9/0 Value of Different Crops as Green Manures, [mar., 



and though in this respect it cannot be replaced by artificial 

 manures, yet a combination of artificial manures with the 

 occasional ploughing in of a green crop will do everything 

 that is necessary towards keeping the soil in the best possible 

 condition. 



It is not, however, the purpose of this communication to 

 discuss either the value of green manuring or the difficulties 

 encountered in practice, but only to set out certain experi- 

 mental results which have been obtained at Rothamsted on 

 the relative value of different crops used for that purpose. 

 Whenever green manuring has been discussed or advocated, 

 it has been assumed as a matter of course that leguminous 

 crops are the best for the purpose, because of the nitrogen 

 they gather from the atmosphere and add to the soil on being 

 ploughed in. It is this atmospheric nitrogen that accounts 

 for the benefits which a good clover crop confers on the 

 succeeding crops in the rotation, even though the green 

 manuring is only that due to the roots and stubble left behind 

 after the clover has been cut ; but the value of the clover is 

 still more pronounced if the second growth is not cut or fed, 

 but turned in so as to form a real green manuring, a practice 

 which is not uncommon among the potato growers in the 

 East of England. The classical illustration of the value of 

 green manuring with leguminous plants is found in the 

 reclamation of the sandy heaths of East Prussia by Schultz, 

 who grew successive crops of lupins by the aid of mineral 

 manures alone, and then turned them in until the soil had 

 been built up. Considering this accepted power of the legu- 

 minous crops to enrich the soil in atmospheric nitrogen, it 

 was somewhat surprising to find in the experiments at the 

 Royal Agricultural Society's Farm at Woburn that Dr. 

 Voelcker always obtained bettenresults/with whieat grown after 

 mustard than after vetches, both crops having been ploughed 

 in. The experiments at Woburn (see Journal of the Royal 

 Agricultural Society, 1906, Vol. 67, p. 300, and 1908, Vol. 

 69, p. 348) have been repeated until no possible doubt of 

 their validity can be left. On the average the yield of grain 

 after mustard has been 50 per cent, higher than after vetches. 

 When the Woburn results were first manifest, similar plots 

 were started at Rothamsted on the Little Hoos field, in order 



