92 VEGETABLE MANURES. 



peas, are some of those more commonly used in this 

 and other countries. They add organic matter largely 

 to the soil, which organic matter they have drawn in 

 great part from the air, and their roots bring inorganic 

 substances from the subsoil to the surface, so that it is 

 within the reach of succeeding crops. There are dif- 

 ferences of opinion in various districts as to the proper 

 period for ploughing these crops under: it is a matter 

 to be settled by experience and convenience. They 

 not only add fertilizing substances to the soil; they 

 also improve its physical character. A light soil is 

 somewhat consolidated, and rendered more retentive 

 of moisture, while a stiff one is mellowed and loosened. 

 Some of these green crops, such as spurry and buck- 

 wheat, will grow well on extremely light, sandy soils. 

 After they have grown up and been ploughed in a few 

 times, the land is so improved that it will bear crops 

 of a more valuable nature; and thus by a continuance 

 of them at proper intervals, it may not only be kept 

 up, but steadily improving. 



The same effects follow the ploughing of grass land, 

 and turning under of the turf. The thicker and hea- 

 vier the sward the better, because then a larger amount 

 of fresh, decomposable organic matter, in the form of 

 roots, is added to the soil. Where land has been in 

 grass for some years, say four or five, the weight of 

 roots under the surface is in some cases twice as much 

 as the weight of the grass above; these roots all de- 

 compose, and of course enrich the soil very materially. 



There are few cases in which a judicious course of 

 green cropping will not improve land. In the worst 

 instances, it is sometimes necessary to make numerous 

 trials before even the hardiest green crop will succeed; 

 when this difficulty is overcome, and a good growth 

 once obtained, experienced farmers say that the land 

 may by proper after management be brought to any 

 desirable state of fertility. It must always be re- 



