Contrasted effects of no-till on bulk density of soil and mechanical resistance

• Published in: Soil & tillage research 2011-01, Vol.111 (2), p.105-114
• Main Authors: Chaplain, V., Défossez, P., Richard, G., Tessier, D., Roger-Estrade, J.
• Format: Article
• Language: English
• Subjects: Agricultural sciences; Agronomy. Soil science and plant productions; Biological and medical sciences; bulk density; Compression index; conventional tillage; crop management; Fundamental and applied biological sciences. Psychology; land use; Life Sciences; methodology; new methods; No-till system; no-tillage; Pedo-transfer function; pedotransfer functions; Physical properties; Physics, chemistry, biochemistry and biology of agricultural and forest soils; Precompression stress; resistance to penetration; saturated conditions; soil compaction; soil density; soil matric potential; soil mechanical properties; soil pore system; soil pore water; Soil science; Soil structure; Soil study; soil texture; soil water content; soil-water-air interactions; Structure, texture, density, mechanical behavior. Heat and gas exchanges; trafficability
• ISSN: 0167-1987; 1879-3444
• DOI: 10.1016/j.still.2010.08.015

▶ Define diagnostic tools, based on mechanical properties, on the lasting effect of practices. ▶ Define a critical threshold, above which soil could be considered as compacted. ▶ Show the influence of water saturation at inflexion point on the compression index. ▶ Show contrasted effects of no-till on bulk density and mechanical resistance among soil. Compaction caused by traffic, results in degradation of soil structure with possible agronomic and environmental consequences. On the other hand, no-till systems have a great impact on soil structure and can improve their mechanical resistance. This property is described by compression curves using two parameters: the precompression stress Pc and the compression index Cc. Both mainly depend on bulk density, water content and soil texture. We aim to study the effect of farming practices on bulk density and mechanical resistance and also on the relation between those two properties in order to define diagnostic tools on the lasting effect of practices. Unsaturated soils were used, since cohesion is mainly attributed to capillary forces, themselves structure-dependent. “Equilibrium states” of soil structure corresponding to a fixed matric potential value, are then compared at various bulk densities. Pedo-tranfer functions (PTF) were defined by the relationship between Pc, Cc and the initial void ratio (e0). Soils originated from two long-term experimental sites: Versailles and Boigneville (France), where till and no-till systems are being compared. PTF have been established from remolded samples taken in till systems using a large range of e0 values. The effect of practices has been measured through mechanical properties of undisturbed soil cores. Uniaxial compression tests were performed in laboratory in drained conditions. In till systems, the global shape of compression curves varies for remolded cores from an S-shaped model to a rounded shape when e0 decreases, followed by a bi-linear one. Cc appeared simply proportional to e0 in all soils due to the progressive water saturation of soil core at inflexion point, when e0 decreases. For intact cores coming from till systems, this PTF should reveal heterogeneities and variability in soil structure. According to this PTF, there is no effect of practices in field. On remolded samples and till system, Pc was mostly constant in Versailles while Pc did strongly increase when e0 decreased in Boigneville, due to progressive saturation of porosity. Effects of no-till we