On the Growth of Barley hy different Manures, ({c. 507 



Let us now for a moment review as a vv^hole, the various field 

 experiments on the growth of barley. It has been found, that the 

 amount of produce when grown after a succession of removed 

 unmanured, or even highly mineral-manured turnip crops, was 

 far below a moderate agricultural yield. It was seen, that by the 

 simple addition of nitrogenous manure to land in this condition, 

 enormous crops were raised. When barley was grown without 

 manure year after year, on land in a less artificially exhausted con- 

 dition than that where ten successive turnip crops had been grown, 

 the produce was considerably greater than after the succession of 

 turnip crops. On this land mineral manures somewhat increased 

 the produce. But, as on the turnip-exhausted land, nitrogenous 

 manures did so much more strikingly. In both fields, indeed, 

 the amount of available nitrogen supplied to the soil, ruled the 

 amount of produce very much more strikingly, than did the 

 supply of the necessary mineral constituents of the crop. In 

 growing barley in rotation, on land previously brought to that 

 comparative state of exhaustion, in which, under ordinary cul- 

 tivation with home manuring and ordinary cropping, the conclu- 

 sion of a course will leave it, the unmanured produce of barley 

 throughout three subsequent courses of an entirely unmanured 

 rotation, was considerably greater than that where barley was 

 grown year after year ; and it was still further in excess of that 

 obtained after a series of unmanured turnip crops. 



Here then is a striking effect upon the produce of barley by 

 gi'owing it in a rotation — even unmanured — of turnips, barley, 

 clover, wheat. When the turnips in such a rotation were 

 grown by superphosphate of lime, and by it larger crops of the 

 roots removed than without manure, the produce of barley was 

 less than after the unmanured turnips. Here too, then, the pro- 

 duce of barley is diminished after unusual exhaustion by turnip 

 cropping. But either the consumption of the superphosphated 

 turnips on the land, the residue of a mixed mineral and nitro- 

 genous manure after turnips grown by it had been carted off, or 

 the consumption of these turnips on the land, greatly increased 

 the subsequent produce of barley above that of the turnip ex- 

 hausted rotation land. It could certainly not be the restoration 

 of mineral matters, to which, in these cases the increased pro- 

 duce of barley was mainly due ; for the increase was greater by 

 the consumption on the land of the merely superphosphated 

 turnips, than by the residue of far richer mineral (and organic) 

 man^i'e where the turnips grown by it had been removed, taking 

 away but a small proportion of the supplied minerals ; and it 

 was greater still where these highly manured turnips Avere fed 

 on the land, and returned to it a considerable amount of nitrogen, 

 in addition to the ah'eady relative excessive amount of minerals. 



