10 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 52 



area in square feet is determined by multiplying the length times 

 the width. 



Nitrogen is the nutrient 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 

 actual nitrogen per 1,000 square feet of area. 



The amounts of phosphorus and potassium in soils vary 

 greatly, and in some areas it may not be necessary to add either 

 to the soil. In others an occasional application may be necessary 

 to provide an optimum supply. Applications of phosphorus and 

 potassium are of little or no benefit if sufficient quantities are 

 already present. The need for phosphorus and potassium and 

 frequency of application should be determined by chemical tests 

 of «oil taken from the area to be fertilized. 



To prevent the soil from becoming deficient in phosphorus 

 or potassium following annual nitrogen applications, it is desira- 

 ble to add these nutrients (at intervals of 3-5 years) at these 

 rates: phosphorus at 3.6 pounds of phosphoric acid (P-O.-,) per 

 1,000 square feet and potassium at 6 pounds of potash (K-O) 

 per 1,000 square feet. 



HOW SHOULD YOU FERTILIZE? 



Three successfully used methods of fertilization are surface 

 application, placement of dry fertilizers in holes in the soil, and 

 injection of liquid fertilizers into the soil. Only fertilizer sources 

 that contain nitrogen alone should be surface applied. 



Surface application 



Nitrogen fertilizers applied to the soil surface are just as 

 effective as or more effective than nitrogen fertilizers applied 

 by any other method. With rainfall or supplemental watering, 

 inorganic nitrogen fertilizers will move readily down into the 

 soil. These fertilizers are uniformly distributed over the root 

 area by using one of two types of spreaders used to fertilize 

 lawns (Fig. 5). This is the easiest, simplest, and most economical 

 means of applying fertilizers containing only nitrogen. 



Fertilizer should be applied when grass blades are dry. 

 After the fertilizer has been distributed, it should be washed off 

 the grass blades immediately using a lawn sprinkler or a spray 

 nozzle on a hose. Fertilizer remaining on grass blades that be- 

 come wet following a light rain or dew formation occasionally 

 causes burning. 



