At a harvest index value of 50%, a 6200 kg/ha(100 bu/ac) grain corn yield would produce 6200 kg/ha(5600 lb/ac) of leaves and stocks plus roots. Warncke and Barber(1974) estimated that in the corn crop, roots accounted for 17% of the dry weight of the shoots, and total residues returned from continuous corn production could equal 7250 kg/ha(6,473 lb/ac) of residue. At this rate of return and at 13% conversion to organic matter, 624 years would be required to achieve a 5% organic matter level. Seventy-five years would be required to raise the organic matter level by 1% if manure was applied at 22.4 t/ ha (10 tons/acre) each year (Anonymous 1977 b).