Humus green manures

Plough (about 20 cm) after prior humus enrichment with green manure or the grower s own humus fertilizer (combined with basal dressing if necessary). 

Although green manure carbon is rapidly oxidized by the soil microorganisms there is little evidence that this carbon is any less valuable in humus formation per unit of carbon added to the soil than is carbon from more carbonaceous crop residues (Pinck et al., 1950 Giddens et al., 1965). This is contrary to past prevailing opinion (Russell, 1961) which considered green manure carbon to be decomposed so rapidly and completely that little was left to contribute to total organic matter. It does decompose rapidly but the residual end products seem to be very well suited for rapid humus formation. 

A discussion of green manures, presumably by the editor of Soils and Fertilizers (Anonymous, 1949), arrives at a similar conclusion. This states that to produce a significant increase in the humus content by the addition of organic matter would require the addition of hundreds of tons of organic matter per acre at frequent intervals. The amounts usually applied are entirely inadequate for this purpose, and in warmer climates at any rate are so rapidly burnt out that the soil is enriched only in the salts left behind. ... 

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