Summary Preferential flow (PF) is a fundamentally important soil hydrologic process that controls a variety of soil physical, chemical, and biological functions. However, the lack of theory in this field and the existence of conceptual and technological bottlenecks continue to hinder the advancement of PF modeling and prediction. This paper explores three theoretical perspectives on the relationships between pedogenesis and flow regimes in field soils. First, we examine non-equilibrium thermodynamics as applied to open dissipative field soils with continuous energy inputs and mass exchanges with the surrounding environment. The dual-partitioning of pedogenesis (dissipating and organizing processes) is consistent with the theory of dissipative structure, which explains the genesis and evolution of soil architecture (structure + matrix) and organized heterogeneity found in various soils. Such organized heterogeneity leads to widespread potential for PF occurrence. Second, we investigate constructal theory to explain the tendency for dual-flow regimes in soils – one with high resistivity (Darcy flow) and the other with low resistivity (PF) – together, they form PF configuration that provides the least global flow resistance. This theory is applied to explain some general characteristics of weathering processes and related flow regime changes, which are supported by limited chronologic data from the literature on subsoil’s saturated hydraulic conductivity decrease after a soil reaches a certain age. Third, the theory of evolving networks sheds light on a variety of PF networks observed in field soils, which increase the effectiveness of energy and mass transfer in the subsurface. This is because networks are a part of the organization resulting from the minimum energy dissipation principle and far-from-equilibrium thermodynamics. All the three theories discussed support the notion that the potential for PF occurrence in field soils is likely universal. However, controversies and challenges associated with these theories require further efforts to rigorously test their applicability in natural soils and to formulate explicit quantitative relationships between PF occurrence and its controls. The principle of soil formation and evolution provides a useful guide to this endeavor.

Linking principles of soil formation and flow regimes.

X-ray micro-computed tomography characterized soil pore network as influenced by long-term application of manure and fertilizer

Variations in the rainfall distribution during the growing season are a major limiting factor restricting the spring maize yield on the semiarid Loess Plateau of China. Conservation tillage can improve yield and water use efficiency but the specific effects of conservation tillage with differing rainfall distributions during the growing season remain unclear. Therefore, a 12-year experiment was conducted and the data were divided into two categories based on rainfall distribution type. If poor rainfall occurred during the jointing-tasseling stage of the maize growing season and adequate rainfall occurred in the filling-maturity stage, the rainfall was named type-A. In contrast, if adequate rainfall occurred in the jointing-tasseling stage and poor rainfall occurred in the filling-maturity stage during the maize growing season, the rainfall distribution was categorized as type-B. This research used conventional tillage (CT) as a control to study the productivity of no-tillage (NT) and subsoiling (ST) under the selected rainfall distributions. The results showed that the type-B rainfall distribution increased dry matter accumulation, yield, soil water use efficiency (WUE) and precipitation use efficiency (PUE) by 18.9%, 32.0%, 21.7% and 45.1%, respectively, when compared with the type-A rainfall distribution. However, under type-A rainfall distribution, NT increased soil water storage by 3.7% and 4.4% and ST increased the soil water storage by 6.0% and 7.0% in the tasseling and grain filling stages, respectively, compared with CT. Moreover, NT and ST increased the dry matter accumulation, yield, WUE and PUE. The relationships among the yield, soil water storage and precipitation showed that the water storage in the sowing stage indirectly affected the maize yield through soil water storage at the tasseling stage, and the increase in precipitation from the jointing to tasseling stages had a directly positive effect on the increase in yield. Based on soil water storage with a value of 202.3 mm in the 0–200 cm soil depth during the tasseling stage, the yield increased by 47.8 kg ha−1 as the soil water storage improved by 1 mm. In conclusion, no-tillage and subsoiling improved the soil water conditions, mitigated the soil drought stress caused by variable rainfall distribution and improved the yield. Therefore, no-tillage and subsoiling practices are recommended for agricultural production in semiarid areas.

Conservation tillage improves soil water storage, spring maize (Zea mays L.) yield and WUE in two types of seasonal rainfall distributions

Variations in the rainfall distribution during the growing season are a major limiting factor restricting the spring maize yield on the semiarid Loess Plateau of China. Conservation tillage can improve yield and water use efficiency but the specific effects of conservation tillage with differing rainfall distributions during the growing season remain unclear. Therefore, a 12-year experiment was conducted and the data were divided into two categories based on rainfall distribution type. If poor rainfall occurred during the jointing-tasseling stage of the maize growing season and adequate rainfall occurred in the filling-maturity stage, the rainfall was named type-A. In contrast, if adequate rainfall occurred in the jointing-tasseling stage and poor rainfall occurred in the filling-maturity stage during the maize growing season, the rainfall distribution was categorized as type-B. This research used conventional tillage (CT) as a control to study the productivity of no-tillage (NT) and subsoiling (ST) under the selected rainfall distributions. The results showed that the type-B rainfall distribution increased dry matter accumulation, yield, soil water use efficiency (WUE) and precipitation use efficiency (PUE) by 18.9%, 32.0%, 21.7% and 45.1%, respectively, when compared with the type-A rainfall distribution. However, under type-A rainfall distribution, NT increased soil water storage by 3.7% and 4.4% and ST increased the soil water storage by 6.0% and 7.0% in the tasseling and grain filling stages, respectively, compared with CT. Moreover, NT and ST increased the dry matter accumulation, yield, WUE and PUE. The relationships among the yield, soil water storage and precipitation showed that the water storage in the sowing stage indirectly affected the maize yield through soil water storage at the tasseling stage, and the increase in precipitation from the jointing to tasseling stages had a directly positive effect on the increase in yield. Based on soil water storage with a value of 202.3 mm in the 0–200 cm soil depth during the tasseling stage, the yield increased by 47.8 kg ha−1 as the soil water storage improved by 1 mm. In conclusion, no-tillage and subsoiling improved the soil water conditions, mitigated the soil drought stress caused by variable rainfall distribution and improved the yield. Therefore, no-tillage and subsoiling practices are recommended for agricultural production in semiarid areas. 

https://www.sciencedirect.com/science/article/am/pii/S0012825221003743

Embracing the dynamic nature of soil structure: A paradigm illuminating the role of life in critical zones of the Anthropocene

Soil pore characteristics and gas transport properties of a no-tillage system in a subtropical climate

Effects of bio-subsoilers on subsoil pore-system functionality: Case study with intact soil columns

Soil macropores largely control the transport of water and solutes in subsurface flows. Preferential flow via soil macropores can substantially affect water quality. Hence, it is important to quantify soil macropore characteristics and link this information with the preferential flow behavior in soils. However, whether macropore structure at one slope position within a field is different than that at another is unclear. With differences in the macropore characteristics, each slope position can contribute differently to the runoff and subsurface flows. The objective of this study was to use X-ray computed tomography (CT) and image analysis to characterize soil pore structure (> 0.75 mm diameter) at upslope, midslope, and downslope positions within a 0.40 ha pasture field. A total of 18 undisturbed soil columns (150 mm diameter and 500 mm depth) were collected from a pasture field located at the Sand Mountain Research and Extension Center, Alabama, during May 2019. The results indicated that both the macropore number and macroporosity values were lowest at the downslope position in the 0–100 mm soil layer. In contrast, a large number of macropores was observed at the downslope soils for depths below 200 mm. The lowest macroporosity values in the surface layer at the downslope position can be attributed to higher degree of trampling induced compaction due to higher soil moisture content at the downslope location, via runoff and seepage losses from the upper slopes. Likewise, it was found that using smaller diameter soil cores for sampling can cause bias in the soil macropore measurements due to considerably high coefficient of variation compared to the larger diameter soil cores. Macropore interconnectivity at the subsurface layer (100–500 mm) increased from the upslope to the downslope position, whereas at the soil surface (0–100 mm), the interconnectivity was lowest at the downslope position as compared to the upslope and midslope locations. The results of this study provide quantitative information of different soil macropore characteristics under varying topographical locations and depths in a pasture field. The relevance of topographical variation of different macropore characteristics found in this study should be tested by investigating a wider range of soil types and slopes in pastures.

Sheela Katuwal

Papers

X-ray micro-computed tomography characterized soil pore network as influenced by long-term application of manure and fertilizer

Soil pore characteristics and gas transport properties of a no-tillage system in a subtropical climate

Effects of bio-subsoilers on subsoil pore-system functionality: Case study with intact soil columns

Using X-ray computed tomography to quantify variability in soil macropore characteristics in pastures

Grassland conversion to croplands impacted soil pore parameters measured via X-ray computed tomography