Assessment Of Soil Structure Research Articles

Controlled traffic farming maintains soil physical functionality in sugarcane fields

The disorderly machinery traffic has been one of the main causes of soil physical degradation in sugarcane fields. In this sense, the adoption of strategies for machinery traffic control has been a viable alternative to reduce the risk of soil compaction and minimize physical restrictions to plant growth. However, the impact of traffic control on soil physical properties is still unknown in sugarcane fields. In this study, we investigated the impacts of machinery traffic control on soil physical properties and functions under contrasting soil textures (clayey and sandy clay), assessed at row and inter-row sugarcane planting positions. Bulk density, soil porosity, soil penetration resistance, the weighted average diameter of aggregates and visual assessment of soil structure (VESS) were measured. In addition, the soil physical quality index (SPQI) was assessed for the following soil functions: support root growth, ability to resist erosion and physical degradation, water supply for plants, edaphic fauna, and its relationship with the exchange of gases between soil and atmosphere. The results revealed that uncontrolled traffic farming increased bulk density, soil penetration resistance, and VESS scores as well as reduced total porosity mainly in the 0–10 cm soil layer. Controlled traffic farming supported soil functions in relation to uncontrolled traffic. Uncontrolled traffic caused a reduction by 12% on the SPQI at row position in both clayey and sandy clay soils, whereas for inter-row position, no difference was observed between the treatments. Controlled traffic in sugarcane fields was able to reduce soil physical degradation induced by agricultural machinery traffic, whose mitigation of compaction occurs mainly at row-position. These results suggest that controlled traffic farming may be a strategy to reduce soil physical restrictions for root growth in sugarcane fields.

Visual assessment of soil structural quality across soil textures and compaction levels – Part I: Examination of intact soil cores

Soil structural degradation has become very common and leads to a serious decline in soil health. Improving or maintaining soil structure is key to build resilience against drought and flooding, and thus contributes to assuring food and water security. Quantification of soil structural quality is usually accomplished by traditional laboratory-based methods, which are time-, labour- and money-consuming. Visual soil evaluation and examination methods comprise rapid and simple tests that offer a numeric semi-quantitative assessment of soil structure. The common criteria are aggregate size and shape, ease of break or rupture resistance, and inter- or intra-aggregate porosity. In this study, the CoreVESS method, a variant of the Visual Evaluation of Soil Structure (VESS) method originally developed for topsoil assessment, was applied on 250 cm3 undisturbed soil core samples. Resulting soil quality scores (Sq, ranging between 1, good, and 5, poor) were compared with soil quality indicators (SQi) derived from traditional quantitative methods of soil structure analysis. Tested SQi’s included penetration resistance, bulk density, soil hydraulic properties, soil organic carbon and texture (percentage of clay, silt and sand). The objective of the study was to assess and quantify the state of soil structural degradation induced by agricultural operations using a suite of methods of analysis at a regional scale, with a special focus on CoreVESS. Soil core samples were taken in Belgium from 42 cropped fields, at two positions (headland and in-field zone) and from three layers, notably the ploughed topsoil (TOP, 10–20 cm), the compacted subsoil (CSUB, 30–40 cm) and the deeper subsoil (SUB, 60–70 cm), totalling the sample horizons to 252. Test and sampling sites comprised all major soil texture classes within the Belgian soil textural triangle and varied from sand to heavy clay. In-field positions (IN-FIELD) showed significantly better coreVESS-based Sq scores as compared to headland positions (HEAD), with the CSUB layers always exhibiting significantly lower quality than the other two layers. Laboratory-derived soil quality indicator (SQi) values portrayed the same trend, with CSUB layers always indicating the poorest soil quality. Significant differences in SQi’s were also found between soils of acceptable (Sq ≤ 3) and degraded (Sq > 3) structure. Likewise, grouping soils into the same categories resulted in significant differences in the soil water retention and hydraulic conductivity curves in their wet ranges. There were good significant relationships between the SQi values and CoreVESS-based Sq scores, with for example Pearson R correlation coefficients of 0.64 for both penetration resistance and bulk density. Also, Sq scores related well with an SQi-based soil quality index (SQI) value averaged per layer and texture class (Pearson R of 0.60). The study confirmed that agricultural operations and their intensity clearly affect soil structural quality across various soil textures, with CoreVESS being as responsive to variation in soil structure quality as traditional quantitative methods, even when applied in the subsoil. VESS methods thus have a potential for monitoring soil structural quality over a variety of textures in a rapid, intuitive, practical and cheap way, as an alternative for or being complementary to more expensive labour-intensive traditional quantitative methods.

Lessons from a landmark 1991 article on soil structure: distinct precedence of non-destructive assessment and benefits of fresh perspectives in soil research

In 1991, at the launch of a national symposium devoted to soil structure, the Australian Society of Soil Science invited Professor John Letey to deliver a keynote address, which was later published in the society’s journal. In his lecture, he shared the outcome of his reflexion about what the assessment of soil structure should amount to, in order to produce useful insight into the functioning of soils. His viewpoint was that the focus should be put on the openings present in the structure, rather than on the chunks of material resulting from its mechanical dismantlement. In the present article, we provide some historical background for Letey’s analysis, and try to explain why it took a number of years for the paradigm shift that he advocated to begin to occur. Over the last decade, his perspective that soil structure needs to be characterised via non-destructive methods appears to have gained significant momentum, which is likely to increase further in the near future, as we take advantage of recent technological advances. Other valuable lessons that one can derive from Letey’s pioneering article relate to the extreme value for everyone, even neophytes, to constantly ask questions about where research on given topics is heading, what its goals are, and whether the methods that are used at a certain time are optimal.

Estimating soil aggregate size distribution from images using pattern spectra

A method for quantifying aggregate size distribution from the images of soil samples is introduced. Knowledge of soil aggregate size distribution can help to inform soil management practices for the sustainable growth of crops. While current in-field approaches are mostly subjective, obtaining quantifiable results in a laboratory is labour- and time-intensive. Our goal is to develop an imaging technique for quantitative analysis of soil aggregate size distribution, which could provide the basis of a tool for rapid assessment of soil structure. The prediction accuracy of pattern spectra descriptors based on hierarchical representations from attribute morphology are analysed, as well as the impact of using images of different quality and scales. The method is able to handle greater sample complexity than the previous approaches, while working with smaller samples sizes that are easier to handle. The results show promise for size analysis of soils with larger structures, and minimal sample preparation, as typical of soil assessment in agriculture.

Knowledge and use of visual soil structure assessment methods in Brazil – A survey

The most recent data from FAO about agricultural production value indicate that Brazil generated about US$ 221.64 billion in agricultural products in 2016, occupying fourth place in the world ranking. However, crop yield is limited in some areas because of low-quality soils resulting from poor soil structure and intensive cropping. The soil structure can be assessed visually by different methods. Based on the information obtained using visual assessment methods, soil management techniques to maintain or improve soil structural quality can be proposed. A survey was conducted to evaluate knowledge and use of visual soil structure assessment methods among agricultural science and technology professionals in Brazil and to identify the best known and most used methods. The survey took the form of a virtual online questionnaire sent to 763 electronic addresses in all five regions of Brazil. Around 49 % of respondents did not know any of the methods listed and 70 % had never used the methods in studies, professional work or research. Knowledge and use of visual soil structure assessment methods in Brazil was limited to the university scientific community, mostly in Southeastern and Southern Brazil. There were fewer users in Midwestern, Northern and Northeastern Brazil, possibly because those regions developed their agriculture later or have limited access to research on soil science. Therefore, actions to increase knowledge and uptake of the methods and highlight their importance for society are necessary.

E-p curve-based structural parameter for assessing clayey soil structure disturbance

Additional void ratio and yield stress that can be easily determined by one-dimensional consolidation test are two representative parameters for the assessment of clayey soil structure. In this paper, a “structural parameter” that defined as the normalization of the integral of additional void ratio times effective vertical stress until yield stress was proposed to evaluate the disturbance induced by soil structure changes. By conducting oedometer tests on Hangzhou clay at various disturbed states, the compression index, yield stress, and structural parameter were obtained. The evolution of normalized additional void ratio during one-dimensional loading is presented to establish the soil structural indexing strategies for assessment of clay structure disturbances. Based on the laboratory investigations, a linear relationship between the normalized structural parameter and normalized yield additional void ratio was obtained. For a certain soil, specimens with the same initial void ratio but different disturbed state have a nearly constant void ratio when yielding. It is also found that soils with a higher plasticity index exhibit stronger structure and lower compressibility. In addition, quick direct shear tests were carried out to examine the undrained shear strength of soils at different disturbed states. The soil disturbance degree quantified from the undrained shear strength is found slightly higher than that from the structural parameter. This study can provide a reference for assessing the clayey soil structure.

Evaluating the long‐term effects of tillage systems on soil structural quality using visual assessment and classical methods

AbstractCurrent agricultural practices and their impacts on the sustainability of crop production can be evaluated by simple and reliable soil structure assessment tools. The study was conducted to determine the effects of long‐term (2006–2017) tillage systems on structural quality of a clayey soil using the visual evaluation of soil structure (VESS) and classical field and laboratory measurements. A field experiment with seven tillage systems, representing both traditional and conservation tillage methods, was conducted on a clayey soil in the Cukurova region, Turkey. Soil samples from 0–10, 10–20 and 20–25 cm depths were analysed for mean weight diameter (MWD), porosity and organic carbon. Penetration resistance (PR) was determined in each treatment plot. The VESS scores (<2) of upper 0–5 cm indicated a good structural quality for all tillage systems. The VESS scores were positively related to PR and MWD and negatively to macroporosity (MaP) and total porosity. In reduced and no‐till systems, poorer soil structures were observed in subsurface layers where firm platy and angular blocky structures were defined. Mean VESS score (3.29) in 20–25 cm depth where PR was 3.01 MPa under no‐till indicated a deterioration of soil structural quality; thus, immediate physical interventions would be needed. Lower VESS scores and PR values under strategic tillage which was created by ploughing half of no‐till plots in November 2015 indicated successful correction of compaction caused by long‐term no‐till. The results suggest that the VESS approach is sensitive and useful in distinguishing compacted layers within the topsoil.

Development of the “mini 3D soil profile” – A visual method derived from the “profil cultural”

Quick and reliable field methods are needed to assess soil structure quality. This is especially true in cropping systems with high proportions of sugar beet, potato and vegetables crops, where the risk of soil and subsoil compaction is high. Visual field methods are a priori well adapted to meeting these needs. These include spade methods and soil profile methods. Spade methods are easy to implement but are mainly used to evaluate topsoil structure quality. The “profil cultural” method allows more detailed structural assessment, particularly in depth, but it requires more training, is time consuming and strongly disturbing for the soil. The proposed method, called "mini3D soil profile", is an intermediate method between spade methods and “profil cultural”: the sampling method is similar to the spade method and the description of morphological units by mapping the structural state on a vertical face is similar to the “profil cultural” method. It consists of taking a soil block with the pallets of a telescopic loader, and assessing soil structure on the vertical face using criteria similar to those of the “profil cultural” method. A study was carried out to test whether (i) extraction and lifting of the soil block did not modify the soil structure and (ii) whether the method produces the same soil structure assessment as that produced by the “profil cultural”. Results show that, despite the extraction and lifting by the loader, the method allows a good characterization of the soil structure by mapping the morphological units on a vertical face. The two methods produced very similar results in the evaluation of soil structure. The correlation between the areas having a massive structure and no visible macropores (percentage of Δ areas) assessed with the “mini3D soil profile” and the areas assessed with the “profil cultural” method was significant (R-squared = 0.79). Similarly, the correlation of the percentage of Φ areas with the presence of cracks was also significant (R-squared = 0.81). Comparing the soil structure assessment in eight fields, the main differences are due to the spatial variability of soil structure within the plot, depending on the location of the soil profiles. In conclusion the method is well adapted to identify the effects of tillage and compaction on soil structure dynamics. Easier to implement than the “profil cultural” method, the "mini3D soil profile" method is an original method to promote the evaluation of soil structure and thus decision-making by advisers and farmers.

Physical attributes of a Dystroferric Red Latosol (Oxisol) under different management systems

The relationship of management and soil quality may be evaluated by the behavior of soil physical, chemical and biological properties. In the assessment of soil structure, it is sought attributes in the view of measuring the porosity and the distribution of pores by size and its implication to permeability and rigidity of the pores, as well as the stability of the units that composes soil structure. The aim of this research was to assess the structure of a Dystroferric Red Latosol (Oxisol) under conventional corn crop, conventional coffee crop, eucalyptus crop and an equilibrium reference (native vegetation), by the determination of the particle density, bulk density, calculated total porosity, microporosity, macroporosity, moisture saturation, determined total porosity, blocked pores and aggregated stability. Soil under native vegetation presented the lowest values of particle density, probably due to the greatest soil organic matter content in this environment. It was verified a tendency of increasing blocked pores and decreasing bulk density. As expected, bulk density varied from 0.87 to 1.03 g cm-3, showing an inversely proportional distribution related to total porosity. The largest values of geometric mean diameter presented by the soil under native vegetation are due to thegreater structuration degree of this soil, which contributes to the stabilization of the aggregates in this environment. The native vegetation environment presented a better soil physical quality in relation to other land uses.

Visual soil evaluation: reproducibility and correlation with standard measurements

Visual soil evaluation (VSE) is a simple and fast method to assess soil quality in situ, and is becoming increasingly popular. Besides soil structure assessment, also other soil properties can be assessed such as grass cover, roots and earthworms. Yet, the full set of visual observations has not been properly evaluated for reproducibility and correlation with standard field or laboratory measurements, for several soil types. The objectives of this study were therefore to evaluate the reproducibility and the correlation of visual observations with closely related field or laboratory measurements. We used quantitative visual observations where possible, to enhance objectivity of VSE. The reproducibility and correlation of visual observations with standard measurements was evaluated for three soil types (sand, peat and clay) in the North Friesian Woodlands, The Netherlands. Reproducibility of quantitative visual observations was tested by comparing observations made by farmers and soil scientists, on the same soils. A linear mixed-effect model indicated that for all quantitative visual observations except for the depth of soil compaction, subjectivity due to the observers’ background (farmer or soil scientist) had no significant effect on the observations. For assessment of relative soil quality differences between sites, the results suggested that a single observer can make the visual observations, when assessing the fraction largest soil structural elements, earthworms, gley mottles and the depth of soil compaction. Spearman’s rank correlation coefficients indicated that visual observations of grass cover, root count, maximum rooting depth and the fraction largest soil structural elements correlated significantly with closely related field or laboratory measurements regardless of soil type. Maximum rooting depth, root count, soil colour, the fraction largest soil structural elements, and the degree of soil compaction only significantly correlated with field or laboratory measurements for specific soil types. Analyses showed that the correlation of visual observations with standard measurements were soil type dependent, suggesting that the evaluation of soil quality should also be soil type dependent.

Coupling X-ray computed tomography and freeze-coring for the analysis of fine-grained low-cohesive soils

This paper presents the coupling of freeze-core sampling with X-ray CT scanning for the analysis of the soil structure of fine-grained, low-cohesive soils. We used a medical scanner to image the 3D soil structure of the frozen soil cores, providing X-ray CT data at a millimetric resolution over freeze-cores that are up to 62.5cm long and 25cm wide. The obtained data and the changes in gray level values could be successfully used to identify and characterize different soil units with distinctly different physical properties. Traditional measurements of soil bulk density, carbon and particle size analyses were conducted within each of the identified soil units. These observations were used to develop a 3D model of soil bulk density and organic matter distribution for five freeze-cores obtained at a restored floodplain in Switzerland. The millimetric X-ray CT scanning was applied to detect the impact of freeze-coring on the soil structural integrity. This allows identifying undisturbed zones, a critical precondition for any subsequent assessment of soil structure. The proposed coupling is thought to be applicable to a wide range of other low-cohesive soil types and has a large potential for applications in hydrogeology, biology or soil science.

Assessment of implement efficiency and soil structure under different conventional tillage implements and soil moisture contents in a silty loam soil

Farmers' use of tillage implements under extremely dry soil conditions, ignoring optimum soil moisture conditions, results in low field efficiency, high fuel consumption and ultimately poor soil structure. Accordingly, the effect of tillage, applied under a range of near-plastic-limit soil moisture contents, on the efficiency of conventional tillage implements and subsequent soil structure, was investigated. Two conventional tillage systems: (i) moldboard plough followed by two cultivator passes and (ii) disk plough followed by two cultivator passes, were factorially combined with four soil moisture contents (θ) at tillage: dry soil, θ=5.0% w/w, and at 70, 80 and 90% of the moisture content at the soil's plastic limit (0.7θpl, 0.8θpl and 0.9θpl, respectively). The lowest field efficiency was observed under dry conditions, with a significant increase in efficiency at 0.7θpl, a further increase at 0.8θpl, and a subsequent decrease, compared to 0.7θpl and 0.8θpl, at 0.9θpl. Similarly, fuel consumption was greatest under dry conditions, decreasing at 0.7θpl and 0.8θpl, only to increase again at 0.9θpl. Overall, the lowest fuel consumption occurred at 0.8θpl. Under dry soil conditions the proportion of large aggregates (>8mm) was the lowest and that of small aggregates (<0.5mm) the greatest, whereas at 0.9θpl the converse was the case. At 0.7θpl and 0.8θpl, the proportions of large and small aggregates were low, while the proportion of desirable aggregates was greatest. At 0.8θpl the proportion of medium aggregates was greater than that at 0.7θpl. Therefore, in terms of post-tillage soil structure 0.8θpl was deemed the optimum θ for tillage of a silty loam soil. The aggregate stability of soil was higher under dry conditions and 0.7θpl, and lower at 0.8θpl and 0.9θpl under both moldboard and disk ploughing. A somewhat similar trend was observed under both conventional tillage implements; however, the disk plough followed by two cultivator passes offered a better performance in terms of field efficiency and soil properties than did the moldboard plough followed by two cultivator passes.

Automated Soil Physical Parameter Assessment Using Smartphone and Digital Camera Imagery

Here we present work on using different types of soil profile imagery (topsoil profiles captured with a smartphone camera and full-profile images captured with a conventional digital camera) to estimate the structure, texture and drainage of the soil. The method is adapted from earlier work on developing smartphone apps for estimating topsoil organic matter content in Scotland and uses an existing visual soil structure assessment approach. Colour and image texture information was extracted from the imagery. This information was linked, using geolocation information derived from the smartphone GPS system or from field notes, with existing collections of topography, land cover, soil and climate data for Scotland. A neural network model was developed that was capable of estimating soil structure (on a five-point scale), soil texture (sand, silt, clay), bulk density, pH and drainage category using this information. The model is sufficiently accurate to provide estimates of these parameters from soils in the field. We discuss potential improvements to the approach and plans to integrate the model into a set of smartphone apps for estimating health and fertility indicators for Scottish soils.

Indicators of earthworm bioturbation to improve visual assessment of soil structure

Earthworm bioturbation, a biological process that strongly influences soil structure dynamics, is attracting more interest with the development of no-tillage farming. However, while methods for Visual Soil Structure Assessment (VSSA) are of great use to agronomists working to improve crop management and preserve soil structure, few methods have indicators that consider earthworm biostructures. One reason is that VSSA methods were initially created for conventional tillage systems, where tillage and compaction are the main drivers of soil structure over time, while bioturbation is a secondary driver. However, bioturbation is now recognised as an important process for soil functioning under no-tillage and reduced tillage systems. Among biostructures, the presence of burrows is one frequently-used indicator, but casts are rarely studied in the field, except in the “Soil-Structure Patterns” method (SSP), which provides a typology of soil structure that includes earthworm features. However the SSP typology appears complex (11 patterns), and implementing the method is time consuming. To improve VSSA methods, we identified patterns to define new indicators of earthworm bioturbation. We first assessed whether the patterns identified were useful for highlighting the real impact of bioturbation on the distribution of soil structures and the impact of tillage on earthworm activity. We then applied the pattern descriptions to the “profil cultural” method, which provides a detailed assessment of soil structure in the soil profile. This study was performed at two experimental sites in France experiencing different types of soil impacts (i.e. tillage, compaction). Identifying patterns in soil morphological units helped us to define four types of bioturbation: (1) type 0: no visible bioturbation; (2) type 1: presence of burrows; (3) type 2: presence of a few fresh cast aggregates; and (4) type 3: high presence of casts in different welded states. This new typology seemed relevant and complementary to typical indicators. When applied to the “profil cultural” method, these bioturbation indicators can improve the assessment of the soil structure usually provided by VSSA methods and provide more accurate information to agronomists and farmers about soil functioning, including biological activities.

Developments in the “profil cultural” method for an improved assessment of soil structure under no-till

In France, agronomists have studied the effects of cropping systems on soil structure using a field method that is based on a visual description of the soil structure. This “profil cultural” method was designed as a field diagnostic tool to identify the effects of tillage and compaction on soil structure dynamics. It is of great benefit to agronomists seeking to improve crop management and preserve soil structure and fertility.However, the “profil cultural” method was developed and has mainly been used in conventional tillage systems with regular ploughing. As there has been an increase in the use of various forms of reduced, minimum and no-tillage systems in many parts of the world, it is necessary to re-evaluate this method’s ability to describe and interpret soil structure dynamics in no-till or reduced tillage. In these situations, changes in soil structure over time are mainly driven by compaction and by regeneration through natural agents (climatic conditions, root growth and macrofauna), therefore it is important to evaluate the effects of these natural processes on soil structure dynamics.These concerns have led to adaptations and amendments to the initial method based on field observations and experimental work in different cropping systems, soil types and climatic conditions. The description of crack types has been improved and a criterion of biological activity based on the visual examination of clods has been introduced.To test this modified method, a comparison with the initial method was undertaken and its ability to make diagnoses tested in five experiments in France, Brazil and Argentina. The adapted method allowed an improved assessment of the impact of cropping systems on soil functioning when natural processes were integrated into the description.

Application of various methodological approaches for assessment of soil micromorphology due to VESTA program applicable to prediction of the soil structures formation

Application of various methodological approaches for assessment of soil micromorphology due to VESTA program applicable to prediction of the soil structures formation

Visual Soil Structure Effects of Tillage and Corn Stover Harvest in Iowa

Core Ideas VESS detected soil structural quality changes under corn stover harvest and tillage systems. A high level of corn stover harvest had an adverse effect on the soil structural quality. Under high stover harvest, structural quality in chisel plow was worse than in no‐tillage. VESS should be further evaluated as an integrative soil quality/health indicator. High levels of corn (Zea mays L.) stover harvest for ethanol production have raised concerns regarding negative consequences on soil structure and physical quality. Visual soil structure assessment methods have the potential to help address these concerns through simple, straightforward on‐farm evaluations. Our objective was to determine if the visual evaluation of soil structure (VESS) approach could detect soil structural quality differences associated with different levels of corn stover harvest and tillage practices. We evaluated no harvest and moderate and high stover harvest levels within no‐tillage (NT) and chisel plow (CP) plots following 7 yr of continuous corn. Undisturbed 10‐ by 20‐ by 25‐cm soil samples were taken using a spade in April 2015. The thickness and structural quality (Sq) scores for the 0‐ to 5‐ (top) and 5‐ to 20‐cm (bottom) soil layers were determined, and an overall Sq was computed. The Sq values showed a significant interaction between corn stover harvest and tillage practice. Soil structural quality showed no significant differences between NT and CP systems for either the no‐ or moderate‐harvest treatments, but with a high stover harvest rate, CP structural quality was worse than NT. With NT, both moderate and high rates of stover harvest significantly increased Sq compared to no harvest; in CP, there was no significant difference between the no‐ and moderate‐harvest treatments. Only a high level of stover harvest had an adverse effect on the Sq rating. The VESS approach was sensitive for detecting the effects of corn stover harvest and tillage systems on soil structural quality and should be further evaluated as an integrative, on‐farm soil quality/health indicator.

Avaliação visual da qualidade da estrutura do solo em sistemas de uso das terras

Sistemas sustentáveis de produção agropecuária demandam solos com boa estrutura, por isso, são necessários métodos eficientes para avaliação dessa estrutura. Objetivou-se, com este estudo, aplicar a metodologia de avaliação visual da estrutura do solo, em áreas previamente cobertas por Floresta com Araucária, em longo período de uso após o desmatamento. Selecionaram-se áreas sob três tipos de usos: floresta nativa, pastagem e cultivo agrícola, considerados como tratamento, sendo realizadas dez amostragens por tipo de uso. Nas amostras coletadas, procedeu-se à avaliação da qualidade da estrutura do solo, seguida da análise estatística dos dados, por meio da análise de variância e do teste de separação de médias. Observaram-se diferenças significativas nos valores médios de escore entre as áreas avaliadas. Os solos da área com floresta apresentaram Qe (Qualidade visual) médio = 1.68, estatisticamente semelhante ao dos solos sob pastagem (Qe médio = 2.25) e inferior ao dos solos cultivados, Qe médio = 2.40. Os valores de Qe obtidos por avaliação visual da qualidade da estrutura do solo mostraram-se eficientes para identificar diferenças entre os sistemas de uso do solo.

Soil structure and its influence on microbial biomass in different soil and crop management systems

Methods for assessment of soil structure in the field are useful for determining the sensitivity of soil to different management systems. Soil and crop management have a fundamental role in the maintenance and improvement of soil quality, as they have a direct influence its structure and on microbiota habitats. The aim of this study was to qualify and quantify homogeneous morphological units (HMUs) in a dystroferric Red Latosol, in a 22-year experiment with treatments consisting of a no-tillage planting system (NT), no-tillage with chiseling every 3 years (NTC) and conventional tillage (CT), using crop rotation (CR) [with five different crop species in 3 years] and succession systems (CS) [only two crop species]. The NT and NTC treatments presented HMUs with a continuous and cohesive structure and increased visible porosity at the surface, and continuous and cohesive units with lower porosity below this layer. The surface layer of the NT treatment presented free units made up of small and medium sized clods, and below this layer, compact, continuous units with little porosity. The soil management systems with crop rotation presented less compact units and roots with fewer morphological deformities than in the treatments with succession systems. Significantly higher levels of carbon and nitrogen microbial biomass (CMB and NMB) were observed in the HMUs in NT and NTC systems under both crop rotation and succession systems, and these had higher visible porosity than the units found in the CT system. On average, HMUs in the NT and NTC treatments presented 20% more CMB and 51% more NMB than in the CT treatment. NMB was the parameter most highly affected by the soil management. At depths of 0–20cm, total organic carbon (TOC), was higher by an average of 21% than in the NT and NTC treatments. Total nitrogen (TN) was also affected by the soil management, increasing by an average of 50% in the NT and NTC treatments. This demonstrates how the tillage of the soil exposes the organic matter in the aggregates to oxidation and nitrogen mineralization.

Diffuse Reflectance Spectroscopic Approach for the Characterization of Soil Aggregate Size Distribution

Assessment of soil structure and soil aggregation remains a challenging task. Routine methods such as dry- and wet-sieving approaches are generally time consuming and tedious, which calls for a robust, fast, and nondestructive method of soil aggregate characterization. Over the last two decades, diffuse reflectance spectroscopy (DRS) has emerged as a rapid and noninvasive technique for soil characterization. Combined with chemometric and data-mining algorithms, it provides an effective way of measuring several soil attributes and has the added advantage of being amenable to a remote sensing mode of operation. The objective of this study was to determine if the DRS approach could be used as a rapid, noninvasive technique to estimate soil aggregate characteristics. The DRS approach was examined for the estimation of soil aggregate characteristics such as the geometric mean diameter and two statistical parameters of the lognormal aggregate size distribution (ASD) functions using 910 soil samples from India representing three important soil groups. Results showed that the geometric mean diameter and the median aggregate size parameter provided excellent predictions, with ratio of performance deviation (RPD) values ranging from 1.99 to 2.28. The RPD value for the standard deviation of the ASD ranged from 1.36 to 1.72, suggesting moderate prediction. It was further observed that soil aggregates influence the incident electromagnetic radiation on soils primarily in the visible region and to some extent the shortwave- and near-infrared regions. Electronic transitions of Fe-bearing minerals, clay minerals, and C–H functional groups of organic matter may be responsible for modifying the spectral reflectance from soils in addition to the self-shadowing effects of surface roughness. The results of this study suggest that the chemometric approach may be combined with DRS to estimate soil aggregate size characteristics.