Scientific Agriculture, 



144 



[August, 1911. 



should however drain freely. By this 

 means, rain and irrigation water instead 

 of stagnating on the land will sink into 

 the soil and out into the drains, carrying 

 with it the noxious salts. Where the 

 land is not very saline, this process may 

 be accelerated and the land at the same 

 time enriched by growing Dhanicha 

 (Sesbania aculeata). The roots of this 

 plant go deep down into the soil, and 

 on their decay leave channels in the 

 soil ; down these water is able to escape 

 quickly, drainage is more effective, and 

 thus the washing out of the salts is 

 hastened. 



THE VALUE OP DIFFERENT CROPS 

 AS GREEN MANURES. 



By A. D. Hall, m.a., f.r.s., 

 Director of the Rotbamsted Experi- 

 ment Station. 



(From the Journal of the Board of 

 Agriculture, Vol. XVII. , No. 12, 

 March, 1911.) 



Green manuring is a practice compara- 

 tively little followed in Great Britain, 

 because wherever fodder crops are at all 

 generally grown the land is suitable for 

 sheep, and the standard custom of the 

 country has always been to feed off the 

 green crop with sheep. Wherever one 

 sees vetches or mustard or rape being 

 turned in by the plough on these light 

 soils, it is generally because the farmer 

 has an excess of keep, and fears he will 

 not be able to feed off the fodder crop 

 in time to get the land ready for the 

 next stage in his rotation. 



On heavy soils, however, where sheep 

 cannot be folded, green manuring might 

 well be more practised; especially as its 

 value in improving the texture of the 

 soil will be even more felt than upon 

 the sands and chalk. Indeed, it is not 

 unlikely that we shall see more green 

 manuring in the future if corn prices 

 continue to rise. Feeding stock is not 

 always the most profitable operation 

 upon the farm, so that many men would 

 be glad to giOW corn crops more fre- 

 quently and reduce the acreage under 

 roots, with their doubtful return for the 

 very considerable expense involved, 

 were it not that they feel they must 

 make as much farmyard manure as 

 possible in order to maintain the condi- 

 tion of the soil. It is in supplying the 

 humus and in ameliorating the texture 

 of the soil that farmyard manure be- 

 comes so indispensable, 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 the green manuring or the diffi- 

 culties encountered in practice, but 

 only to set out certain experimental 

 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-man- 

 uring, a practice which is not un- 

 common among the potato growers iu 

 the East of England. The classical illus- 

 tration 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. Con- 

 sidering this accepted oower of the 

 leguminous 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 better results with wheat 

 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. 6y, 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 to see if 

 the results obtained on the light dry 

 land at Woburn would hold for the 

 heavier and cooler soil that prevails at 

 Rothamsted. 



At the time the experiments were 

 begun in 1904, this field was in a very 



