92 MISC. PUBLICATION 4 3 4, IT. S. DEPARTMENT OF AGRICULTURE 



minimum quantity needed to keep the trees from actual drought 

 injury. 



In soils having a retentive subsoil, the amount of water lost by 

 under drainage is small, and the effects of a fairly heavy irrigation may 

 persist for as long as 2 to 4 weeks before additional water is necessary. 

 Care should be taken, especially in midsummer and with fairly large 

 nursery stock, to add enough water in any one irrigation so that the 

 soil is well moistened to a depth of 2 feet. Two or three inches of 

 water, depending somewhat on the relative dryness of the soil just 

 previous to irrigation, may safely be applied on a medium-textured 

 soil with a retentive subsoil. Watering should then be dispensed with 

 until the trees show signs of needing more water. This procedure will 

 force maximum root development and prevent the formation of a 

 top-heavy plant. 



In sandy soils with a somewhat porous subsoil of fine sand, more 

 frequent irrigation will be necessary and the quantity of water for 

 one irrigation should be reduced to 1 to 2 inches. Amounts in excess 

 of this will be lost through underdrainage. 



The volume of water applied in any one irrigation will also depend 

 somewhat on the time of year and the size of the trees. Smaller 

 quantities will suffice and more frequent irrigations are needed on 

 small trees that are just past the germination stage; at this time the 

 seedlings have not developed the spread or depth of root system 

 which they will attain by midsummer, nor is their water demand so 

 great. 



The method of distributing the water — whether by furrows or 

 overhead system — will also influence the amount of water applied. 

 Since furrow irrigation does not distribute the water as evenly as an 

 overhead system, more water must necessarily be applied by the former 

 method. If the trees at the far end of a furrow are to be watered 

 adequately, the water used invariably soaks up the end of the tree 

 row nearest the lateral ditch more than is absolutely necessary, and 

 some wastage thus occurs because of underdrainage. 



With ditch irrigation, fairly close control can be maintained over 

 the amount of water to be applied by varying the head or volume 

 going down the individual furrows. If a small quantity is desired, a 

 large head should be used for a short time, since the water will then 

 proceed rapidly down the furrows, thus limiting the time permitted 

 for infiltration. If a thorough irrigation is desired, a small head of 

 water should be run down the furrows over a considerably longer 

 period. 



Hardening Off 



Hardening off the seedlings is a process largely controlled by 

 weather conditions. A long cool fall season with an average amount 

 of rainfall and number of frosts, the latter gradually increasing in 

 intensity, represents the natural and therefore the ideal method of 

 hardening off the seedling crop. Since he cannot depend upon such 

 conditions, the nurseryman should strive to have his seedlings in 

 condition to withstand the other extreme of abnormal rainfall and 

 warm weather, followed by a sudden, killing frost. In the plains 

 region such fall weather conditions are not uncommon. 



When fall rains are not too heavy, moisture control, in the form of 

 holding off all irrigation and ceasing cultivation, is the common, 



