118 



THE ROTHAMSTED EXPERIMENTS. 



Failure of 



continuous 



clover-crop- 



ing on 



ordinary 



arable 



land. 



yield of nitrogen was, without nitrogenous manure 32 lb., and 

 with it 36 lb. Reckoned, however, over the years of crop 

 only, the yield of nitrogen in the clover and other crops was 

 77.5 lb. per acre per annum without, and 80.2 lb. with, the 

 nitrogenous manuring. Or, reckoning the nitrogen in the 

 clover alone, and only over the years when it gave any crops, 

 the average annual yield of it over those 7 years was, without 

 nitrogenous manure 100.1, and with it 109.3 lb. There was, 

 therefore, comparatively little increase, either in the pro- 

 duce, or in the yield of nitrogen, by the use of nitrogenous 

 manures. 



To conclude in regard to these experiments : The attempt 

 to grow clover year after year on this ordinary arable land, by 

 means of such mineral manures as increase the luxuriance of 

 growth when there is a fair plant, or even by the addition to 

 these of nitrogenous manures, has entirely failed. In view 

 of this failure to grow the crop continuously on ordinary 

 arable land, the next results to which we have to call atten- 

 tion are of much interest and significance. 



Success of 

 continuous 

 clover-crop- 

 ping on 

 garden soil. 



Condition 

 of the gar- 

 den soil. 



Table 38 

 explained. 



Growth of Red Clover, year after year, on rich Garden Soil. 



In 1854, after it seemed clear that the plant would not 

 continue to grow on the arable land, clover was sown in a 

 garden only a few hundred yards distant from the experi- 

 mental field, on soil which had been under ordinary kitchen- 

 garden cultivation for probably two or three centuries. It is 

 remarkable that, under these conditions, the crop has grown 

 luxuriantly almost every year since — 1893 being the fortieth 

 season of the continuous growth. Further particulars will be 

 given on the point presently, but it may here be premised 

 that, at the commencement, the percentage of nitrogen in the 

 surface-soil of the garden was four or five times as high as in 

 that of the arable soil in the field ; and it would doubtless be 

 richer in all other manurial constituents also. Indeed, after 

 the growth of clover for 25 years in succession, even the 

 second 9 inches of depth was found to be still very much 

 richer in nitrogen than the first 9 inches in the field. 



Table 38 gives the results for each of the 40 years of 

 experiment with clover on the rich garden-soil. The first 

 column after the dates shows the number of cuttings each 

 year, the second the amounts of produce per acre, reckoned 

 in the condition of dryness as hay, the third the amount of 

 dry substance, the fourth that of the mineral matter, and the 

 last the estimated amounts of nitrogen per acre in the crops. 

 At the bottom of the table are given the average annual 

 results, over periods of 10, 10, 10, 10, and 40 years. It 



