128 The Great World's Farm 



of animal or vegetable matter, whether in the soil or else- 

 where. 



Their work in the soil seems to go on chiefly in the 

 upper nine inches, and most rapidly when the weather is 

 warm and damp. 



The multitudes of leaves drawn in by worms, the old 

 roots of former crops, or green crops which have been 

 grown only that they may be plowed in — all are decayed, 

 and so converted into food, of which the next crop can 

 avail itself. 



As has been more than once remarked, all soils contain 

 more or less organic matter; but unless the amount is 

 very large, as it is in the Russian black earth region, 

 Manitoba, and elsewhere, not much of the nitrates formed 

 by its decay will be left in the upper twenty-seven inches 

 of the soil after a crop of corn has been grown in it. 

 Organic matter there will still be, but decay is gradual, 

 and nitrates take time to form; so the farmer must sup- 

 ply the want in one way or other. 



In former days, till within the last century in fact, his 

 way of doing so was simple. He merely plowed up the 

 field, and let it alone to recover itself; in other words, he 

 allowed it to lie fallow. 



And what goes on in a fallow field? Generally speak- 

 ing it is, or was, both plowed and harrowed repeatedly, so 

 that the soil might be exposed as much as possible to the 

 action of the air and rain, by which the mineral matter 

 would be dissolved ready for the next crop. Then in the 

 winter the soil would be yet further broken up by the 

 freezing of the moisture in its pores, wiiich would separate 

 grain from grain, reducing it to powder in a way that no 

 plow or harrow yet invented can do. The crumbling of 



