NITROGEN ACCUMULATED IN CLoVKi: CI.'OPS 117 



Now even this latter amount eorrcspon*!.-- lo what wdiiM I'r 

 considered a fair, though not a large erop, when elovrr is grown 

 in rotation once only in four or eight years or more ; so tliat tin* 

 produce in the earlier years on this rich garden soil was very 

 unusually heavy. Indeed the average annual produce over tlie 

 whole period of fifty years — namely, 5794 lit., or more than 2\ 

 tons of hay — would be a good yield for the eroj) grown only 

 occasionally in the ordinary course of agriculture. 



But it is when we look at the figures in the last eohunn of 

 the table, which show the estimated amounts of nitrogen in the 

 crops, that the importance and significance of these results 

 obtained on rich garden soil are fully recognised ; and this is 

 especially the case wdien they are compared with those 

 obtained on ordinary arable land. 



Thus the amount of nitrogen in fair crops of wheat, barley, 

 or oats, would be 40-50 lb. j^er acre, of beans about 100 lb., of 

 meadow hay about 50 11)., and of clover grown in rotation, from 

 100 to 150 lb. ; but on this rich garden soil the produce of 

 clover has in one year contained more than 400 lb. of niti-ogen, 

 and the average over the first ten years was 247 il>. The 

 average over the whole period of fifty years is 140 lb., or about 

 as much as a fair but not large crop gi'own occasionally under 

 the ordinary conditions of agriculture. 



Analysis of the soil taken at intervals would seem to show 

 a considerable falling-off in the amount of nitrogen and carbon 

 contained in the surface soil, not sufiicient however to account 

 for all the nitrogen removed by the clover crop. 



It will be apparent from a consideration of the eiops 

 reported for the later years of the experiment that great dilli 

 culty is beginning to be experienced in maintaining a plant 

 of clover ; re-seeding, which was only necessary live times in t In- 

 first twenty years, had to be carried out nine times in the last 

 ten years, during which time also the crop has wholly failed for 

 two years, and almo.st wholly for a third. 



Dm-ing January 1897 the plots were inoculated with the 

 watery extract of the rich kitchen-garden soil at Kothamsted. 



