No. 6. 



DEPARTMENT OF AGRICULTURE. 



217 



pounds of potash, 4,000 pounds of phosphoric acid and 5,000 pounds 

 of nitrogen. As compared with the amount of each of these ele- 

 ments required by a single crop in one year, these quantities are 

 enormous. 



Some of the common farm crops extract from the land the follow- 

 ing amounts of plant food per year: 



o 



ft 



Wheat, 30 bushels and the straw, 

 Oats, 60 bushels and the straw, . 



Clover, 2 tons, 



Potatoes, 200 bushels 



lbs. 

 29 

 62 

 83 

 70 



Each acre, therefore, has enough of the elements of plant food 

 for many generations of crops. But fields differ and while one 

 may be richer in one of the elements than the figures given above, 

 it may be quite lacking in some other element. 



One of the earlier theories of farm fertilization was based on the 

 idea, that by chemical analysis, what the soil was most lacking 

 could be learned, and then this lack supplied. When the agricul- 

 tural colleges were founded more than forty years ago, one of the 

 principal aids they were expected to bring to the farmer was along 

 this line. The farmer was to send a sample of his soil to the college, 

 the chemist would analyze it and then send back word just what 

 fertilizers to apply. But when the colleges were started, the agri- 

 cultural constituency was surprised to learn that chemical analysis 

 could not help them. The chemist could of course analyze the soil, 

 but in their poorest soils where they could not grow profitable 

 crops, he would find enormous quantities of plant food. The trouble 

 was that the chemist used strong acids and learned the total amount 

 of plant food present, but he could not tell whether or not it was 

 available for the plant, and where he found ten thousand pounds of 

 food there may not have been ten pounds in such condition that the 

 plant could use them, therefore, his analysis was of no agricultural 

 value. Of late years the attempt has been made to devise some 

 method of analysis that would show the amount of available plant 

 food in a soil. So far success has not been attained and if the later 

 ideas of this paper are correct, then the solution of this problem 

 would be of scant use to agriculture. 



When the agricultural colleges realized that chemical analysis 

 would not aid the farmer in his search for the proper fertilization 

 of his farm, they evolved a new scheme. They said, "Ask the land 

 15 



