FERTILIZING AND WATERING TREES 13 



with an auger attached to an electric drill (Fig. 6). Holes may be 

 drilled if the soil is dry and punched if it is wet. Holes should 

 be 12-15 inches deep. They are placed at 2-foot intervals in a 

 series of parallel lines 2 feet apart throughout the area to be 

 fertilized (Fig. 7). Holes should not be made within 2V& feet of 

 the tree trunk. Approximately 250 holes should be made in each 

 1,000 square feet of area to be fertilized. 



If holes are properly spaced, the following quantities of fer- 

 tilizer 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 



(N, P, and K) 



10-10-10 V 2 cup 



12-12-12 slightly less than 



V2 cup 



Preparing holes for this method of application requires con- 

 siderable labor. The method is therefore time consuming and 

 expensive if the proper number of holes is made and filled with 

 fertilizer. Placing holes in a circle around the drip line of a tree 

 is unsatisfactory because there is inadequate distribution of fer- 

 tilizer. Also, root injury may occur if too much fertilizer is 

 placed in too few holes. 



Injection of liquid fertilizers 



A second method of placing phosphorus and potassium fer- 

 tilizers in the soil is injecting solutions into the soil with a 

 hydraulic pump and a soil needle (Fig. 8). Expensive equipment 

 is required for this method of fertilizing. A second requirement 

 is that fertilizer materials be completely soluble in water. Water- 

 soluble fertilizers containing both phosphorus and potassium are 

 much more expensive per pound of nutrient than are the 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. 



The readily available commercial water-soluble fertilizers 



