Root recolonization of previous root channels in corn and alfalfa rotations

Distribution of root systems through soils and recolonization of root chann els by successive crops are fundamental, though difficult to study, process es of soil ecology. This article reports a minirhizotron (MR) study of corn and alfalfa root systems throughout the soil profile of Kalamazoo loam (fi ne-loamy, mixed, mesic Typic Hapludalf) monolith lysimeters for a three-yea r succession of corn, alfalfa and corn. Multiple-date comparisons within an d between years were conducted to estimate total root densities in each soi l horizon. Root recolonization was assessed by comparing every video frame of paired minirhizotrons, from recordings conducted one growing season apar t. Distributions of corn root systems were modified by tillage practices. I n 1994, root populations of corn in the Bt(1) horizon peaked 75-90 days aft er planting (DAP). Numbers of corn poets per m(2) in the Bt(1) horizon were consistently higher for ns-tillage (NT) than for conventional tillage (CT) lysimeters, in 1994 and 1996. Distribution of alfalfa roots within the soi l profile was not significantly modified by tillage. However, alfalfa root decomposition rates responded to conventional and no-tillage practices and were specific for each soil horizon. Corn root systems growing in soils pre viously cropped with alfalfa presented similar patterns of root distributio n by horizons as that of the previous alfalfa crop. Successive corn root sy stems did not display similar distribution patterns throughout the soil pro file from one growing season to the next. Proportions of roots of the curre nt crop recolonizing root induced macropores (RIMs) of the previous crop av eraged 18% for corn after corn, 22% for alfalfa after corn and 41% for corn after alfalfa, across Bt horizons and tillage treatments. In conclusion, d istribution of corn root systems appeared to be modified by tillage practic es and root recolonization of RIMs was controlled by the preceding crop.