No. VIII.] EXPERIMENTS UPON OATS AND WHEAT. 69 



employed as a manure has been in top-dressing the wheat crop (see the prece- 

 ding part of this Appendix, p. 19). Has it,therefore, some s;7e^«a^ adaptation to 

 the wheat crop — which will account at once for its comparative failure upon oats, 

 turnips, and potatoes, and for its superior efficacy to guano upon the wheat crop 

 — in the proportions stated, and even in a very dry summer 1 The comparative 

 efficacy of the two substances applied in various proportions is certainly deserv- 

 ing of further investigation. It will be a gain not only to practical but to theo- 

 retical agriculture, should it be established that rape-dust can be profitably 

 applied to the wheat crop, in circumstances when it would be thrown away upon 

 oats or turnips. By turning to the next series, that of Mr. Fleming (p. 54), it 

 will be seen that the last result there stated is also favourable to the action of 

 rape-dust upon the wheat crop.* 



3°. Mntuaily counteracting injiuence of different nmnures. — But another curi- 

 ous observation presents itself in the table of Lord Blantyre's results. It is in 

 the apparent struggle between the good and evil influences of the rape-dust on 

 the one hand, and of the saline substances on the other, when they we re applied 

 together to the same plot of wheat (see Appendix, p. 19). Thus, when applied 

 in the proportions above stated — 



Increase. Decrease. 



Common salt gave .... — IJ bush. 



Rape-dust gave 3j bush. — 



One-half of each gave . . . 2| bush. — 



Or the natural effect of the rape-dust was lessened one-third when mixed with 

 the given weight of common salt. So, also — 



Increase. Decrease. 



Sulphate of soda gave ... — 9y bush. 



Rape-dust gave 3j bush. — 



One-half of each gave ... — 3 bush. 



Or the influence of 1 cwt. of sulphate of soda for evil was one-third greater than 

 that of 16 cwt. of rape-dust for good — in the given circumstances of soil, climate, 

 and crop. This result, which at present seems only curious, may hereafter lead 

 to the establishment qf interesting truths capable of practical application. 



Suppose, for instance, that upon two fields rape-dust were applied to the 

 wheat crop at the rate of 16 cwt. per acre, and that the one field contained na- 

 turally in its surface soil the proportion of sulphate of soda employed in Lord 

 Blantyre's experiment, while the other contained none — then in the one case 

 the rape-dust would not only expend all its influence in overcoming the tenden- 

 cy of the sulphate to lessen the crop, — but would even seem to do harm if the 

 produce were compared with that of another field, of apparently similar soil, 

 near the surface of which this abundance of sulphate did not exist ; while, in the 

 other case, the rape-dust, having no counteracting influence to overcome, would 

 spend itself entirely in increasing thegrowth of the plant and the final yield of 

 • grain. 



Or suppose an artificial guano or other mixed manure artificially prepared, 

 to contam two or more substances which, in the soil they are applied to, have 

 a tendency to produce opposite eflfects — the one to increase, the other to 

 diminish, the amount of produce — the effect of this conflicting action of its 

 component substances would be such as to render the mixture of less efficacy, 

 perhaps of no efficacy at all — it might be even injurious to the crops, — although 

 It contained substances which, if applied alone, would have exhibited a power- 

 ful fertilizing action. 



These two illustrations are sufficient to show the kind of light which obser- 

 vations, such as the one above adverted to, may hereafter throw upon practical 

 agriculture. 



II. The substance of Mr. Fleming's table (p. 54), may be thus presented. 



* See also the subsequent observations on the experiments upon beans. 



