Preferential spread of the pathogenic fungus Rhizoctonia solani through structured soil
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Keywords:
Macropore
Colonisation
Soil structure
Abstract Soil pore structure is essential for storing and transporting water, and it can be affected by different tillage practices. Strip tillage (ST) is an innovative technology aimed at addressing the challenge of reduced crop yield caused by no‐tillage (NT) in the cool black soil region of Northeast China. Nevertheless, what remains unclear is the influence of ST on soil pore structure in the cool black soil region. After conducting a 14‐year long‐term positioning experiment, this study investigated the variations in spatial distribution patterns of soil macropores under ST practice using X‐ray computed microtomography (μCT). The research also examined, the response of soil organic carbon (SOC) and soil bulk density to ST compared to conventional tillage (CT). This finding revealed that ST significantly increased the macroporosity (>25 μm) at 0–20 cm depths in comparison with CT. The detailed analysis of soil pore size distribution revealed a significant increase in macroporosity of the >2000 μm pore sizes in 0–10 cm layer by 144.79% because of ST. Furthermore, ST significantly increased pore connectivity at the 0–10 cm depth by 3.37% and pore fractal dimension at the 10–20 cm depth by 13.42%. Meanwhile, there was a significant correlation among the changes in soil bulk density, SOC content, macroporosity, pore connectivity, and pore tortuosity, indicating soil bulk density and SOC have a substantial impact on the pore structure. Overall, the implementation of ST leads to a significant enhancement in soil pore structure, improving the understanding of the regulatory mechanism of ST in the cool black soil region of Northeast China. This research aids in advancing the conservation and sustainable utilization of black soil.
Macropore
Soil structure
Tortuosity
Soil carbon
Soil morphology
Conventional tillage
Soil horizon
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Abstract. Erosion and excessive runoff from a crusting and hard‐setting red‐brown earth may he ameliorated with suitable management. A field trial, near Cowra, New South Wales, to assess the long‐term effect of different tillage systems was used to compare the effect of direct drilling with conventional district cultivation practices under continuous wheat. The soil was sampled in the eighth year for assessment of the soil macropore structure, measurement of bulk density and hydraulic conductivity under tension. Vertical faces were prepared from resin impregnated blocks and the macropore structure described mathematically and visually using digital images and data generated from these images. Infiltration, bulk density and image analysis data all lead to the same conclusions about changes in pore structure. Under direct drilling no crust was evident, and there was greater macroporosity (> 0.175 mm diameter in section). The treatment effects appeared to be significant to about 30 to 35 mm depth at the time of sampling. Greater root and faunal activity were observed under direct drilling.
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Soil structure
Conventional tillage
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Macropore
Chisel
Soil structure
Plough
Soil horizon
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Macropore
Soil structure
Paddy field
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Abstract Roots growing into soil interact with soil structure in numerous ways. They can grow into the soil matrix and leave elongated macropores after decomposition, that is, biopores. Conversely, the soil may already have a large and connected macropore system through which the roots can expand, and thus reach deeper soil layers. Both, the formation of new biopores or the reuse and occupation of existing macropore systems are expected to affect major soil processes like water and gas flow through the soil profile, as well as water flow toward the root. Despite the increasing research interest in the limitation of root growth by soil structure, as well as the modification of soil structure by roots, the mutual interactions between the two are largely overlooked. This study highlights new methodological developments which enable describing interactions between roots and soil structure with X‐ray computed microtomography. It further shows how roots affect the pore system and can create a massive biopore system in less than a decade. After this, it is evaluated how the mutual interaction of roots and structure determines the physical properties of the rhizosphere. It is outlined that this has implications for major rhizosphere processes. Thus, it is emphasized, that the role of structure needs to be considered in future experiments with plants, in particular if extrapolation of results from laboratory experiment with sieved, homogenized substrates to field conditions with well‐established soil structure is intended. Lastly, in this study, research gaps are outlined remaining in respect to the dynamics of biopore creation and destruction and their consequences for processes in rhizospheres like carbon storage. These reveal the need for novel research approaches that consider the mutual interactions of root growth and soil structure.
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Soil structure
Bulk soil
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Structure liming aims to improve soil structure (i.e., the spatial arrangement of particles and pores) and its stability against external and internal forces. Effects of lime application on soil structure have received considerable interest, but only a few studies have investigated effects on macro- and mesopore networks. We used X-ray computed tomography to image macropore networks (ø ≥ 0.3 mm) in soil columns and mesopores (ø ≥ 0.01 mm) in soil aggregates from three field sites with (silty) clay soils after the application of structure lime (3.1 t ha−1 or 5 t ha−1 of CaO equivalent). Segmented X-ray images were used to quantify soil porosity and pore size distributions as well as to analyse pore architecture and connectivity metrics. In addition, we investigated the amount of readily dispersible soil particles. Our results demonstrate that structure liming affected both, macropore networks and amounts of readily dispersible soil to different degrees, depending on the field site. Significant changes in macropore networks and amounts of readily dispersible soil after lime application were found for one of the three field sites, while only some indications for similar changes were observed at the other two sites. Overall, structure liming tended to decrease soil macroporosity and shift pore size distribution from larger (ε>1.0 mm) and medium sized macropores (ε0.3–1.0 mm) towards smaller macropores (ε0.1–0.3 mm). Furthermore, liming tended to decrease the critical and average pore diameters, while increasing the surface fractal dimension and specific surface area of macropore network. Structure liming also reduced the amounts of readily dispersible soil particles. We did not find any changes in mesopore network properties within soil aggregates or biopore networks in columns and aggregates. The effects of lime on macropore networks remain elusive, but may be caused by the formation of hydrate phases and carbonates which occupy pore space.
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Soil structure
Specific surface area
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Macropore
Soil structure
Infiltration (HVAC)
Soil morphology
Soil horizon
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Abstract Soils are typically subjected to multiple wetting–drying ( WD ) cycles due to irrigation and seasonal climate cycles, which directly impact soil pore structure and soil aggregate stability. Poly‐γ‐glutamic acid ( γ‐PGA ) is a polymer used to improve soil water holding capacity and plant growth. However, the impact of γ‐PGA on soil pore structure requires further research, particularly under WD cycles. Therefore, we investigated the different amounts of γ‐PGA on soil structure, including soil aggregate stability, macropore (>100 μm) structure characteristics and the relationship between macropore characteristics (equivalent pore diameter, pore shape factor, soil porosity, fractal dimension (FD), soil connectivity and the percentage of aggregate content with particle size larger than 0.25 mm) and soil aggregate stability by structural equation modelling ( SEM ) under WD cycles. A sandy soil and a loam soil were studied, and amended with γ‐PGA at three different concentrations: 0 ( P0 ), 0.4% ( P4 ) and 0.8% ( P8 ) (w/w, %). Results showed that γ‐PGA amendment increased the mean weight diameter ( MWD ) and the percentage of aggregate content with particle size larger than 0.25 mm ( R 0 .25 ) under WD cycles in both sandy and loam soils, while the MWD between P4 and P8 did not differ significantly. As the number of WD cycles increased, soil porosity ( TP ) increased due to an increase in pores of 100–500 μm. With γ‐PGA added to soil, large microporosity (>1000 μm) increased in sandy soil, but decreased in loam soil. In addition, 8WD cycles also increased the FD (2.6%–4.2%) and pore connectivity (Con) compared with 4WD . Structural equation modelling ( SEM) revealed that soil pore characteristics accounted for 74% and 98% of the variation in sandy and loam soils, respectively. TP , FD , Con and R 0 .25 directly contributed to MWD, according to the SEM . These findings improve our understanding of pore characteristics and aggregate stability, which are key factors influencing soil quality when amended with γ‐PGA during the seasonal WD period.
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Soil structure
Amendment
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Roots are essential drivers of soil structure and pore formation. This study aimed at quantifying root induced changes of the pore size distribution (PSD). The focus was on the extent of clogging vs. formation of pores during active root growth.Parameters of Kosugi's lognormal PSD model were determined by inverse estimation in a column experiment with two cover crops (mustard, rye) and an unplanted control. Pore dynamics were described using a convection-dispersion like pore evolution model.Rooted treatments showed a wider range of pore radii with increasing volumes of large macropores >500 μm and micropores <2.5 μm, while fine macropores, mesopores and larger micropores decreased. The non-rooted control showed narrowing of the PSD and reduced porosity over all radius classes. The pore evolution model accurately described root induced changes, while structure degradation in the non-rooted control was not captured properly. Our study demonstrated significant short term root effects with heterogenization of the pore system as dominant process of root induced structure formation.Pore clogging is suggested as a partial cause for reduced pore volume. The important change in micro- and large macropores however indicates that multiple mechanic and biochemical processes are involved in root-pore interactions.
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Soil structure
Clogging
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