June, 190S.] HUMUS IX N. H. SOILS. l''~ 



changed to ammonia and held by the humus, as in the addition 

 of ammonia salts. 



The compounds of humus with the soluble superphosphate of 

 lime, ammonia and potash must undergo decompositions similar 

 to those by which the original fertility elements of the humus 

 are made available in the soil. Thus in the presence of humus 

 not only are there plant elements from decaying vegetable mat- 

 ter, but also added fertility elements may be held in a similar 

 condition of availability. 



Without the humus, phosphates and potash salts must at 

 length change to the insoluble compounds of those elements nat- 

 urally present in the soil minerals," while nitrates are leached 

 from the soil by the drainage water. 



When these different effects of humus are considered, it can 

 be readily seen how important it is to soils and why sandy loams 

 are regarded as poor soils. 



There is a difference of .75 per cent between the sandy loam 

 and the clay loam in the humus, which, calculated on a basis of 

 3,000,000 pounds of soil per acre-foot, in eight inches would 

 mean 15,000 pounds of humus or 7.5 tons, requiring over twenty- 

 eight tons of stable manure to make it good. The manure is 

 calculated on the basis of its containing 26 per cent of organic 

 matter,^ not all of which would be humus, and consequently a 

 pound of organic matter in manure would not be equivalent to 

 a pound of humus in the soil. 



Such a difference in humus means also a difference in the 

 moisture, nitrogen, phosphoric acid and potash associated with 

 it, which, as has been shown, are in the most surely available 

 forms for plants to use. 



Since sandy soils are especially favorable to the destruction of 

 humus, these available forms of plant food change to less soluble 

 forms, or leach away, as the humus decomposes, unless taken 

 up by the crop then on the land. Large dressings of manure 

 therefore have not the lasting effect that is noted on heavier 

 soils, and the same is true of chemical fertilizers. Frequent 

 rotations of crops are especially beneficial on these soils, since 



• Bull. 30, Bureau of Soils. " Bull. 83, N. H. Agr. Exp. Sta. 



