ROOT MASS-DISTRIBUTION UNDER CONVENTIONAL AND CONSERVATION TILLAGE

Tillage effects on the soil environment suggest that it may influence rooting depth and root distribution. In this study, corn (Zea mays L.) rooting depth and root mass distribution were compared under conventi onal and conservation (chisel, ridge, no- ) tillage on sandy loam and clay loam soils at Ottawa, Ontario. Root depth and distribution in 0.1 0-m vertical increments during vegetative growth were estimated using a combination of excavation of the surface horizon (0-0.10 m) and 0.05 -m diameter cores obtained in the row and midway between two rows over a 3-yr period. An exponential model was used to fit root mass distrib ution data normalized with respect to total root density summed over a ll increments and maximum rooting depth in the profile. Soil moisture, temperature, mechanical resistance and bulk density varied with tilla ge treatment, but differences were not associated with root mass distr ibution. Rooting depth varied with soil texture, year and tillage, wit h increased rooting depth associated with increased tillage and decrea sed moisture in surface soil layers. In contrast, a common exponential model was found to fit normalized root mass distribution data under a ll tillage treatments. Our data suggest that simulation of root mass d istribution under all tillage practices is possible if rooting depth a nd root mass density of the surface soil layer are known.