No. 4.] SOIL FERTILITY. 125 



moisture, — factors which are found to have controlling rela- 

 tions to plant growth, and whose importance is clearly seen 

 by noting some of the causes which determine the 3'ield of 

 crops on difierent soils and in different seasons. 



One of the facts most commonly observed is the variation 

 on the same soil of the yield of crops in different scasonSj 

 even though the treatment of the soil does not vary from 

 season to season in any essential particular. The most 

 apparent cause for this uneven production is the variation 

 in tlie times and quantity of the rainfall. A deficiency of 

 water sui:)ply at certain critical periods in the life of the plant 

 is disastrous to its welfare. Of course this is so, you say, 

 because water is plant food as trul}^ as is potash. Certainh^ 

 it is, but it sustains such essential relations to the full utili- 

 zation of other forms of plant food that it possesses an 

 importance different from, and entirely apart from, the mere 

 matter of a ledger account Avith the soil elements. 



Certain soils, regarded as barren when cultivated in the 

 ordinary way for field crops, have, to my personal knowl- 

 edge, produced surprising crops without being fertilized, 

 when used in a forcing house where the water supplv and 

 temperature were made as favorable as possible. The ordi- 

 nary explanation of the sterility of such soils has been that 

 they are deficient in the mineral elements of plant growth, — 

 a supposed explanation which fails to fully explain. 



Consider for a moment a striking illustration, so familiar 

 to us all, of two adjacent farms of greatly unlike crop- 

 })roducing capacity. The soil of these farms was originally 

 entirely similar. Not unlikely the pounds of nitrogen, 

 phosphoric acid and potash withdrawn from one farm have 

 been as many as those taken from the other, but the soil 

 management has been different. One farm has received 

 organic, the other commercial, manures. The systems of 

 rotation of crops have differed in the two cases, so that the 

 amount of or^uiic matter introduced into the soil has been 

 much greater for one farm, thus causing a superior condition 

 of texture. Tillage has been more thorough for the better 

 farm, thus fiivorably modifying its soil conditions. In short, 

 the explanation of the advance of one farm and of the retro- 



