TXCKEASKI) FKiniLrrV OF DT'Xr.F.r) IMOT :;•! 



lb. of potash per acre in tlie top \) inches of soil, though of 

 course tlie greater part of the hitter would only ])econie avail- 

 able for the plant very slowly. 



On Plot '2 there has been a yearly dressing of 14 tons of 

 farmyard manure, and though the composition of the duuL: is 

 so far variable that it is impossible to say exactly what 

 quantity of plant food has been supplied, the annual applica- 

 tion is estimated to contain al)out '200 lb. of nitrogen, 78 lb. of 

 phosphoric acid, and 235 lb. of potash ; whereas the average 

 crop has only removed al)out ^fo lb. of nitrogen, 27 lb. of 

 phosphoric acid, and 52 lb. of potash per acre. There should 

 be an accumulation of fertihty on this plot, and an examination 

 of the curve shows that after a rapid rise during the first eight 

 years of the experiments, when the land was recovering from 

 a state of comparative exhaustion, the yield of grain has been 

 slowly increasing, despite the depression during the decade 

 1872-81. The increase is particularly manifest during the last 

 ten years, on the whole a period of dry seasons, when the 

 moisture retained by the accumulation of hunuis from the dung 

 also had its effect. Tlie increased fertility of this plot would 

 doubtless have been more manifest were it not for the tendency 

 of the crop to be laid in the heavier yielding seasons. The 

 analyses show that enormous reserves of plant food have been 

 accumulated in the soil of this plot, the amount of nitrogen in 

 the surface soil l)eing more than double that of the unmanuretl 

 plot, the phosphoric acid being also almost doubled, and the 

 potash showing a very considerable increase. While some of 

 these reserves are in a readily available form, there is evidence 

 from the other experiments at Itothamsted that even in fifty 

 years it would ])e impossible to crop them entirely out, if ;i 

 course of iirowin^i; corn without further nianuiinu were now 

 entered on. 



Regarding now Plots 6 and 7, receiving artilicial manures 

 which supply nitrogen, potash, and phosphoric acid, but no 

 organic matter to form humus, we see that Plot 7 has 

 throughout yielded a crop very little inferior to that lmowu 



