The value of green manuring lies in the fact that organic matter is worked into the soil and the organic matter in the 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. This book discuss the amount of organic matter in soil, its sources, 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. A brief survey of the nitrogen problem and nitrogen fixation, with consideration of green manuring crops, their composition, decomposition and use.