1 907. J 



Green Manuring. 



231 



Green manuring or the ploughing under of green crops is 



one of the oldest methods used to maintain or to increase the 



productivity of the soil. The effect 



varies with the character of the soil ; 

 Green Manuring. , „ ., ,, , , 



sandy or gravelly soils are made darker 



in colour and become more retentive of 

 moisture, while clayey soils are made more porous and friable. 

 The most important object achieved by green manuring is the 

 addition of humus to the soil, and, other things being equal, 

 the best green manure crop is that which furnishes the largest 

 amount of material which will readily decay in the soil and thus 

 form humus. There are, however, additional ways in which such 

 a crop may be beneficial. Deep-rooted plants are decidedly 

 preferable to shallow-rooted ones because they penetrate 

 into the sub-soil and thus admit air and water. Leguminous 

 plants also are more valuable for green manuring, because 

 they not only provide humus but also collect nitrogen from the 

 air, which is thus added to the soil. 



Green manuring as a definite farm practice can only be 

 recommended under certain conditions. It is very advan- 

 tageous in improving the physical condition of sandy soils, 

 and for this reason it has become a very common practice in 

 Germany where large areas of light soil exist. It was, in fact, 

 the success obtained by M. Schultz at Lupitz, in Saxony, in 

 green manuring light sandy soil with lupins that first directed 

 attention to the value of leguminous crops as a means of adding 

 nitrogen to the soil.* There is not so much evidence of its 

 value on medium and heavy clay soils, though several German 

 agriculturists appear to have practised it with success for many 

 years. Generally speaking, it cannot be recommended on 

 good soils unless there is reason to believe that more humus is 

 required, but where clover or some similar crop is used in 

 rotation it is seldom necessary. 



With regard to the crops employed for the purpose, legu- 

 minous plants are unhesitatingly recommended by practically 

 all authorities both in Germany and the United States. In 

 this country rape, mustard, &c, are still employed, and in 

 experiments carried out for a number of years at Woburn 

 by the Royal Agricultural Society, these crops have given 



* See " Green Manuring," Journal, Vol. xii., p. 29, April, 1905. 



