6 FUNDAMENTALS OF FRUIT PRODUCTION 



30 to 70 units of water needed for the production of one unit of dry matter 

 in spruce, fir and pine trees. Thus the range in water requirement for at 

 least some of the ordinary deciduous trees is similar to that of herbaceous 

 crops grown under similar conditions. 



Two striking points are shown by these figures on water requirements : 

 (1) the great differences in the water requirements of different species 

 and (2) the variation shown by the same plant in different sections, 

 according to the determinations of different investigators. 



These differences carry two suggestions of practical import in fruit 

 production; first, that certain species or certain fruits can do more than 

 others with a given amount of water, second, that the same species of 

 fruit plant will produce more vegetative growth with a given supply of 

 water under certain conditions than under others. 



The Water Requirements of Plants in Terms of Precipitation. — 

 Figures have been given showing the approximate water requirements 

 of plants in terms of the number of units of water used while one unit of 

 dry matter is produced. It is interesting to speculate as to what these 

 figures mean in terms of rainfall or amounts of irrigation water. 



Amounts Used by the Plants Themselves. — Thompson ^^^ has calcu- 

 lated the average weight of wood, roots and leaves produced by a normal 

 healthy peach tree up to the time it has attained the age of 9 years as 

 approximately 215 pounds. This represents an average annual dry 

 weight production of wood, leaves and roots of approximately ^5 pounds. 

 With increasing age the amount would be somewhat greater. If a 300 

 bushel per acre yield is assumed, it means the production of approximately 

 20 pounds of dry matter per tree to be taken away in the form of fruit. 

 In other words, the mature peach tree would be expected to produce 

 about 45 pounds of dry matter per year. Assuming a stand of 100 trees 

 to the acre this would mean a production of 4,500 pounds of dry matter 

 per acre. If it takes 500 parts of water to produce one part of dry 

 weight, it would require 22,500 pounds, over 11 tons or nearly 3,000 gallons 

 per tree to mature the crop properly. This estimate considers only the 

 amount actually taken up by the roots and for the most part transpired 

 through the leaves and does not make any allowance for run-off from the 

 surface, or for seepage and evaporation.' It means 300,000 gallons per 

 acre equivalent to a rainfall of approximately 11 inches, or an equivalent 

 amount of irrigation water. For each additional 100 bushels of fruit 

 per acre approximately 2 acre-inches more would be required b}^ the 

 plant. Looking at the matter from another angle, for every acre- 

 inch under the 11 that is denied the trees, there would be a decrease in 

 yield of approximately 50 bushels. Of course, if the water requirement of 

 this fruit is only 300 instead of 500 under a given set of conditions, 7 acre- 

 inches actually available to the trees would mature as large a crop as 

 the 11 acre-inches in the first instance. 



