238 



THE ROTHAMSTED EXPERIMENTS. 



Effects of 

 manures. 



Rotation 

 and contin- 

 uous crops. 



Unfavour- 

 able me- 

 chanical 

 condition 

 jof soil. 



accumulation of potash with the greatest accumulation of 

 sugar. 



Looking to the actual amounts of potash in the total pro- 

 duce, roots and leaves together, of the rotation crops, it is 

 seen that, without manure, there was only from 4 to 6 lb. of 

 potash per acre per annum ; but with superphosphate, without 

 potash supply, from 25 to 28 lb. That is, without any supply 

 by manure the plants were able to gather about 20 lb. more 

 potash per acre per annum from the soil itself, by virtue of the 

 greatly increased development of fibrous feeding root under the 

 influence of the phosphatic manure. With the mixed manure, 

 however, containing potash, there was about three times as 

 much of it taken up as with superphoshate alone. But, with 

 the supply of potash there was also a liberal supply of available 

 nitrogen, to which the greatly increased growth is largely to 

 be attributed ; and with the increased luxuriance much more 

 potash was of course required if there were to be a correspond- 

 ingly increased formation of the characteristic non-nitrogenous 

 product of the cultivated root-sugar. Thus, we have — without 

 manure only 4 to 6 lb. of potash taken up, with superphos- 

 phate (without potash) from 25 to 28 lb., and with the mixed 

 manure, supplying besides phosphoric acid both nitrogen and 

 potash, nearly 80 lb. of potash per acre per annum in the 

 crops. 



Comparing the amounts of potash in the rotation crops 

 with those in the continuously growm ones, it is seen that — 

 without manure, and practically no growth, there was but 

 little difference in the amounts taken up ; with superphos- 

 phate there was little more than half as much taken up in 

 the continuous as in the rotation crops ; whilst with the 

 mixed manure, with full supply of potash, and much larger 

 amounts of it in both the rotation and continuous crops, 

 there was rather less than two-thirds as much in the con- 

 tinuous as in the rotation crops. The deficient amounts in 

 the continuous crops are, however, as in the case of the other 

 constituents, coincidents of the less amounts of produce of 

 the continuous crops ; which, as has been pointed out, were, 

 in the case of the superphosphate plot, due partly to the 

 greater exhaustion of available nitrogen of the surface soil 

 with the continuous growth, but partly also to the unfavour- 

 able mechanical condition of the soil induced by such 

 growth ; and this was probably the chief cause of the deficient 

 produce in the case of the mixed manure crops also. 



The Potash in the Barley Crops. — The second division of 

 Table 64 records the results on this point. 



In the case of the turnips it was found that much more 

 potash was accumulated in the roots than in the leaves ; and 



