Soil Recovery Research Articles

Changes in Enzyme Activity in Post-Pyrogenic Soils (Physical Model Experiment)

Presented data on changes in the enzymatic activity of soils under pyrogenic effects in model experiments simulating natural fires. A series of experiments aimed at studying pyrogenic inhibition of enzyme activity and dynamics of their recovery in post-pyrogenic soils were performed under laboratory and natural conditions. The objects of the study were sandy soil (Seropeski, Arenosol) and migratory-segregation black soil (Haplic Chernozem (Loamic, Pachic) Rostov region. Model experiments were carried out by treating soil samples with gas burner flame (amount of heat 87–435 × 103 J) and pyrogenic action of wood fuel combustion (10–279 × 106 J). In the first case, the exposure duration was 1 to 5 min, and in the second case from 1 to 120 min. The response of enzymes (catalase, invertase, urease, peroxidase and phosphatase) to low-temperature plasma exposure (1–120 min) was found to differ depending on the enzyme group and degree of exposure. It was found that the depth of penetration of thermal effects in simulated fires was limited to the top soil layer (0–10 cm), and the radius of spread relative to the combustion source did not exceed 20 cm. Temperature values varied according to time, source of exposure and amount of fuel (400–600°C). Sandy soils and chernozem were heated and cooled down at different rates. The activity of catalase, invertase and urease were found to be inversely related to the intensity of pyrogenic exposure. The dynamics of enzyme activity recovery in post-pyrogenic soils was traced. Invertase activity recovered faster than catalase and urease activity, but full recovery after a year does not occur. The results obtained indicate a significantly prolonged effect of inhibition of enzymatic activity during simulation of natural fires.

Natural surfactant mediated bioremediation approaches for contaminated soil.

The treatment of environmental pollution by employing microorganisms is a promising technology, termed bioremediation, which has several advantages over the other established conventional remediation techniques. Consequently, there is an urgent inevitability to develop pragmatic techniques for bioremediation, accompanied by the potency of detoxifying soil environments completely. The bioremediation of contaminated soils has been shown to be an alternative that could be an economically viable way to restore polluted soil. The soil environments have long been extremely polluted by a number of contaminants, like agrochemicals, polyaromatic hydrocarbons, heavy metals, emerging pollutants, etc. In order to achieve a quick remediation overcoming several difficulties the utility of biosurfactants became an excellent advancement and that is why, nowadays, the biosurfactant mediated recovery of soil is a focus of interest to the researcher of the environmental science field specifically. This review provides an outline of the present scenario of soil bioremediation by employing a microbial biosurfactant. In addition to this, a brief account of the pollutants is highlighted along with how they contaminate the soil. Finally, we address the future outlook for bioremediation technologies that can be executed with a superior efficiency to restore a polluted area, even though its practical applicability has been cultivated tremendously over the few decades.

Effects of Livestock Exclusion on Pollutant Export From a North Carolina Beef Cow Pasture

Highlights Exclusion of beef cattle from two streams resulted in significant reductions in nitrogen, phosphorus, and sediment exports. Reductions in nutrient and sediment export improved following four or more years of exclusion. Nitrogen and phosphorus concentrations in storm samples decreased more than those in baseflow samples. Abstract. Fences were installed to exclude cattle from two adjacent small streams on a beef and swine farm located in central North Carolina. The two streams, referred to as UTA and North, originated in a pasture used for beef cow production and the application of swine waste. Rainfall and discharge were continuously monitored for 1.34 years prior to and 1.8 years after the fencing was installed in order to quantify the effect of the livestock exclusion on pollutant export/loads in the two streams originating in the pasture. Monitoring results documented reductions in total nitrogen (TN), phosphorus (TP), and total suspended solids (TSS) exports via the North stream of 15%, 54%, and 67%, respectively. Monitoring on the UTA stream was restarted 3.7 years after the initial 1.8 years and continued for about 1 year to assess the effect of natural vegetation growth and stream channel soil recovery. The combined reductions for the two periods were 39%, 64%, and 74% for TN, TP, and TSS, respectively. Exports of TN, TP, and TSS during the later monitoring period decreased by 13%, 60%, and 22%, respectively, compared to the initial 1.8-year monitoring period. These results indicated that exclusion fencing was effective at reducing pollutant exports during the first 1.8 years and that its effectiveness increased after about four years. Consequently, studies that report effectiveness during the first 2 to 4 years after exclusion likely underestimate the long-term effectiveness of the exclusion fencing. Keywords: Best management practices, Discharge monitoring, Livestock exclusion.

Green Manure as an Alternative for Soil Recovery in a Bauxite Mining Environment in Southeast Brazil

The objective of this study was to evaluate plant cover and dry mass produced by green manures and their influence on the chemical attributes of soil for the ecological restoration of an area around bauxite mine environment in Southeast Brazil. Soil preparation, chemical fertilization and sowing of three species of green manures were carried out: Cajanus cajan, Crotalaria juncea and Stylosanthes guianensis. In general, C. cajan and C. juncea showed the best performance in plant cover. C. cajan and S. guianensis produced more phytomass. Green manures were efficient to promote rapid plant cover and increase in soil organic matter and total-N contents in all treatments. Therefore, green manure is a viable alternative that contributes to the success of ecological restoration projects in areas in the bauxite mining environment.

Microbiological indicators as sensitive indicators in the assessment of areas contaminated by heavy metals

Context As one of the world’s largest mining spills, the Aznalcóllar pyrite mine accident in Spain in 1998 resulted in ~45 km2 of agricultural soils polluted by arsenic and heavy metals. The Guadiamar Green Corridor (GGC) helped with soil remediation but residual pollution is still detected 20 years later. Aims Several methodologies based on chemical indicators have been used to assess the recovery of these areas. However, simple microbiological indicators (e.g. microbial activity and biomass, and metabolic quotient (qCO2)) are yet to be uesed. The aim of this study was to evaluate areas contaminated by arsenic and heavy metals using microbiological indicators of soil quality. Methods We used a systematic random sampling design to collect soil samples from two soil groups with different recovery trajectories. We analysed the total and water-soluble concentrations of arsenic (As), lead (Pb), copper (Cu), and zinc (Zn), the main soil properties, and bioassays including microbial activity and biomass, and metabolic quotient or microbial stress (qCO2). Key results Twenty years after the accident, soils with As and Pb concentrations that consistently exceeded regulatory levels had altered soil microbial biomass and functioning. Although overall rates of microbial respiration were not significantly different between polluted soils, microbial biomass was lower and qCO2 was higher in the more polluted than in less polluted soils. Conclusions The metabolic quotient and microbial biomass are sensitive indicators in the monitoring over time of soil polluted by arsenic and heavy metals. Implications Microbial indicators must be considered in the assessment of potential ecotoxicity and in the evaluation of soil biological properties influencing soil recovery in the long term.

Are We Putting the Money in the Right Pocket? Ascertaining the Eventual Relationship between Silvoagricultural Subsidies, Ecosystem Threats, and Ecosystem Services in Chile

Due to the Aichi targets, the international community committed to the sustainable management of silvoagricultural activities and to the elimination or reform of detrimental subsidies relative to biodiversity conservation. In this context, countries should have implemented specific actions to address these commitments. In Chile, the Instruments of Productive Promotion to Finance Field Work (IPP-FFW) framework was used to fund activities related to silvoagricultural systems, including, irrigation, plantations with exotic species, and the recovery of soils. However, concerns have been raised that are associated with the need for evaluating their effectiveness, including whether impact assessments should be carried out systematically. Considering that these subsidized activities may negatively impact nature, whether IPP-FFWs had been allocated is analyzed regardless of the threat degree of terrestrial ecosystems at the commune level in Chile using the International Union for Conservation of Nature (IUCN) ecosystem risk assessment methodology; moreover, the eventual relationship between changes in land use and ecosystem service provisions in case study for the Biobio region in Chile is also examined, for which the monetary consequences of the loss of ecosystem services—via the analysis of benefit transfers—are calculated. Evidence reveals that higher amounts of IPP-FFWs are allocated in communes with higher levels of threats and that a decrease in ecosystem service provision is associated with IPP-FFW’s allocation.

Inoculation of Indigenous Arbuscular Mycorrhizal Fungi as a Strategy for the Recovery of Long-Term Heavy Metal-Contaminated Soils in a Mine-Spill Area.

Symbiotic associations with arbuscular mycorrhizal fungi (AMF) offer an effective indirect mechanism to reduce heavy metal (HM) stress; however, it is still not clear which AMF species are more efficient as bioremediating agents. We selected different species of AMF: Rhizoglomus custos (Custos); Rhizoglomus sp. (Aznalcollar); and Rhizophagus irregularis (Intraradices), in order to study their inoculation in wheat grown in two soils contaminated with two levels of HMs; we tested the phytoprotection potential of the different AMF symbioses, as well as the physiological responses of the plants to HM stress. Plants inoculated with indigenous Aznalcollar fungus exhibited higher levels of accumulation, mainly in the shoots of most of the HM analyzed in heavily contaminated soil. However, the plants inoculated with the non-indigenous Custos and Intraradices showed depletion of some of the HM. In the less-contaminated soil, the Custos and Intraradices fungi exhibited the greatest bioaccumulation capacity. Interestingly, soil enzymatic activity and the enzymatic antioxidant systems of the plant increased in all AMF treatments tested in the soils with both degrees of contamination. Our results highlight the different AMF strategies with similar effectiveness, whereby Aznalcollar improves phytoremediation, while both Custos and Intraradices enhance the bioprotection of wheat in HM-contaminated environments.

Multiscale responses and recovery of soils to wildfire in a sagebrush steppe ecosystem

Ecological theory predicts a pulse disturbance results in loss of soil organic carbon and short-term respiration losses that exceed recovery of productivity in many ecosystems. However, fundamental uncertainties remain in our understanding of ecosystem recovery where spatiotemporal variation in structure and function are not adequately represented in conceptual models. Here we show that wildfire in sagebrush shrublands results in multiscale responses that vary with ecosystem properties, landscape position, and their interactions. Consistent with ecological theory, soil pH increased and soil organic carbon (SOC) decreased following fire. In contrast, SOC responses were slope aspect and shrub-microsite dependent, with a larger proportional decrease under previous shrubs on north-facing aspects compared to south-facing ones. In addition, respiratory losses from burned aspects were not significantly different than losses from unburned aspects. We also documented the novel formation of soil inorganic carbon (SIC) with wildfire that differed significantly with aspect and microsite scale. Whereas pH and SIC recovered within 37 months post-fire, SOC stocks remained reduced, especially on north-facing aspects. Spatially, SIC formation was paired with reduced respiration losses, presumably lower partial pressure of carbon dioxide (pCO2), and increased calcium availability, consistent with geochemical models of carbonate formation. Our findings highlight the formation of SIC after fire as a novel short-term sink of carbon in non-forested shrubland ecosystems. Resiliency in sagebrush shrublands may be more complex and integrated across ecosystem to landscape scales than predicted based on current theory.

Fitorremediación para recuperar suelos contaminados por metales pesados: discusión de revisión sistemática

Soil contamination by metals is an environmental problem and phytoremediation has proven to be a technique that promises the recovery of these soils. Even so, the selection of species to be used in phytoremediation is key to obtaining promising results. Next, through a systematized literature review, 125 research published between 2016 and 2021 on the different species of accumulator plants were analyzed to reduce pollution and recover soils. At the beginning of the investigation, the consequences of soil contamination are mentioned, and phytoremediation is presented as a viable alternative to reduce it. The research analyzed was obtained from significant documentary sources such as journal articles indexed in the Scopus, Intech, IOPScience and Scielo databases due to their international relevance and high impact index. The review of the fifteen most relevant articles between 2016 and 2021 proves that this method of phytoremediation is viable and effective in the recovery of soils contaminated with heavy metals.

Recovery of soil biological quality (QBS-ar) and soil microarthropod abundance following a prescribed fire in the Quercus frainetto forest

Low-intensity prescribed fire has significant influences on the community structure and biodiversity of the soil. The recovery rate of microarthropods following a fire is not well understood. The present study focused on the effects of prescribed fire on the biological quality of soil, using the QBS-ar (The Soil Biological Quality-arthropods) index, the recovery rate and community structure of microarthropods with the Shannon diversity index. The study was conducted in a pure oak stand (Quercus frainetto Ten.), and treatment sites were burned in the autumn with low-intensity prescribed fire following heavy litterfall. The Mann-Whitney U test revealed that fire treatments resulted in significant increases in soil pH (5.1 %), as well as significant decreases in microarthropod density (72.2 %), the number of taxa (37.1 %), Shannon diversity (H) (8.4 %), and soil biological quality (QBS-ar) (43.2 %). The density of microarthropods was also correlated with some soil parameters (soil temperature, moisture, pH, and nitrogen). Following the fire, the recovery rate of each soil microarthropod was different each other; Mesostigmata and Prostigmata recovered faster than Oribatid mites. Other microarthropod taxa, such as Isotomidae and Protura, had a slow recovery. Linear mixed-effects model showed that monitoring of Entomobryidae, Hypogastruridae, Isotomidae, Mesostigmata, Onychiuridae, Oribatida, Prostigmata, Protura, Tomoceridae taxa after a fire may contribute to determine soil ecosystem recovery. Microarthropods recovered their community structures quickly one year after the fire. It also demonstrated that microarthropods and the QBS-ar index can be used to monitor the ecosystem of the soil recovery following low-intensity prescribed fire.

Pyrolysis temperature influences the capacity of biochar to immobilize copper and arsenic in mining soil remediation.

Biochar is a promising material used for multiple remediation approaches, mainly in polluted soils. Its properties can differ depending on feedstock and pyrolysis temperature. In this context, we tested the capacity of three biochar products made from corncob, pyrolyzed at different temperatures (350, 500, and 650°C), to remediate a mining soil affected by high levels of Cu and As. We performed an exhaustive characterization of the biochar. We found that biochar showed a higher surface area with increasing pyrolysis temperature, whereas high molecular weight PAHs were detected in biochar produced at the maximum temperature, thus indicating potential ecotoxicological risks. After the application of biochar to the soil, Cu was partially immobilized, especially when using that obtained at 500°C. This effect is attributed to the structure of this material and an increase in soil pH and organic matter content. Conversely, As was increased in the soluble fraction for all three types of biochar but in a proportion that lacks relevance. On the whole, given its lower PAH content, higher Cu immobilization ratio, and an almost negligible increase in As availability, biochar obtained at 500°C outperformed the other two products with respect to soil recovery. Of note, data on Cu and As availability were doubled-checked using two extraction methodologies. We propose that this operational approach for determining the most suitable pyrolysis temperature will find application in other soil remediation actions.

Resilience of ecosystem service delivery in grasslands in response to single and compound extreme weather events

Extreme weather events are increasing in frequency and magnitude with profound effects on ecosystem functioning. Further, there is now a greater likelihood that multiple extreme events are occurring within a single year. Here we investigated the effect of a single drought, flood or compound (flood + drought) extreme event on temperate grassland ecosystem processes in a field experiment. To assess system resistance and resilience, we studied changes in a wide range of above- and below-ground indicators (plant diversity and productivity, greenhouse gas emissions, soil chemical, physical and biological metrics) during the 8 week stress events and then for 2 years post-stress. We hypothesized that agricultural grasslands would have different degrees of resistance and resilience to flood and drought stress. We also investigated two alternative hypotheses that the combined flood + drought treatment would either, (A) promote ecosystem resilience through more rapid recovery of soil moisture conditions or (B) exacerbate the impact of the single flood or drought event. Our results showed that flooding had a much greater effect than drought on ecosystem processes and that the grassland was more resistant and resilient to drought than to flood. The immediate impact of flooding on all indicators was negative, especially for those related to production, and climate and water regulation. Flooding stress caused pronounced and persistent shifts in soil microbial and plant communities with large implications for nutrient cycling and long-term ecosystem function. The compound flood + drought treatment failed to show a more severe impact than the single extreme events. Rather, there was an indication of quicker recovery of soil and microbial parameters suggesting greater resilience in line with hypothesis (A). This study clearly reveals that contrasting extreme weather events differentially affect grassland ecosystem function but that concurrent events of a contrasting nature may promote ecosystem resilience to future stress.

Organic amendments from recycled waste promote short-term carbon sequestration of restored soils in drylands

Soils are considered as a major reservoir for terrestrial carbon and it can act as a source or sink depending upon the land management activities. In semi-arid areas, the natural recovery of soils degraded by mining activities is complicated. A possible solution to recover soil quality and functionality, plant cover and carbon sequestration capacity could be the application of organic amendments. This work focuses on a restoration carried out in 2018 by applying with different composted organic amendments (stabilized sludge, gardening and greenhouse waste) in a limestone quarry under semi-arid climate (SE Spain). The objective was to evaluate the effects of different organic amendments on net CO2 exchange in two microcosms: soil-Stipa tenacissima and soil-spontaneous vegetation. Soil physical and chemical properties, environmental and ecological variables and their interrelationship were studied in amended and unamended soils. The results obtained under soil-forming factors in the study area showed an increase in soil organic carbon and nitrogen content, improved moisture and plant growth, and plant canopy development in amended soils. Soil moisture, soil temperature and plant cover significantly influenced net CO2 exchange. In general, microcosms with S. tenacissima showed higher carbon sequestration rates than soils with only spontaneous plant cover. Soils treated with a vegetable-only amendments showed higher plant cover and CO2 fixation rates after significant rainfall. On the other hand, the plots treated with sludge compost presented more soil respiration than photosynthesis, especially in the wet seasons. Soils with sludge and greenhouse compost mixed had higher CO2 fixation rates than soils restored with a mixture of sludge and garden compost. Soils with greenhouse waste compost showed CO2 fixation in the microcosm with plants in all campaigns, being the best treatment to promote atmospheric CO2 sequestration in soil restoration.

Optimization of a High-Pressure Soil Washing System for Emergency Recovery of Heavy Metal-Contaminated Soil

Recent natural disasters, such as typhoons in South Korea and other countries around the globe, have resulted in loss of human life and damage to property, often causing contamination of nearby soil environments. This study focused on the emergency recovery of soil contaminated by heavy metals following a disaster such as typhoon flooding by applying a soil washing technique that used high-pressure water rather than chemical cleaning agents. Artificially contaminated soil containing 700 mg/kg Cu, 530 mg/kg Pb and 900 mg/kg Zn, was used. All three metals were present at levels higher than the Korean Warning Standards (500 mg/kg Cu, 400 mg/kg Pb, 600 mg/kg Zn) for region 2 (miscellaneous area). A high-pressure soil washing device was designed to treat 0.6 tons/h and optimal treatment was sought for varying levels of pressure (1, 3, 5 MPa), solid to liquid ratios (S/L) (1:1, 1:3, 1:5), and number of washing cycles (1, 2, 3). The high-pressure soil washing results showed that a 5 MPa washing pressure, 1:1 solid-liquid ratio, and one washing cycle were the optimum conditions to generate the highest heavy metal removal rates. Under optimal conditions, high-pressure soil washing attained removal efficiencies of Cu (37.7%), Pb (36.6%), and Zn (45.1%), and the residual concentrations of heavy metals in the remediated soil satisfied the Korean Warning Standard (Region 2). A comparison of the changes in particle size showed that after high-pressure washing, the mass fraction of coarse sand (CS, 2–0.42 mm) decreased by 23.3%, while that of fine sand (FS, 0.42–0.074 mm), silt, and clay (SC, <0.074 mm) increased by 4.2% and 19.1%, respectively. In addition, 31.1–34.6% of the CS heavy metal mass loading shifted to FS and SC fractions after washing. A comparative analysis of the soil surface morphology before and after washing using scanning electron microscopy (SEM) showed that the particles in the remediated soil became noticeably cleaner after high-pressure washing. This study demonstrated the feasibility of emergency recovery of heavy metal-contaminated soil using high-pressure washing without a chemical cleaning agent.

Fifty years of reduction in sulphur deposition drives recovery in soil pH and plant communities

Abstract Sulphur deposition through rainfall has led to species loss and ecosystem degradation globally, and across Europe huge reductions in sulphur emissions since the 1970s were expected to promote the recovery of acidified ecosystems. However, the rate and ecological impact of recovery from acidification in terrestrial ecosystems is still unclear as is the influence of management and climate, as to date there has been no long‐term spatially extensive evaluation of these changes. Here, we present data from thousands of sites across Great Britain (pH range 3.3–8.7) surveyed repeatedly from 1978–2019 and assess change in soil pH and plant acidity preference (Ellenberg R) in response to atmospheric deposition of sulphur and nitrogen. We analyse change in grasslands managed for pasture, referred to as high‐intensity habitats, and compare to seminatural habitats comprising rough grassland, broadleaved woodland, bog and heathland, referred to as low‐intensity habitats. Soil pH increased from 1978 to 2007 but then decreased between 2007 and 2019, resulting in a net increase of ~0.2 pH units in low‐intensity habitats but no change in high‐intensity habitats. The community average Ellenberg R increased in seminatural habitats by ~0.2 units but remained stable in intensive grasslands. In seminatural habitats, but not intensive grasslands, these changes in plant community composition were associated with the soil pH changes which were in turn linked to decreasing sulphur deposition and differences in rainfall. Nitrogen deposition, which was relatively stable over the survey period, showed no additional effect upon soil acidity once sulphur deposition was accounted for. Synthesis: Our results provide conclusive evidence that reductions in acid emissions are stimulating the gradual recovery of chronically acidified terrestrial ecosystems at a whole‐country scale, while also suggesting this recovery is being compromised by changing climate and land management.

Environmental impact evaluation of landfill mining of legacy waste with on-site sorting using life cycle assessment.

The present research is aimed at assessing the environmental impacts of landfill mining of soil-like material with on-site sorting for land application using life cycle assessment. The scenario is compared with no-landfill mining (base scenario) and future scenario (including material recycling and incineration). Soil-like material is processed using windrow composting. The impact assessment was performed using the EASETECH™ software tool. ReCipE 2016 midpoint world impact method with eight impact categories was used for assessing the environmental profiles. The functional unit of the assessment was 1 t of recovered waste in India. Overall, the results showed that excavation of landfilled waste with on-site recovery of soil and land application of soil resulted in higher environmental benefits compared to no mining condition in global warming potential (GWP), freshwater eutrophication (FEW), human toxicity (HT), and fossil depletion (FD), while higher impacts were observed in terrestrial acidification (TA), terrestrial ecotoxicity (TE), marine eutrophication (ME), and photochemical oxidation (PCO). After composting, land application of recovered soil contributed to environmental offsets in GWP, HT, and FEW while contributing to TE emissions. Emissions associated with excavation and on-site sorting contributed 55.1% to freshwater toxicity, 25.5% to human toxicity, 16.2% to climate change, and 10.8% to terrestrial acidification. The choice of energy, transportation, and fuel for waste activities affected the performance of alternative scenarios in GWP. Application of recovered metals in the manufacturing process, incineration of plastic, and textile components improved the environmental performance. The outcomes of this research will equip regulatory bodies in the development of guidelines and frameworks on material and energy recovery from the waste components mined from legacy waste.

Stabilization of biomass ash granules using accelerated carbonation to optimize the preparation of soil improvers

After the revision of the Fertilizer Regulation (EC 2019/1009), biomass ash can be used as component material for soil improvers to be placed on the EU market. This provides opportunities for large scale recycling of biomass ash. However, this material cannot be directly applied to soil without stabilization by carbonation, which also creates an opportunity for CO2 capture and storage. Here, accelerated carbonation in an atmospheric fixed-bed reactor (AFR) was applied to prepare ash granules (AG). Relative humidity of gas, temperature, reaction time and CO2 concentration were optimized and further tested in a closed high-pressure reactor (HPR). Materials resulting from both reactors were compared with those obtained after 1-year of carbonation under atmospheric conditions.This study showed that AFR accelerated tests resulted in a significant reduction of the reaction time than HPR to achieve a similar pH adjustment. Also, under 100 vol.% CO2 atmospheric conditions, pH and electrical conductivity reached target values faster than under 15 vol.% CO2 conditions. Based on results obtained here we recommend AFR operating at 25 °C and 100 vol.% CO2 for 20 h, as the optimal procedure for stabilization of AG. In this study we provide evidence that accelerated carbonation enables a much faster and cost-efficient preparation of potentially valuable soil additives than natural carbonation. Also, leaching tests revealed that plant nutrient availability (B, Mg, Mn, Mo and P) was increased under accelerated carbonation compared to natural carbonation. The present work paves the way towards the development of optimized protocols to effectively recycle biomass ashes for soil recovery.

Effects of silage crops between crop seasons on soybean grain yield and soil fertility in tropical sandy soils

Soybean production in sandy soils under the recovery process presents risks that can be mitigated by growing crops between crop seasons, focused on silage production, which can assist in environmental improvement, accelerating soil recovery, in addition to improvement in soybean grain yield. The objective of this study was to evaluate soybean grain yield, silage yield and soil fertility in an area converted from degraded pasture to soybean production. The study was conducted a sandy soil, in Presidente Bernardes, São Paulo, Brazil, from 2015 to 2018. The treatments consisted of six silage crops (maize, sorghum, sunflower, palisade grass, millet, and pigeon pea) and a control with fallow (March-July) between soybean crop seasons (October-March). The mean soybean grain yield in the soybean-millet system (4400 kg ha−1) was, on average, 42% higher than that in the soybean-fallow (3100 Mg ha−1). The mean soybean grain yield (three crop seasons) in the systems with maize, sorghum, and sunflower was similar to that in the soybean-fallow system. The mean palisade grass silage yield was higher in two of the three crop seasons (16.8 Mg ha−1); maize also presented a good performance in the second crop seasons (10200 kg ha−1). The higher palisade grass silage production resulted in higher mean (three crop seasons) extraction of macronutrients (136, 129, 65, 54, 13.2 9.6 kg ha−1, for K, N, Ca, Mg, P, and S, respectively). The growth of millet and palisade grass crops between soybean crop seasons improved the soil fertility, but the effect of millet was faster (first harvest). The main soil fertility attributes affected were: phosphorus, potassium, organic matter, cation exchange capacity, and base saturation. The best crop option to be grown between soybean crop seasons are millet and palisade grass for silage when focused on improvements in soil fertility and grain yield of the following soybean crop, and the choice between these two species depends on the farmer's priority.

Soil resistance and recovery during neotropical forest succession.

The recovery of soil conditions is crucial for successful ecosystem restoration and, hence, for achieving the goals of the UN Decade on Ecosystem Restoration. Here, we assess how soils resist forest conversion and agricultural land use, and how soils recover during subsequent tropical forest succession on abandoned agricultural fields. Our overarching question is how soil resistance and recovery depend on local conditions such as climate, soil type and land-use history. For 300 plots in 21 sites across the Neotropics, we used a chronosequence approach in which we sampled soils from two depths in old-growth forests, agricultural fields (i.e. crop fields and pastures), and secondary forests that differ in age (1-95 years) since abandonment. We measured six soil properties using a standardized sampling design and laboratory analyses. Soil resistance strongly depended on local conditions. Croplands and sites on high-activity clay (i.e. high fertility) show strong increases in bulk density and decreases in pH, carbon (C) and nitrogen (N) during deforestation and subsequent agricultural use. Resistance is lower in such sites probably because of a sharp decline in fine root biomass in croplands in the upper soil layers, and a decline in litter input from formerly productive old-growth forest (on high-activity clays). Soil recovery also strongly depended on local conditions. During forest succession, high-activity clays and croplands decreased most strongly in bulk density and increased in C and N, possibly because of strongly compacted soils with low C and N after cropland abandonment, and because of rapid vegetation recovery in high-activity clays leading to greater fine root growth and litter input. Furthermore, sites at low precipitation decreased in pH, whereas sites at high precipitation increased in N and decreased in C : N ratio. Extractable phosphorus (P) did not recover during succession, suggesting increased P limitation as forests age. These results indicate that no single solution exists for effective soil restoration and that local site conditions should determine the restoration strategies. This article is part of the theme issue 'Understanding forest landscape restoration: reinforcing scientific foundations for the UN Decade on Ecosystem Restoration'.

Economic analysis of irrigation in the production system of soybean and second‐season maize in sandy soil areas in Brazil

AbstractThe objective of the present work was to perform an economic analysis of centre‐pivot irrigation implantation on a sandy soil area with different previous land uses. Thus, it was possible to analyse three initial soil conditions inside (irrigated) and outside (rainfed) the centre pivot. The opening area (P1) was characterized by soybean planting for the first time after degraded pasture, P2 consisted of the second year of harvesting soybean/maize second season, and P3 consisted of the third year of harvest. Two crops were evaluated: soybean and maize. The centre‐pivot irrigation system was not profitable at the earliest stage of soil recovery (P1) immediately after degraded pasture because soil fertility limited yields. There was a 23% and 33% increase in soybean yield for the areas with 2 years (P2) and 3 years (P3) of soil recovery, respectively, compared to the first year. However, second‐season maize had an increased yield of 19% for the third‐year area (P3) compared to the first year (P1). Profit increased from P3 to P1 by $1541 ha−1 for soybean, $2654 ha−1 for maize and $2097 ha−1 overall. Irrigation treatments increased profit by 45%.