LEGUMINOUS CROPS. 



121 



years 159 lb ; whilst, as the details show, the yield of nitrogen 

 in the thirty-first year (1884) was about 240 lb., in the 

 thirty-second year 156 lb., in the thirty-sixth year 208 lb., in 

 the thirty-eighth year 161 lb., and in the fortieth 143 lb. 

 Further, the averages over the second, third, and fourth, 10 

 years of the continuous growth (133, 122, and 125 lb.) were 

 about as much as in a fair but not large crop grown occa- 

 sionally under the ordinary conditions of agriculture ; whilst 

 the average of the 40 years, 159 lb., is as much as in a 

 really good crop grown occasionally in rotation. 



There would seem, then, to be clearly indicated, a soil- Condition 

 source of failure on the arable land, and a soil-source of fj^L f£ 

 success on the garden-soil. ftuence. 



The results given in Table 39 will throw some further 

 light on this point. It shows the percentage of nitrogen in 

 the first 9 inches of depth of the garden-soil, in 1857 and in 

 1879, between which periods the growth of 21 years had 

 been removed. It also shows the estimated amounts of 

 nitrogen per acre in the surface-soil at the two periods, and 

 the reduction in the amount during the 21 years. 



TABLE 39. — Red Clover, grown on rich Garden-Soil. Nitrogen 

 per cent, and per acre, in the fine soil, dried at 100° C. (First 

 9 inches of depth.) 



It may be mentioned that the percentage of nitrogen given 

 for the sample collected in October 1857, is the mean of 

 duplicate or more determinations, made in 1857, in 1866, and 

 again in 1880 ; and it is almost identical with the results 

 obtained at the latest of these dates. 



The first point to notice is that the first 9 inches of depth Richness of 

 of this rich garden-soil contained more than half a per cent the garden 



SOIL t7h 



of nitrogen — that is, nearly four times as much as the average nitrogen. 

 of the Eothamsted arable soils, and nearly five times as much 

 as the exhausted arable clover-land-soil where the crop failed. 

 It is, of course, true that the garden-soil would be corre- 

 spondingly rich in all other constituents ; but some portions 

 of the arable soil where the clover failed, had received much 

 more of mineral constituents by manure than had been re- 

 moved in the crops. 



The result given for 1879 is the mean of determinations 



