Abstract
Soil organic matter (SOM) is important for maintaining soil structural stability (SSS). This study quantified the influence of soil organic carbon (SOC) and different organic matter components on various SSS measures. We used a silt loam soil with a wide range of SOC (8.0–42.7 g kg−1 minerals) sampled in spring 2015 from the Highfield Ley-Arable Long-Term Experiment at Rothamsted Research. Four treatments were sampled: Bare fallow, continuous arable rotation, ley-arable rotation, and grass. Soils were tested for clay dispersibility (DispClay), clay-SOM disintegration (DI, the ratio between clay content without and with SOM removal) and dispersion of particles <20 μm. The SSS tests were related to SOC, permanganate oxidizable carbon (POXC), hot water-extractable carbon (HWC), mid-infrared photoacoustic spectroscopy (FTIR-PAS) and mineral fines/SOC ratio. SSS increased with increasing content of SOM components. The relationships between SOM components and SSS followed a broken-stick regression with a change point at ~23.0 g SOC kg−1 minerals (clay/SOC~10) coinciding with a change from the tilled treatments to the grass treatment. We found a greater influence of SOC, POXC and HWC on SSS at contents below the change point than above. A stronger linear relation between POXC and DispClay compared to SOC and HWC suggests that POXC was a better predictor of the variation in DispClay. POXC and HWC were less related to DI than SOC. The grass treatment had a very stable structure, shown in all SSS tests, probably due to the absence of tillage and large annual inputs of stabilizing agents. This suggests that a change in management from arable rotation to permanent grass is one effective tool for improving SSS.
Highlights
The importance of soil organic matter (SOM) on key soil functions is well known (e.g., Johnston et al, 2009), and loss of Soil organic matter (SOM) is considered a major threat to sustained soil functions (Amundson et al, 2015)
A stronger linear relation between permanganate oxidizable carbon (POXC) and DispClay compared to soil organic carbon (SOC) and hot water-extractable carbon (HWC) suggests that POXC was a better predictor of the variation in DispClay
cation exchange capacity (CEC) was significantly higher for G than for bare fallow (BF) treatment, and the amount of exchangeable Ca2+ was significantly higher for G compared to other treatments
Summary
The importance of soil organic matter (SOM) on key soil functions is well known (e.g., Johnston et al, 2009), and loss of SOM is considered a major threat to sustained soil functions (Amundson et al, 2015). Soil structure is the relative arrangement of particles and pores (Dexter, 1988), and the ability of soil structure to resist external stresses both mechanical and or from water is termed soil structural stability (SSS). SOM content is an important factor affecting. Soil organic carbon (SOC) is the main constituent of SOM and may serve as a proxy for SSS. Labile organic compounds are potentially better indicators for soil functions (Haynes, 2005). Permanganate oxidizable carbon (POXC) is considered a labile component of SOM and has been found to be more sensitive to differences in management than total SOC (Culman et al, 2012). Hot waterextractable carbon (HWC) is highlighted as a soil quality indicator more sensitive to management changes than total SOC (Ghani et al, 2003)
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