PHOSPHATE FERTILIZERS 1 99 



up 80 per cent of its phosphoric acid in the first half of the 

 growing period, 37 while clover has assimilated all it requires 

 by the time the plant reaches full bloom. 43 Phosphorus 

 compounds accumulate, to a great extent, in the seeds 

 of grains, and hence, when grain farming is extensively 

 followed, are sold from the farm. All crops are very 

 sensitive to the absence of phosphoric acid ; an imper- 

 fect supply results in the production of light-weight 

 grain. The nitrogen and phosphorus are to a great 

 extent stored up in the same parts of the plant, par- 

 ticularly in the seed, which is richer in both of these 

 elements than is any other part. Nitrogen is the chief 

 element of protein, while phosphorus is also necessary 

 for the formation of some of the phosphorus and ni- 

 trogen compounds, as the nucleo-albumins and lecithin. 

 Phosphorus aids in the production of the protein com- 

 pounds. In speaking of the phosphorus compounds in 

 plants and in fertilizers, as well as in soils, the term 

 'phosphoric anhydride' or 'phosphorus pentoxide,' P 2 O 5 , 

 commonly called phosphoric acid, is used. This is be- 

 cause phosphorus is an acid-forming element and, as 

 already explained, the anhydride of the element is al- 

 ways considered instead of the element itself. 



226. Amount of Phosphoric Acid removed in Crops. 



Grain crops remove about 20 pounds per acre of phos- 

 phoric acid ; the amount removed by other farm crops 

 ranges from 1 8 to 28 pounds, as will be observed from 

 the following table : 



