clover. 



120 THE ROTHAMSTED EXPERIMENTS. 



should be stated that, as the garden clover plot is only a few 

 yards square, calculations of produce per acre can only give 

 approximations to the truth ; but it is believed that they can 

 be thoroughly relied upon so far as their general indications 

 are concerned. It may be added that five times during the 

 whole period, gypsum has been applied to one-third, and a 

 mineral manure containing potash, but no nitrogen, to another 

 third of this plot. 

 Produce of We shall confine attention to the amounts of produce 

 tinuouky rec koned as hay, and to the estimated amounts of nitrogen in 

 grown the produce. Casting the eye down the column of produce 

 as hay, it is seen at a glance that, excepting a few occasional 

 years of very high produce during the later periods, the 

 amount of crop is very much greater during the first than 

 during either of the subsequent periods of 10 years. In fact, 

 as is seen at the foot of the table, there was an average 

 annual produce equal to 10,689 lb. of hay over the first 

 period of 10 years, but of only 5561 lb. over the second, 

 5099 lb. over the third, and 5202 lb. over the last 10 years. 



Now, even these latter amounts correspond to what would 

 be considered fair though not large crops, when clover is 

 grown in an ordinary course of rotation, once only in 4, 

 or in 8 years, or more ; so that the produce in the earlier 

 years on this rich garden-soil was very unusually heavy. 

 Indeed the average annual produce over the whole period of 

 40 years — namely, 6638 lb., or nearly 3 tons of hay — would 

 be a very good yield for the crop grown only occasionally in 

 the ordinary course of agriculture. 

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

 nitrogen m ^ e table, which show the estimated amounts of nitrocren in 



tii/€ C07ltl7t m ^ 



uously the crops, that the importance and significance of these 

 grown results obtained on rich garden-soil are fully recognised ; 

 cover 7 op. ^^ ^j s j s especially the case when they are compared with 

 those obtained on ordinary arable land. 



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

 or oats, will be from 40 to 50 lb. per acre ; of beans about 

 100 lb.; of meadow-hay about 50 lb.; and of clover grown 

 occasionally in rotation from 100 to 150 lb. ; but here, on 

 this rich garden-soil, the produce of clover has in one year 

 contained more than 400 lb. of nitrogen, in three years more 

 than 300 lb., in several more than 200 lb., and in only 

 thirteen years of the 40 less than 100 lb. 



In fact, as the figures at the bottom of the table show, the 

 estimated average annual yield of nitrogen in the above- 

 ground growth was — over the first 10 years 257 lb., over the 

 second 10 years 133 lb., over the third 10 years 122 lb., over 

 the last 10 years 125 lb., and over the whole period of 40 



