Root Recolonization of Previous Root Channels in Corn and Alfalfa Rotations

Rasse, D.P. and A.J.M. Smucker

Presented at the All Scientist Meeting (1998-07-21 to 1998-07-22 )

Distribution of root systems in the soil profile is an important factor in the determination of water and nutrients available to plants. A minirhizotron (MR) study was conducted at the Agroecosystem Interactions site of the LTER on corn and alfalfa root systems throughout the soil profile of Kalamazoo loam (fine-loamy, mixed, mesic Typic Hapludalf) monolith lysimeters for a three-year succession of corn, alfalfa and corn. Multiple-date comparisons within and between years were conducted to estimate total root densities in each soil horizon. Root recolonization was assessed by comparing every video frame of paired minirhizotrons, from recordings conducted on successive growing seasons.In 1994, root populations of corn in the Bt1 horizon peaked 75 to 90 days after planting (DAP). Numbers of corn roots per m2 in the Bt1 horizon were consistently higher for no-tillage (NT) than for conventional tillage (CT) lysimeters, in 1994 and 1996. Distribution of alfalfa roots within the soil profile was not significantly modified by tillage. However, alfalfa root decomposition rates responded to tillage practices and were specific to each soil horizon. Corn root systems growing in soils previously cropped with alfalfa presented similar patterns of root distribution by horizons as that of the previous alfalfa crop. Successive corn root systems did not display similar distribution patterns throughout the soil profile from one growing season to the next. Proportions of roots of the current crop recolonizing root induced macropores (RIMs) of the previous crop averaged 18% for corn after corn, 22% for alfalfa after corn and 41% for corn after alfalfa, across Bt horizons and tillage treatments (Table 1). In conclusion, distribution of the corn root system appeared modified by tillage practices and by the root system distribution of the preceding crop.Table 1. Proportion of new roots recolonizing RIMs along decomposed roots from the previous growing season, for 1994 (corn after corn), 1995 (alfalfa after corn), and 1996 (corn after alfalfa).TillageHorizonCorn (94) after corn (93)Alfalfa (95) after corn (94)Corn (96) after alfalfa (95)%CTBt19.3 (4.1)a15.5 (0.7)45.0 (10.1)Bt216.5 (6.8)30.5 (13.4)37.8 (2.6)NTBt116.4 (12.7)21.4 (2.6)35.6 (4.5)Bt229.6 (7.8)22.0 (9.0)43.8 (1.3)a Standard deviations for two replicates.Return to Contents  

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