Patterns and Factors of Soil Structure Recovery as Revealed From a Tillage and Cover-Crop Experiment in a Compacted Orchard

Degraded soil structure recovery is much less documented than structure degradation and in particular compaction. In this field experiment, the effects of rotary spade tillage followed by Sorghum cover crop (cover-crop treatment) on the degraded structure of the soil from an orchard were evaluated on undisturbed soil samples collected at 5–10 cm and 20–25 cm depth, respectively, using CoreVESS visual scoring of structure quality and shrinkage analysis. The cover-crop treatment took place from April to September and despite a particularly dry climate, the development of Sorghum was good. A large and significant improvement of the structure quality scores were obtained at both depths. Similar recovery trends in the physical properties were observed at the two depths, however the changes were significant at 5–10 cm depth only and were associated with a small increase of soil organic carbon (SOC) content. Analysis of covariance revealed a significant impact of the tillage and root development on the structure recovery, larger than the effect of SOC content. The structure recovery showed an increase of the positive role of SOC content on the physical properties. This structural change pattern was similar to those reported from other structure degradation or compaction studies. The slopes of the relationship between physical properties and SOC is an indicator of structure quality in general. Though the observed final structure quality of the top layer was good, we assume that its vulnerability remains large due to its small SOC to clay ratio. Our results are in close agreement with previous studies highlighting the relationships between SOC to clay ratio and structure quality

Apprentissage et pratique du test bêche VESS par application mobile

L’attention portée à la structure du sol connaît actuellement un regain d’intérêt, en relation avec l’évolution et la diversification des pratiques de travail du sol et la conception de systèmes de culture plus agro-écologiques. Les méthodes visuelles ont largement été utilisées pour évaluer et porter au champ un diagnostic sur la structure du sol. Dans ce numéro, nous passons en revue les principales méthodes et regardons leurs atouts et limites. Les méthodes se différencient en deux grands groupes suivant les modalités d’échantillonnage des volumes de sols observés : les méthodes basées sur la description de la face d’observation d’un profil de sol comme le profil cultural et les méthodes « bêche » basées sur la description de blocs de sol extraits de la parcelle. Elles utilisent toutes les mêmes types de critères pour observer l’état structural : l’analyse des vides du sol à travers une évaluation de la porosité visible à l’œil et l’organisation de la fraction solide (forme, distribution des tailles, le degré de cohésion des mottes, importance de la terre fine…). Cependant, la procédure d’évaluation de la structure est très différente suivant les méthodes. Le profil cultural privilégie une analyse spatiale de l’état structural pour inférer sur sa genèse alors que les méthodes « bêche » conduisent à une note globale de la qualité de la structure du sol. Cette revue montre que nous disposons de plusieurs méthodes fiables, qui peuvent être choisies en fonction des objectifs poursuivis et de leur plus ou moins grande facilité de mise en œuvre.The attention paid to soil structure is increasing in relation to the evolution and diversification of tillage systems and the move towards to more agro-ecological systems. Visual methods have been widely used to evaluate and make a diagnosis of soil structure in field conditions. In this issue we review the main methods and look at their strengths and limitations. The methods are divided into two main groups according to the sampling methods: the methods based on the description of the vertical face of a soil profile and the "spade" methods based on the description of soil blocks extracted from the plot. The different methods use the same type of criteria to evaluate the soil structure: the analysis of the voids of the soil through an evaluation of the visible porosity and the organization of the solid fraction (shape, the size distribution, the degree of cohesion of clods, proportion of fine aggregates, ...). However how to evaluate the soil structure is very different between methods. The “profil cultural” method favours a spatial analysis of the soil structure to infer on its genesis whereas the "spade" methods assign an overall score to evaluate the soil structure quality. The review shows there are several reliable visual methods, but the differences in the way to evaluate soil structure and in the implementation of the methods mean that the choice of methods must be made according to the objectives pursued and the users

Patterns and Factors of Soil Structure Recovery as Revealed From a Tillage and Cover-Crop Experiment in a Compacted Orchard

Degraded soil structure recovery is much less documented than structure degradation and in particular compaction. In this field experiment, the effects of rotary spade tillage followed by Sorghum cover crop (cover-crop treatment) on the degraded structure of the soil from an orchard were evaluated on undisturbed soil samples collected at 5–10 cm and 20–25 cm depth, respectively, using CoreVESS visual scoring of structure quality and shrinkage analysis. The cover-crop treatment took place from April to September and despite a particularly dry climate, the development of Sorghum was good. A large and significant improvement of the structure quality scores were obtained at both depths. Similar recovery trends in the physical properties were observed at the two depths, however the changes were significant at 5–10 cm depth only and were associated with a small increase of soil organic carbon (SOC) content. Analysis of covariance revealed a significant impact of the tillage and root development on the structure recovery, larger than the effect of SOC content. The structure recovery showed an increase of the positive role of SOC content on the physical properties. This structural change pattern was similar to those reported from other structure degradation or compaction studies. The slopes of the relationship between physical properties and SOC is an indicator of structure quality in general. Though the observed final structure quality of the top layer was good, we assume that its vulnerability remains large due to its small SOC to clay ratio. Our results are in close agreement with previous studies highlighting the relationships between SOC to clay ratio and structure quality

Soil organic carbon content and soil structure quality of clayey cropland soils ::a large‐scale study in the Swiss Jura region

Soil organic carbon (SOC) fashions soil structure, which is a key factor of soil fertility. Existing SOC content recommendations are based on SOC:clay ratio thresholds of >1:10. However, the corresponding SOC content might be considered hard to reach in clayey soils, whose structure degradation risk is assumed to be high. Here, we analysed the SOC content and soil structure quality of soils under similar cropping practices with clay contents ranging from 16% to 52%. Five undisturbed soil cores (5–10 cm layer) were collected from 96 fields at 58 farms in the Swiss Jura region. We assessed the soil structure quality visually using the CoreVESS method. Gravimetric air content and water content, and bulk density at −100 hPa were also measured, and the soil structure degradation index was calculated. We found that the relationship between SOC and clay content held over the clay content range, suggesting that reaching an acceptable SOC:clay ratio is not limited by large clay contents. This suggests that the 1:10 SOC:clay ratio may remain useful for clayey soils. In contrast to what was expected, it is not more challenging to reach this ratio in clayey soils even if it implies reaching very large SOC contents. SOC content explained the considered physical properties better than clay content. From a soil management point of view, these findings suggest that the soil texture determines a potential SOC content, while the SOC:clay ratio is determined by farming practices regardless of the clay content

Optimal organic carbon values for soil structure quality of arable soils. Does clay content matter?

Most soil structure-related physical properties are correlated to soil organic carbon (SOC) content. Texture, mineralogy, and SOC:clay ratio are also acknowledged to affect physical properties, however there is no consensus or general conclusions in this respect. Against this background, the present study aims at determining objectives for the management of SOC in terms of structural quality of agricultural soils. The large area in which 161 free-to-swell undisturbed samples were obtained for this research represents a major part of the Swiss agricultural land and belongs to one broad soil group (Cambi-Luvisols). The structural quality was scored visually, and bulk volumes (inverse of bulk density) were measured at standard matric potentials. To define the effect of SOC without interference of soil mechanical degradation, soils with good structural quality scores were considered first in studying the relationship between SOC and soil pore volumes. Results suggest that the relationship is always linear, irrespective of the clay content of the soils. No optimum of SOC corresponding to a fraction of the clay content is found, contrary to the theory of “complexed organic carbon” (Dexter et al., 2008). However, the SOC:clay ratio decreases with decreasing soil structure quality. The SOC:clay ratio of 1:8 is the average for a very good structure quality. A SOC:clay ratio of 1:10 is the limit between good and medium structural quality, thus it constitutes a reasonable goal for soil management by farmers. A SOC:clay ratio of 1:8 or smaller leads to a high probability of poor structural state. These ratios can be used as criteria for soil structural quality and SOC management, and in that context, the concept of complexed organic carbon appears relevant

Corrigendum to “Optimal organic carbon values for soil structure quality of arable soils. Does clay content matter?” [Geoderma 302 (2017) 14–21]

Corrigendum to “Optimal organic carbon values for soil structure quality of arable soils. Does clay content matter?” [Geoderma 302 (2017) 14–21

Optimal organic carbon values for soil structure quality of arable soils ::does clay content matter?

Most soil structure-related physical properties are correlated to soil organic carbon (SOC) content. Texture, mineralogy, and SOC:clay ratio are also acknowledged to affect physical properties, however there is no consensus or general conclusions in this respect. Against this background, the present study aims at determining objectives for the management of SOC in terms of structural quality of agricultural soils. The large area in which 161 free-to-swell undisturbed samples were obtained for this research represents a major part of the Swiss agricultural land and belongs to one broad soil group (Cambi-Luvisols). The structural quality was scored visually, and bulk volumes (inverse of bulk density) were measured at standard matric potentials. To define the effect of SOC without interference of soil mechanical degradation, soils with good structural quality scores were considered first in studying the relationship between SOC and soil pore volumes. Results suggest that the relationship is always linear, irrespective of the clay content of the soils. No optimum of SOC corresponding to a fraction of the clay content is found, contrary to the theory of “complexed organic carbon” (Dexter et al., 2008). However, the SOC:clay ratio decreases with decreasing soil structure quality. The SOC:clay ratio of 1:8 is the average for a very good structure quality. A SOC:clay ratio of 1:10 is the limit between good and medium structural quality, thus it constitutes a reasonable goal for soil management by farmers. A SOC:clay ratio of 1:8 or smaller leads to a high probability of poor structural state. These ratios can be used as criteria for soil structural quality and SOC management, and in that context, the concept of complexed organic carbon appears relevant