1864,] CHEMISTRY OF MANURES. 211 



making a most satisfactory reply. We know, from the results of 

 numberless analyses of soils, that wheresoever we plunge a spade 

 ten inches deep into an average arable soil, we intersect a layer of 

 nitrogenous plant-food, held as " availably " as the cinereal stores, 

 and sufficient in quantity to nourish good wheat-crops, year after 

 year, ybr upwards of seven centuries. 



To this magnificent nitrogenous reserve large-handed Nature 

 liberally adds, out of our plenteous atmospheric stores, at least 

 two thirds of the quantity annually required, even when this is 

 calculated at the most liberal rate of farming ; so that it will take 

 2100 years to exhaust our underground stock of nitrogen. If 

 therefore we have, as we are assured, phosphates for 1000 years, 

 our ammoniacal wealth (computed by the same rule) is fully twice 

 as great ; and these figures, be it observed, do not take into 

 account (on either side) so much as a third of the depth really 

 explored by the absorbent roots. 



Why, then, do these annual wheat-crops refuse to grow ? With 

 all this ammonia lying amongst their roots, and with cinereal sup- 

 plies in similar profusion, why are these corn-plants (to use the 

 husbandman's metaphor) so " shy ?" We turn naturally to the pro- 

 pounders of the " inexhaustible " theory for an explanation. Alas ! 

 we find that they studiously refrain from pressing the ammoniacal 

 half of their argument. They place at our disposal phosphates 

 for 1000 years, potash for twenty centuries, and silica for a three- 

 fold cycle of time ; but of ammonia, by the same rule similarly 

 abundant, they will not grant us one poor century's supply, nor, 

 indeed, a single year's. 



They supply us, instead, with the curious fact, that an artificial 

 saline dressing, calculated to supply to a cornfield " 100 lbs. of 

 ammonia per acre," and "only increasing the percentage of am- 

 monia in the soil by 0-0007," — a chemically inappreciable addi- 

 tion, — will give " a produce at least double that of the unmanured 

 land.'"^ Thus, with the ammonia of centuries crowded into a 

 span-deep layer beneath our feet, we have still to go, money in 

 hand, year by year, to the gas-works or the guano-stores for each 

 succeeding crop's supply. 



One consolation remains. Though ammonia, the " good sub- 

 stitute " for cinereals, is withheld, and the application of the " in- 



* On Agricultural Chemistry,' &c., loc. prec. 



