24 



in the spring before the roots. The fact that the corn harvest is 

 earlier in this part of the country, so that green crops can be sown 

 earlier, also helps. Outside of this region autumn sown green 

 crops do not in general make enough growth by the spring to be 

 useful for green manuring purposes; this has happened at 

 Rothamsted for three successive seasons (1921-1924). 



The problem therefore arises of finding a system of green 

 manuring for roots which is applicable to the colder northern 

 and eastern districts. 



Undersowing of green crops in the corn, and possible new 

 crops are being tried : and at certain centres the relative economic 

 values of folding the green crops to sheep, and of turning them 

 in for manure, are being ascertained. 



THE LEGUMINOUS CROPS. 



Considerable attention has been devoted to the leguminous 

 crops, owing to their great importance in the rotation and as 

 stock foods. The effect of manures applied to the barley on the 

 clover sown in is shown on pp. 114, 115. Sulphate of ammonia 

 had no bad effect on the clover although it increased the yield of 

 barley. We have met cases where the application of sulphate of 

 ammonia to barley reduced the yield of the clover, but in our 

 experience this happens only when the land badly needs lime, and 

 it is attributable to the increased acidity which sulphate of 

 ammonia is liable to produce on such soils. The phosphate 

 apparently had no action while the potash exerted a distinct 

 residual effect, giving an additional 6 cwts. of clover hay in 1924 

 and 12 cwts. in 1923. The results indicate that potash should be 

 applied to the clover if the barley crop has been good, unless it 

 has already been given to the barley. 



Inoculation of leguminous crops, especially lucerne. 



Ever since 1890, when Hellriegel and Wilfarth discovered 

 that leguminous plants live in association with micro-organisms 

 inhabiting the nodules on their roots, efforts have been made to 

 improve the growth of leguminous crops by adding the appro- 

 priate organisms to the soil. Some successes were obtained on 

 the Continent, but the method failed in this country; the results 

 at Rothamsted in 1906 and 1907 were not then considered suf- 

 ficiently good to justify extension to farm practice. 



There is no doubt, however, that for certain crops the prin- 

 ciple is sound ; the failure of inoculation in Britain must 

 be attributed to the lack of compliance with the conditions 

 necessary to success. During the past three years the whole 

 subject has been re-examined in the Bacteriological Department. 



The subject affords an admirable illustration of the way in 

 which a practical problem of great importance remains unsolved, 

 in spite of many empirical efforts, until the underlying principles 

 have first been studied and a solid groundwork of definitely 

 ascert .lined facts has been obtained. 



The failure of inoculation in many cases has been traced 



to the Circumstance that the organisms were already present in 



il, but pome condifn i : 1 1 t<> the growth of the plant 



