FOOD FOR PLANTS 29 



in water, but of distinctly lower quality because plants 

 in general find it less available than in the Nitrate 

 form. This change is effected in the soil by the action 

 of certain organisms, under favorable conditions. 

 The weather must be suitable, the soil in a certain 

 condition; and besides there are considerable losses 

 of valuable substance in the natural soil process of 

 nitrating such Nitrogen. By unfavorable weather 

 conditions, or very wet or acid soils, nitration may be 

 prevented until the season is too far advanced, hence 

 there may be loss of time, crop and money. The 

 quality of nitrogens, such as cotton-seed meal, dried 

 fish, dried blood, and tankage, is limited by conditions 

 similar to those which limit sulphate of ammonia. 

 Perfectly authentic experiments, and made under 

 official supervision, have shown that 100 pounds of 

 Nitrogen in these organic forms have only from one- 

 half to three-fourths the manurial value of 100 pounds 

 of Nitrate of Soda. 



Special Functions of Plant Food. 



As stated before, plants must have all three of the 

 plant food elements — Nitrate, Phosphates and Potash 

 — but notwithstanding this imperative need, each of 

 the three elements has its special use. There are 

 many cases in which considerations of the special 

 functions of plant food elements become important. 

 For example, a soil may be rich in organic ammonia 

 from vegetable matter turned under as green manure, 

 and through a late wet spring fail to supply the avail- 

 able Nitrate in time to get the crop well started 

 before the hot, dry, summer season sets in. In this 



