230 



THE ROTHAMSTED EXPERIMENTS. 



Advant- 

 ages of 

 rotation. 



Soil nitro- 

 gen in- 

 creased by 

 leguminous 

 crops. 



Nitrogen 

 in grain 

 and straw 

 of wheat. 



an average of more than 42 lb. in the rotation crops, and 

 of 34 lb. in those grown continuously. There is direct 

 evidence, therefore, that there was, under all conditions, 

 more nitrogen available to the crops grown in rotation, 

 than to those growing year after year on the same land; 

 and the advantage is relatively much the greater where no 

 nitrogen had been supplied in manure. The beneficial effect 

 of the interpolation of other crops with the cereals is, there- 

 fore, very obvious. 



In the case of the second crop of the course — the barley — 

 it was shown that without manure the increased produce in 

 rotation was due to scarcely any roots having been grown, so 

 that the land was practically fallowed for the barley; and 

 now in the case of the fourth crop — the wheat — there was 

 the preparation either of the growth of a leguminous crop 

 leaving a highly nitrogenous residue, or of fallowing. Then 

 with superphosphate alone, the produce of barley, and the 

 yield of nitrogen in it, were less than without manure where 

 the turnips had been removed, but more where they had not, 

 and where, therefore, there was an available nitrogenous 

 residue from the roots ; and now in the wheat, the effects on 

 the available supply of nitrogen, on the one hand of the 

 growth and removal of a leguminous crop, and on the other 

 of actual fallow, are observable. Lastly, with the mixed 

 manure the influence of the direct supply of nitrogen for the 

 first crop of the course is obvious. But, as the amounts of 

 nitrogen taken up were not very much more than where none 

 had been supplied, it is evident that in both cases much must 

 have been due to the influence of the preceding leguminous 

 crop or fallow. 



Upon the whole, there can be no question that, so far as 

 nitrogen is concerned, the supply within the soil in a con- 

 dition of combination and of distribution available to the 

 wheat is increased, both by fallow, and by the growth of a 

 leguminous crop, especially of clover ; and, further, that such 

 accumulation of available nitrogen by fallow, and of nitro- 

 genous crop-residue by the growth of leguminous crops, is 

 the greater when the soil and subsoil are not abnormally ex- 

 hausted of organic nitrogen. 



Lastly, it is to be observed that, under all conditions of 

 manuring, or other treatment, there was, both in the rotation 

 and in the continuous wheat crops, more than twice, and in 

 some cases considerably more than twice, as much of the 

 total nitrogen of the produce stored up in the grain as in the 

 straw. Hence, in the sale of the grain, and the retention of 

 the straw for home use, by far the greater part of the nitrogen 

 of the crop is exported from the farm. 



