NITROGENOUS FERTILIZERS 163 



their nitrogen shall become available, the substances them- 

 selves must decompose in the soil, the nitrogen undergoing 

 the usual transformations. 



Many of the organic fertilizers contain phosphoric acid, 

 or potash, or both. These ingredients add to the value of 

 the fertilizer. They will be discussed under the heads of 

 (1) vegetable products, (2) animal products, (3) guano. 



213. Vegetable products. — Among these are cottonseed 

 meal, linseed meal and castor pomace together with other 

 materials that are less used and that will not be discussed 

 here. 



The meals here mentioned are primarily stock-foods and 

 are more profitably fed to live-stock, the resulting manure 

 being applied to the soil, than used directly as fertilizer. 

 Nevertheless, cottonseed meal is used extensively as a fer- 

 tilizer and linseed meal to a less extent. The former is much 

 used for tobacco of better grades and as a top dressing for 

 lawn grasses, as it does not have the offensive odor that char- 

 acterizes many of the organic fertilizers. 



Cottonseed meal contains between 6 and 7 percent of nitro- 

 gen when free from hulls, and 4 percent when these are pres- 

 ent. It also contains about 2.5 percent of phosphoric acid 

 and 1.5 percent of potash. 



Linseed meal contains about 5.5 percent of nitrogen, and 

 between 1 and 2 percent of phosphoric acid and of potash. 



Castor pomaj2% which is the residue after the extraction 

 of castor oirlrom the beans, has a nitrogen content of between 

 5.5 and 6 percent, and a rather variable amount of phos- 

 phoric acid and potash. 



214. Animal products. — These include the slaughter house 

 products among which are red dried blood, with about 13 

 percent of nitrogen ; black dried blood, with 6 to i2 percent 

 nitrogen ; dried meat and hoof -meal, with 12 to 13 percent 

 nitrogen; tankage, of which the concentrated product has 



