The Physical Character of Soils 37 



her old materials, getting again the carbonic acid, water, 

 nitrogen, and the ash elements for the building of new 

 forms. In northern sections, where the snowfall is heavy 

 and the winters long and cold, the vegetable matter in the 

 forest waste is held in place, and its decay being slower 

 than in warmer regions there is always in the virgin soils 

 of the north a greater accumulation of humus than in a 

 southern and warmer region. When we come to the 

 tropics, with their uniform heat in the soil and rapid 

 oxidation as a consequence, the amount of humus is very 

 slight. In the high open woodlands of our own southern 

 country the leaves of the deciduous trees blow into the 

 hollows and low lands and there help to form the fertile 

 bottoms, while the hills retain very little. Hence, for the 

 careful farmer in the red clay hills of the South, it is of 

 far more importance to increase the humus content of his 

 soil than it would be with the deeper humus soils of the 

 North. 



Nothing has tended more to the impoverishment and 

 improductiveness of the southern uplands than tiie con- 

 stant cultivation of cotton on them, with only the aid of 

 commercial fertihzers, which return no humus to the soil. 

 The first steps in their improvement must be the restora- 

 tion of the organic decay that has been burnt out of them 

 in the long clean culture of cotton. These soils have 

 become really dead, because the microscopic Hfe that finds 

 its food in the humus has been starved out. Since the 

 products of the life of the soil-bacteria are of the greatest 

 importance to our cultivated plants, it is evident that the 

 greatest value of the humus Hes in its being the home and 

 food of these microscopic forms. Stable manure, while 



