16 Illinois Natural History Survey Circular 56 



Holes should be 12-15 inches deep and placed at 2-fbot 

 intervals in a series of parallel lines 2 feet apart throughout 

 the area to be fertilized (Figure 7). Holes should not be made 

 within 2 'A' feet of the tree trunk. Approximately 250 holes 

 are required in each 1 ,000 square feet of area to be fertilized. 



If holes are properly spaced, the following quantities of 

 fertilizers by source materials should be placed in each hole 

 (select one P and one K source or an NPK source): 



Material Amount per hole 



Phosphorus (P) 



Superphosphate 0-20-0 2 level tablespoons 



Double superphosphate 0-40-0 1 level tablespoon 



Potassium (K) 



Muriate of potash 0-0-60 1 level tablespoon 



Nitrogen, phosphorus, and 



potassium (NPK) 



10-10-10 1/2 cup 



12-12-12 slightly less than 



'/> cup 



Preparing and filling holes is time consuming and labor 

 intensive, but merely drilling holes in a circle around the 

 drip line of a tree is unsatisfactory because the fertilizer is 

 inadequately distributed. In addition, root injury may occur 

 if too much fertilizer is placed in too few holes. 



Injection of liquid fertilizers 



Nitrogen, phosphorus, and potassium fertilizers in solution 

 may also be injected into the soil with a hydraulic pump and 

 a soil needle (Figure 8). Relatively expensive equipment is 

 required for this method of fertilizing, and fertilizer 

 materials must be completely soluble in water. Water-soluble 

 fertilizers containing both phosphorus and potassium are 

 much more expensive per pound of nutrient than are farm 

 and lawn fertilizers not soluble in water. Potassium chloride 

 and potassium nitrate are water-soluble sources of potassium. 

 Ammonium phosphate and potassium phosphate are 

 water-soluble sources of phosphorus. These materials can 

 be purchased from chemical supply stores. 



