Long-Term Tillage, Rotation, and Perennialization Effects on Particulate and Aggregate Organic Matter.

Perennialization and reducing tillage have shown increased soil organic carbon (SOC) in both protected aggregate and particulate organic matter (POM). This study investigates how 20 years of management varying in crop rotation, tillage intensity and organic management have affected POM and aggregate C and N. The six systems from the Wisconsin Integrated Cropping Systems Trial (WICST) were: chisel plowed continuous corn (Zea mays L.) (CC), strip-tilled corn-soybean (Glycine max L.) (CS), organically managed corn-soybean-winter wheat (Triticum aestivum L.) inter-seeded with red clover (Trifolium pretense L.) (CSW), three years of alfalfa (Medicago sativa L.) followed by corn (C3A), organically managed oats (Avena sativa L.)/alfalfa for two years followed by corn (C2A) and a rotationally grazed pasture seeded to a mixture of red clover, timothy (Phleum pretense L.), smooth bromegrass (Bromusintermis L.) and orchardgrass (Dactylisglomerata L.) (P). We found significantly lower concentrations of POM in CS and CSW, and significantly greater concentrations of POM-C in P and POM-N in P and C2A. The CSW system had a lower proportion of soil in macroaggregates and lower stocks of C and N within macroaggregates. Our results indicate that the regular cultivation for weed control in CSW is likely disrupting formation of aggregates and storage of C and N therein. However in systems which were chisel plowed every one to three years high levels of biomass C inputs may support high levels of POM-C and POM-N as well as soil aggregation equivalent to the P system.