Quantification of Soil Pore Dynamics During a Winter Wheat Cropping Cycle Under Different Tillage Regimes

TLDR: In this article, the water retention characteristic (WRC) and hydraulic conductivity characteristic (HCC) vary in time due to the tillage system, weather conditions and biological activity.

Abstract: The water retention characteristic (WRC) and the hydraulic conductivity characteristic (HCC) vary in time due to tillage system, weather conditions and biological activity. These changes in WRC and HCC are a result of varying pore size distributions (PSD). Considering these alterations in soil hydrological models has been shown to improve simulations of water dynamics. An important prerequisite for such an approach is the periodic quantification of WRC and HCC, e.g., over a cropping cycle. Therefore, our study frequently quantified WRC and HCC together with other soil physical and chemical properties on a long-term (23 years) tillage experiment with a silt loam soil. The aim was to identify differences between the three treatments conventional tillage (CT) with a moldboard plow, reduced mulch tillage (RT) with a cultivator and no tillage (NT) with direct seeding. WRC and HCC were parameterized using the bimodal version of the well-known Kosugi retention model together with the Mualem conductivity model to account explicitly for both textural and structural pores. Consequently, bimodal PSD were inferred using the Kosugi parameters. The structural part of the bimodal Kosugi model clearly showed a shift in the PSD on CT and RT from larger to smaller pores throughout the winter wheat growing season with a recovery later in the season on RT. Saturated hydraulic conductivity was positively correlated with the abundance of transmission pores (diameter 50–500 μm) which has implications for infiltration processes under the influence of seasonal PSD changes. Overall, a frequent experimental quantification of PSD may be warranted for modeling soil water on short time scales, e.g., during a cropping cycle, while for longer time frames one to two measurement campaigns per year may be sufficient to describe soil hydraulic behaviour.