The value of Green Manuring lies in the fact that organic matter is worked into the soil and the organic matter in soil is recognized as being one of its most valuable constituents. The soil nitrogen is associated with the organic matter and the decay of this organic matter influences the availability of the soil minerals. For these reasons, it has seemed advisable to discuss the amount of organic matter in soils, its source, and the influences which operate for the destruction of or the increase of organic matter, as well as the part it plays in the soil. Such a discussion is a necessary preliminary to the study of green manuring. For this material the writer has drawn freely upon the standard texts on soils, and on original papers. This matter is presented in chapter III, and in chapters IV and V are given a brief survey of the nitrogen problem and nitrogen fixation, all preliminary to the more special consideration of green manure crops, their composition, decomposition and use.
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