ECONOMY OF GREEN MANURE. 189 



land with carbon, which was absorbed from the 

 atmosphere by the leaves of plants. That it sup- 

 plies the soil with nitrogen is very important to 

 corn plants, for they possess the power of attracting 

 nitrogen (which is one of their chief sources of 

 nutrition) from the air only in a very slight degree. 

 Green crops, moreover, keep dry soils cool and 

 moist, because the humus which is engendered by 

 their decomposition not only absorbs much moisture, 

 but retains it for a long time. Their strong herbage 

 and woody roots act mechanically on heavy land by 

 loosening it. After manuring with a green crop, 

 corn is never laid, although it grows as luxuriantly 

 as after a dressing of dung. The reason is, that 

 while the latter supplies the ground suddenly with 

 a great amount of nitrogen, green manure affords 

 it much more gradually, in consequence of the 

 slowness of its decomposition, acting most power- 

 fully when the plant requires most nourishment. 

 Its effects will not last, however, more than two 

 years, as the mass of herbage ploughed in is often 

 not more than a third of the weight of the dung. 



" This method of enriching land is very econom- 

 ical, not requiring more than one ploughing and 

 harrowing, and the seed is generally very cheap. 

 When fields are at a distance, it saves much carriage ; 

 and it prevents the soil from losing its humus by 

 evaporation ; because, as soon as the corn is gath- 

 ered in, the field is ploughed and the crop for green 



