WARM WATER DESIRABLE 57 



Fall and winter irrigation are very important in gardening in 

 regions of uncertain rainfall because they bring the soil into condi- 

 tion for the early planting which is often the secret of satisfaction 

 and success. In southern California and the interior of the central 

 regions of the state as well, he who waits for rainfall to start his 

 gardening often loses half the season's producing capacity. In 

 parts of the state the rain at its maximum is seldom excessive, con- 

 sequently one incurs no danger, but invites every benefit by wetting 

 the soil well and going to work at least with the hardier vegetables 

 while the autumn sunshine still imparts warmth to the soil. 



The use of winter storm water often results in a considerable 

 contribution to the fertility of the soil in the form of silt and other 

 materials rich in plant food. 



TEMPERATURE OF IRRIGATION WATER. 



It is a fact of common observation that a considerable amount 

 of water either from cold rains or from cold irrigation water may 

 cause a "shock" to a growing plant and interfere with its normal 

 development. This fact is accounted for by Professor Hilgard in 

 this 'way : 



Since the capacity of water for heat is approximately five times greater 

 than that of the average soil, equal weights being considered, it follows that 

 the temperature of the soil water must exert a controlling influence over that 

 of the soil. It is not surprising, then, that the occurrence of cold or warm 

 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- 



