EXPERIMENT STATION BULLETINS. 179 



removing in the crops, substances which the soil unaided can supply but 

 slowly or insufficiently, and thus impair or destroy one or several of those 

 conditions which are indispensable to plant production." (Prof. S. W. 

 Johnson.) By putting farm manure in the forefront of the line of battle, 

 and using the concentrated manures as the cavalry to protect the flanks 

 and rear of the agricultural army, defeat may be averted and the field 

 won and permanently held. 



HOW, AND WHY BENEFICIAL? 



Concentrated manures are used in doses varying from 100 to 500 

 pounds to the acre. Let us take the larger dose and estimate how much 

 of the three especially active elements we add to the soil. The best com- 

 plete manures contain a large amount of secondary materials produced in 

 making a superphosphate. Such are sulphate of lime made by acting on 

 bones or mineral phosphates by sulphuric acid, tankage and drying 

 materials, etc., so that only about 300 pounds in a ton consist of the three 

 special manurial elements. Thus, I find that 500 pounds of a very 

 valuable fertilizer made in this state would contain of 



Ammonia 15.65 pounds 



Available phosphoric acid 45.35 pounds 



Real potash 11.00 pounds 



Active materials in 500 pounds 72.00 



By applying 500 pounds of such fertilizer we add to the 4,000,000 

 pounds of an acre of soil one part of ammonia in 250,000 parts of soil, one 

 part of phosphoric acid in 90,000 parts of soil, and one part of potash in 

 364,000 parts. How can this trifling amount of fertilizer have any in- 

 fluence on the growth of a crop? There are many soils in this State 

 which would receive no benefit from such an application of manure. 

 Many virgin soils, the prairies and bottom lands of our rivers, would 

 receive no benefit from such application of fertilizers because they con- 

 tain in available form all the plant food that any crop can use; the table 

 spread for the plant feast is loaded with every food and viand the plant 

 can use, and enough is as good as a feast. The attempt to fill dishes 

 already full would be futile. 



It has been shown that the great mass of all soils is inert and inactive 

 as plant food, that only a small per cent of the soil ever serves as food of 

 plants, and the amount at any time available for the plant is still smaller, 

 seldom exceeding one part in a thousand. It is only the part soluble 

 in water or in weak acids that is available for the plant. When this 

 small fraction is still further reduced, so that the plant does not find in 

 all parts of the soil a full supply for all its needs, then fertility falls off, 

 and in proportion to this reduction is the exhaustion of the soil. In such 

 cases a supply of the needed material in a form soluble in the soil water 

 and capable of being taken up by the roots of the plant may restore 

 the conditions of fertility and arrest the exhaustion of the soil. It is 

 mainly for the purpose of offering to the plant in immediately available 

 form the deficient elements of fertility, and to supplement the food ele- 

 ments that exist in the soil in insoluble form, that concentrated manures 



