6 On Paring and Burning. 



The failure of Liebig's mineral manures, to whatever it may 

 have been due, however, does not prove the unsoundness of the 

 principle so clearly announced in Liebig's writings, namely, the 

 principle that plants cannot grow vigorously if the mineral con- 

 stituents found in their ashes are deficient in the soil or in the 

 manure applied to it. Liebig's position in enforcing this truth 

 is unassailable ; nor has it indeed been assailed by any one who 

 can lay claim to the title of a man of science. It is, in reality, 

 not in principle but in practice that Liebig has failed. And 

 this need not excite surprise ; for, however true a principle 

 may be in the abstract, such a principle, if applied to a subject 

 upon which it can have no bearing, is evidently misapplied, and 

 likely to lead to errors in practice. Thus it is unquestionably 

 necessary upon a purely sandy soil, containing very little besides 

 silica, to use a manure which includes all the mineral elements 

 found in the ashes of the crop intended to be raised. In this 

 case the abstract principle finds a strict application hence a 

 corresponding useful practical effect. But if a manure, composed 

 entirely of the ash-constituents of plants, is applied to clay soils, 

 and many other soils, containing an almost inexhaustible supply 

 of those very minerals which are added to it in the shape of a 

 mineral manure, it is plain that the same abstract truth can find 

 no application. The result of such misapplications of a correct 

 principle naturally must be what it has since proved to be in 

 numerous instances a complete failure. But, as just mentioned, 

 the failure which has in many instances attended the application 

 of purely mineral manures does not show that mineral substances 

 are useless in relation to vegetable life, much less that organic 

 matters after all are more important in relation to the growth of 

 plants than mineral substances. These mineral matters are 

 essential to the very existence of every kind of agricultural pro- 

 duce, and must, therefore, be present in the soil, or in the manure 

 applied to it, or else they will not grow ; organic food may be 

 altogether wanting in the soil or the manure, for under favourable 

 circumstances the plant can get it from the atmosphere. Thus 

 in a certain sense mineral matters are the more important. 



Whether it is advisable to apply mineral or organic food to the 

 soil, in cultivating certain crops on land of a particular descrip- 

 tion, is another and, as far as practice is concerned, an equally 

 important question. Here it may happen, and does happen, in 

 the case of many soils, at least in England, that the artificial or 

 direct application of minerals (not the minerals themselves) is of 

 no use whatever. Speaking of the application of mineral matters 

 in such a case, most purely mineral manures may justly be con- 

 sidered to be unimportant, or at any rate of doubtful efficacy 

 much less valuable than organic manures. But it cannot be said, 

 in a general way, that mineral matters are less important than 

 organic manuring elements, nor the reverse. 



