Article

Influence of Plants on the Spatial Variability of Soil Penetration Resistance

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Abstract

Soil penetration resistance is an informative indicator to monitor soil compaction, which affects a range of ecological processes in floodplain ecosystems. The aim of the investigation was to reveal the influence of vegetation cover on the spatial variability of penetration resistance of floodplain soils. The study was carried out in the elm oak forest in the floodplain of the Dnipro River (Dniprovsko-Orilsky Nature Reserve, Ukraine). The study of the soil profile morphology was performed in accordance with the guidelines of the field description of soils FAO. The soil penetration resistance was measured in the field using the Eijkelkamp manual penetrometer to a depth of 100 cm at 5-cm intervals within the polygon consisted of 105 sampling points. Vegetation descriptions were made in a 3×3-meter surrounding from each sampling point. The soil penetration resistance was found to regularly increase with increasing depth. The changes in resistance values were insignificant until 25–30 cm depth. After that, there was a sharp increase in penetration resistance up to the depth of 70–75 cm, after which the indicators plateaued. In the three-dimensional aspect, the spatial variation of soil penetration resistance can be fractionated into broad-scale, medium-scale, and fine-scale components. Tree vegetation induces a broad-scale component of soil penetration resistance variations, which embraces the whole soil profile. The herbaceous vegetation induces a medium-scale component, which embraces the upper and middle parts of the soil profile. The fine-scale component is influenced by pedogenic factors.

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Compaction of agricultural soils is a concern for many agricultural soil scientists and farmers since soil compaction, due to heavy field traffic, has resulted in yield reduction of most agronomic crops throughout the world. Soil compaction is a physical form of soil degradation that alters soil structure, limits water and air infiltration, and reduces root penetration in the soil. Consequences of soil compaction are still underestimated. A complete understanding of processes involved in soil compaction is necessary to meet the future global challenge of food security. We review here the advances in understanding, quantification, and prediction of the effects of soil compaction. We found the following major points: (1) When a soil is exposed to a vehicular traffic load, soil water contents, soil texture and structure, and soil organic matter are the three main factors which determine the degree of compactness in that soil. (2) Soil compaction has direct effects on soil physical properties such as bulk density, strength, and porosity; therefore, these parameters can be used to quantify the soil compactness. (3) Modified soil physical properties due to soil compaction can alter elements mobility and change nitrogen and carbon cycles in favour of more emissions of greenhouse gases under wet conditions. (4) Severe soil compaction induces root deformation, stunted shoot growth, late germination, low germination rate, and high mortality rate. (5) Soil compaction decreases soil biodiversity by decreasing microbial biomass, enzymatic activity, soil fauna, and ground flora. (6) Boussinesq equations and finite element method models, that predict the effects of the soil compaction, are restricted to elastic domain and do not consider existence of preferential paths of stress propagation and localization of deformation in compacted soils. (7) Recent advances in physics of granular media and soil mechanics relevant to soil compaction should be used to progress in modelling soil compaction.
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Soil compaction affects soil physical properties and, eventually, crop production. A severe drop in the productivity of the state of Parana, southern Brazil, was observed due to soil compaction. Two oxisols from this region, a Haplic Acrothox from the site of Cascavel and a Haplic Eutrothox from the site of Palotina, presenting different compaction behaviors in the field, are studied under laboratory conditions. Uniaxial compressive pressures, from 50 to 1000 kPa, are applied to soil samples at different initial matric potentials, varying from -0.1 to -1000 kPa. The bulk density of the Palotina soil is always higher than that of the Cascavel soil and is the highest when the initial matric tension is -32 kPa. Differences in pH, cation-exchange capacity, organic matter, and clay particle thickness also tend to explain the different compaction behaviors. A model of the soil bulk density increase during compaction is proposed and compared with a multiplicative model and a logarithmic model. The performances of the proposed and the multiplicative models are practically similar and better than those of the logarithmic model. The major advantage of the proposed model is that it has one fitting parameter less than the multiplicative model. Compaction affects the soil water retention curves for the whole range of matric tensions, up to -100 MPa. An approach that allows the evaluation of the hydraulic conductivity functions of the compacted samples is proposed. Applied to the Brooks and Corey relationship, the main drying curves of the compacted samples are well reproduced using one fitting parameter only.
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Chapter
Soil macrofauna are ecosystem engineers. They create soil structure. In the steppe zone, differences in soil macrofauna, the intensity of their activity and particular effects of individual invertebrate communities may be observed within different facets of the landscape. In Calcic chernozem, under herbaceous vegetation and forest plantations, the casts of various animals that feed on decaying organic matter are an important component of the structure of A horizons, and the droppings of insect larvae are prominent. In Luvic chernozem, Luvic chernic phaeozem and Pantofluvic fluvisol under native forest, worm casts are the predominant component of the soil structure. The ecology of macrofaunal communities is correlated with soil morphology and can be applied to reconstruct possible mechanisms of soil genesis.
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Compaction, often promoted by animal trampling and loss of forage plants, is a main cause of soil degradation in pastures. Our objectives were to evaluate various pasture management strategies for maintaining soil physical quality and to evaluate penetration resistance as an indicator of soil compaction in pastures. For each strategy, the goal was to maintain or extend least limiting water range (LLWR) and soil compressive behavior. Three treatments [Brachiaria (Br); Br intercropped with forage peanut (Arachis pintoi) (Br + L); and Br fertilized with 150 kg N ha −1 (Br + N) were compared to a native forest reference (Ref) in four pasture areas in Brazil. Pasture management strategy did not significantly influence LLWR, but the Br + N treatment resulted in greater soil degradation evidenced by a lower LLWR. These results are useful for improving pedotransfer functions and decision aides that predict physical-mechanical soil quality, impact on vegetative cover, and the appropriate animal carrying capacity for specific pasture areas. They also confirm that soil moisture and penetration resistance are effective for calculating load carrying capacity, factors that help with decision making regarding implementation of new management practices in pasture areas.
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Zhukov O., Kunah O., Dubinina Y., Zhukova Y., Ganga D.: The effect of soil on spatial variation of the herbaceous layer modulated by overstorey in an Eastern European poplar-willow forest. The tree species composition can influence the dynamics of herbaceous species and enhance the spatial heterogeneity of the soil. But there is very little evidence on how both overstorey structure and soil properties affect the spatial variation of the herb layer. The aim of this study is to evaluate the factors of the soil and overstorey structure by which it is possible to explain the fine-scale variation of herbaceous layer communities in an Eastern European poplar-willow forest. The research was conducted in the "Dnipro-Orils'kiy" Nature Reserve (Ukraine). The research polygon (48º30'51"N, 34º49"02"E) was laid in an Eastern European poplar-willow forest in the floodplain of the River Protich, which is a left inflow of the River Dnipro. The site consists of 7 transects. Each transect was made up of 15 test points. The distance between rows in the site was 3 m. At the site, we established a plot of 45×21 m, with 105 subplots of 3×3 m organized in a regular grid. The adjacent subplots were in close proximity. Vascular plant species lists were recorded at each 3×3 m subplot along with visual estimates of species cover using the nine-degree Braun-Blanquet scale. Within the plot, all woody stems ≥ 1 cm in diameter at breast height were measured and mapped. Dixon's segregation index was calculated for tree species to quantify their relative spatial mixing. Based on geobotanical descriptions, a phytoindicative assessment of environmental factors according to the Didukh scale was made. The redundancy analysis was used for the analysis of variance in the herbaceous layer species composition. The geographic coordinates of sampling locations were used to generate a set of orthogonal eigenvector-based spatial variables. Two measurements of the overstorey spatial structure were applied: the distances from the nearest tree of each species and the distance based on the evaluation of spatial density of point objects, which are separate trees. In both cases, the distance matrix of sampling locations was calculated, which provided the opportunity to generate eigenvector-based spatial variables. A kernel smoothed intensity function was used to compute the density of the trees' spatial distribution from the point patterns' data. Gaussian kernel functions with various bandwidths were used. 354 of sampling locations in the space obtained after the conversion of the trees' spatial distribution densities were used to generate a set of orthogonal eigenvector-based spatial variables, each of them representing a pattern of particular scale within the extent of the bandwidth area structured according to distance and reciprocal placement of the trees. An overall test of random labelling reveals the total nonrandom distribution of the tree stems within the site. The unexplained variation consists of 43.8%. The variation explained solely by soil variables is equal to 15.5%, while the variation explained both by spatial and soil variables is 18.0%. The measure of the overstorey spatial structure, which is based on the evaluation of its density enables us to obtain different estimations depending on the bandwidth. The bandwidth affects the explanatory capacity of the tree stand. A considerable part of the plant community variation explained by soil factors was spatially struc-tured. The orthogonal eigenvector-based spatial variables (dbMEMs) approach can be extended to quantifying the effect of forest structures on the herbaceous layer community. The measure of the overstorey spatial structure, which is based on the evaluation of its density, was very useful in explaining herbaceous layer community variation.
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A better understanding of preferential water flow is important because water-related crises, i.e., water scarcity and security, are strongly associated with water retention rates in different landscapes. This review aims to evaluate significant advances in the main themes of preferential water flow to establish the inconsistent roles of preferential water flow in eco-hydrology and suggest promising areas for future work. Results showed that preferential water flow studies have made significant advances in our understanding of certain parameters functioning at multiple scales but that most studies focus on preferential water flow in the vadose zone, whereas few studies on the soil surface. Preferential water flow can have a positive effect on averting water crises, such as when it affects surface runoff soil erosion, soil formation as ecosystem services, nutrient cycling in root zone, and overall water regulation of the water cycle. Conversely, preferential water flow can have a negative effect on eco-hydrological issues via slope stability, gully erosion, geological disaster, waste treatment, water supply in root zone, and food production. Our review concludes that more information is required on preferential water flow before we can assess its role in mitigating water-related crisis events.
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Water is the most limiting resource for global crop production. The projected increase of dry spells due to climate change will further increase the problem of water limited crop yields. Besides low water abundance and availability, water limitations also occur due to restricted water accessibility. Soil penetration resistance, which is largely influenced by soil moisture, is the major soil property regulating root elongation and water accessibility. Until now the interactions between soil penetration resistance, root system properties, water uptake and crop productivity are rarely investigated. In the current study we quantified how interactive effects between soil penetration resistance, root architecture and water uptake affect water accessibility and crop productivity in the field. Maize was grown on compacted and uncompacted soil that was either tilled or remained untilled after compaction, which resulted in four treatments with different topsoil penetration resistance. Higher topsoil penetration resistance caused root systems to be shallower. This resulted in increased water uptake from the topsoil and hence topsoil drying, which further increased the penetration resistance in the uppermost soil layer. As a consequence of this feedback, root growth into deeper soil layers, where water would have been available, was reduced and plant growth decreased. Our results demonstrate that soil penetration resistance, root architecture and water uptake are closely interrelated and thereby determine the potential of plants to access soil water pools. Hence, these interactions and their feedbacks on water accessibility and crop productivity have to be accounted for when developing strategies to alleviate water limitations in cropping systems.
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Improper soil management, increasing farm machinery mass and traffic frequency threaten the ecological functionality of soils under intensive agricultural use. Especially in Brazil, no-tillage (NT) cropping was adopted as a type of soil management that possibly preserves soil functions. Hence, the objective of the present study is to evaluate the effect and intensity of long-term NT compared to soil under natural forest (NF) or grassland (NG) based on parameters of composition (density, porosity, water retention) and functionality by means of mechanical strength (precompression stress σp, cyclic compressibility cn), air permeability Ka, and saturated hydraulic conductivity ks. The studied Hapludox, Hapludalf and Quartzipsamment from southern Brazil under subtropical climate mostly reacted based upon their grain size distribution, namely clay, loamy sand and loamy fine sand. The largest impact appeared in the Hapludox, where compaction occurred (higher σp, lower cn and smaller porosity, especially macroporosity). ks and Ka were highest at the surface of the Hapludox under NF, but were reduced strongly under NT. In both the Hapludox and the Hapludalf deeper soil layers were also affected by NT, but in the clayey Hapludox the applied pressure resulted in the largest compacted layer. The Hapludalf of loamy sand texture showed, supposedly due to shallow soil operations, a weak, but permeable surface layer under NT above a dense layer, while the other layers were only slightly affected by cropping. In the Quartzipsamment, there was no increase in σp and little in cn, whereas density in deeper layers slightly decreased. While ks was increased strongly under NT compared to NG, the opposite was found for Ka which could not be explained by the investigated parameters. The results demonstrate that soil under NT might be significantly affected by soil compaction with regard to soil functions if not adequately managed by adjusted machinery. This is of even greater importance in fine-textured soils like the investigated Hapludox, compared to coarse-textured soils of poor aggregation like the investigated Quartzipsamment.
Chapter
We shall, in this last chapter, treat the floristic-sociological or Braun-Blanquet approach to classification and interpretation of communities.
Article
Compaction of the subsoil due to heavy traffic in moist and wet soil is widespread in modern agriculture. The objective of this study was to quantify the effects from realistic field traffic on soil penetration resistance and barley crop yield for three Luvisols developed from glacial till. Undisturbed soil cores were used for quantifying the precompression stress (sigma_pc) of non-compacted soil. Tractor-trailer combinations for slurry application with wheel loads of ~3, ~6 and ~8 Mg (treatments M3, M6, M8) were used for the experimental traffic in the spring at field-capacity. For one additional treatment (labelled M8-1), the soil was loaded only in the first year. A tricycle-like machine with a single pass of wide tyres each carrying ~12 Mg (treatment S12) was included at one site. Traffic treatments were applied in a randomized block design with four replicates and with treatments repeated in four consecutive years (2010–2013). After two years of repeated experimental traffic, penetration resistance (PR) was measured to a depth of 1 m. The yield of a spring barley crop (Hordeum vulgare L.) was recorded in all four years of the experiment. The results did not support our hypothesis of sigma_pc as a soil strength measure predicting resistance to subsoil compaction. The tyre inflation pressure and/or the mean ground pressure were the main predictors of PR in the upper soil layers. For deeper soil layers, PR correlated better to the wheel load. The number of wheel passes (M-treatments vs the S12 treatment) modified this general pattern, indicating a very strong impact of repeated wheel passes. Our data indicate that a single traffic event may mechanically weaken the soil without inducing major compaction but with influence on the effect of subsequent traffic even after as long an interval as a year (treatments M8 vs M8-1). Crop yields were much influenced by compaction of the plough layer. Due to the repeated wheel passes for the M-treatments, significant yield penalties were observed, while the single-pass treatment with 12 Mg wheel load in S12 did not have significant effects on crop yield. Our hypothesis of 3 Mg wheel load as an upper threshold for not inducing subsoil compaction was confirmed for the tractor-trailer treatments with repeated wheel passes but not supported for the single-pass machinery. The results call for further studies of the potential for carrying high loads using wide, low-pressure tyres by crab steering/dog-walk machinery.
Article
Grazing cattle on forest plantations in the interior of British Columbia (B.C.) is a common practice, but its impact on soil compaction is not well documented. This study evaluated the effects of cattle grazing and forage seeding on soil compaction in lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) plantations near Kamloops, B.C. Grazing regimes consisted of ungrazed exclosures and pastures grazed to achieve 50% utilization of forage vegetation. Seeding treatments were 0 and 12 kg ha(-1). Soil bulk density and penetration resistance were determined in 1996 and 1997, before and after the one-month grazing period on study sites grazed since 1989. Water infiltration rates were measured in 1997 after the one-month cattle grazing period. Bulk density was 6% higher on grazed pastures compared to the exclosures. Pastures seeded to domestic forage species had significantly greater soil bulk density at the 0-7.5 cm depth than unseeded pastures. Soil penetration resistance was higher throughout most of the soil profile in the grazed treatments than in the ungrazed exclosures. On pastures without grazing, seeding of the domestic forage species resulted in lower soil penetration resistance relative to unseeded pastures. This was especially true at depths below 6 cm. The rate of water infiltration was not affected by long-term grazing and forage seeding. The bulk density and penetration resistance data indicate that plantation grazing at 50% forage utilization does not lead to root-limiting increases in soil compaction.