LEGUMINOUS CROPS. 127 



with the same descriptions and quantities of manuring sub- 

 stances, applied to the surface-soil. Further, whether the 

 success in some cases, and the failure in others, would afford 

 additional evidence as to the source of the nitrogen of the 

 Leguminosae generally, and as to the causes of the failure of 

 red clover when grown too frequently on the same land. 



Accordingly, fourteen different Leguminosse were selected, Crops 

 and sown in 1878. These included eight species or varieties s ^l ed ^ or 

 of Trifolium, two species of Medicago, Melilotus leucantha, 

 Lotus corniculatus, Vicia sativa, and Lathyrus pratensis. 

 Of these, six of the eight Trifoliums have already failed, and 

 been replaced by other plants ; as also have the Medicago 

 lupilina, the Lotus corniculatus, and the Lathyrus pratensis, 

 the last being replaced in the second year by Onoorychis 

 sativa. The plants which have maintained fair, but very 

 varying, character of growth, are the Trifolium rejpens, Vicia 

 sativa, Melilotus leucantha, and Medicago sativa ; and we pro- 

 pose to give some account of the growth of these plants on 

 the clover-exhausted soil. 



That the surface-soil had become very poor in nitrogen is Soil poor 

 evident from the fact that the mean percentage of it in the in nltr0 9 en - 

 sifted dry surface-soil of five of the clover plots was, in March 

 1881, only 0.1058, which is considerably lower than was 

 found in the same field many years before ; and lower than 

 has been found in any of the fields at Eothamsted, excepting 

 those where crops have been grown for many years on the 

 same land without nitrogenous manure. It is a point of 

 interest, however, that the percentage in the surface-soil was 

 not so low as in immediately adjoining land, which had been 

 under alternate wheat and fallow for nearly 30 years without 

 manure. 



The real interest of the results depends on the amounts, Thepoints 

 and on the difference in the amounts, of nitrogen which the °f mterest - 

 various plants have assimilated over a given area, all growing 

 side by side on the same red clover-exhausted land, and with 

 the same mineral manures, without any supply of nitrogen. 



Accordingly, the upper part of Table 42 (p. 128) shows the Table 42 

 estimated average amounts of nitrogen in the gramineous ex v laA ' Md " 

 crop — wheat, grown in alternation with fallow, over 27 years 

 to 1877 inclusive, and in the red clover (together with other 

 crops when it failed) over 29 years, also to 1877 inclusive. 

 Then, in the body of the table are given the amounts of nitro- 

 gen in the wheat alternated with fallow, and in the produce 

 of five different leguminous plants during the subsequent 

 years, commencing with 1878, and extending in some cases 

 to 1891. 



Thus, over the preliminary period, the wheat gave an 



