Agricultural Chemistry. 297 



simultaneous action of these terrestrial elements ; for if they are 

 not present, during the same time, in due quantity and of due, 

 that is, available quality, and If they are not taken up by the 

 plants, the most abundant supply of carbonic acid and of ammo- 

 nia can produce no effect. ('Agricultural Chemistry,' p. 187.) 



The dialning of the soil promotes vegetation, because it gives 

 to the atmospheric elements of nutrition free access to the roots 

 of the plants, and it augments the produce, because vegetation is 

 thus accelerated, and time is gained for the absorption of nutritive 

 matters. 



In agriculture, no factor, or element of the calculation, is 

 more important than that of time ; and the too great neglect of 

 this consideration In farming Is unquestionably the most serious 

 obstacle to its progress. The Just appreciation of the value of 

 any special manure depends on a hnoxcledye of its effects in time. 

 An Individual manure, which, in one year, may increase the 

 produce of a field In the most astonishing manner, may, if 

 applied to the same field in the same way for five years, produce 

 not the slightest effect, or even a diminution of the produce. 

 Hence arises, when the manure is used for a short time, an over- 

 estimate of its value, and in a longer period, an unmerited 

 depreciation of it. Two farmers, who are to day of precisely 

 the same mind as to the value of a special manure, come, after 

 a few years, to opinions diametrically opposed on the same 

 subject, because the same manure, applied to different kinds of 

 soil, exerts very unequal influences, if we look to the duration, 

 that Is, the time, of its effects. 



An additional source of carbonic acid and ammonia accelerates 

 the action of the terrestrial elements of nutrition in the same 

 time ; the increased produce means nothing else. 



If the produce of a field, without the addition of ammonia, be 

 = 1000, then a certain amount or sum of terrestrial or mineral 

 elements has been transferred from the soil to the plants in this 

 crop = 1000. 



11, by the use of ammonia, the produce has risen in the same 

 time, a year, to be = 2000, then, twice as much of the mineral 

 elements has l)een removed from the soil in the same time. 



It follows from this, that if a soil contain so much of these 

 mineral elements that it can yield, in 100 years, without anv- 

 thing being restored to the soil, exactly 100 crops of wheat, it 

 will (ease, after tliat period (100 vears), to be fertile for wheat. 



If, now, by the addition of carbonic acid and ammonia, or of 

 ammonia alone, tlie produce of this soil, in one year, be doubled, 

 then tiie soil thus treated will suj)ply, in 50 years, as much 

 produce as it would have done, without ammonia, in 100 y/^ars. 

 The soil will have lost, In 50 years, as much of the mineral ele- 



