56 INFLUENCE OF PREVIOUS MANURING. 



Isle of Bute, in 1847. Three portions of the same field manured 

 alike at the rate of 24 carts of farm-yard dung, and 16 bushels 

 of bones per acre, gave respectively 34f , 32J, and 27J tons of 

 Swedish turnips. The differences, therefore, were- 

 Between the 1st and 2d portions, 2 tons. 

 1st and 3d portions, 7? tons. 



Some of this enormous difference of 7 tons must be ascribed 

 to a natural difference in the quality of the soil on the several 

 experimental plots, but some of it may fairly be ascribed also to 

 the unlike quality of the farm-yard manure applied to the several 

 portions, and to its consequent unlike action upon the bones. 



I might select from the materials now before me many other 

 experiments which lead to the same conclusion : and if such 

 differences may exist in the quality of the manure made on the 

 same farm, much more may it be the case with that of different 

 farms. Hence the reason why in some cases that is, on 

 some farms an admixture of sulphate or of nitrate of soda, or 

 of sulphate of ammonia, with the fold-yard manure, made a 

 sensible increase of the crop ; in others no appreciable benefit 

 seemed to follow from the addition ; while in others, again, the 

 produce was actually diminished. The admixtures being the 

 same, such differences might be ascribed altogether to the 

 unlike qualities of the manure employed, were it not that the soil 

 in the different cases might have varied also, and thus have 

 produced differences in the results, which we have no means of 

 estimating. As in so many other published experiments, we 

 have two disturbing causes, and only one result out of which 

 to extract the precise effect of each. 



2. Influence of the previous treatment of land upon the results 

 of field experiments. Long-continued action of bones. 



Every practical man knows that the previous treatment of a 

 field or farm, the kind of cropping and manuring to which it 

 has been subjected in former years, has an important influence 

 upon its fertility at any given time. Such previous treatment 

 may materially affect the results of experimental trials made 

 upon the land. 



The effect of bones applied for the first time is not forgotten 



