Food for 0.13% phosphoric acid 



PUntt 0.12% potash 



i6g 0.14% nitrogen 



or about the same quantity of each plant-food. The per- 

 centage of nitrogen, therefore, is normal. Many soils are 

 much poorer. The question then is, is the soil nitrogen 

 difficult of assimilation, or is it difficultly soluble. The ex- 

 periments will answer this point. These experiments were 

 carried on not for one year, but for three successive years in 

 the same pots, and by analysis of the crops harvested it was 

 possible to show how much nitrogen the plants had removed 

 from the store in the soil. The results of the mean of three 

 years' work show that of every 100 parts of soil-nitrogen, 

 2.6% had been yielded to the plants, not quite 3%. Soil- 

 nitrogen is, therefore, of difficult solubility. The soil bacteria 

 which have to decompose the humus, work slowly. The 

 humus offers them no very attractive food, and they consume 

 it slowly. Green substance, blood, meal, and horn meal, 

 work up much more rapidly. 



It is clear, therefore, that even when the chemical 

 analysis of a soil shows relatively much nitrogen, the soil 

 may remain poor in nitrogen, so far as the plants are con- 

 cerned. 



The Results of Pot Experiments are Confirmed 

 by Field Trials. 



A very pertinent question is : Do the relations obtained 

 under pot experiments also hold true under the conditions 

 of the open field? Circumstances in the field differ from 

 those in pot culture, and it may be assumed that in deeply 

 cultivated and well ventilated field soil, the humus is decom- 

 posed more rapidly and abundantly than in the earth with 

 which the pots are filled. The results of field experiments 

 carried out in ten different districts in Hesse, for 2, 3, 6 or 8 

 successive years, show this point very clearly. In order to 

 bring the results of the individual years to a common unit 

 capable of comparison, the market values of the extra yields 

 have been calculated and called "gross profit." 



