The 24-year study was conducted in southern Illinois (USA) on land similar to that being removed from Conservation Reserve Program (CRP) to evaluate the effects of conservation tillage systems on: (1) amount and rates of soil organic carbon (SOC) storage and retention, (2) the long-term corn and soybean yields, and (3) maintenance and restoration of soil productivity of previously eroded soils. The no-till (NT) plots did store and retain 7.8？Mg？C？ha？1 more and chisel plow (CP) ？1.6？Mg？C？ha？1 less SOC in the soil than moldboard plow (MP) during the 24 years. However, no SOC sequestration occurred in the sloping and eroding NT, CP, and MP plots since the SOC level of the plot area was greater at the start of the experiment than at the end. The NT plots actually lost a total of ？1.2？Mg？C？ha？1, the CP lost ？9.9？Mg？C？ha？1, and the MP lost ？8.2？Mg？C？ha？1 during the 24-year study. The long-term productivity of NT compared favorably with that of MP and CP systems. 1. Introduction Conservation program was established to take highly erodible lands out of production. In the United States, the Food Security Act of 1985, the 1990, 1995, 2001, 2006, and 2011 Farm bills, and the Illinois T by 2000 Program have resulted in millions of hectares of erodible land previously in row crops being put into the CRP for 15 to 25 years. Any conversion of Conservation Reserve Program (CRP) land back to corn and soybean production could require the use of conservation tillage systems such as NT to meet soil erosion control standards. Evaluations of yield response of these conservation tillage systems over time are needed to assess returning this land to crop production, the effects on SOC storage and retention and crop yields. Conservation tillage (defined as having 30% residue at the time of planting) can result in an increase in crop yield when compared with that of a moldboard plow system. Lawrence et al. [1] showed in a 4-year study in a semiarid environment in Australia that no-till had a higher crop yield than did reduced till fallow or conventional till fallow. Wilhelm et al. [2] observed a positive linear response between yields of corn and soybean, and amount of residue applied to a no-till system. Lueschen et al. [3], in a corn-soybean rotation in Minnesota, found an increase of 6.30？Mg ha？1 in yield of the NT system above the MP system in a dry year. Kapusta et al. [4] studied the effects of tillage systems for 20 years and found equal corn yield for no-till, reduced till, and conventional tillage systems despite the lower plant population in no-till. Maintaining crop
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