198 X. H. AGR. EXPERIMENT STATION. [Bulletin 138 



there is thus added many hundred pounds per acre of vegetable 

 matter in the form of roots and stubble, by the decay of Avhich 

 humus is formed and the texture of the soil and also the chem- 

 ical composition improved. 



The Destruction of Humus. 



Humus is not a stable constituent of soils but is modified by 

 the treatment which they receive. All authorities on soils agree 

 that stirring the soil and admitting the air more freely results 

 in a reduction of the proportion of humus. 



Hence continuous cropping with hoed crops or letting the 

 land lie fallow will cause a more rapid decrease in humus than 

 where the land is seeded with a crop of rye or oats, and much 

 more rapidly than a soil which is developing a sod. Samples of 

 soil taken in another series of experiments the fall before those 

 already described serve to illustrate these points clearly. The 

 samples were collected at the end of the season in October and 

 in this series were drawn to the depth of 12 inches; hence they 

 cannot be compared with the grass land samples, but only with 

 each other. The soil types represented are the clay and clay 

 loam. On the former soil, the samples represented some tillage 

 and rotation plots which had been under the plow for four years. 



One was from a corn plot and one from a fallow plot, both of 

 which had been cultivated throughout the summer, but the fal- 

 low plot had been bare, while the other had been covered with a 

 good growth of corn. A rye plot adjacent to the fallow plot and 

 an alfalfa plot completed the list. The rye had been harvested 

 in the summer, the alfalfa was in its first season and had made 

 a fair growth at the time, and the soil had been fairly well shaded 

 by it. 



On the clay loam the comparisons were between two vegetable 

 plots in the variety tests, an old abandoned raspberry patch and 

 a crimson clover sod. 



The vegetable plots had been well manured with stable manure 

 for three or more seasons, the raspberry plot had been tilled 

 until this season when the last crop of berries had been picked 

 and the plot left until it could be cleared. • The crimson clover 



