Abstract: The reliable correlation model for intelligent compaction (IC) is to be developed by integrating characteristics of the filling material and control parameters of the vibratory roller. Key characteristics of the backfill soil from the construction site of Rongwu Highway are tested through the modified Proctor test and the direct shear test. A well-documented dataset is built by summarizing 4000 shear strengths from open literature and 246 data from laboratory tests in this study. The PSO-BP-NN model is developed based on this dataset to predict the shear strength and compactness of the subgrade soil in the scope of mechanical properties and compaction powers. The importance analysis of the input variables is performed with the Random Forest algorithm. The influence mechanism is analyzed in sequence. The plain soil and the lime soil demonstrate typical compaction curves, and the lime soil is less sensitive to the influence factors. An optimal compaction power exists for determining the optimal moisture content utilizing the shear strength, tending to be less conservative. The moisture content is the most important factor for the compactness, followed by the compaction power; the particle size is suggested to be considered for real-time evaluations. The compaction mechanism is mainly attributed to the water film theory and the electrochemical property of the filling soil. This study aims to provide a reliable model to estimate the compactness in the aspect of material properties so as to enhance the accuracy of the IC model.

Abstract: Several studies on soil physical quality have related soil structural properties to bulk density, proposing values for critical limits in relation to the soil compaction status. However, these values are not applicable to Andosols due to their very low bulk density (< 0.9 Mg m−3). This work aimed to evaluate the short-term effects of soil compaction on the soil physical quality of an Andosol. The experiment was established in May 2019. Soil cores were collected from the soil surface and field measurements (penetration resistance, volumetric water content and air conductivity) were conducted to monitor changes in the soil physical quality after compaction events. The soil was compacted using rollers (weighing between 1.20 and 1.37 Mg) to reach three bulk densities (T0: 0.65, T1: 0.75 and T2: 0.85 Mg m−3) by controlling the number of roller passes. Soil compaction induced an increase in the soil bulk density that resulted in an increase in the mechanical strength (e.g. maps of penetration resistance revealed values from (T0) 500 kPa to (T2) 1500 kPa) and caused a decrease in the volume of macropores (e.g. air capacity in T0 and T2 was 22% and 11%, respectively) responsible for water infiltration and flow. The latter provoked an increase in the volumetric water content in the upper 10 cm of the soil, which decreased the field air conductivity due to the reduced pore space and its continuity. Bulk density also increased due to wetting and drying cycles, showing the effect of the natural rearrangement of soil particles, which was more intense in the soil with the lowest bulk density. When the bulk density of the tilled soil increased to values over 0.80 Mg m−3, soil pore functions related to soil aeration reached critical values (air capacity < 10% and air permeability < 1 µm2) concerning soil compaction, while the soil precompression stress (around 60 kPa) and plant available water (> 20%) remained within an optimal range.

Abstract: Abstract Nitrous oxide (N 2 O) is the contributor to agricultural greenhouse gas emissions with the highest warming global potential. It is widely recognised that traffic and animal-induced compaction can lead to an increased potential for N 2 O emissions by decreasing soil oxygen supply. The extent to which the spatial and temporal variability of N 2 O emissions can be explained by soil compaction is unclear. This review aims to comprehensively discuss soil compaction effects on N 2 O emissions, and to understand how compaction may promote N 2 O emission hotspots and hot moments. An impact factor of N 2 O emissions due to compaction was calculated for each selected study; compaction effects were evaluated separately for croplands, grasslands and forest lands. Topsoil compaction was found to increase N 2 O emissions by 1.3 to 42 times across sites and land uses. Large impact factors were especially reported for cropland and grassland soils when topsoil compaction—induced by field traffic and/or grazing—is combined with nitrogen input from fertiliser or urine. Little is known about the contribution of subsoil compaction to N 2 O emissions. Water-filled pore space is the most common water metric used to explain N 2 O emission variability, but gas diffusivity is a parameter with higher prediction potential. Microbial community composition may be less critical than the soil environment for N 2 O emissions, and there is a need for comprehensive studies on association between environmental drivers and soil compaction. Lack of knowledge about the interacting factors causing N 2 O accumulation in compacted soils, at different degrees of compactness and across different spatial scales, limits the identification of high-risk areas and development of efficient mitigation strategies. Soil compaction mitigation strategies that aim to loosen the soil and recover pore system functionality, in combination with other agricultural management practices to regulate N 2 O emission, should be evaluated for their effectiveness across different agro-climatic conditions and scales.

Abstract: Steep-slope viticulture is a common practice in the Mediterranean basin, and provides landscapes of considerable socio-economic value. However, these complex agricultural systems are intrinsically fragile. One of the main problems is soil erosion due to extreme rainfall events. This may cause a progressive reduction in soil fertility and the occurrence of instabilities and land degradation phenomena. To worsen this condition there is the increasing mechanisation of agricultural management causing soil compaction, and the pressure of climate change, with an intensification of extreme weather events. In this context, vineyard soil management plays a key role, as it can accelerate or mitigate overland flow and soil erosion phenomena. There are various techniques for quantifying these processes, often based on field measurements through prolonged data collection using experimental plots. However, the advent of new technologies in remote sensing opens new frontiers in the acquisition of high-resolution spatial data. Indeed, they could be used in runoff/erosion simulation models and integrated with site-specific data. The aim of this paper is to assess runoff and soil erosion processes in vineyard under four different soil managements. Specifically, four practices were tested: (1) Reference (inter-row managed with standard farm grass cover; RF); (2) Continuous Tillage (bare soil obtained by continuous mechanical weeding using roto-tiller; CT); Nectariferous (a mix of herbaceous species capable of attracting insects favouring inter-row biodiversity; NF); (4) Single Tillage (inter-row weeding once a year using roto-tiller; ST). The research proposes a modelling approach using a physically-based model (SIMWE) using samples of runoff and sediment as an assessment, collected with a low-cost methodology. In particular, a cost-effective approach easily replicable in different contexts (such as developing countries) is sought. In addition to cultivation specifics, areas of soil compacted by the passage of agricultural vehicles were also analysed using the connectivity index. In general, results show an interesting capacity of ST in mitigating soil erosion, as well as for NF. Furthermore, the negative role of wheel tracks as preferential pathways for surface runoff and sediment is highlighted. Finally, the work shows that CT aggravated soil erosion as compared to RF.

Abstract: Intensive soil disturbance by conventional tillage and heavy machinery traffic for planting, cultivation, and harvesting operations are the main causes of soil compaction and degradation of soil physical quality in sugarcane fields. However, the adoption of conservation soil tillage practices, such as no-till and reduced tillage associated with traffic control have been proposed as a key strategy to preserve soil physical quality, enhancing water availability and air fluxes. Nevertheless, the effects of reduced tillage associated with traffic control in sugarcane fields are still not well documented. A study was carried out to quantify soil water availability and air flux indicators in two soils with contrasting textures (named Sandy Loam and Clayey soil) under conventional and reduced tillage practices associated with and without controlled machinery traffic in central-southern Brazil. Soil physical parameters such as bulk density, total porosity, air-filled porosity, air permeability, pore continuity index, and the least limiting water range (LLWR) were measured. In both soils, there was no difference between conventional and reduced tillage in bulk density, air permeability, and LLWR. However, reduced tillage with non-traffic decreased bulk density and increased macroporosity, air-filled porosity, air permeability, pore continuity, and LLWR in Sandy Loam soil. In Clayey soil, the bulk density and LLWR did not change between tillage practices, but air permeability and pore continuity index were larger under reduced tillage with non-traffic. These results highlighted that soil disturbance by conventional tillage does not improve the water availability and air permeability during the crop cycle. However, the traffic control is essential to support the adoption of reduced tillage in sugarcane fields, preserving soil water availability and air fluxes for the subsequent ratoons. Reduced tillage and traffic control are two of the most important pillars for reducing soil compaction and promoting sustainability of sugarcane production in Brazil.

Abstract: Mechanization in agriculture has greatly improved the efficiency of field operations, but also resulted in heavier agricultural vehicles, which has led to increased risks of soil compaction. Hence, farmers benefit from machinery with higher capacity but may suffer from decreased yields caused by compaction. Compaction may result in further environmental costs to society. We present a framework that relates the machinery capacity to soil compaction and its impacts on crop yields and environmental disservices, and associated revenues and costs for farmers and society. We combined simulations using a soil compaction model and a soil-crop model with simple economic analyses. We applied the framework to a case study of cereal production in Sweden, to derive the optimal combine harvester size that maximizes the farmer's private profit and the societal net benefit, respectively. Increased machinery size decreased harvesting costs, but also reduced simulated crop yields and thus crop revenue as a result of soil compaction. Furthermore, in the model simulations, compaction also increased surface run-off, nitrogen leaching and greenhouse gas emissions. Intermediate machinery size maximized the farmer's net revenue. Net benefits for society were highest for the lowest possible compaction level, due to the considerable external costs from soil compaction. We show that the optimal machinery size and thus compaction level for maximum farmer revenue would decrease if either producer prices were higher, harvesting costs savings from larger machinery were smaller, or if farmers were charged for (part of the) environmental costs.

Abstract: Soil compaction caused by highly mechanized agriculture can constrain soil microbial diversity and functioning. Physical pressure on the soil decreases macropores and thereby limits oxygen diffusion. The associated shift from aerobic to anaerobic conditions can reduce nitrification and promote denitrification processes, leading to nitrogen (N) losses and N depletion that affect plant productivity. High soil moisture content during trafficking can exacerbate the negative effects of soil compaction. However, the extent to which soil moisture amplifies the effects of compaction on the soil microbiome and its control over N cycling is not well understood. Using a controlled greenhouse experiment with two different crops (pea and wheat), we compared the effects of compaction at three different soil moisture levels on soil physicochemical properties, microbial diversity, and the abundance of specific N species and quantification of associated microbial functional groups in the N cycle. Soil compaction increased bulk density from 15% (light compaction) to 25% (severe compaction). Compaction delayed germination in both crops and reduced yield by up to 60% for pea and 40% for wheat. Compaction further induced crop-specific shifts in microbial community structures. After compaction, the relative abundance of denitrifiers increased along with increased nitrate (NO3–) consumption and elevated nitrous oxide (N2O) concentrations in the soil pores. Conversely, the relative abundance of nitrifiers remained stable under compaction, but potentially decelerated nitrification rates, resulting in ammonium (NH4+) accumulation in the soil. This study showed that soil compaction effects are proportional to the initial soil moisture content, which could serve as a good indicator of compaction severity on agricultural fields. However, the impact of soil compaction on crop performance and on microbial communities and functions associated with the N cycle were not necessarily aligned. These findings demonstrate that not only the soil physical properties but also various biological indicators need to be considered in order to provide more precise recommendations for developing sustainable farming systems.

Abstract: Soil compaction constrains root growth and crop yield. Previous studies have shown that localized nutrient supply can significantly improve maize plant growth in field conditions at the early growth stage. However, this promoting effect has not been tested in the compacted soil. We describe 2-year field experimentation on a fluvo-aquic soil in the North China Plain to investigate the effect of localized vs. broadcast ammonium and phosphorus supply on maize under three soil compaction treatments (NC: non-compacted, C: compacted and SC: severely compacted) during 2012 and 2013. Results showed that compared with broadcast ammonium and phosphorus (BNP), localized ammonium and phosphorus supply (LNP) resulted in significantly higher PFPN in the NC (by 31–37%), C (by 43–44%) and SC (by 45%) treatments at harvest. When soil was compacted (C and SC), the enhancement of nitrogen (N) utilization in the LNP treatment was attributed to the increased root growth, including greater specific root length (a greater proportion of fine roots), lower root tissue density and deeper rooting at the seedling stage, especially in the compacted treatment (C). The enhanced root penetration capacity contributed to the increased N and water uptake from the deep soil layers. Our study highlighted the importance of nutrient management for mitigating negative impacts of soil compaction on crops, and will underpin new soil compaction management practices by considering optimal fertilization to strengthen the root-soil interactions.

Abstract: Agricultural fields are usually subjected to high amounts of traffic from field operations. The influence of traffic on sandy loam soil in three tillage systems were investigated in a field experiment. The field was located in a Canadian prairie region. In the experiment, the treatments were three tillage systems: no-tillage, disc tillage, and spring-tine tillage. Following tillage operations, field plots were trafficked with one pass of a sub-compact tractor. Soil properties were measured before and after the traffic to examine the effects of tillage systems and wheel traffic. For the effects of the tillage systems on the soil bulk density, soil shear strength, soil surface resistance, and soil cone index, the no-tillage system had higher values for all the soil properties when compared with the disc and spring-tine tillage systems. The plant (canola) population density ranged from 18.2 plants/m2 to 34.9 plants/m2, with the no-tillage having the lowest plant densities. For the effects of wheel traffic, one pass of the tractor in the disc and spring-tine tillage plots resulted in a 2.7% and 17.4% reduction in soil moisture content, respectively. After wheel traffic, the average soil shear strength for the disc and spring-tine systems were still significantly lower than the no-tilled system. Sinkages of 40 and 50 mm were observed for the spring-tine and disc tillage systems, respectively. The results of this study highlight the importance of preventing the demerits of soil compaction induced by wheel traffic after tillage operations.

Abstract: Despite its importance for hydrological and ecological soil functioning, characterizing, and quantifying soil structure in the field remains a challenge. Traditional characterization of soil structure often relies on point measurements, more recently, we advanced the use of minimally invasive geophysical methods that operate at plot-field scales and provide information under natural conditions. In this study, we expand the application using geoelectrical and time-domain reflectometry (TDR) monitoring of soil water dynamics to infer impacts of compaction on soil structure and function. We developed a modeling scheme combining a new pedophysical model of soil electrical conductivity and a soil-structure-informed one-dimensional water flow and heat-transfer model. The model was used to interpret Direct Current (DC)-resistivity and TDR monitoring data in compacted soils at the Soil Structure Observatory (SSO) located in the vicinity of Zürich, Switzerland. We find that (1) soil compaction leads to a persistent decrease in soil electrical resistivity and (2) that compacted soils are typically drier than non-compacted soils during long drying events. The main decrease in electrical resistivity is attributed to decreasing macroporosity and increasing connectivity of soil aggregates due to compaction. Higher water losses in compacted soils are explained in terms of enhanced evaporation. Our work advances characterization of soil structure at the field scale with electrical methods by offering a physically based explanation of the impact of soil compaction on electrical properties and by interpreting DC-resistivity data in terms of soil water dynamics.

Abstract: Soil compaction (SC) is a major threat for agriculture in Europe that affects many ecosystem functions, such as water and air circulation in soils, root growth, and crop production. Our objective was to present the results from five short-term (<5 years) case studies located along the north–south and east–west gradients and conducted within the SoilCare project using soil-improving cropping systems (SICSs) for mitigating topsoil and subsoil SC. Two study sites (SSs) focused on natural subsoil (˃25 cm) compaction using subsoiling tillage treatments to depths of 35 cm (Sweden) and 60 cm (Romania). The other SSs addressed both topsoil and subsoil SC (˃25 cm, Norway and United Kingdom;˃30 cm, Italy) using deep-rooted bio-drilling crops and different tillage types or a combination of both. Each SS evaluated the effectiveness of the SICSs by measuring the soil physical properties, and we calculated SC indices. The SICSs showed promising results—for example, alfalfa in Norway showed good potential for alleviating SC (the subsoil density decreased from 1.69 to 1.45 g cm−1) and subsoiling at the Swedish SS improved root penetration into the subsoil by about 10 cm—but the effects of SICSs on yields were generally small. These case studies also reflected difficulties in implementing SICSs, some of which are under development, and we discuss methodological issues for measuring their effectiveness. There is a need for refining these SICSs and for evaluating their longer-term effect under a wider range of pedoclimatic conditions.

Abstract: Bio-tillage has recently been proposed as a measure to alleviate soil compaction through biopores created by cover crop roots. The objective of this study was to determine the effect of different cover crops on soil physical properties and the succeeding maize (Zea mays L.) growth in compacted soil. Four treatments, including no cover crop as a control (Con), alfalfa (Medicago sativa L.), oilseed rape (Brassica napus L.), and radish and hairy vetch mixture (Raphanus sativus L. and Vicia villosa Roth), were carried out under both compacted and noncompacted soil conditions. Soil physical properties, such as the volumetric soil water content (SWC), bulk density, saturated hydraulic conductivity (Ks) and air permeability at water potential of −60 hPa (Ka60), and maize root characteristics and yield were measured. The cover crops did not affect the soil bulk density but significantly decreased the SWC in both the compacted and noncompacted soils relative to the Con treatment. The alfalfa treatment presented significantly higher Ks in the noncompacted soil and Ka60 in both the compacted and noncompacted soils than the Con treatment in the soil layer depth of 20–50 cm. The three cover crop treatments improved the maize root biomass density (173.2% for 2018 and 35.6% for 2019) and root length density (50.9% for 2018 and 51.8% for 2019) relative to the Con treatment in the soil layer depth of 10–70 cm in 2018 and soil layer depth of 10–50 cm in 2019 in the compacted soil rather than in the noncompacted soil. Compared with the Con treatment, the radish mixed with hairy vetch treatment in 2018 and the oilseed rape treatment in 2019 significantly enhanced the maize yield in the compacted soil. Our results suggest that alfalfa is the best crop for improving air permeability; however, the oilseed rape and mixture of radish and hairy vetch lead to better maize growth in the compacted soil. Bio-tillage using cover crops is effective in alleviating soil compaction.

Abstract: Facing the need to adopt a laboratory compaction method of natural or lime-treated soils which is repeatable and representative of real in-situ compaction conditions for dike or road constructions, the effects of compaction mode, dry density and suction on the tensile strength of natural and lime-treated silty soil compacted in laboratory have been investigated in a systematic way. Soil specimens were prepared from three different modes of compaction: the static kneading compaction, the standard Proctor compaction and a dynamic in-mold compaction. For kneading and Proctor compaction, small cylindrical samples were extracted at different locations in larger compacted specimen with a milling machine controlled by computer. On the contrary, the so-called “in-mold compaction” consists in compacting the soil in a mold with the final required dimensions. The small cylindrical samples were then submitted to various suctions from 0 to 2000 kPa during seven days. At the end, dry density of samples was measured with a 3-dimensionnal scanner and tensile strength was determined from indirect (Brazilian) tensile tests. The same investigation was also performed, with similar number of specimens, on untreated soil. In-mold compaction provides the best repeatability of obtained tensile strength (essentially because of the controlled and uniformly distributed dry density though the specimen) but is not representative of real compaction condition. Also, it is observed that the tensile strength of untreated soils is strongly affected by suction level and slightly by dry density. At the opposite, for lime-treated soil, little variations of dry density may have a significant impact on the tensile strength while suction plays a secondary role. This study reveals that, when compacted lime-treated soils are used as a bearing element (like in road subgrades or subbases), a particular attention must be paid on the quality of compaction process to avoid under-compacted zones that could lead to material weakness.

Abstract: The traffic-induced soil compaction in the field has gradually become an important constraint to sustainable agricultural development. A field experiment was conducted to acquire the stress transmitted caused by multiple passes with different types of tractors and to investigate the impact of these stresses on soil bulk density and crop growth. The experiment applied two tractors with different masses: LOVOL M904 (HC) and John Deer 280 (LC), and six different treatments of 0 (C0), 1 (C1), 3 (C3), 5 (C5), 7 (C7), and 9 (C9) tractor passes for each tractor. The results showed that at each number of passes, tractors with small axle-loads at 0–20 cm depth generated higher soil additional stress, while tractors with large axle-loads at 20–80 cm depth generated higher soil additional stress. In the 0–20 cm soil layer, when the number of continuous passes is less than 7 times, the passes of a small axle-load tractor lead to larger soil bulk density, and when the number of continuous passes is more than 7, the compaction of large axle-load tractor leads to larger soil bulk density. At depths of 20–80 cm, compaction by large axle-load tractors results in larger soil bulk density. In this study, different levels of tractor compaction inhibited key growth indicators of maize, resulting in yield reductions. The effect of different tractor load compaction on maize yield increased significantly with the number of compaction passes, with 1–5 tractor passes having no significant effect on yield and 7–9 passes producing greater yield reductions for HC. This study will provide a theoretical basis and technical support for the selection of agricultural machinery and reasonable tillage technology.

Abstract: Background: The compaction of subsoils in agriculture is a threat to soil functioning. Measures aimed at the prevention, amelioration, and/or impact alleviation of compacted subsoils have been studied for more than a century, but less in smallholder agriculture. Methods: A meta-analysis was conducted to quantitatively examine the effects of the prevention, amelioration, and impact alleviation measures in mechanized and small-holder agriculture countries, using studies published during 2000~2019/2020. Results: Mean effect sizes of crop yields were large for controlled traffic (+34%) and irrigation (+51%), modest for subsoiling, deep ploughing, and residue return (+10%), and negative for no-tillage (−6%). Mean effect sizes of soil bulk density were small (<10%), suggesting bulk density is not a sensitive ‘state’ indicator. Mean effect sizes of penetration resistance were relatively large, with large variations. Controlled traffic had a larger effect in small-holder farming than mechanized agriculture. Conclusion: We found no fundamental differences between mechanized and smallholder agriculture in the mean effect sizes of the prevention, amelioration, and impact alleviation measures. Measures that prevent soil compaction are commonly preferred, but amelioration and alleviation are often equally needed and effective, depending on site-specific conditions. A toolbox of soil compaction prevention, amelioration, and alleviation measures is needed, for both mechanized and smallholder agriculture.

Abstract: An emerging real-time ground compaction and quality control, known as intelligent compaction (IC), has been applied for efficiently optimising the full-area compaction. Although IC technology can provide real-time assessment of uniformity of the compacted area, accurate determination of the soil stiffness required for quality control and design remains challenging. In this paper, a novel and advanced numerical model simulating the interaction of vibratory drum and soil beneath is developed. The model is capable of evaluating the nonlinear behaviour of underlying soil subjected to dynamic loading by capturing the variations of damping with the cyclic shear strains and degradation of soil modulus. The interaction of the drum and the soil is simulated via the finite element method to develop a comprehensive dataset capturing the dynamic responses of the drum and the soil. Indeed, more than a thousand three-dimensional (3D) numerical models covering various soil characteristics, roller weights, vibration amplitudes and frequencies were adopted. The developed dataset is then used to train the inverse solver using an innovative machine learning approach, i.e. the extended support vector regression, to simulate the stiffness of the compacted soil by adopting drum acceleration records. Furthermore, the impacts of the amplitude and frequency of the vibration on the level of underlying soil compaction are discussed. The proposed machine learning approach is promising for real-time extraction of actual soil stiffness during compaction. Results of the study can be employed by practising engineers to interpret roller drum acceleration data to estimate the level of compaction and ground stiffness during compaction.

Abstract: Soil compaction can negatively affect a range of soil hydraulic, biogeochemical and plant physiological processes. A study conducted in Lujan (Argentina) investigated the effect of three traffic treatments (zero, controlled, and random traffic) on soil physical properties and soybean yield over a period of eight years. The soil at the site (Typic Argiudoll) had been managed under continuous no-tillage for nine years. Field-wheeled areas under controlled and random traffic management were 3309 m2 ha−1 or 33.1% and 4622 m2 ha−1 or 46.2%, respectively. ‘Random’, non-controlled traffic farming represented the standard mechanisation management practice. The three traffic treatments relied on commercially available (unmodified) farm equipment. Results showed that soil cone Index (depth range: 0–450 mm) increased in the order: zero (1.90 ± 0.31 MPa) > controlled (2.46 ± 0.19 MPa) > random (3.75 ± 0.21 MPa) traffic, respectively, which therefore explained treatment differences in root biomass. Water infiltration rates decreased significantly with increased traffic footprint (by up to 35% in random traffic), which therefore reduced plant available water and influenced crop performance. Grain yields with zero traffic were fairly consistent between-years, but increased with controlled traffic (which progressively approached the yields achieved with zero traffic) and decreased in random traffic at average rates of 33 and 29 kg ha−1 per year, respectively. Treatment differences in grain yield widened in drier compared with wetter years when plant growth and yield were less constrained by water availability. An average yield penalty of ≈ 30% was recorded in random traffic relative to the other treatments. Gross income with random traffic was USD787 per ha, which compared to USD1179 and USD1116 per ha with zero and controlled traffic, respectively. The proposed approaches to mitigating adverse effects of compaction on crop productivity, sustainability and profitability appear to be cost-effective options and may be adopted when fully-matched machinery is not available. There is potential for future development of controlled traffic farming in Argentina.

Abstract: Soils have many ecological functions and provide various ecosystem services including support for global food and fuel production. However, FAO reports indicate that approximately one-third of the planet’s arable lands show levels of degradation from processes including soil erosion, low levels of nutrients, acidification, salinization, compaction, sealing, and contamination. These conditions are also found in Brazil where soil degradation is largely caused by inadequate land management. Worldwide, strategic policies have been presented to mitigate this problem, with emphasis on sustainable agriculture. Among them, agroforestry has been identified as a viable system for mitigating and recovering degraded areas. Agroforestry techniques have been developed and tested but are still not understood by farmers, due to their complexity. This study aimed to analyze experiences and studies with agroforestry reported from Australia, some countries in Africa, and Brazil to search for similarities in these complex systems and identify possible correlations to support the hypothesis that land recovery can be enhanced through soil management using agroforestry. A Sankey diagram was developed to illustrate relationships among problems, the adoption of agroforestry and improvements, and the most important contributions. Data analysis shows that the main problems related to soil degradation are soil erosion and decreased soil fertility, while the adoption of agroforestry systems proved to improve different aspects of soil quality and to be a safe path to sustainable agricultural production. To obtain more information on the adoption of these systems in different locations, soils, and climates, it is important to implement policies for reducing land degradation. Furthermore, the assessment of the economic, environmental and social benefits of improving soil fertility and decreasing erosion in agroforestry systems is necessary to validate the use of agroforestry as a sustainable agricultural practice.

Abstract: Abstract Aims Soil compaction is a major yield-reducing factor worldwide and imposes physico-chemical constraints to plant growth and development. Facing limitations, roots can adapt and compensate for loss of functioning through their plasticity. Being primarily a belowground challenge, tolerance to soil compaction needs to be associated with root phenotype and plasticity. It is therefore of importance to distinguish between size-related apparent and size-independent adaptive plasticity. We determined the above- and belowground plasticity of sorghum genotypes varying in overall plant size. Methods We quantified plasticity as the degree response (adaptive and apparent plasticity) to soil compaction and conducted two experiments with sorghum and two soil density levels (1.4 and 1.8 Mg m −3 ). First, we quantified the shoot biomass plasticity of 28 sorghum genotypes. Second, we studied the root plasticity of six genotypes varying in shoot size and tolerance to soil compaction. Results Plasticity was correlated with plant biomass with larger genotypes responding earlier and more intensely. Soil compaction affected roots more than shoots and plasticity was expressed foremost in nodal root number and fine root length. Impeded plants produced 35 and 47% less root mass and length, respectively. Conclusions Plasticity to soil compaction varies among genotypes, but less-sensitive lines are in general smaller-sized genotypes. The association between tolerance and plant biomass may pose challenges to crop production; however, vigorous genotypes with unresponsive shoots to soil compaction do exist. Maintaining shoot growth relatively stable while the root modifies its structure can be an important adaptation mechanism to soil compaction.

Abstract: Porosity, pore shape and pore size distribution were measured on thin sections prepared from undisturbed soil samples by means of electro-optical image-analysis. Soil samples were taken from the topsoil compacted by the tractor wheels and in uncompacted topsoil, and just below the tilled layer where the ploughpan or ploughsole was developed. In the compacted topsoil the porosity strongly decreased, particularly the irregular pores while the elongated ones strongly reduced their size and modified their orientation pattern. The microscopic observation revealed that these elongated pores were thin fissures parallel to the soil surface, thus giving rise to a platy structure, and very often they lòst their continuity in a vertical sense. After one year there were no visible differences between the compacted and uncompacted topsoils. The ploughpans were very thick (in many cases more than 10 cm) but it was the first cm that was more strongly compacted and contained few, if any, pores.