in it may be readily used by the crop; and not Avail- |™^ or 



able when it is transformed so slowly in the soil as to 



offer but little plant-food to the crop at any one time. 2 33 

 A striking illustration of the significance of Availability 

 in fertilizers is found in the action of comparatively 

 small amounts of Nitrate on grass or grain applied early 

 in the spring. It has been repeatedly observed that 

 soils containing as much as .15 per cent, of Nitrogen, 

 or 6,000 pounds per acre-foot out of a total of 2,000 

 tons, which such an acre-foot weighs, and capable of 

 yielding about one ton of hay per acre, may be made to 

 produce two tons of hay when top-dressed in the spring 

 with only 100-150 pounds of Nitrate. At first it may 

 seem strange that the 23 or 24 pounds of Nitrogen in 

 150 pounds of Nitrate of Soda should produce this 

 magic effect, when measured against the 6,000 pounds 

 of ordinary Nitrogen already in the soil. But the mys- 

 tery is made clear to us when we remember that Nitrate 

 of Soda is a soluble food that may be directly taken up 

 by plant-roots, whereas the Nitrogen of the soil itself is 

 nearly all locked up in inert humous compounds which 

 must first pass through the various stages of Nitration 

 before they become available. With some qualifica- 

 tions a similar comparison could be made between the 

 phosphoric acid in ground phosphate rock, known as 

 "floats," and that in acid phosphate; or between 

 potash in feldspar rock or clay and that in sulphate of 

 potash. 



In order to protect the farmer against fraud, fer- 

 tilizer laws have been enacted in most of the Eastern 

 States. These laws compel the mixers and dealers to 

 guarantee their goods, that is, to state on the bags or 

 tags how much Nitrogen, phosphoric acid and potash 

 their fertilizers contain; furthermore, they are also 

 compelled, but in an incomplete measure, to guarantee 

 the quality, i. e., Availability, of the plant-food sold by 

 them. The farmer is given, however, a fair measure of 

 protection in so far as the phosphoric acid and potash 

 purchased by him are concerned. He is told definitely 

 how much phosphoric acid is present in available form. 

 He knows, also, that the potash in mixed fertilizers is 

 derived almost exclusively from the German potash 



