ROTATION OF CROPS. 



221 



tilth for great development of fibrous root within the soil. 

 The results with the mixed manure are, of course, the most Greater 

 comparable with those of ordinary practice ; and it is clear ^^ m 

 that, however explained, much more produce is obtained 

 under rotation than with continuous growth. It need only 

 further be remarked that, of the total dry matter produced, 

 there are many times as much in the edible root as in the leaf 

 which almost wholly remains only for manure again. 



The Dry Matter in the Barley Crops. — The second division 

 of Table 60 compares the amounts of dry matter yielded in 

 barley, grown, respectively, in rotation, and continuously — 

 that is, year after year on the same land. The results for the 

 continuously grown crops relate to the average produce of the 

 same eight seasons as those in which the rotation crops were 

 obtained. The unmanured and the superphosphate conditions Manurial 

 were also quite parallel in the two series of experiments. In tnatment - 

 the case of the mixed manure results, it should be borne in 

 mind that in the rotation experiments a quantity of manure 

 was applied for the preceding crop — the turnips — which is 

 supposed to carry the whole of the crops of the four years' 

 course ; whilst, in the continuous experiments, the quantity 

 of nitrogen, for example, which is applied each year for the 

 immediate crop, amounts to rather more than one-fourth of 

 that applied for four years in the rotation experiments. 



The figures show that — without manure — there was much No man- 

 less dry matter in grain, straw, and total produce, in the crops ure " 

 grown continuously than in those grown in rotation ; in fact, 

 in the total produce only about three-fifths as much. The 

 much higher amount under rotation is quite consistent with 

 the explanation that in the rotation experiments without 

 manure, the roots having failed, the barley crop had, in point 

 of fact, the benefit of the preparation which bare fallow is 

 known to confer. 



With superphosphate alone, the continuously grown barley With 

 crops yielded more dry matter in grain, straw, and in total s ^^ hos ' 

 produce, than those without manure ; the excess being largely 

 due to increased capability of utilising the available nitrogen 

 of the surface-soil, under the influence of the phosphatic man- 

 ure. Both sets of the superphosphate rotation crops yielded 

 more dry matter than the continuous ones, the excess being, 

 however, much less where the rotation roots had been removed 

 than where they had been consumed or spread upon the land. 

 The effect of the growth and accumulation by the previous Crop 

 root-crop, and of the more or less available manurial residue residue ' 

 left under the different conditions, as compared with the re- 

 sult when the barley is grown year after year on the same 

 land, is thus very evident. 



