CHAPTEB XII 



MAINTAINING AND INCREASING THE ORGANIC- 

 MATTER CONTENT OF SOILS 



THE maintaining of the organic matter in soils is the most dif- 

 ficult problem on the average farm. It, with the nitrogen it con- 

 tains, is the limiting factor on most of the farms of the southern 

 and eastern states and is fast becoming of primary importance on 

 corn and wheat belt farms of the middle west. 



To maintain the organic matter requires something else than 

 money. It is not to be had for any price, because there is no 

 adequate supply. It must be grown on the farm and put back 

 largely as residues which are of low value for any other purpose 

 or as manure or both. To maintain this constituent requires very 

 careful planning of rotations and the proper handling of the crops 

 grown. A few farmers may buy organic matter as grain or hay 

 from their neighbors, but this is a very short-sighted policy for 

 the latter. The lack of active organic matter is the primary cause 

 of soil exhaustion. Many farmers realize its value, but very few 

 have made any definite plans for its permanent maintenance. To 

 improve a worn-out farm is not an easy task. Since the organic 

 matter for our soils must be grown on our farms, the first require- 

 ment is that the soil shall be in condition to grow it. Legumes, 

 and more especially the clovers, are the best crops to grow for soil 

 improvement. They require larger amounts of minerals in the 

 soil, especially calcium and phosphorus, than almost any other 

 crop. One or both must usually be supplied. 



1. By Addition of Limestone. Many soils are so acid or sour 

 that the best soil-renovating crops, the clovers, will not grow suc- 

 cessfully. Before these soils can be improved to any extent, unless 

 an unlimited supply of manure is available, limestone must be 

 applied. Many experiments have shown that the best form to use 

 is ordinary ground or crushed limestone. This neutralizes the 

 acid, prevents leaching of organic matter and furnishes the plant 

 with the element calcium. 



Limestone is rather readily soluble. In humid regions from 

 500 to 800 pounds are leached out of the soil each year. In many 

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