Potato cropping systems are subjected to intensive tillage and minimal plant residue return which has led to concerns about soil organic matter decline and soil degradation. A central question for farmers and agronomists is which organic matter amendments are most effective at ameliorating soils: those associated with the largest amount of biomass or those with higher quality, nitrogen-enriched residues. There are significant economic implications because growing a cover crop or green manure with high quality residues (e.g., legumes) is often ten-fold more expensive than a cereal cover crop. Livestock manure is another option for amending soil, with highly variable cost implications. We are testing the extent that soil quality, crop yields and nitrogen availability are regulated by the presence of nitrogen-enriched and highly available carbon sources from legume residues or manure amendments. Biochemical qualities of residues are being evaluated using forage analytical methods. Preliminary findings indicate that poultry manure has surprisingly similar biochemical qualities to legume shoot residues, but quite different properties from legume and cereal root residues. Potato yields indicate that productivity and nitrogen availability is similar in a red clover-wheat cover crop system and a poultry manure-rye system, which both outperformed a bare winter fallow potato system in all but one year of a long-term field experiment. Mineralizable nitrogen pools have been enhanced best with the use of rye-hairy vetch or wheat-red clover cover crops in combination with manure. Wheat-red clover or corn rotations with potatoes have improved soil aggregate stability, but rye-hairy vetch and manure have not improved aggregation. Longer-term soil quality performance is still being tested for these different organic matter amendments.