14 



■indicated by this method, in vegetable matters is supposed to be due 

 to the large amount of non-nitrogenous matter found in this class of 

 products. The low availability of the nitrogen in hair, wool waste, 

 garbage tankage, ground leather, and Philadelphia tankage, marks 

 these materials as rather inactive sources of plant food. 



This element is never found in nature unassociated 

 Potassium, with other elements. The \.Q.rm potas/i used in connec- 

 tion with fertilizers is known to chemists as potassium 

 oxide (KgO), a compound of potassium and oxygen. The potassium 

 in all potash -salts is equivalent chemically to a certain amount of 

 potash (potassium oxide), and through custom and for the sake of 

 comparison is usually guaranteed and reported as such. Potassium 

 is found in a great variety of minerals which, by slow decomposition 

 furnish potash gradually to growing plants. Potash tends to accum- 

 ulate in the leaves and stems of plants and if these are returned to 

 the soil in the form of manure, the soil is kept better supplied with 

 this valuable constituent. Potash is not as readily lost by leaching 

 as is nitrogen ; on the other hand it is more easily diffused and much 

 more apt to pass beyond the downward limit of the roots of some 

 plants than is phosphoric acid. The writer has found by actual 

 analysis in a number of instances in the case of tobacco soils, as 

 high as 500 lbs. of water soluble potash in one acre of soil eight 

 inches deep, and in only one or two instances has he ever found 

 more than traces of water soluble phosphoric acid. Potash has also 

 been found in soil drainage waters collected several feet under the 

 •surface of the soil. 



Soils vary in their power to retain potash. Sandy soils are much 

 less retentive of potash than clay soils, although sandy soils become 

 more retentive in proportion as their content of humus is increased. 

 The various potash compounds are peculiarly adapted for the pro- 

 duction of a superior quality of certain farm crops. For instance, 

 carbonate of potash and sulphate of potash are particularly useful in 

 growing a superior quality of tobacco ; the latter salt is especially 

 favorable to the production of sugar and starch in such crops as 

 fruit, potatoes, sugar beets and legumes ; while the muriate or chloride 

 is valuable as a source of potash for grass and farm forage crops. 



The following table gives a list of the principal potash fertilizers 

 :together with the average per cent of potash furnished by each. 



