Restore Soil Function Research Articles

Natural forest colonisation as a management strategy to restore soil functioning of abandoned agricultural lands

Abstract Land abandonment promotes forest expansion into abandoned agricultural lands in Europe. This process leads to changes that affect several ecosystem services, but it is considered a low‐cost strategy to restore soil functions in past agricultural lands. Soil microbial communities play a key role in restoring functions. However, the relationship among forest expansion, microbial communities, and soil functioning is unclear. In this study, we used a Juniperus thurifera expansion gradient on abandoned agricultural lands in Alto Tajo National Park (Spain) to discover the changes elicited by the soil microbial communities and their functions along this gradient considering two microhabitats, under the canopy and open areas. Specifically, our objectives were (i) to analyse how soil properties (organic matter and pH), microbial communities (using PLFAs‐NFLAs) and enzymatic activities (related to C, N and P cycling) varied along the forest expansion gradient and between microhabitats and (ii) to decipher the pathways by which soil properties control the carbon and nutrient cycling in soils. The forest expansion gradient had a direct negative effect on phosphatase activity. The microhabitat showed a positive direct effect on organic matter content, pH, actinomycetes and arbuscular mycorrhizal fungi biomass and on soil C and P cycling. Moreover, the biomass of gram‐positive bacteria determined the biomass of other microbial groups. Synthesis and Applications: Though its effectiveness is variable, passive restoration can be more effective than active restoration. Our research indicates that passive tree colonisation of past agricultural land is enough to achieve soil functionality similar to a mature forest for most variables studied. However, some variables would need more time to reach mature forest levels, such as total microbial biomass and organic matter content. Therefore, to support ecosystem recovery, the management of this applied forest ecology strategy requires continuous monitoring of newly established trees and soil to elucidate the time needed to achieve mature soil properties.

Soil macroaggregate-occluded mineral-associated organic carbon drives the response of soil organic carbon to land use change

Understanding land use effects on carbon sequestration in various soil fractions is vital to mitigating climate change and restoring soil functions. The objective of this study was to explore the effects of land use on soil organic carbon (SOC) fractions in different soil types. For this purpose, we studied the effects of long-term (>20 years) land use including dryland pasture (DP), irrigated pasture (IP) and irrigated cropland (IC) on SOC in water-stable aggregates, particle-size fractions, and their coupling relations at the surface soils (0–7.5 cm) in the Canterbury Plains, New Zealand. For each land use, three typical soil types with contrasting drainage levels (i.e. well drained Lismore soil, LIS; imperfectly drained Templeton soil, TEM; and poorly drained Waterton/Temuka soil, WAT) were selected. Macroaggregate-occluded mineral-associated organic carbon (M-MAOC) contributed to the majority of the total SOC difference and drove the response of SOC to land use change. On average, M-MAOC followed an order of IP > DP > IC. The effects of land use change from DP to IP and IC on M-MAOC varied, and these variations were dependent on soil type. The relative gain in M-MAOC with change in land use from DP to IP was the greatest in the well drained LIS soil, while both the relative and absolute loss in M-MAOC following the land use change to IC was the greatest in the poorly drained WAT soil. The interactive effects of managements (e.g. irrigation and cultivation) and soil type (e.g. soil water condition) on aggregate size distribution and macroaggregate-associated C concentration were important in explaining the responses of M-MAOC to land use change. This study advances the mechanistic understanding of total SOC dynamics in response to land use (changes) in different soil types. It also highlights the potential of M-MAOC to serve as a diagnostic fraction to reflect changes in total SOC, which may have application to global warming mitigation.

Building Soil Health and Fertility through Organic Amendments and Practices: A Review

Soil health and quality are foundational to agricultural sustainability and meeting global food security priorities. However, intensive farming practices have degraded soil ecosystems. Organic amendments and regenerative management practices can restore soil function by overcoming nutritional limitations, improving physical and biological properties, and promoting general soil and crop resilience. This review synthesizes research on major sources of organic soil amendments including animal manures, composts, cover crops, crop residues and living mulches. We describe their multifaceted edaphic and agronomic benefits from providing a slow release bank of macro and micronutrients, increasing soil organic matter, and stimulating beneficial microbial communities. Complementary and synergistic soil building practices are also covered, encompassing conservation tillage techniques like no-till, crop diversification via rotations and intercropping, and agroecological integration of trees and livestock. Although transitioning from degraded conventional systems requires patience as years of soil regeneration are needed to enable high system performance, outcomes consistently show integrated practices that minimize disturbance and maintain living ground cover while leveraging organic inputs can transform the foundation of agricultural systems by enhancing soil ecosystem function. Widespread adoption of this soil health paradigm can thereby enable sustainable intensification and resilience.

Enhanced soil function and health by soybean root microbial communities during in situ remediation of Cd-contaminated soil with the application of soil amendments.

The interactions between soil microbiomes at various trophic levels are essential for restoring soil functions. Legumes are considered as "pioneer crops" in degraded or contaminated soils because they can fix nitrogen through symbiotic relationships with rhizobacteria, which promotes soil fertility. However, little is known about the abilities of legumes to contribute to the health of soil contaminated with cadmium (Cd). In this research, we applied a soil amendment (commercial Mg-Ca-Si conditioner, CMC) at two rates (1,500 and 3,000 kg/ha) in a Cd-contaminated soybean field. Bulk and rhizosphere soil samples were collected to assess the amendment-induced effects on four microbial lineages (bacteria, fungi, arbuscular mycorrhizal fungi [AMF], and nematodes) and their functions including Cd stabilization, nutrient cycling, and pathogen control. Compared with the control, both CMC application rates increased the pH and reduced labile Cd fraction in the bulk and rhizosphere soils. Although the total Cd concentrations in the soil were similar, the Cd accumulation in the grains was significantly reduced in treatments of soil amendments. It was observed that the application of CMC can significantly reduce the AMF diversity but increased the diversity of the other three communities. Moreover, the biodiversity within keystone modules (identified by co-occurrence network analysis) played key roles in driving soil multifunctionality. Specifically, key beneficial groups in module 2 such as Aggregicoccus (bacteria), Sordariomycetes (fungi), Glomus (AMF), and Bursaphelenchus (nematode) were strongly associated with soil multifunctionality. By co-culturing bacterial suspensions with the soybean root rot pathogen Fusarium solani in the in vitro assays, we experimentally validated that the application of CMC promoted the suppression of soil bacterial community on pathogens by inhibiting the mycelium growth and spore germination. Also, the bacterial community was more resistant to Cd stress in soils receiving CMC amendment. Our findings provide valuable theoretical references for enhancing soil functions and health via applying a soil amendment (CMC) during Cd-contaminated soil remediation. IMPORTANCE Restoration of microbiome-driven soil functions and health is of great importance during Cd-contaminated soil remediation via soil amendment. Soybean and its symbiotic mutualism can provide abundant nitrogen and phosphorus to relieve the nutrient deficiency of Cd-contaminated soil. This study provides a novel perspective on the potential role of applying a soil amendment (CMC) in enhancing the functions and health of Cd-contaminated soils. Our results showed the distinct differences in soil microbial community responding to amendment-induced changes in edaphic properties. The biodiversity within keystone modules had major contributions to the maintenance of the soil's multifunctionality and health. Additionally, a higher CMC application rate showed more beneficial effects. Collectively, our results enhance our understanding about the effects of applying CMC, together with soybean rotation, to enhance and maintain soil functions and health during the field Cd stabilization process.

Afforestation inhibited soil microbial activities along the riparian zone of the upper Yangtze River of China

Afforestation strongly influences soil microbial traits, especially microbial biomass and enzyme activity. However, the magnitude and direction of soil microbial traits and their controls following afforestation remain unclear. Here, we examined microbial carbon (C), nitrogen (N), and phosphorus (P) biomass and activities of the most common enzymes involved in C (α-1,4-glucosidase, β-1,4-glucosidase, β-D-1,4-cellobiohydrolase, and β-1,4-xylosidase), N (β-1,4-N-acetyl-glucosaminidase and l-leucine aminopeptidase), and P (alkaline phosphatase) cycling under a 15-year-old forest stands (Morus alba, Salix bablyonica, and a mix of the two species) and adjacent croplands along the riparian zone of the upper Yangtze River of China. Unexpectedly, we found that the 15-year afforestation significantly lowered the contents of total C and N, available P, and NO3– compared to the adjacent cropland soils. The microbial biomass C, N, and P contents were also approximately 14–60%, 34–88%, and 9–89% lower, respectively, in the afforested soils than in the adjacent cropland soils across afforestation types and soil depths. Correspondingly, enzymatic C and N activities were 71–90% and 54–75% lower, respectively, under the S. bablyonica stands across soil depths, whereas enzymatic P activity was 39–72% lower in the afforested soils than in the adjacent cropland soils across afforestation types and depths. Reduced microbial biomass and enzymatic activities after afforestation were attributed to the decreased total C and nutrients in the afforested soils than in the adjacent cropland soils, likely due to high plant uptake nutrients and low soil organic matter inputs during the early stages of forest development. Overall, afforestation with plantations of Morus alba or Salix bablyonica species may reduce soil functions such as C storage and N fertility, suggesting that large-scale afforestation using these species should not be prioritized to restore soil functions within a short period.

Long-term tillage and irrigation effects on aggregation and soil organic carbon stabilization mechanisms

Sustainable soil management practices are required in agriculture to enhance carbon sequestration and restore soil functions. Here, the aim was to investigate the effect of different tillage practices combined with or without irrigation on (i) soil organic carbon (SOC) content, (ii) fungal biomass and their relationships with aggregate size classes in the soil surface layer; further, (iii) the concept of soil particle saturation with SOC was tested to evaluate if a threshold was reached in a 14 year-experiment. Our hypothesis was that long-term irrigation, intensive tillage and their combination, would negatively affect soil aggregation and SOC stabilization. The experiment has started in 2003 on a research farm in Canterbury, New Zealand. The present work focused on two contrasting tillage practices –intensive tillage with 20–25 cm ploughing (IT) and direct drill (DD)– combined with sprinkler-irrigated and non-irrigated (hereafter called Rainfed) conditions in a split-plot experimental design. Soil samples (0–5 cm layer) were analyzed for pore size distribution, specific surface area and microbial biomass. Further, wet sieving was used to isolate large macroaggregates (LM, > 2000 μm), small macroaggregates (SM, 250–2000 μm), microaggregates (m, 53–250 μm), particle sized silt + clay fractions (s+c, < 53 μm) and Fine20 particles (<20 μm), followed by the analysis of aggregate morphology and SOC quantification in them. Results showed that both DD and Rainfed management increased total SOC content of the bulk soil. Only the LM fraction and the SOC therein (OC-LM) increased significantly in DD compared to IT, while m and s+c fractions and OC-m and OC-s+c did not differ between treatments. Macroaggregate breakdown processes and measured SOC therein had likely not reached steady-state conditions, as suggested by the lack of any SOC differences in the aggregate size classes < 250 µm. In contrast, the Fines20:SOC ratio differentiated between soils that had reached (i.e., DD) or not reached (i.e., IT) the saturation threshold. Finally, it was observed that a higher fungal:bacteria (F:B) ratio was generally accompanied by a greater LM fraction and mean weight aggregate diameter, highlighting the importance of fungi in the formation of LM. These results suggested that our hypothesis of detrimental effects on soil aggregation and SOC accumulation of both tillage and irrigation was not fully demonstrated yet. A longer study period would be required to better understand the effects of such practices of SOC storage.

Pengaruh Penambahan Limbah Kulit Udang Terhadap Kualitas Kompos Tandan Kosong Kelapa Sawit untuk Memperbaiki Sifat Tanah di Majene

Oil palm empty fruit bunches are palm oil industry waste that has not been processed and utilized optimally. Utilizing palm oil industrial waste as compost material can reduce the negative impact of waste on the environment. Compost as a source of organic matter and nutrients that can improve properties and restore soil function, so that plant nutrients are complete. The addition of shrimp shell waste can improve the quality of oil palm empty fruit bunches compost, namely the availability of macro and micro nutrients in the compost. The purpose of this study was to analyze effect of composting empty palm oil bunches with the addition of shrimp shell waste on the soil in Majene. The results of the analysis of primary macronutrients such as pH, C-Organic, Nitrogen, Phosphorus, Potassium and C/N Ratio in the soil after the addition of composted oil palm empty fruit bunches and shrimp shell waste increased. Meanwhile, secondary macro nutrients such as Calcium, Magnesium, Sulfur and micro nutrients such as Aluminum, iron and Manganese did not increase after the addition of composted empty fruit bunches of oil palm and shrimp shell waste.

Do native grasses emerge and establish in areas rehabilitated using vetiver grass?

Species-rich grasslands provide important ecosystem services, and in South Africa, approximately 40% of these grasslands are degraded. Vetiver grass (from India) is often used during rehabilitation efforts to restore soil function without a thorough understanding of the potential negative ecological impacts. Hence, a study was initiated to investigate vetiver’s ecological impacts during grassland rehabilitation. Firstly, a field survey was conducted using a contiguous quadrat method to evaluate the extent of grass secondary succession in these rehabilitated sites. Secondly, the effect of vetiver competition and seed sowing method on the recruitment of two native grasses (Eragrostis curvula and Megathyrsus maximus) was examined using pot trials. The field survey results showed no evidence of grass secondary succession, but rather the abundance of bare ground around vetiver, and a marked increase in grass species richness with increasing distance from planted vetiver. Subsequently, in the pot trial, vetiver facilitated emergence in both native grasses, and soil surface sowing of indigenous grass seeds showed greater emergence than other sowing methods. However, vetiver inhibited native grass seedling establishment, even when root competition was excluded. This study suggests that areas rehabilitated using vetiver are unlikely to become productive grasslands with good grazing, because vetiver inhibits colonisation by native grasses.

The effect of added organic matter on the soil formation of oil-based drill cutting pyrolysis residue.

In order to explore the effects of added organic matters on the soil formation process of oil-based drill cutting pyrolysis residue, two experiment groups (pure and adding) were studied to indicate the soil microbial community and the function of nitrogen cycling. Samples were collected in the third and fourth years based on the plant growth. The 16S rRNA high-throughput sequencing technology and PICRUSt were used to study microbial communities and the function of nitrogen cycling. The results showed that MND1 (2.5-4.5%), Sphingomonas (1.4-2.4%), and other typical oil-degrading bacteria were discovered. The diversity of the microbial community decreased with the duration of the experiment. However, it was higher than that of the background soil. The relative abundance of microbial nitrogen dissimilation reduction (0.9-1.0‰) was the highest among the two experiment groups and the background soil. The second and third were denitrification and nitrogen fixation. Nitrification gene abundance was the lowest among the five main steps of nitrogen cycling. The addition of organic matters could improve soil formation of pyrolysis residues. This study provides scientific data for pyrolysis residue to restore soil functions.

Soil microbiota as game-changers in restoration of degraded lands.

Land degradation reduces soil functioning and, consequently, the services that soil provides. Soil hydrological functions are critical to combat soil degradation and promote soil restoration. Soil microorganisms affect soil hydrology, but the role of soil microbiota in forming and sustaining soil is not well explored. Case studies indicate the potential of soil microorganisms as game-changers in restoring soil functions. We review the state of the art of microorganism use in land restoration technology, the groups of microorganisms with the greatest potential for soil restoration, knowledge of the effect of microorganisms on soil physical properties, and proposed strategies for the long-term restoration of degraded lands. We also emphasize the need to advance the emerging research field of biophysical landscape interactions to support soil-plant ecosystem restoration practices.

Perennial legume intercrops provide multiple belowground ecosystem services in smallholder farming systems

Soil degradation is a major underlying cause of poverty and malnutrition in smallholder agrarian communities across the globe. Legume diversification, through polyculture or intercropping, is a strategy that increases yields and income while improving family nutrition. However, the potential for these legume-cereal intercrops to restore soil functions in smallholder fields remains uncertain, with many studies failing to detect increases in soil organic matter (SOM). In sub-Saharan Africa, smallholders typically grow maize either intercropped with short-lived annual food legumes or as a monoculture. Recently, a novel maize system which includes perennial legumes in the genus Desmodium as intercrops, known as “push-pull” (hereafter, PP) has been increasingly adopted by smallholders across the region. The yield, nutritional and economic benefits of the PP system are well-documented. We investigated the effects of PP maize intercropping on soil fertility compared to the predominant maize culture systems (hereafter, NPP) using soils from long-term experiments and smallholder fields in western Kenya. Maize-desmodium intercrops promoted SOM accrual and increased plant available phosphorus. In the long-term research station experiments soil organic N was 20% greater and labile organic N reserves were five-fold greater in PP compared to NPP soils. Despite equal P fertilizer application rates, extractable soil P was two-fold greater in PP compared to NPP soils. Soils under maize-food legume intercrops did not show any detectable accrual of SOM compared to maize monocultures. Soil benefits in smallholder PP fields tended to mirror those found in the controlled experiments. Taken together, our results demonstrate that the perennial legumes in PP system restore soil function and fertility. Developing additional well-designed intercropping systems that include perennial legumes could play a significant role in reversing the trajectory of soil degradation in smallholder farming systems while enhancing human well-being.

Higher free-living N2 fixation at rock-soil interfaces than topsoils during vegetation recovery in karst soils

The widely distributed karst ecosystem in China has experienced rapid deterioration by deforestation and intensive cultivation in the last 50 years. Under the “Grain for Green” program, disturbed croplands were progressively abandoned to restore soil functions and ecosystem services, observed as discrete vegetation recovery phases: cultivated land, abandoned land and secondary forest, and compared to natural primary forest. Karst soils are naturally poor in nitrogen and cessation of nitrogen fertilizer application after abandonment presents an opportunity to explore the reemergence of indigenous soil N2 fixation mechanisms. In this study, we investigated how vegetation recovery affects key soil properties and their relationships with free-living N2 fixation (FLNF) activity and nifH gene abundance, microbial community structure and network interactions at different soil depths from the surface to the rock-soil interface at the bottom of the soil profile. Soil FLNF activity was increased slightly but not significantly after abandonment and was greatest in primary forest soils. High levels of FLNF activity in primary forest soils was facilitated directly by larger total organic carbon to total nitrogen ratios and an altered free-living diazotrophic community composition that was mainly modified by soil moisture content and pH. Higher FLNF was identified at rock-soil interfaces compared to topsoils, which was mainly driven by altered diazotrophic community composition stimulated by increases in soil pH and dissolved organic carbon to available inorganic nitrogen ratios. Diazotrophic network interactions also contributed to variations in FLNF activity, with relatively stable and competitive, while less niche-separated, diazotrophic communities supporting high FLNF activity in primary forest soils, while complex and mutualistic interactions facilitated the high FLNF at rock-soil interfaces. These results suggest that there is considerable and persistent FLNF in degraded karst landscapes at rock-soil interfaces which enables the provision of a vital biological source of nitrogen to overcome the nutrient limitations of karst rock weathering at the bottom of the soil profile.

The advantages and limitations of global datasets to assess carbon stocks as proxy for land degradation in an Ethiopian case study

Land degradation leads to ecosystem degradation, reducing ecosystem functioning and depleting ecosystems' resilience. The majority of factors linked to land degradation are closely related with the depletion of below- and above-ground stocks of organic carbon. Organic carbon stock is important for climate change mitigation and for restoring soil functions such as those crucial to support food security. In this study, we mapped carbon stocks to infer land degradation in a small area in the Ethiopian Great Rift Valley. The study aimed to assess carbon stock status and to identify limitations and advantages of using global data in mapping at local scale relative to using local data. Two different datasets were developed; i) a “global dataset” characterised by data from datasets with global coverage data, and ii) a “hybrid dataset” that coupled data from global datasets, soil data derived from a local survey, and land cover data derived from a supervised classification of satellite images. The results showed that i) global datasets introduced inaccuracy that must be taken into account for advocating interventions at a local scale, and ii) global datasets could be used at a small catchment level for decision-making, if a simple rank of values is sufficient, but they might provide an optimistic picture of land degradation because they overestimate stocks.

Design of a Soil-based Climate-Smartness Index (SCSI) using the trend and variability of yields and soil organic carbon

Climate-Smart Agriculture (CSA) has had an increasing role in the agricultural policy arena, as it aims to address climate change mitigation, adaptation and food security goals in an integrated way. In regions where agriculture has been constrained because of soil degradation and climate change, CSA aims to implement soil-based strategies that restore soil function and increase carbon storage. The extent to which such strategies succeed in achieving mitigation, adaptation and productivity goals is referred to as climate-smartness. The co-evolution of yield and Soil Organic Carbon (SOC) over the years presents a proxy for the trade-off between productivity, soil fertility and carbon sequestration. Yield and SOC are widely monitored, analysed and used to inform CSA planning. Yet their analysis is often conducted separately and for a small number of years, which neglects long-term soil fertility dynamics and their impact on crops. Given the absence of integrated climate-smartness metrics to capture the trade-offs and synergies between SOC and yield, we present a soil-based Climate-Smartness Index (SCSI). The SCSI is computed using normalized indicators of trend and variability of annual changes on yield and SOC data. The SCSI was calculated for a set of published experiments that compared Conservation Agriculture (CA) practices with conventional management. The CA treatments scored higher SCSI during the first 5 years of evaluation as compared to conventional management. Analysis of the temporal dynamics of climate-smartness indicated that minimum SCSI values typically occurred before 5 years after the start of the experiment, indicating potential trade-offs between SOC and yield. Conversely, SCSI values peaked between 5 and 10 years. After 20 years, the SCSI tended towards zero, as substantial changes in either SOC or yield are no longer evidenced. The SCSI can be calculated for annual crops under any soil management and at different time periods, providing a consistent metric for climate-smartness across both practices and time.

Soil Organic Matter Research and Climate Change: Merely Re-storing Carbon Versus Restoring Soil Functions

Over the last two decades, the sequestration of carbon in soils has often been presented as a possible way to mitigate the steady increase in the concentration of CO2 in the atmosphere, one of the most commonly mentioned causes of climate change. A large body of literature, as well as sustained efforts to attract funding for the research on soil organic matter, have focused on the soil carbon sequestration – climate change nexus. However, because CO2 is not the only greenhouse gas released by soils, and given the fact that the feasibility of large-scale carbon sequestration remains controversial, this approach does not appear optimal to convince policy makers. In this perspective article, we argue that a far better strategy revolves around the effect of climate change on functions/services that soils render. In particular, since climatologists forecast less frequent but more intense rainfall events in the future, which may lead to food shortages, catastrophic flooding, and soil erosion if soils are not able to cope, a more suitable focus of the research would be to increase soil organic matter content so as to strengthen the water regulation function of soils. The different conceptual and methodological shifts that this new focus will require are discussed in detail.

Soil reconstruction after mining fails to restore soil function in an Australian arid woodland

The biogeochemical properties of soils drive ecosystem function and vegetation dynamics, and hence soil restoration after mining should aim to reinstate the soil properties and hydrological dynamics of remnant ecosystems. The aim of this study is to assess soil structure in two vegetation types in an arid ecosystem, and to understand how these soil properties compare to a reconstructed soil profile after mining. In an arid ecosystem in southeast Australia, soil samples were collected at five depths (to 105 cm) from remnant woodland and shrubland sites, and sites either disturbed or totally reconstructed after mining. We assessed soil physico‐chemical properties and microbial activity. Soils in the remnant arid ecosystem had coarse‐textured topsoils that overlay clay horizons, which allows water to infiltrate and avoid evaporation, but also slows drainage to deeper horizons. Conversely, reconstructed soils had high sand content at subsoil horizons and high bulk density and compaction at surface layers (0–20 cm). Reconstructed soils had topsoils with higher pH and electrical conductivity. The reconstructed soils did not show increased microbial activity with time since restoration. Overall, the reconstructed soil horizons were not organized in a way that allowed rainfall infiltration and water storage, as is imperative to arid‐zone ecosystem function. Future restoration efforts in arid ecosystems should focus on increasing sand content of soils near the surface, to reduce evaporative water loss and improve soil quality and plant health.

Agroforestry shows higher potential than reforestation for soil restoration after slash-and-burn: a case study from Bangladesh

ABSTRACT Increasing land demands for food production has led to large-scale soil degradation in the hilly regions of south-eastern Bangladesh. An intensification of slash-and-burn techniques, where fallow intervals have shortened considerably in recent years, has led to widespread losses in soil quality. Here we sought to test to what extent do current agroforestry practices in the area, compared with current reforestation efforts, can ameliorate different physicochemical soil properties after the abandonment of slash-and-burn practices. We observed that concentrations of soil organic matter (4.75%), available phosphorous (12.17 μg g−1) and exchangeable potassium (0.39 mg kg−1) in agroforestry plots were significantly higher than in reforestation (3.18%, 6.50 μg g−1 and 0.21 mg kg−1, respectively) or slash-and-burn plots (1.83%, 5.90 μg g−1 and 0.03 mg kg−1, respectively). While reforestation and agroforestry may both serve to restore soil functions but we observed higher benefits in the latter system. Thus, agroforestry systems may be a suitable land management system for replacing ancestral slash and burn techniques but care should be taken to diminish soil compaction.

Plant community characteristics and functional traits as drivers of soil erodibility mitigation along a land degradation gradient

AbstractPlant community characteristics and functional traits may respond to soil erosion due to their high plasticity in varied environments. However, the linkages between plant functional traits and soil properties under erosion stress remain poorly understood, despite the fundamental role they play in controlling soil erosion. Here, we selected 50 plots on degraded land caused by long‐term water erosion representing three degrees of erosion that differed in terms of soil profile and erosion landform. We measured aboveground plant characteristics, root functional traits, and soil properties to explore their responses to the degree of erosion and to identify the main factors mitigating soil erodibility (K r). The results showed that vegetation cover and root length density (RLD) were the plant variables that were most sensitive to the erosion stress. Topographic parameters strongly affected plant community characteristics (vegetation cover and litter mass) by favouring thicker soil layers and lower bulk densities, and soil texture strongly affected root functional traits (root mass density [RD] and RLD) by favoring lighter soils. Importantly, plant community characteristics and root functional traits were the main drivers of K r mitigation through their mediation effects on a range of soil properties (e.g., soil organic matter, aggregate stability, and shear strength) during the restoration, and vegetation can still be efficient in maintaining and restoring soil functions, even on severely degraded land. Overall, these findings could guide restoration practices to meet soil conservation and ecosystem function goals in degraded ecosystems.

Soil organic matter and silt contents determine soil particle surface electrochemical properties across a long-term natural restoration grassland

Vegetation restoration is an effective way to rebuild degraded ecosystems and restore soil function. Soil surface electrochemical properties, including specific surface area, cation exchange capacity, surface charge density, surface electric field strength, and surface potential, are often used as indicators to evaluate agricultural soil quality and fertility. However, little attention has been payed to the effect of natural revegetation on soil surface electrochemical properties. In this work, we selected a grassland restoration chronosequence (slope cropland, 0 years; natural grasslands restored for 3, 8, 22 and 24 years, i.e. NR3, NR8, NR22 and NR24, respectively) to investigate the changes of soil surface electrochemical properties along with vegetative restoration. Our results showed that surface charge density and surface potential for restored grassland ranged from 0.16 to 0.20 C m−2 and from −94 to −109 mV, with an average of 0.18 C m−2 and −101 mV, respectively. The value of surface electric field strength could reach to the order of magnitude of −107 V m−1 and showed a decreasing trend with increasing period of natural vegetation recovery. Cation exchange capacity and specific surface area significantly increased with the extension of natural restoration period except for NR3 (P < 0.05). It was found that soil organic matter (SOM) and silt content were the main factors to determine cation exchange capacity and specific surface area. Both cation exchange capacity and specific surface area were closely related to silt content but weakly related to clay content, possibly due to the high silt content in our studied soils. Moreover, cation exchange capacity and specific surface area showed a significant linear relationship with SOM, which may be ascribed to the diversity in cation substitution sites and high specific surface area of SOM. Our results indicated that the long-term natural restoration of grassland contributed to the improvement of cation exchange capacity and specific surface area.

Water erosion aspects of land degradation neutrality to landscape planning tools at national scale

The soil erosion by water is a land degradation process identified the Land Degradation Neutrality (LDN) conceptual framework and a soil threat recognized in the Soil Thematic Strategy. It is also a very significant problem in the Mediterranean area. The common cause of land degradation is incorrect land use and management practices, which enhance the importance of planning the future of the landscape. When solving a soil erosion problem, not only land degradation is being reversed, but soil safety is provided: water conservation, biodiversity improvement, ecosystem services provision and better landscape equilibrium.The Land Degradation Neutrality (LDN) target, referred in the United Nations Sustainable Development Goals for 2030, is defined as a state whereby the amount and quality of land resources necessary to support ecosystem functions and services and enhance food security remain stable or increase within specified temporal and spatial scales and ecosystems. Despite some initiatives and recent projects about the achievement of LDN target, the link to landscape planning tools is still lacking.The approach followed in this study incorporates the centric and holistic perspective of soil, and aims to contribute to a definition of a mapping methodology of the areas that should be submitted to land degradation neutrality plans providing ecosystem restoration planning and the co-benefits of restoring soil functions. This goal will be supported by the assessment of the soil conservation status at a national scale (Portugal), using an integrated approach between soil maintenance/improvement and soil degradation, with the current soil cover protection. The evaluation of soil cover protection was established with the interpretation of land use classes and its cover-management factor (C-factor) from the Universal Soil Loss Equation and was tested in three different scenarios: (S1) the higher C-values collected in the research studies (S2) the more recent C-value collected in the research studies and (S3) an adapted scenario with assumptions considered by the authors.The study applied to mainland Portugal showed that Scenario S3 was more equilibrated regarding the distribution of the results (conservation vs. restoration) but was dependent of a set of defined assumptions especially regarding the different forest trees characteristics and management practices performed in Portugal. In this scenario, it was identified that 45.6% of Portugal needs LDN planning towards ecosystem restoration. The proposed methodology also identifies different priority classes of intervention, where the public or private investments could be targeted. Those LDN planning areas are easily framed in the responses to achieve LDN: avoid, reduce or reverse.