On Agricultural Chemistry. 



35 



of rotation and home manuring ! Collateral experiments also 

 clearly prove the im.portance of a liberal supply of organic sub- 

 stance rich in carhon — which always contains a considerable quan- 

 tity of nitrogen also — if w e would in practical agriculture increase 

 the yield much beyond the amount which can be obtained by 

 mineral manures alone; and these conditions being fulfilled, 

 the direct supply of nitrogen, on the other hand, is by no means 

 so generally essential. And it is where w^e have provided a 

 liberal supply of constituents for organic formations, in addition 

 to the mineral manures, that we have found the use of alkalies 

 not to be without effect. 



But it is at any rate certain that phosphoric acid, though it 

 forms so small a proportion of the ash of the turnip, has a very 

 striking effect on its growth when applied as manure ; and it is 

 equally certain that the extended cultivation of root crops in 

 Great Britain cannot be due to the deficiency of this substance 

 for the growth of corn, and to the less dependence upon it of the 

 root crops, as supposed by Baron Liebig. 



These curious and interesting facts in relation to the growth 

 of turnips, as well as those which have been given in reference to 

 wheat and to the leguminous crops, are sufficient to prove how 

 impossible it is to form correct opinions on agricultural chemistry 

 without the guidance of direct experiment in the field. And we 

 are convinced that if Baron Liebig had watched the experiments 

 which we have had in progress during the last eight years, he 

 would long ago have arrived at conclusions in the main agreeing 

 with those to which we have been irresistibly led : and we are 

 disposed to believe that had he even seen the more detailed 

 accounts of our results given in our own papers in this JournaL 

 instead of the mere reference to them made by Mr. Pusey, he 

 would rather have accepted them, as a step in an inquiry to 

 which his own researches and writings had given such an impetus, 

 than have designated them, as he has done, as entirely without 

 value. 



So much, then, for the results of experiments in the field, and 

 for the considerations in relation to the functional actions of 

 plants, as bearing upon the character of the manure required for 

 their growth in a course of practical agriculture. Let us now 

 consider for a few moments what really are the main and cha- 

 racteristic features of practical agriculture, as most generally 

 followed in this country. 



Let us suppose that the rotation adopted is that of Turnips, 

 Barley, Clover, Wheat ; that the turnips and clover are consumed 

 upon the farm by stock, and that the meat thus produced, 40 

 bushels of barley and 30 bushels of wheat, are all the exports 

 from the farm, the manure from the consumed turnijos and clover, 



D 2 



