MUST BE MOISTURE ENOUGH 69 



rains or the use of cold or warm irrigation water, at a critical period, may 

 largely determine the success or failure of a crop. 



It is therefore often essential that cold water from a well or 

 stream often needs exposure to the sun in a reservoir, or by run- 

 ning a distance in a shallow ditch or furrow, before reaching the 

 roots of the plant. No temperature gained by such exposure need 

 be considered too high. 



This fact, however, has sometimes induced too great expecta- 

 tions from the use of hot water from springs or wells for forcing 

 early vegetables. Warm air is essential to free aerial growth of the 

 plant. 



HOW MUCH IRRIGATION IS NEEDED? 



It is impossible to answer this question exactly for any crop, 

 but it can be approximated more nearly for an orchard or vineyard 

 or a field crop than for a garden which should be held up to its 

 maximum of free water nearly all the time. Evidently the require- 

 ment for gardening is greater than for any other cropping. How 

 much water will be required to hold any piece of land up to its best 

 estate of moisture, depends upon the plant grown, the soil and sub- 

 soil, the slope and exposure, the local heat and dryness of the air, 

 the rainfall, etc. The quantity can, then, only be determined for 

 each piece of ground with the data of its conditions and environ- 

 ment, and the observing man will allow the plants to tell him by their 

 vigor and speed of growth how the supply suits them. 



It is possible to tell how much water will bring a certain depth 

 of soil into the best condition for growth and working. With this 

 knowledge the gardener can more rationally follow the results of 

 his observation of the plants themselves. The following are the 

 conclusions of the late Professor F. H. King from very careful in- 

 vestigation and experiment: 



The maximum capacity of upland field soils for water ranges from about 

 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. The growth of plants will be seriously checked in 

 sandy soils when the water content falls below eight per cent, and in heavy, 

 clayey types when it falls below fourteen per cent of the dry weight of the 

 soil. 



The dry weight of a light sandy soil and subsoil will average about one 

 hundred and five pounds per cubic foot, and the heavy clayey type about 



