CARTER: ILLINOIS TREES: THEIR DISEASES 29 



blood, pulverized sheep manure. Phosphorus can be furnished as 

 superphosphate and potassium as muriate of potash. Although 

 an effective tree food can be prepared from inorganic materials 

 alone, more lasting effects are obtained when one-third to one- 

 half of the nitrogen is supplied by organic materials. 



There is no established rule as to the amounts of nitrogen, 

 phosphorus, and potassium a tree food must contain. In fertilizer 

 formulas, nitrogen is expressed as nitrogen (N), phosphorus as 

 "phosphoric acid" (P.0-), and potassium as potassium oxide or 

 potash (K2O). Prepared tree foods, some designed for dry feed- 

 ing and some for liquid feeding, can be purchased ready for use 

 through local dealers in fertilizers. 



Tree foods designed for dry feeding commonly contain avail- 

 able N, P,0.-i, and K,0 in proportions of 12-6-4, 10-8-6, 10-6-4, 

 10-3-3, or 8-5-3. A 10-8-6 fertilizer is 10 per cent available N, 

 8 per cent available P0O5, and 6 per cent available K.^O. 



Some of the tree foods designed for liciuid feeding contain 

 N, PjOo, and KjO in proportions similar to those of dry foods. 

 Others have these constituents in proportions of 23-21-17, 21-18- 

 17, 20-20-20, 19-28-14, and 15-15-15. 



A common method of determining the amount of tree food 

 needed for a specimen tree is based on the amount of nitrogen 

 required to maintain uniform growth of the tree. To calculate 

 the amount of a 10-8-6 formula tree food required to give 6 

 pounds of nitrogen, divide 6 by 0.10 (10 per cent available nitro- 

 gen). The amount needed is 60 pounds. A few examples of the 

 amounts of tree food needed by trees of different kinds and sizes 

 are given in the sections "Feeding Rates for Deciduous Trees" 

 and "Feeding Rates for Evergreens."' 



Tree feeding can be done at any time of year, but feeding 

 during April, May, October, or November, when the soil contains 

 ample moisture, is especially beneficial. Tree foods are not avail- 

 able except when in water solution ; hence, it is highly desirable 

 that, at the time of application of tree food in dry form, suf- 

 ficient water should be present in the soil to dissolve the food. 



To be effective, tree food must be placed where it is readily 

 available to the roots, as described in the sections "Dry Feeding" 

 and "Liquid Feeding." 



When the feeding of trees is repeated over a period of years, 

 the amounts of phosphorus and potassium should be reduced, 

 because these two materials do not leach from the soil. Nitrogen 

 is readily soluble in water, and any that is not quickly utilized 



