CHANGES IN SOIL PHYSICAL-PROPERTIES WITH DEPTH IN A CONVENTIONALLY TILLED SOIL AFTER NO-TILLAGE

A no-tillage system was imposed on a structurally degraded fine-textured soil (Humic Gleysol) that had been under continuous com with moldboard tillage for more than 20 years. After 3 years of no-tillage, several soil structural properties were compared with the conventional tillage treatment to assess whether the soil structure had improved. No significant difference (P<0.05) was found between tillage treatments for the saturated hydraulic conductivity, porosity and penetration resistance in the surface 5 cm. Measurements of soil penetration resistance and in situ saturated hydraulic conductivity (K(wp)) using the well permeameter method were sensitive to structural changes that had occurred at 5-20 cm depth. The K(wp) at this depth was significantly greater in the moldboard treatment than in the no-tillage treatment. Resistance measurements indicated significantly greater soil strengths at 10-20 cm under no-tillage. Aggregate stabilities were assessed by wet sieving twice during the growing season. No-tillage resulted in larger soil aggregates, especially at the surface, compared with the moldboard tillage. These data suggest that degraded soils with low structural stability may initially suffer further deterioration with the elimination of tillage, owing to the loss or reduction of mechanically formed pores.