54 VERMONT AGRICULTURAL REPORT. 



FUNCTIONS OF NITROGEN. 



Each element used by plant life helps in the building of certain parts 

 of the plant and likewise, doubtless, each has some one or more special 

 functions. What some of these are is not well understood, but some 

 are known. 



Nitrogen is known to show its effects on plant life in three ways: 



1. It promotes stem and leaf growth, and, if in excess, delays seed 

 and fruit formation. 



2. It deepens the green coloration of the leaves. 



3. Its abundance may increase and its deficiency may lessen the 

 relative amount of nitrogen in the plant. This means variation in food 

 value. 



If nitrogen is freely applied in fertilizers or is present in plentiful 

 quantities in the soil, its effect is generally shown by a vigorous, dark 

 green leaf growth and by a somewhat retarded flower and seed forma- 

 tion. If available nitrogen is relatively lacking either in the soil or in 

 the added fertilizer, a somewhat more scanty foliage than occurs under 

 better conditions, one of a rather lighter green, is grown. The seed, 

 moreover, is apt to mature rather earlier than usual. One may by 

 careful observation judge somewhat as to the crop needs in this man- 

 ner. It should be remembered in this connection that nitrogen is 

 essential to plant growth, that available nitrogen is in small quantity 

 and easily exhausted from soils, and that consequently it is and always 

 has been the most costly form of plant food. (See article on farm 

 manure in this volume in this connection.) 



PHOSPHORIC ACID. 



Phosphoric acid is a combination of phosphorus and oxygen, the one, 

 a gas and the other, a yellowish, waxy solid. It occurs in animal bones 

 and other debris, in various mineral deposits and in soil and ores. 

 Like nitrogen it is useful in agriculture only in the combined state, as the 

 poisonous phosphorus or the virulent acid can only be used when they 

 are united with other materials as binders. In bones it is combined with 

 lime and organic matter, in the rocks, ores and soils, with lime, iron, 

 alumina and magnesia, the combinations being known as phosphates 

 of lime, iron, alumnia or magnesia, as the case may be. 



Phosphoric acid is usually found in the fertilizer trade combined with 

 lime as soluble, reverted or insoluble phosphoric acid, the three to- 

 gether forming the so-called total phosphoric acid. 



Soluble phosphoric acid is soluble in water and readily taken up by 

 the plant roots. Different from nitrate nitrogen, however, it is not 

 lost to any extent by leaching, being fixed by soil constituents. 



Reverted phosphoric acid, while insoluble in water, is usually suffi- 

 ciently soluble in the acids of the soil and plant roots to nourish the 

 latter. Being largely if not entirely assimilable by the plant roots, it 

 is nearly as serviceable as the "soluble." The two together are termed 

 "available" phosphoric acid. 



