24 RESULTS OF EXPERIMENTS AT ROTHAMSTED, 



has been seen, fairly average, and even good crops, were still grown, it 

 is obvious that coincidently with this great reduction in the stock of 

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

 the Clover-growing capability of the soil. 



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

 sown four times during the first 1 7 of the 35 years, it has been fully or 

 partially sown 16 times during the last 18 years. It is obvious, there- 

 fore, 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 T 



It is admittedly necessary to accept with some reservation results of 

 calculations of produce per acre, from amounts obtained on a few 

 square yards, but the general indications may doubtless be trusted. 

 Such estimates show more than 160 Ibs. of nitrogen to have been 

 removed per acre per annum in the crops, over the 21 years ; whilst the 

 estimated loss of the surface-soil corresponds to about 130 Ibs. per acre 

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

 account for rather more than three-fourths of the amount of nitrogen 

 removed in the crops. 



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

 case of soils to which excessive amounts of farmyard manure are 

 applied, as, for instance, to such a garden soil, there may be some loss 

 by the evolution of free nitrogen ; and obviously so far as this may 

 have occurred in the garden soil, 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 root 

 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 were 

 only taken to the depth of nine inches, so that no comparison can be 

 made of the condition of the subsoil at the two periods. It may be 

 observed, however, that in 1879 the second nine inches showed about 

 three times as high a percentage of nitrogen as the subsoils of the arable 

 field at the same depth ; indeed nearly twice as high a percentage as 

 some of the exhausted arable surface-soils. It cannot be doubted, 

 therefore,- that the subsoil of the garden plot has contributed nitrogen 

 to the Clover crops. 



Here then, notwithstanding the very little effect of direct nitrogenous 

 manures, on either the Beans or the Clover, on the ordinary arable 

 land, there would seem to be very clear evidence of a. soil-source of, at 

 any rate much, if not indeed of the whole, of the enormous amounts of 

 nitrogen assimilated over a given area by the Clover growing on the 

 rich garden soil. 



