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The benefits of using cover crops for improving soil and water quality are well known. Less clear is whether cover crops, especially those forming a taproot system, can favor solute transport down to the groundwater by modifying soil hydraulic properties and solute dynamics. In this study, we employed 12 lysimeters to conduct a comparative analysis between a taproot cover crop, specifically forage radish (FR), and bare soil (BS), under three water table management conditions. Our objective was to evaluate whether the enhancement of root‐derived macroporosity could have modified water and solute dynamics, and offset the benefits provided by FR that is commonly used to mitigate solute leaching. A tracer solution of bromide (Br−) was added to lysimeters, and solute flux concentrations were determined at different depths during a 25‐day test. Soil moisture and pressure heads were monitored. Water and solute transport parameters were estimated by inverse modeling using HYDRUS‐1D. A complementary laboratory experiment was performed to quantify the effect of FR root apparatus on the macropore structure by using noninvasive X‐ray microtomography (µCT). Results showed that the growth of FR within the lysimeters induced alterations in water and solute dynamics compared with BS. This is primarily attributed to its proficiency as solute scavenger, with an uptake capacity of up to 47% of the total injected tracer. Our comparative analysis instead revealed subtle differences in soil structure and hydraulic properties brought about by the presence of FR. Major changes were observed for the saturated hydraulic conductivity (Ks), which increased from an average of 8.4–49.8 cm day−1 within the 20–45 cm layer in BS and FR, respectively. Additionally, there was a difference in immobile water content (θim), with the values in FR averaging 21% lower than those in BS. These modifications can be attributed to the formation of fissures and channels, primarily concentrated in the proximity of taproot development, without extending into deep preferential flow pathways. These structural changes were supported by the nondestructive µCT analyses. Upon aggregating the effects observed, solute movement to groundwater was not affected by FR compared to BS conditions. Core Ideas: Taproot served as solute scavenger, offsetting the risk of leaching at −60 cm, below its fleshy portion.Taproot‐induced soil hydraulic changes were mainly observed in the 0–45 cm layer.Forage radish caused an increase in the macroporosity where the taproot mainly developed. [ABSTRACT FROM AUTHOR]

Soil organic matter (SOM) plays a key role in soil structure formation, although the bidirectional relationship between SOM and the soil pore network is complex and needs further investigation. Despite great advances provided by X-ray computed microtomography ([micro]CT), it has only been used in a few studies to investigate the organic matter 3D-arrangement within the soil matrix. Results are based on the X-ray linear attenuation coefficient (a), and mixtures of organic and mineral soil fractions could imply overlapping of information that makes any segmentation procedure difficult. The aim of this study was to visualise, segment, and quantify the particulate organic matter fraction (POM) within the soil matrix through X-ray [micro]CT in combination with contrast agents (phosphomolybdic acid and silver nitrate). Two series of repacked soil cores, 'dry' and 'wet', were scanned through X-ray [micro]CT at a 7-[micro]m resolution. Different segmentation approaches were tested to separate POM from other soil phases: manual, global, and local thresholding methods. Reported algorithms were also compared with a supervised grey value-based (GV) approach followed by morphological operations. Results showed contrast agents increased [alpha] of POM, simplifying its identification and the following segmentation on dry cores. The POM was discriminated from the mineral fraction and its content correctly estimated. This was particularly accurate when applying manual thresholding or GV approach with respect to indicator kriging, suggesting that operator-based ability to set threshold level is still the best solution for accurate POM segmentation. Beyond single-phase accounting, different thresholding algorithms and morphological operations also affected POM morphological characteristics. In particular, the simpler was an object shape, the easier was its segmentation. Improvements are thus required to increase the efficiency of automated thresholding algorithms. Moreover, wet cores were exposed to washing-out phenomena that compromised any digital image processing and further POM quantification, implying that more effort should be made to find other suitable staining agents. Additional keywords: soil image analysis, soil organic matter, X-ray computed microtomography., Introduction Understanding soil organic matter (SOM) spatial arrangement is essential for developing theoretical models on soil carbon fluxes and SOM-related properties. The SOM is recognised as a key driver leading [...]

Increasing soil organic carbon (SOC) in agricultural soils is nowadays receiving growing attention also due to the COP21 initiative of "4 per 1000". In this study, the effect of five decades of different residue management (residue removal, residue incorporation, and residue incorporation + poultry manure) was investigated on SOC stock and related to the 4 per 1000 and C saturation concepts. Preliminary results showed that higher 0–60 cm SOC stock was found after 54 years of the experiment when residues were incorporated into the soil compared to residue removal (75.0 vs 69.0 t ha−1) while poultry manure had a negligible effect. Comparing the 0–30 cm SOC stock with pre-existent data series, a general decreasing trend was observed from the start of the experiment in 1966 up to 1986, being greater in residual removal (−8.6 t ha−1) than residual incorporation (−4.8 t ha−1, irrespective of poultry manure addition). In 2020, the difference between the above-mentioned systems was 4.1 t ha−1 corresponding to a 2.2 ‰ which is lower than what was suggested by the 4 per 1000 initiative. This SOC stock attributed to residue retention arose in response to 141 t C ha−1 residue resulting in a 0.1 % yearly conversion rate that is sensibly lower than what is generally reported in the literature. Therefore, an alternative use (e.g., bioenergy production) of at least part of crop residues is conceivable in temperate climate for a more efficient C cycle. The studied soil was demonstrated also to be far from C saturation, being in the 30−47 % degree of saturation range. Therefore, specific studies on how both organic and inorganic (i.e., carbonates) C fractions related to different soil aggregates and aggregate mineralization are namely requested. [ABSTRACT FROM AUTHOR]