Fertilizing and Watering Trees 



change it into a form that can be used by plants. In addition, 

 some atmospheric nitrogen is added to the soil during 

 electrical rainstorms. Most soil nitrogen available to trees, 

 however, is derived from decomposed plant material 

 returned to the soil. Microorganisms in the soil must break 

 down this complex plant material into simple inorganic 

 compounds before the nitrogen can be used by trees. 



Nitrogen in plants occurs in proteins, which are the primary 

 components of protoplasm, the living material in plant cells. 

 Nitrogen is a component of chlorophyll pigments and 

 therefore is important in the production of food in plant 

 leaves by photosynthesis. Nitrogen is also found in some 

 plant vitamins and enzymes and is consequently essential in 

 metabolism. 



An abundance of available nitrogen in the soil promotes 

 plant growth, particularly of the above-ground portions as 

 compared with the roots. When nitrogen is deficient, stunted 

 top growth, pale green to yellow foliage, and the yellowing 

 or drying of older leaves are common, especially during 

 drought. 



Materials commonly used to supplement nitrogen in the soil 

 are ammonium nitrate, ammonium sulfate, and urea. These 

 materials are readily soluble in water. When they are applied 

 to the soil surface and followed by adequate rainfall or 

 supplemental watering, nitrogen is carried down into the 

 soil and made available to roots. Since nitrogen is also carried 

 away by water, nitrogen must be added to the soil at regular 

 intervals to maintain an ample supply. 



Phosphorus 



Most phosphorus in soil came from the rock material f rom 

 which the soil was derived. This form of phosphorus is 

 abundant but not readily available to plants. Soils with the 

 greatest amount of readily available phosphorus contain 

 abundant organic matter and a high perc entage of clay. Most 

 soils have sufficient phosphorus for adequate plant growth. 



