29 



favors the absorption of heat from the sun, and the process of deea}", 

 being in its final effect precisely like combustion by fire, helps to raise 

 the temperature of the soil. 



Many of the most valuable green-manuring crops are distinguished 

 by the fact that they send their roots into the soil to an enormous depth. 

 Such crops are highly beneficial in two ways : first, by means of their 

 deep roots thej' bring up from the subsoil food not available to ordinary 

 crops, but having been thus pumped up, as it were, it becomes available 

 to succeeding shallow-rooted crops ; second, it has been found that crops 

 whicli are ordinarily shallow-rooted send their roots much deeper than 

 usual when they are made to follow a deep-rooted green-manuring crop 

 Thus, for example, Schultz-Lupitz has noticed that the roots of the po- 

 tato, which ordinaril}^ develop almost entirely near the surface, pene- 

 trate deeply into the ground after a crop of lupines, following the 

 furrows left by the decay of the roots of the lupines. This renders the 

 potato less liable to injury from drought, inci-eases enormously the store 

 of food within its reach and so makes the crop more certain and larger. 



Green-manuring may be made the means of cleansing the field from 

 weeds, for which purpose, of course, as has been pointed out, only the 

 crops of the most rapid growth are useful. Green-manuring increases 

 the store of organic matter in the soil, and so furnishes the conditions 

 favorable for the multiplication of earth worms, and these, as Darwin 

 has pointed out, by their activities improve the soil in many ways ; most 

 important among which are better aeration, bringing of the finer mate- 

 rials to the top, pulverization and increased solubility of its constituents. 



Finall}^ green-manuring may be made to protect the soil from the in- 

 jurious action of violent winds and from surface washing, for which pur- 

 poses, as has been pointed out, those crops which occupy the land in 

 winter are by far the most useful, although those which are killed bj- 

 frosts, if allowed to remain upon the surface during the winter, will 

 prove useful in the same direction. 



The list of possible benefits from green-manuring, it will be seen, is 

 a long one, and these benefits are undoubtedly, under the proper condi- 

 tions, ver}' great. It may be wondered then why the practice is not 

 more general. It might seem that the benefits are sufficiently great to 

 warrant a much more general practice of green-manuring than we find 

 among our farmers ; and yet the indiscriminate adoption of the practice 

 is by no means to be recommended. It has its place ; but the conditions 

 under which it is best to turn under a catch-crop are, I believe, compar- 

 atively seldom met with. 



Conditions under m^iiicii Green-manuring should be practised. 

 In the majority of instances a crop which has been grown will be 

 worth more to feed in Massachusetts than it is for turning under. A 

 crop standing in the field has a certain value as a means of soil improve- 

 ment, — a certain manurial value. It has also, in almost all cases, a 

 certain value as food. It may be used as a food either by pasturing it 

 or cutting in the barn. In either case, under proper management the 

 excreta of the animals consuming the crop will be worth as manure 



