June, 190S.] HUMUS IN N. H. SOILS. 201 



acre, and the soil of an adjacent farm, cropped for fifteen years 

 with wheat, showed sixty-three tons, a shrinkage of 40 per cent. 

 Our soils shrink in humus relatively faster than this because 

 they contain less organic matter. We have found from 5.5 to 

 7.5 per cent of volatile matter, while North Dakota reports as 

 high as 15 to 20 per cent. Since all organic matter is not humus 

 but only that portion of it which dissolves in strong ammonia 

 water, a large reserve of organic matter would serve to renew 

 the humus as it w^as destroyed by tillage, while a small reserve 

 could not maintain it. 



Conservation of Humus. 



Our analj'ses and the observations of others show that the 

 saving of humus and its development can be accomplished only 

 by such a rotation of crops that the soil has frequent rests from 

 tillage on the one hand, and the addition of stubble, turf and 

 roots by the plow on the other. The table preceding shows that 

 rest from tillage made a saving of humus equivalent to organic 

 matter in over 50 tons of barnyard manure, when the rye and 

 fallow plots are compared, while liberal dressings could not 

 maintain the humus in the vegetable plots at the level of the ad- 

 joining clover sod. 



Continuous tillage is not common in this state in general farm 

 practice, but sometimes a field favorably situated is used for a 

 crop of silage corn several years in succession, and it is usually 

 observed that the yields decrease from year to year until the 

 corn crop is given up for another. 



On the other hand, a continuous rest from tillage is too com- 

 mon, as grass land is cropped year after year, although the 

 yield may be less than a ton per acre. Humus does not tend 

 to accumulate in grass land but rather to decrease, although not 

 as rapidly as under tillage. 



We have found in three samples of old grass land on the 

 clay soil, which had been cropped with hay for more than 

 twenty years, percentages of humus ranging from 2.95 to 3.69 

 and averaging 3.27, while the average of immediately adjoin- 

 ing fields, which had been under tillage for two years, re-seeded 



