216 THE POTATO 



living vegetable or animal tissue. The inorganic 

 particles usually compose the greater portion of the 

 soil (95 per cent, to 98 per cent, of sandy or gravelly 

 soils, 80 to 95 per cent, of loams and clayey soils, 

 less than 80 per cent, of muck or peaty soils) and 

 supply the necessary mineral elements of plant 

 food. The organic portion of the soil furnishes 

 the supply of nitrogen, a very necessary element 

 of plant food, without which no crop can make 

 any growth; supplies also the other elements which 

 were taken up in the growth of the plant or animal 

 and which by their decay are returned to the soil 

 in a form readily available for plants; helps to 

 render the mineral elements of the soil avail-able 

 by the action upon the inorganic matter of the 

 acids produced in the decay of organic matter; 

 affects very beneficially the physical properties of 

 the soil, increasing its ease of tilth, moisture hold- 

 ing capacity, capacity to absorb heat, and decreas- 

 ing the tendency to ' puddle' when wet or 'bake' 

 when dry. Too much organic matter usually 

 results in a soil which dries out very rapidly and 

 which is likely to be 'sour' from the excess of or- 

 ganic acids which it contains. Very few, if any, 

 well-drained lands contain an excess of organic 

 matter, however. 



"It is apparent, therefore, that the maintenance 

 of a proper balance between the organic and the 

 inorganic or mineral portions of the soil is one of 

 the first essentials to fertility and to proper physi- 

 cal condition of the soil. Many of the so-called 

 'wornout' soils have only had their store of 

 organic matter depleted by improper methods of 

 cropping and can be restored to fertile condition 

 by the plowing under of some additional supply of 

 vegetation to decay* 



