PREPARATION OF SOILS FOR CROPS 259 



able amount of inherent fertility produced by disin- 

 tegration and other changes to which soils are subject. 

 In some long-cultivated soils the amount of fertility 

 produced annually by weathering and natural agencies 

 is sufficient to yield from 10 to 15 bushels of wheat. 

 This does not represent the maximum crop producing 

 power of the soil but simply the inherent or natural 

 fertility. When the natural fertility is reinforced 

 with farm manures and other fertilizers, cumulative 

 fertility has been added and maximum yields of crops 

 are secured. In many soils there are large amounts 

 of cumulative fertility or residues from former appli- 

 cations of manures. The condition of a soil as to crop 

 producing power is dependent both upon the inherent 

 and the cumulative fertility, as well as upon the 

 mechanical condition of the soil. In the production 

 of crops, it should be the aim to utilize all of the in- 

 herent fertility to the best advantage, and to add to 

 the cumulative fertility so that the stock of total fer- 

 tility may be increased. Soils of the highest fertility 

 are those which are composed of a large amount of 

 silt or particles of equivalent value, are well drained, but 

 sufficiently retentive of moisture for crop production, 

 and are of good capillarity. Such soils have usually 

 been deposited by water ; they are uniform in texture, 

 of great depth and contain large amounts of organic 

 matter rich in nitrogen and mineral matter contain- 

 ing all of the essential elements of plant food. When 

 such soils are cultivated, the organic matter readily 

 undergoes decay with liberation of plant food. 



346. Balanced Soil Conditions. A high state of 



