252 A VISIT TO EOTHAMSTED. 



food tlins liberated, but such is not the case. Either the soil 

 retains this nitrogen in a form which renders it difficult for the 

 plant to assimilate it, or it is carried down to depths where the 

 plant cannot reach it, and ultimately finds its way into the 

 drains. 



The investigation of this problem has long occupied the 

 attention of the experimenters at Eothamsted, and plot 7 (1) 

 forms a contribution to the investigation. This plot, after the 

 removal of the twentieth crop in 1871, had the application of 

 farmyard manure discontinued in order to see how much of the 

 large residue of ammonia derived from these twenty years 

 manuring was still in the soil and available for the growth of 

 succeeding crops. The result is that each year since the discon- 

 tinuance of the manure the crop has diminished, and that the 

 average crop during the six years in which manure has been 

 withheld is 10 bushels less per acre than during the preceding 

 twenty yeiirs ; thus shewing that a large amount of valuable 

 nitrogenous plant food has been carried away out of the reach of 

 the plant. It is intended to continue the experiment until the 

 crop on 7 (1 h) shall have reached the same state of fertility as the 

 unmanured plot at the beginning of the experiment (viz., 21^ 

 bushels per acre), and thus some information will be gained 

 regarding the vexed question of the value of unexhausted 

 manure. 



There is another interesting point brought out in this in- 

 vestigation which does not appear in the above table, viz., that 

 since the beginning of the experiments there has been a gradual 

 increase in the weight per bushel of the barley over all the plots, 

 amounting to from 2 to 3 pounds per bushel, but whether this 

 is due to the increased density of the grain or its diminished size 

 enabling it to pack closer does not appear. 



The experiments upon wheat come next to be noticed. These 

 are carried on on Broadbalk Field, which consists of about 13 

 acres. It was put under the first experimental crop of wheat in 

 1844, and has borne wheat crops continuously ever since. There 

 was then probably no one in England who would have been rash 

 enough to predict that after thirty-five years continuous wheat 

 growing there would be found in this field plots showing no 

 diminution in the quantity or equality of the annual crop ; yet 

 such is really the case, notwithstanding the many reservations 

 and doubts as to the amount of success in the various experi- 

 ments and the anticipations of probable failure of the scheme 

 when it was first propounded. 



The following table of experiments with wheat gro\vn con- 

 tinuously, stating the manure per acre per annum and the 

 j'jroduce per acre, exhiluts the results olitained on the more 

 imT)t)rtant plots of Broadbalk Field : — 



