On Agricultural Chemistry, 



31 



this result with a theory which supposes the produce of wheat to 

 rise and fall with the quantity of minerals available within the 

 soil. If, however, we admit that the first crop of wheat could 

 not take up the mineral matters existing in the soil for want of 

 nitrogenous supply, and that the clover crop, not being so de- 

 pendent upon supplied nitrogen, was able to take up the minerals 

 required for its growth, and that it moreover left in the soil, 

 sufficient ammonia, or its equivalent of nitrogen in some form, to 

 give the increased crop of wheat, we have a much more consistent 

 and probable solution of the results. There is little doubt that 

 M. Boussingault could have increased his produce of wheat by 

 means of ammoniacal salts : whether he could have done so 

 economically is another question, depending of course upon the 

 relative prices of grain and ammonia. 



In our paper upon the growth of wheat, published in the 

 Journal of the Royal Agricultural Society in 1847, we have 

 attempted an estimate of the probable amount of nitrogen 

 required to obtain a given amount of it in the increased produce. 

 We there provisionally assumed that 5 lbs. of ammonia were 

 required to produce an increase of one bushel of corn and its 

 equivalent of straw. We do not intend to enter fully into the 

 question of the accuracy of this estimate on the present occasion, 

 but we may observe in passing, that among the plots the history 

 of which we have given in the foregoing pages down to the last 

 harvest, there is not one, even under the best conditions as to 

 artificial mineral supply, where the ammonia, on the average of 

 seasons, has given an increase equal to that supposed in our 

 estimate. And even supposing that the farm-yard manure em- 

 ployed in our experiments contained no more nitrogen than we 

 have stated would have been provided in merely wetted straw, we 

 have not obtained by its means as much as a bushel of corn and 

 its equivalent of straw for each 5 lbs. of ammonia thus supplied 

 in the manure. It may be said, perhaps, that the circumstances 

 of experiments wherein wheat has been grown for several years 

 successively on the same land, are very artificial ; but such is the 

 result which they have yielded, and it is at any rate worthy of the 

 serious attention of the reader. In some cases of our experi- 

 ments, however, which are in no degree less artificial, a slightly 

 better result has been obtained. But to this point we shall recur 

 on some future occasion. 



Without further inquiring then, into the correctness of our 

 estimate, it would seem that a loss of this kind during the growth 

 of the plant is a fact which is sufficiently substantiated, at once by 

 the practical experience of the farmer, and by experiments of an 

 irulependent kind relating to it. And, let it once be recognised, 

 in agricultural science, that there is a definite expenditure or 



