CENTURIES before there was any science that acquainted people with the intricacies of plant nutrition, decaying organic matter, as in manure or other forms, was recognized as an effective agent in the nourishment of plants. The high productivity of most virgin soils has always been associated with their high content of organic matter, and the decrease in the supply with cultivation has generally been paralleled by a corresponding decrease in productivity. Even though we can now feed plants on diets that produce excellent growth without the use of any soil whatever, yet the decaying remains of preceding plant generations, resolved by bacterial wrecking crews into simpler, varied nutrients for rebuilding into new generations, must still be the most effective basis for extensive crop production by farmers. Soil organic matter is one of our most important national resources; its unwise exploitation has been devastating; and it must be given its proper rank in any conservation policy as one of the major factors affecting the levels of crop production in the future
The stock of organic matter in the virgin soils taken over by the homesteading pioneers was a heritage from an extensive past. Its accumulation in our northern soils began with the recession of the last glacier, possibly some 25,000 years ago, and continued long enough to ripen the residues into compounds that were ready to be used quickly by growing plants
How Can Soil Organic Matter Be Restored?
Conservation and restoration of soil organic matter as a national problem calls for a program of soil and farm management in which (1) needless losses are eliminated or reduced to a minimum, and (2) the stock in process of consumption is regularly maintained with attention to its possible economical increase. Experimental results indicate the steps in such a program
First attention should be given to eliminating accelerated erosion. When, according to the long-continued soil erosion studies at the Missouri Agricultural Experiment Station (263), the entire plowed surface soil under continuous corn may be washed away in 50 years, it would be foolhardiness to attempt soil building by processes so slow as to make only an inch in hundreds of years. Erosion can be eliminated, as the investigations have shown and recent extensive erosion-control experience demonstrates, by sod cover crops, reduction in the amount of tillage, and other measures. The establishment of sod crops on badly eroded land often requires proper fertilization and liming