 in the form of showers in the heated sunny season of the year, and 

 where the wind velocities are high and the air extremely dry, it is 

 plain that a much larger per cent of water falling as rain must be at 

 once lost by evaporation from the surface of the soil, before it has 

 had an opportunity to enter it deeply enough to be retained by soil 

 mulche 5 . 



In the second place, a frequent surface wetting of the soil, such as 

 takes place in Kansas, tends strongly to hold the roots near the sur- 

 face, where with scanty mulches they are certain to suffer severely 

 whenever a period of 10 days without rain occurs; and if, under these 

 conditions, the plant is able to send new roots more deeply into the 

 soil, they can find there but a scanty supply of moisture, because there 

 have been no winter rains sufficient to produce percolation. Then, 

 again, after such a 10-day drought, with the surface roots now become 

 inactive through a dying off of the absorbing root-hairs, when the 

 next rain does fall, unless it is a very heavy one, the major part of it 

 will be lost by evaporation from the soil, in the case of crops like 

 wheat, oats, rye and barley, long before the plants are able to put 

 themselves in position to take full advantage of it. 



In California and eastern Washington, the case is radically differ- 

 ent. There the water gets well into the soil before the crop is put " 

 upon the ground. Moisture enough is present to produce germination, 

 and the roots develop first near the surface, when there is ample 

 moisture present; but later, under the rainless conditions, it is quite 

 likely that they advance more and more deeply into the ground as the 

 moisture in the upper layers of the soil becomes too scanty, and thus 

 day by day the effectiveness of the soil-mulch is increased, while the 



