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Two decades of no-till in the Oberacker long-term field experiment: Part II. Soil porosity and gas transport parameters

Abstract:

This is the second in a series of papers describing the impact of two decades of no-till in the Oberacker long-term field experiment in Switzerland. The first focused on crop yields, soil organic carbon and nutrient distributions in the soil, while this study investigated the impact on soil gas transport properties. The Oberacker long-term field experiment was established in 1994 on a sandy loam and compares two tillage systems, mouldboard ploughing (MP) and no-till (NT). Undisturbed soil cores were collected at 0.1 (topsoil) and 0.4 m depth (subsoil) from both tillage treatments. Permanent grass (PG) strips located between the experimental plots were also sampled, as references. The soil cores were used for measurements of air-filled porosity (εa), air permeability (ka) and relative gas diffusion coefficient (Dp/D0) at five matric potentials ranging from -30 to -500 hPa. The results show that the soil pore system and gas transport properties of the NT soil were similar to those under PG for both topsoil and subsoil. In contrast, the soil under MP showed a clear stratification: εa, ka and Dp/D0 were higher than in NT and PG in the topsoil, but lower in the subsoil. The Dp/D0 vs. εa relationship was accurately described by a model derived from percolation theory. A linear relationship between log ka and log εa was found, but the slope was smaller than could be expected from percolation theory, in particular for subsoil, possibly because of the anisotropy of macropores. The pore system showed slightly higher specific diffusivity and much higher specific air permeability in the topsoil of MP than in NT or PG, but the relations were reversed in the subsoil. Thus it is highly important to consider both the topsoil and subsoil when tillage systems are evaluated.