400 SOIL PHYSICS AND MANAGEMENT 



3. Cyanamid or Calcium Cyanarnid. This is an artificial 

 product made by passing nitrogen into retorts containing highly- 

 heated calcium carbide. It is a heavy, black, granular powder, and 

 should be incorporated with the soil for some days before planting 

 to avoid any toxic effect that might be injurious to the seeds and 

 young plants. It contains about 16 per cent of nitrogen. 



4. Organic Substances. Certain materials that were formerly 

 waste products are valuable for their nitrogen. Among these are 

 cottonseed meal, containing 7 or 8 per cent of nitrogen; linseed 

 meal, with about 5.5 per cent; dried blood, containing from 13 to 

 15 per cent, and tankage, which has from 4 to 10 per cent of 

 nitrogen and 1 to 8 per cent of phosphorus. 



Phosphorus. Large areas of land all over the world are 

 deficient in the element phosphorus to such an extent that it be- 

 comes the limiting factor. It is especially important in the pro- 

 duction of grain and in the growth of legumes. Its addition helps 

 to make possible the building up of soil by larger growth of nitrog- 

 enous soil-renovating crops. In addition to this it improves the 

 quality and increases the weight of the grain (Figs. 192 and 193). 



The needs of a soil for phosphorus may be determined by apply- 

 ing two hundred and fifty pounds of steamed bone meal per acre to 

 wheat or corn by sowing broadcast before the seed bed is prepared 

 and securing accurate yields of equal areas of the treated and un- 

 treated land. Definite conclusions, however, should not be based 

 upon a single year's results. 



Phosphorus may be purchased in several forms: (1) raw bone 

 meal, (2) steamed bone meal, (3) raw rock phosphate or floats, (4) 

 acid phosphate, and (5) basic or Thomas slag. 



Bone meal is made from the bones of animals slaughtered at 

 the packing houses. The bones are a by-product and their high con- 

 tent of phosphorus makes them valuable. The raw bones may be 

 ground up into meal, but this contains three to five per cent of 

 nitrogen and large amounts of fat and oil. The nitrogen is very 

 expensive, while the fat is of no value to the soil. The bones may be 

 steamed under high pressure, thus removing the fats and oils and 

 gelatin. The bones are then ground into meal that is placed on the 

 market as steamed bone meal. This contains less nitrogen and more 

 phosphorus than the raw bone. 



Rock Phosphate. Phosphorus has been deposited in large 

 quantities as a mineral combined with other elements forming the 

 tri-calcium phosphate, practically the same as bone in composi- 



