FERTILIZERS. 73 



to enable the farmer to determine what form of nitrogen, 

 potash, or phosphoric acid is best adapted to his soil, or to 

 produce any particular crop ; also a set to determine what 

 special fertilizer was most profitable for any special crop. 

 These sets are supplied by the Mapes Formula and Peru- 

 vian Guano Company, 158 Front Street, New York ; also 

 by the Bowker Fertilizer Company of Boston. I believe 

 Messrs. Mapes, and probably Bowker & Co., send out 

 explanatory circulars, giving full instructions how to use 

 them. Several of our agricultural papers have been very 

 active in encouraging this good work. I have used one 

 of these test sets on my own land with profit. 



One fact may be safely inferred without a test; viz., 

 that all old pasture-lands, when brought under cultivation, 

 especially need phosphoric acid to give back to the soil 

 the great draught that has been made upon it by the 

 phosphate carried away in the milk of cows and in the 

 bones of the young calf. I advocate the Stockbridge 

 theory as modified by the soil-test plan advocated by 

 Professors Atwater and Johnson: first, to determine by 

 actual tests what our soils lack,-and then use the Stock- 

 bridge formulas, modified by the knowledge so obtained. 

 The -fundamental idea is, that, to use manures economi- 

 cally, we must select those which fit the wants of the 

 special cases where they are to be applied. The old idea 

 of the practicability of analyzing the soil to determine 

 what plant-food it is necessary to apply, is exploded. It 

 is found, that, if ten times the amount of plant-food for 

 any crop is mixed with the soil, the chances are not one 

 in ten that the chemist can detect its presence. The crop 

 can do it far better than the chemist can. A few pounds 

 of guano applied to an acre of land would be found by 

 the crop, and make a difference in the yield ; while Pro- 

 fessor Johnson tells us, that, even if a thousand pounds 



