196 N. H. AGR. EXPERIMENT STATION. [Bulletin 138 



those due to the slow decay of the humus and the liberation of 

 the nitrogen, phosphorus and potassium of the original vege- 

 table matter from which it came. 



The nitrogen is especially important and Hilgard* says : ' ' Soil 

 humus is doubtless the chief depository of soil nitrogen, and the 

 main source from which, through process of nitrification, the 

 nitrogen supply to plants is usually derived." 



The total nitrogen in the soils of the college farm was nearly 

 proportional to the humus and averaged one part of nitrogen 

 to 14.8 parts humus in the clay loam and 1 to 12.8 in the clay. 



There is also considerable evidence that humus can unite with 

 some of the compounds used in fertilizing our soils. It has 

 been shown that ammonia salts will combine with humus. ^ the 

 ammonia of the salts replacing lime in the humates. 



Similar results have been obtained in this laboratory when 

 potash salts were used instead of ammonia salts. The potash 

 disappeared from solution when humus was added and lime was 

 found instead, showing that the potash must have combined. 



It is stated also that humus absorbs monocalcium phosphate,^ 

 or what is commonly called superphosphate of lime. 



It was also noted in our work that nitrates did not seem to 

 leach away in the presence of humus. On three plots used for a 

 top dressing experiment, fertilizers had been applied as follows : 



a. 300 lbs. per acre of complete chemical fertilizer, includ- 

 ing nitrate of soda. 



b. No manure or fertilizer. 



c. 300 lbs. per acre of nitrate of soda. 



The humus and total nitrogen percentages were : 



a. Humus 2.56 Nitrogen 0.18 



b. Humus 2.57 Nitrogen 0.16 



c. Humus 2.51 Nitrogen 0.20 



'f ^ 



Experiments are needed to determine whether humus can com- 

 bine with nitrates as well as with ammonia salts. However, it 

 is more likely to be the fact that by reduction nitrates are 



« " SoiLs," p. 135. » Hall and Glminghani, Jour. Chem. Soc, 1907. p. 686. 



"J. Damont, Exp. Sta. Record, Vol. 13, p. 28. 



