THE FUNCTION OF WATER IN AGRICULTURE 247 



sun and its distribution, and the periods of low tem- 

 perature and their distribution. Thus the bumper crop 

 of wheat which we are now harvesting is due chiefly to 

 seasonal influences over which the fanner has no con- 

 trol. Among these the water factor plays a dominant 

 part. Water, therefore, is charged with a great agri- 

 cultural duty. The failure of the water to perform its 

 normal functions, either through a deficiency or an ex- 

 cess of supply, affects most profoundly the total yield. 

 Thus among the factors of environment the most im- 

 portant to be considered is water itself. 



Dr. McGee, shortly before his untimely death, pub- 

 lished a most interesting article, in which he developed 

 along many lines this idea of the agricultural duty of 

 water. From Dr. McGee's paper we learn the per- 

 centages of water in various types of soil which are 

 most favorable to crop production. The optimum of 

 moisture ranges from 4 to 45 per cent., and in some 

 vegetable soils the optimum percentage of moisture is 

 even higher. If the depth of the soil under cultivation 

 is represented by a foot, the quantity of water per acre 

 to this depth should average about 2,000 tons. The 

 average quantity of water required per acre for the pro- 

 duction of a good crop is about 6,000 tons per year. 



In general it may be said that under favorable con- 

 ditions of the natural distribution of water, the weight 

 of crop produced is about one one-thousandth of the 

 amount of water used in its production. In other 

 words, a pound of wheat and straw in natural propor- 

 tions requires about one thousand pounds of water for 

 its production. On the other hand, including the soil to 

 a depth of one foot, under favorable conditions of mois- 

 ture and other elements of the environment, a pound of 

 soil produces about 1/333 of its weight of a crop. In 



