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Rooting is a continuous response to the soil physical environment, but root responses in the field are sufficiently complex to require a least limiting approach. Rooting limitations of available water, soil aeration, and penetration resistance are linked into a least limiting water range (LLWR) as a function of bulk density (ρ b ). The LLWR concept and associated measurements were used to evaluate the impact of tillage and tracking on root and hydrologic environment at two depths in a poorly drained clay loam: (i) the 5- to 10-cm depth in nontracked and tracked interrows of three long-term tillage treatments (chisel plow, CH; moldboard plow, MB; and no tillage, NT); and (ii) a plow pan at 25- to 30-cm depth. Soil shrinkage, ρ b , saturated hydraulic conductivity, water retention characteristic (WRC), and penetration resistance characteristic (PRC) were all measured in undisturbed soil cores (5 cm long by 5 cm in diameter). Both the WRC and PRC included ρ b as an independent variable. Linearized fits of the WRC and PRC, with R 2 > 0.70, were sensitive to tracking and to CH vs. MB tillage; compaction in the plow pan and tracking in the NT reduced by 75% the impact of ρ b on the PRC. Tracking reduced the LLWR as much as 0.04 to 0.06 m 3 m -3 in CH and NT treatments, but the reduction in the MB treatment was |
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