CHAPTER VII 



THE MANURING OF WINTER GREENS 



The dominant manurial ingredient for such quick- 

 growing and dense foliage crops of winter greens as are 

 necessary to the continuous-cropping system is nitro- 

 gen. This, whilst being the dearest fertilising element 

 the farmer has to buy, is most plentifully supplied 

 by nature if one troubles to get it. 



Four-fifths of the atmosphere consist of nitrogen, 

 and the farmer who carries on his occupation on 

 scientific lines can obtain some of this nitrogen free for 

 his soil. 



Like most things easily obtained, however, atmo- 

 spheric nitrogen is least valued. Instead of a farmer 

 drawing on nature for a supply of free nitrogen, he 

 prefers to buy it in the form of nitrate of soda or 

 sulphate of ammonia, in which manures it exists to the 

 extent of 15 J and 20 per cent, respectively. 



NITROGEN FIXERS 



Now, there are certain farm plants, called legumes, 

 which possess the extraordinary power of taking 

 nitrogen from the air, utihsing a certain amount for 

 their own use, and storing up the balance in the soil 

 for succeeding crops. To these legumes belong such 

 crops as clover, beans, peas, and vetches. 



A study of the standard rotation will show that in 

 our five years' cropping we have the land occupied 

 for four years with nitrogen fixers. That is, four 



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