PHOSPHORUS 123 



nitrogen in this form is a little cheaper than it is in the 

 form of sodium nitrate. It is not so desirable as the nitrate 

 because it tends to make the soil acid. If used continu- 

 ously, lime must also be used unless the soil is rich in 

 lime. Nitrate of soda has a slightly opposite effect. 



123. Dried Blood, Tankage and Bone Meal are products 

 from the meat-packing houses. Tankage is made up of 

 all kinds of waste material from the slaughter-houses. 

 The names of the others indicate their origin. They con- 

 tain 5 to 15 per cent of nitrogen. Good dried blood con- 

 tains about 14 per cent. These products have to be acted 

 on by soil bacteria before the nitrogen is available for crop 

 growth. There is less danger of loss of nitrogen than in 

 the case of sodium nitrate. These forms are particularly 

 desirable for fall-sown crops. Some farmers who mix 

 their own fertilizers use about half of the nitrogen in the 

 form of dried blood and half in the form of nitrate of soda. 

 This seems to be a good practice. 



PHOSPHORUS 



124. Forms of Phosphorus Fertilizers. The chief forms 

 of phospnorus fertilizers are barnyard manure, dissolved 

 phosphate rock, bone meal, dissolved bone, tankage, 

 Thomas slag. 



125. Phosphate Rock. This rock is found in many 

 parts of the United States, particularly in the Carolinas, 

 Florida and Tennessee. It is sometimes called South 

 Carolina rock. The deposits are remains of marine life. 

 As the rock is mined, it is about 50 per cent tricalcium 

 phosphate (Ca 3 (P0 4 ) 2 ). The rock is sometimes finely 



