r.>12] mi Recent Advances in At/n'cnUiiral tSciciice. 517 



weeds. As these losses do not appear in the hahmce-sheet we must 

 conclude that some recuperative action is at work keeping up the 

 stock, thouirh the process is not sufficient wholly to make up for 

 the removals in the crop. The results of rhis plot show two 

 principles at work — the tendency of the land under an unchanging 

 system of farming to reach a position of equilibrium when the 

 only variations in the crop are those brought about by seasons ; 

 and, secondly, that regeneration of the nitrogen stock in the soil 

 is possible by natural causes alone. 



We may now turn to one of the other plots which receives 

 an excess of farmyard manure each year, the manure supplying 

 about 200 lbs. of nitrogen per acre, whereas the crop only takes 

 away about ;")() lbs. Naturally the land in this case increased in 

 fertility, but after twenty or thirty years another position of 



BUOADKALK WlIEAT FlELD. 



Nitro;;cn in Soil, lb. per acre. 



In Soil, In Soil, I f±?^ ! '^'^i.'''^ '^In'''' Removed |u„accounted 



T^fii; iQiu ^°^s in in in in f 



1865. 1904. 39 ^.^^^.^ ! J^lanu^e. Riiin. Crop. | ^°^- 



Plot 3 — Unmauured. 



equilibrium was attained at a level of about 36 bushels per acre, 

 after which, despite the continued additions of manure, the crop 

 again did not vary except as the result of exceptional favourable 

 seasons. If we now consider a similar balance-sheet for this plot, 

 we find that the additions of nitrogen are balanced neither by the 

 removals in the crop nor by the accumulation of nitrogen in the 

 soil ; indeed half of the nitrogen applied is unaccounted for. The 

 soil has been getting no richer for the last twenty or thirty years, and 

 the greater part of the nitrogen is wasted, doubtless because bacterial 

 action sets the nitrogen free as gas. Here, then, we see another prin- 

 ciple illustrated, that in very rich land the wasteful agencies are so 

 speeded up as to prevent any continued accumulation of fertihty out 

 of the unused residues of the manures put on. Higher fertility means 

 a higher level of waste, and this explains the rapidity with which the 

 very rich virgin soils lose their fertility when they are put under 

 arable cultivation. In this Rothamsted plot, the soil of which still 



2 M 2 



