122 



THE ROTHAMSTED EXPERIMENTS. 



Reduction 

 in nitrogen 

 in garden 

 soil under 

 clover. 



Reduced 

 persistence 

 and re- 

 duced pro- 

 duce of the 

 clover. 



Amounts oj 

 nitrogen 

 removed in 

 the crop 

 and lost by 

 the soil. 



Glover 

 drawing 

 upon sub- 

 soil. 



made on three separate samples, for which the determinations 

 agreed very well. The results can leave no doubt that there 

 had been a great reduction in the stock of nitrogen in the 

 surface-soil since 1857. The reduction amounts to nearly 29 

 per cent of the whole in the 21 years ; and, reckoned per acre, 

 it corresponded, as shown in the table, to a loss of 2732 lb. 

 during the 21 years ; and although, as has been seen, fairly 

 average, and even good crops, were still grown, it is obvious 

 that coincidentally with this great reduction in the stock of 

 nitrogen in the surface-soil, there has been a very marked re- 

 duction in the clover-growing capability of the soil. 



On this point it may be mentioned that, whilst fresh seed 

 was only sown five times during the first 20 of the 40 years, 

 it has been fully or partially sown twenty-one times during 

 the last 20 years. It is obvious, therefore, that the plant was 

 able to stand very much longer in the earlier than in the later 

 condition of the soil. Indeed, both the reduced persistence 

 of the plant, and the reduced produce, have been coincident 

 with a considerable reduction in the stock of nitrogen in the 

 soil. 



The question arises, What relation does the amount of 

 nitrogen lost by the soil bear to the amount taken off in 

 the crops ? 



It is admittedly necessary to accept with some reservation 

 results of calculations of produce per acre from amounts ob- 

 tained on a few square yards, but the general indications may 

 doubtless be trusted. Such estimates show more than 160 lb. 

 of nitrogen to have been removed per acre per annum in the 

 crops over the 21 years ; whilst the estimated loss of the sur- 

 face-soil corresponds to about 130 lb. per acre per annum. 

 That is to say, the loss by the surface-soil is sufficient to 

 account for a large proportion of the nitrogen removed in 

 the crops. 



There is, however, evidence leading to the conclusion that, 

 when excessive amounts of farmyard manure have been 

 applied, as had been the case with this garden-soil, there 

 may be some loss by the evolution of free nitrogen ; and 

 obviously, so far as this may have occurred, there will be the 

 less of the ascertained loss to be credited to assimilation by 

 the growing clover. 



On the other hand, it is known that when growing on 

 ordinary arable soil, the clover plant throws out a large 

 amount of feeding roots in the lower layers ; and although 

 in the case of so rich a surface-soil the plant may derive a 

 larger proportion of its nutriment from that source, we must 

 at the same time suppose that it has also availed itself of the 

 resources of the subsoil. Unfortunately, in 1857 samples 



