Changes in soil physical charactersistics during transition from intensive tillage to direct seeding

Converting from intensive tillage to no-till systems often increases soil strength, but the long-term impact of no-till on soil strength is not fully understood. Soil strength (evaluated with a hand-held cone penetrometer) and soil water content were evaluated in the top 30 cm of a replicated wheat/fallow rotation in a Pacific Northwest silt loam (coarse-silty, mixed, mesic, typic Haploxeroll). Soil water content was significantly lower in the no-till plots than in intensive tillage plots, which required a correction to remove the impact of soil water on penetrometer resistance. A regression equation was developed to adjust cone index values for soil water content. Comparisons of cone penetration resistance, adjusted for soil water, were made among intensive tillage, first-year no-till, and 17-year no-till. First-year no-till soil was resistant to penetration, but after 17 years of no-till the soil strength was lower and approached tilled conditions. Cone index values just below the plow layer (18 cm) increased from 2 to 3 fold the first year of no-till, but after 17 years of no-till the cone index values were not statistically different between no-till and intensive tillage below the tillage layer. This research demonstrated that silt loam soil structure improved with time during transition from intensive tillage to no-till.