Manures and Commercial Fertilizers 105 



by hand. As we have pointed out, one of the chief values 

 of farm manure Hes in the large amount of vegetable 

 matter carried with it, v\rhich keeps up the humus supply 

 in the soil and makes it more mellow and easy to work, 

 and more retentive of moisture for the sustenance of 

 crops in dry weather. The commercial fertilizers have 

 a far larger amount of plant food in a more readily avail- 

 able form, but they do not furnish this organic decay. 

 How we may make the fertilizers take the place of stable 

 manure will be the subject of future treatment. 



While Ume is essential to the Ufe of plants, 

 Lime and Its ^ao^X of our cultivated soils have a large sup- 

 Agriculture P^y i^ them. It has been shown that a good 

 wheat soil which will produce a crop of 

 twenty-five bushels of wheat per acre, will contribute to 

 the grain and straw about seven to eight pounds of lime 

 per acre, while there will probably be in this acre of soil 

 fully two tons of hme. And yet it has been found that 

 appHcation of freshly water-slaked lime on this same 

 soil will increase the wheat crop. We are therefore forced 

 to beHeve that it is something beside the Hme itself which 

 causes the increase, since the crop had already at com- 

 mand a far larger supply than it could possibly use. 

 Careful investigations have shown that, aside from a Hm- 

 ited use by plants as food direct, Hme has a still greater 

 influence as a reagent in the soil. 



Soils having a large amount of humus from the decay 

 of organic matter may get into an acid condition which 

 is unfavorable to the growth of many crops. This acid 

 condition may be brought about also in soils which have 

 not an excess of organic matter, through long contmued 



