IRRIGATION IN HUMID CUMATKS. 46 1 



subsequent to irrigation. The amount needed for a 

 single watering must be determined by the quantity 

 of water the soil contains at the time it is to be irri- 

 gated, and by the amount it should contain in order 

 that plants should work to the best advantage. The 

 maximum capacity of upland field soils for water 

 ranges from eighteen per cent, of their dry weight for 

 the light sandy types to about thirty per cent, for the 

 heavy clayey varieties, while the amounts of water 

 these soils should contain in order that plants may 

 thrive in them best is from twelve to fourteen per cent, 

 for the former and from eighteen to twenty per cent, 

 for the latter. Since water should be applied as soon 

 as the water content of the sandy soil falls to eight per 

 cent. , and that of the clayey soil to fourteen per cent. , 

 it follows that under these conditions 10.5 pounds of 

 water, or two inches, is the maximum amount which 

 would be needed to fill the surface foot of sandy soil, 

 and 12.8 pounds, or 2.46 inches, is enough to fill the 

 surface foot of clay soil. 



If w^e consider the second foot of soil to have been 

 dried out to a corresponding extent, and that it is de- 

 sirable to also saturate this with water, then the 

 amounts just stated would need to be doubled. In 

 humid irrigation not more than 800 to 1,500 barrels an 

 acre should be applied at one time, for if heavy rains 

 should follow the ground may be saturated. Even 

 with the most thorough cultivation, anywhere from a 

 half inch to two inches of water a week can be used to 

 advantage by vegetables during May, June, July and 

 August, and unless the natural supply available ap- 

 proximates this amount, it should be supplied arti- 



