Tillage systems need to be compared over an extended period of time to determine their transitional and long-term impacts on crop growth and soil properties. A 15-yr experiment established in 1976 compared reduced tillage systems with conventional fall moldboard plowing for production of continuous corn (Zea mays L.) on a Maryhill silt loam soil (Typic Hapludalf). Corn plant growth and yield and soil properties were compared for five tillage systems: fall plow (fall mold-board plow + spring secondary tillage), fall chisel plow (fall chisel plow + spring secondary), spring plow, spring plow/secondary (spring plow + secondary), and no-till. No-till consistently resulted in slower plant growth than most or all of the other tillage systems. The fall plow and spring plow/secondary treatments resulted in grain yields averaging 5% more than fall chisel plow, 9% more than spring plow, and 16% more than no-till yields. From 1976 to 1983, no-till yields tended to increase relative to fall plow; from 1988 to 1990, however, no-till yields were much less than fall plow. No-till resulted in the lowest proportion of aggregates < 5 mm in diameter, highest bulk density, and greatest penetrometer resistance. Penetrometer resistance of the spring plow plots increased at a slower rate with depth than the fall chisel plow system. Among soil properties measured, the proportion of aggregates < 5 mm in diameter was most often significantly correlated with yield.
