Stochastic model for posttillage soil pore space evolution

Abstract

Abstract. Tillage operations disrupt surface layers of agricultural soils, creating a loosened structure with a substantial proportion of interaggregate porosity that enhances liquid and gaseous exchange properties favorable for plant growth. Unfortunately, such desirable soil tilth is structurally unstable and is susceptible to change by subsequent wetting and drying processes and other mechanical stresses that reduce total porosity and modify pore size distribution (PSD). Ability to model posttillage dynamics of soil pore space and concurrent changes in hydraulic properties is important for realistic predictions of transport processes through this surface layer. We propose a stochastic modeling framework that couples the probabilistic nature of pore space distributions with physically based soil deformation models using the Fokker-Planck equation (FPE) formalism. Three important features of soil pore space evolution are addressed: (1) reduction of the total porosity, (2) reduction of mean pore radius, and (3) changes in the variance of the PSD. The proposed framework may be used to provide input to hydrological models concerning temporal variations in near-surface soil hydraulic properties. In a preliminary investigation of this approach we link a previously proposed mechanistic model of soil aggregate coalescence to the stochastic FPE framework to determine the FPE coefficients. An illustrative example is presented which describes changes in interaggregate pore size due to wetting-drying cycles and the resulting effects on dynamics of the soil water characteristic curve and hydraulic conductivity functions. IntroductionThe tilled "plow layer" of agricultural soils plays a crucial role in determining crop productivity and transport of gas, The primary objective of this study was to develop a framework for modeling posttillage evolution of soil PSD based on coupling of stochastic formulation with physically based process models. We propose the use of the forward Kolmogorov 1641

Effects of tillage on the soil water retention curve during a fallow period of a semiarid dryland

“…3). Similarly to that reported by Calonego and Rosolem (2011), an increase of the S Dexter index was observed after tillage As reported by several authors (Schwen et al, 2011a(Schwen et al, , 2011bOr et al, 2000;Leij et al, 2002;Moret-Fernández et al, 2013), the rainfall was the main factor that conditions the changes in the θ(ψ) parameters (Table 2, figures 5 and 7). These changes should be related to the wetting process of the freshly tilled soil that promotes the disintegration and deformation of the more unstable soil aggregates (Shiel et al, 1988;Day and Holmgren, 1952).…”

“…Although PSD does not provide direct information about the porosity, it gives a measure of the relative abundance of pore size (Or et al, 2000).…”

Changes in pore size distribution and hydraulic properties of forest soil resulting from structural development

“…Following the study of Hara (1984), Or et al (2000) and Leij et al (2002) proposed using the advection-dispersion equation, which is a special form of the Fokker-Planck equation, for stochastic modeling of changes in soil pore size distributions associated with tillage operations. In the simplest case for the application of this equation to the change in pore size distribution as a result of structure development, the following simple growth equation for an individual pore size r may be used:…”

Effects of long-term soil and crop management on soil hydraulic properties for claypan soils

“…These differences can be attributed not only to vehicular traffic at the Field site but also to tillage. Rousseva et al (1988) and Or et al (2000) found that after tillage operations, cycles of wetting and drying might cause an increase in soil bulk density due to reconsolidation. The differ- Effects of management and depth on porosity for selected pore size classes: (a) macropores (>1,000 μm diameter), (b) coarse mesopores (60 to 1,000 μm diameter), (c) fine mesopores, (10 to 60 μm diameter), and (e) micropores (<10 μm diameter ences in bulk density due to soil depth were mainly due to differences in structure and texture.…”