How LEGUMES HELP THE FARMER 167 



covered, hence the importance of a rotation which will bring cover crops as 

 often as possible on the land The ease with which nitrates are washed out 

 of the bare soil, and the fact that there is very little of this loss when the 

 soil is covered with a growing crop, shows the reason why the cotton lands of 

 the South have lost fertility, through the leaving of the land bare and fully 

 exposed to the heavy rainfall in winter. In the South especially, there 

 should always be shading crops of peas in summer, on all land not in culti- 

 vation with hoed crops; but the hoed crops should always be followed by 

 crops that will keep a green growth on the land during the winter. In a cli- 

 mate where the soil is locked up with frost during the whole winter, there 

 may be some advantage gained by fall plowing of a heavy soil, and letting it 

 lie to freeze and mellow in a rough state all winter. But in the South, where 

 there is always more rain than freezing, bare land will lose fertility faster in 

 winter, so far as the nitrogen is concerned, than it will in the" summer crop- 

 ping. Fortunately we have crops especially fitted for a winter cover to fol- 

 low the cotton or corn, and crops, too, that will be gathering nitrogen from 

 the air instead of allowing it to waste. 



NITROGEN FIXING CROPS AND THEIR PLACE IN A ROTATION. 



We have pretty thoroughly discussed the subject of nitrification, or the 

 change of organic ammonia into nitrates, in the soil, but we must remember 

 that this is a different process from the acquisition of the aerial nitrogen by 

 the microbes that live on the roots of clover, peas and other leguminous 

 plants. These get the free nitrogen-gas of the air and leave it in the form 

 of organic matter in the roots of the peas or clover grown on the land, and 

 this organic matter must then go through the process of nitrification before 

 plants can use it. This is a fortunate thing for the farmer, for if the work 

 of the microbes on the roots of legumes was confined to only the formation 

 of nitrates in the soil they would probably be all washed away before the next 

 season's crop came on the land. Probably a considerable portion is thus 

 formed and lost to the soil, 'for the exact process by which the microbes so 

 transform the free nitrogen that the legumes can take it up, is one of the 

 things of which little is known; but the larger part, perhaps, is left in the 

 form of organic matter, which must go through the process of decay and 

 nitrification before it can be used, and, hence, is held in the soil till the fol- 

 lowing crop has a chance to make use of it. 



