Fertilizing and Watering Trees 13 



Rate of application 



Nitrogen is the mitiieiit most often lacking in the soil and, 

 therefore, the first to limit plant growth. Nitrogen fertilizers 

 can safely be added to the soil annually at the rate of 6 

 pounds of nitrogen per 1 ,000 square feet of area. 



The amounts of phosphorus and potassium in soils vary 

 greatly. In some areas additions of either are unnecessary; 

 in others, an occasional application may be required to 

 provide optimum supplies. Applications of phosphorus and 

 potassium are of little or no benefit when sufficient quantities 

 are already present. The need for phosphorus and potassium 

 and the frequency of application should be determined by 

 chemical tests of soil. Contact your cooperative extension 

 agent for the locations of experiment station or private 

 soil-testing laboratories. 



To prevent the soil from becoming deficient in phosphorus 

 or potassium following increased tree growth from annual 

 nitrogen applications, add these nutrients at intervals of 3— 5 

 years and at these rates: phosphorus at 3.6 pounds 

 of phosphoric acid (P2O5) per 1 ,000 square feet and 

 potassium at 6 pounds of potash (KyO) per 1,000 square feet. 



How should you fertilize? 



Three successful methods of fertilization are surface 

 application, the placement of dry fei tilizers in holes in the 

 soil, and the injection of liquid fertilizers into the soil. 



Surface application 



Nitrogen fertilizers applied directly to the soil surface are as 

 effective as or more effective than nitrogen fertilizers 

 applied by other methods. With rainfall or supplemental 

 watering, inorganic nitrogen fertilizers readily move down 

 into the soil. These fertilizers can be uniformly distributed 

 over the root area with one of two types of spreaders used 

 to fertilize lawns (Figure 5). Lawn spreaders are the easiest, 

 simplest, and most economical means of applying fertilizers 

 containing only nitrogen. 



