46 FIRST PRINCIPLES OF AGRICULTURE. 



essential mineral constituents, potash, phosphoric acid, 

 and lime, light lands may be rapidly improved and made 

 very fertile, while lands used for growing vegetables or 

 fruits may be kept in a high state of cultivation and 

 in good mechanical condition, without the expenditure of 

 money and labor for stable manure, now regarded as so 

 essential by the majority of farmers. 



Rye and Buckwheat as Catch Crops. — Eye and 

 buckwheat are of considerable advantage, even though they 

 are able to secure their nitrogen only from soil sources, 

 because their habits of growth permit them to be used as 

 catch crops, or those not interfering with regular rotations. 



The addition of the vegetable carbonaceous matter 

 which is contained in these crops is, of course, quite as 

 advantageous as that contained in those having the special 

 power of securing nitrogen ; though recent studies of 

 crimson clover show it to be quite as well adapted for a 

 catch crop as those already mentioned, thus limiting the 

 usefulness as green manures of other crops than the 

 clovers or legumes. 



Care in the Use of Green Manures. — The turning 

 under of heavy crops of clover or rye in the summer, when 

 the conditions are most favorable for rapid decay, namely, 

 a high temperature, and an abundance of moisture, is some- 

 times followed by unfavorable results. Whether this is 

 due to the too great development of organic acids from the 

 rapid decay of vegetable matter, as some believe, is not 

 thoroughly established ; though it is knovm that where the 

 soil contains sufficient lime, or when lime is added, the 

 danger in this direction is very much reduced, or altogether 

 obviated. 



