Changes in soil organic carbon under perennial crops

Spatially-explicit land use change emissions and carbon payback times of biofuels under the Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA)

The Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA) requires airlines to offset their greenhouse gas (GHG) emissions above 2019 levels by either buying carbon offsets or using Sustainable Aviation Fuels (SAFs). These are drop-in jet fuels made from biomass or other renewable resources that reduce GHG emissions by at least 10 % compared to kerosene and meet certain sustainability criteria. This study assesses the direct land use change (DLUC) emissions of SAF, i.e., GHG emissions from on-site land conversion from previous uses (excluding primary forests, peatlands, wetlands, and protected and biodiversity-rich areas) into alternative feedstocks, considering spatial variability in global yields and land carbon stocks. The results provide DLUC values and carbon payback times at 0.5-degree resolution for six SAF pathways, with and without irrigation and a medium-input intensity, according to CORSIA sustainability criteria. When excluding CORSIA non-compliant areas, soybean SAF shows the highest mean DLUC factor (31.9 ± 20.7 gCO2/MJ), followed by reed canary grass and maize. Jatropha SAF shows the lowest mean DLUC factor (3.6 ± 31.4 gCO2/MJ), followed by miscanthus and switchgrass. The latter feedstocks show potential for reducing GHG emissions over large areas but with relatively greater variability. Country-average DLUC values are higher than accepted ILUC ones for all pathways except for maize. To ensure the GHG benefits of CORSIA, feedstocks must be produced in areas where not only carbon stocks are relatively low but also where attainable yields are sufficiently high. The results help identify locations where the combination of these two factors may be favourable for low-DLUC SAF production. Irrigated miscanthus offers the highest SAF production potential (2.75 EJ globally) if grown on CORSIA-compliant cropland and grassland areas, accounting for ∼1/5 of the total kerosene used in 2019. Quantifying other environmental impacts of SAFs is desirable to understand sustainability trade-offs and financial constraints that may further limit production potentials.

Ecosystem multifunctionality is more related to the indirect effects than to the direct effects of human management in China's drylands

Drylands provide a wide range of important ecosystem functions but are sensitive to environmental changes, especially human management. Two major land use types of drylands are grasslands and croplands, which are influenced by intensive grazing activities and agricultural management, respectively. However, little is known about whether the ecosystem functioning of these two land use types is predominated affected by human management, or environmental factors (intrinsic environmental factors and factors modified by human management). This limits our understanding of the ecosystem functions under intensive human management in drylands. Here we reported a study where we collected data from 40 grassland and 30 cropland sites along an extensive aridity gradient in China's drylands to quantify the effects of human management intensity, intrinsic environmental factors (i.e., aridity), and environmental factors modified by human management (i.e., soil bulk density and plant density) on specific ecosystem functions (ecosystem multifunctionality, productivity, carbon storage, soil water, and soil nutrients). We found that the relative importance of each function differed between croplands and grasslands. Ecosystem functions varied with human management intensity, with lower productivity and plant carbon storage in grasslands under high grazing intensity than un-grazed, while multifunctionality and carbon storage increased with greater fertilization only in arid croplands. Furthermore, among environmental factors, soil bulk density had the greatest negative effects, which directly reduced multifunctionality in grasslands and indirectly reduced multifunctionality in croplands via suppressing crop density. Crop density was the major environmental factor that positively related to multifunctionality in croplands. However, these effects would be exacerbated with increasing aridity. Our study demonstrated that compared with the direct impacts of human management, environmental factors modified by human management (e.g., soil bulk density) are the major drivers of ecosystem functions, indicating that improving soil structure by alleviating human interferences (e.g., reducing livestock trampling) would be an effective way to restore ecosystem functions in drylands under global warming and drying.

Impacts of deforestation and land use/land cover change on carbon stock dynamics in Jomoro District, Ghana

Tropical deforestation in the African continent plays a key role in the global carbon cycle and bears significant implications in terms of climate change and sustainable development. Especially in Sub-Saharan Africa, where more than two-thirds of the population rely on forest and woodland resources for their livelihoods, deforestation and land use changes for crop production lead to a substantial loss of ecosystem-level carbon stock. Unfortunately, the impacts of deforestation and land use change can be more critical than in any other region, but these are poorly quantified. We analyse changes in the main carbon pools (above- and below-ground, soil and litter, respectively) after deforestation and land use/land cover change, for the Jomoro District (Ghana), by assessing the initial reference level of carbon stock for primary forest and the subsequent stock changes and dynamics as a consequence of conversion to the secondary forest and to five different tree plantations (rubber, coconut, cocoa, oil palm, and mixed plantations) on a total of 72 plots. Results indicate overall a statistically significant carbon loss across all the land uses/covers and for all the carbon pools compared to the primary forest with the total carbon stock loss ranging between 35% and 85% but with no statistically significant differences observed in the comparison between primary forest and mixed plantations and secondary forest. Results also suggest that above-ground carbon and soil organic carbon are the primary pools contributing to the total carbon stocks but with opposite trends of carbon loss and accumulation. Strategies for sustainable development, policies to reduce emissions from deforestation and forest degradation, carbon stock enhancement (REDD+), and planning for sustainable land use management should carefully consider the type of conversion and carbon stock dynamics behind land use change for a win-win strategy while preserving carbon stocks potential in tropical ecosystems.

Phylogenomic analysis reveals five independently evolved African forage grass clades in the genus Urochloa

BACKGROUND AND AIMS

The grass genus Urochloa (Brachiaria) sensu lato includes forage crops that are important for beef and dairy industries in tropical and sub-tropical Africa, South America and Oceania/Australia. Economically important species include U. brizantha, U. decumbens, U. humidicola, U. mutica, U. arrecta, U. trichopus, U. mosambicensis and Megathyrsus maximus, all native to the African continent. Perennial growth habits, large, fast growing palatable leaves, intra- and interspecific morphological variability, apomictic reproductive systems and frequent polyploidy are widely shared within the genus. The combination of these traits probably favoured the selection for forage domestication and weediness, but trait emergence across Urochloa cannot be modelled, as a robust phylogenetic assessment of the genus has not been conducted. We aim to produce a phylogeny for Urochloa that includes all important forage species, and identify their closest wild relatives (crop wild relatives). Finally, we will use our phylogeny and available trait data to infer the ancestral states of important forage traits across Urochloa s.l. and model the evolution of forage syndromes across the genus.

METHODS

Using a target enrichment sequencing approach (Angiosperm 353), we inferred a species-level phylogeny for Urochloa s.l., encompassing 54 species (~40 % of the genus) and outgroups. Phylogenies were inferred using a multispecies coalescent model and maximum likelihood method. We determined the phylogenetic placement of agriculturally important species and identified their closest wild relatives, or crop wild relatives, based on well-supported monophyly. Further, we mapped key traits associated with Urochloa forage crops to the species tree and estimated ancestral states for forage traits along branch lengths for continuous traits and at ancestral nodes in discrete traits.

KEY RESULTS

Agricultural species belong to five independent clades, including U. brizantha and U. decumbens lying in a previously defined species complex. Crop wild relatives were identified for these clades supporting previous sub-generic groupings in Urochloa based on morphology. Using ancestral trait estimation models, we find that five morphological traits that correlate with forage potential (perennial growth habits, culm height, leaf size, a winged rachis and large seeds) independently evolved in forage clades.

CONCLUSIONS

Urochloa s.l. is a highly diverse genus that contains numerous species with agricultural potential, including crop wild relatives that are currently underexploited. All forage species and their crop wild relatives naturally occur on the African continent and their conservation across their native distributions is essential. Genomic and phenotypic diversity in forage clade species and their wild relatives need to be better assessed both to develop conservation strategies and to exploit the diversity in the genus for improved sustainability in Urochloa cultivar production.

A unifying modelling of multiple land degradation pathways in Europe

Land degradation is a complex socio-environmental threat, which generally occurs as multiple concurrent pathways that remain largely unexplored in Europe. Here we present an unprecedented analysis of land multi-degradation in 40 continental countries, using twelve dataset-based processes that were modelled as land degradation convergence and combination pathways in Europe's agricultural (and arable) environments. Using a Land Multi-degradation Index, we find that up to 27%, 35% and 22% of continental agricultural (~2 million km2) and arable (~1.1 million km2) lands are currently threatened by one, two, and three drivers of degradation, while 10-11% of pan-European agricultural/arable landscapes are cumulatively affected by four and at least five concurrent processes. We also explore the complex pattern of spatially interacting processes, emphasizing the major combinations of land degradation pathways across continental and national boundaries. Our results will enable policymakers to develop knowledge-based strategies for land degradation mitigation and other critical European sustainable development goals.

Phyloecology of nitrate ammonifiers and their importance relative to denitrifiers in global terrestrial biomes

Nitrate ammonification is important for soil nitrogen retention. However, the ecology of ammonifiers and their prevalence compared with denitrifiers, being competitors for nitrate, are overlooked. Here, we screen 1 million genomes for nrfA and onr, encoding ammonifier nitrite reductases. About 40% of ammonifier assemblies carry at least one denitrification gene and show higher potential for nitrous oxide production than consumption. We then use a phylogeny-based approach to recruit gene fragments of nrfA, onr and denitrification nitrite reductase genes (nirK, nirS) in 1861 global terrestrial metagenomes. nrfA outnumbers the nearly negligible onr counts in all biomes, but denitrification genes dominate, except in tundra. Random forest modelling teases apart the influence of the soil C/N on nrfA-ammonifier vs denitrifier abundance, showing an effect of nitrate rather than carbon content. This study demonstrates the multiple roles nitrate ammonifiers play in nitrogen cycling and identifies factors ultimately controlling the fate of soil nitrate.

Revising the global biogeography of annual and perennial plants

There are two main life cycles in plants-annual and perennial1,2. These life cycles are associated with different traits that determine ecosystem function3,4. Although life cycles are textbook examples of plant adaptation to different environments, we lack comprehensive knowledge regarding their global distributional patterns. Here we assembled an extensive database of plant life cycle assignments of 235,000 plant species coupled with millions of georeferenced datapoints to map the worldwide biogeography of these plant species. We found that annual plants are half as common as initially thought5-8, accounting for only 6% of plant species. Our analyses indicate that annuals are favoured in hot and dry regions. However, a more accurate model shows that the prevalence of annual species is driven by temperature and precipitation in the driest quarter (rather than yearly means), explaining, for example, why some Mediterranean systems have more annuals than desert systems. Furthermore, this pattern remains consistent among different families, indicating convergent evolution. Finally, we demonstrate that increasing climate variability and anthropogenic disturbance increase annual favourability. Considering future climate change, we predict an increase in annual prevalence for 69% of the world's ecoregions by 2060. Overall, our analyses raise concerns for ecosystem services provided by perennial plants, as ongoing changes are leading to a higher proportion of annual plants globally.

Restoring particulate and mineral-associated organic carbon through regenerative agriculture

Sustainability of agricultural production and mitigation of global warming rely on the regeneration of soil organic carbon (SOC), in particulate organic carbon (POC) and mineral-associated organic carbon (MAOC) forms. We conducted a global systematic meta-analysis of the effects of regenerative management practices on SOC, POC, and MAOC in cropland, finding: 1) no-till (NT) and cropping system intensification increase SOC (11.3% and 12.4%, respectively), MAOC (8.5% and 7.1%, respectively), and POC (19.7% and 33.3%, respectively) in topsoil (0 to 20 cm), but not in subsoil (>20 cm); 2) experimental duration, tillage frequency, the intensification type, and rotation diversity moderate the effects of regenerative management; and 3) NT synergized with integrated crop-livestock (ICL) systems to greatly increase POC (38.1%) and cropping intensification synergized with ICL systems to greatly increase MAOC (33.1 to 53.6%). This analysis shows that regenerative agriculture is a key strategy to reduce the soil C deficit inherent to agriculture to promote both soil health and long-term C stabilization.

Climate change mitigation potentials of biofuels produced from perennial crops and natural regrowth on abandoned and degraded cropland in Nordic countries

Bioenergy expansion is present in most climate change mitigation scenarios. The associated large land use changes have led to concerns on how bioenergy can be sustainably deployed. Promising win-win strategies include the production of perennial bioenergy crops on recently abandoned cropland or on cropland prone to land degradation, as perennial crops typically reduce soil erosion rates. Natural vegetation regrowth is an alternative nature-based solution that can also co-deliver negative emissions and other environmental benefits. In this study, we explore the potential to deploy bioenergy crops in Nordic countries (Norway, Sweden, Finland, and Denmark) on abandoned cropland and on cropland threatened by soil erosion and compare the achievable climate change mitigation benefits with natural regrowth. We found 186 thousand hectares (kha) of abandoned cropland and 995 kha of cropland threatened by soil erosion suitable for bioenergy crop cultivation. The primary bioenergy potential in the region is 151 PJ (PJ) per year, corresponding to 67-110 PJ per year of liquid biofuels depending on biorefinery technology. This has a climate change mitigation potential from -6.0 to -17 megatons of carbon dioxide equivalents (MtCO_2eq) per year over the first 20 years (equivalent to 14-40% of annual road transport emissions), with high-end estimates relying on bioenergy coupled to carbon capture and storage (BECCS). On the same area, natural regrowth can deliver negative emissions of -10 MtCO_2eq per year. Biofuel production outperforms natural regrowth on 46% of abandoned cropland with currently available biorefinery technologies, 83% with improved energy conversion efficiency, and nearly everywhere with BECCS. For willow windbreaks, improved biorefinery technology or BECCS is necessary to ensure the delivery of larger negative emissions than natural regrowth. Biofuel production is preferable to natural regrowth on 16% of croplands threatened by soil erosion with the current biorefinery technology and on 87% of the land area with BECCS. Without BECCS, liquid biofuels achieve larger climate benefits than natural regrowth only when bioenergy yields are high. Underutilized land and land affected by degradation processes are an opportunity for a gradual and more sustainable bioenergy deployment, and local considerations are needed to identify case-specific solutions that can co-deliver multiple environmental benefits.

Effects of land clearing for agriculture on soil organic carbon stocks in drylands: A meta-analysis

Agricultural activities have been expanding globally with the pressure to provide food security to the earth's growing population. These agricultural activities have profoundly impacted soil organic carbon (SOC) stocks in global drylands. However, the effects of clearing natural ecosystems for cropland (CNEC) on SOC are uncertain. To improve our understanding of carbon emissions and sequestration under different land uses, it is necessary to characterize the response patterns of SOC stocks to different types of CNEC. We conducted a meta-analysis with mixed-effect model based on 873 paired observations of SOC in croplands and adjacent natural ecosystems from 159 individual studies in global drylands. Our results indicate that CNEC significantly (p < .05) affects SOC stocks, resulting from a combination of natural land clearing, cropland management practices (fertilizer application, crop species, cultivation duration) and the significant negative effects of initial SOC stocks. Increases in SOC stocks (in 1 m depth) were found in croplands which previously natural land (deserts and shrublands) had low SOC stocks, and the increases were 278.86% (95% confidence interval, 196.43%-361.29%) and 45.38% (26.53%-62.23%), respectively. In contrast, SOC stocks (in 1 m depth) decreased by 24.11% (18.38%-29.85%) and 10.70% (1.80%-19.59%) in clearing forests and grasslands for cropland, respectively. We also established the general response curves of SOC stocks change to increasing cultivation duration, which is crucial for accurately estimating regional carbon dynamics following CNEC. SOC stocks increased significantly (p < .05) with high long-term fertilizer consumption in cleared grasslands with low initial SOC stocks (about 27.2 Mg ha^-1 ). The results derived from our meta-analysis could be used for refining the estimation of dryland carbon dynamics and developing SOC sequestration strategies to achieve the removal of CO₂ from the atmosphere.

Organic carbon and nitrogen accumulation in orchard soil with organic fertilization and cover crop management: A global meta-analysis

In orchard systems, organic amendments and cover crops may enhance soil organic carbon (SOC) and total nitrogen (STN) stocks, but on a global scale a comprehensive understanding of these practices is needed. This study reports a worldwide meta-analysis of 131 peer-reviewed publications, to quantify potential SOC and STN accumulation in orchard soils induced by organic fertilization and cover cropping. Annual gains of 3.73 Mg C/ha and 0.38 Mg N/ha were realized with the introduction of organic fertilizer, while cover crop management led to annual increases of 2.00 Mg C/ha and 0.20 Mg N/ha. The SOC and STN accumulation rates depended mostly on climatic conditions and initial SOC and STN content. The SOC and STN accumulated fastest during the first three years of cover crop implementation, at 2.98 Mg C/ha/yr and 0.25 Mg N/ha/yr and declined thereafter. Organic fertilization caused significantly more annual SOC and STN accumulation at higher (400-800 mm) than lower (<400 mm) rainfall levels. When cover cropping for more than five years, SOC accumulated the fastest with <800 mm of mean annual rainfall. Organic fertilization led to faster SOC accumulation with mean annual temperature between 15 and 20 °C than >20 °C. Organic amendments led to the slowest SOC accumulation rate when the initial SOC concentration was <10 g C/kg. This study provides policy makers and orchard managers science-based evidence to help guide adaptive management practices that build SOC stocks, improve soil conditions and enhance resilience of orchard systems to climate change.

Medium-term evaluation of the 4‰ initiative, soil organic carbon storage and stabilisation in a Mediterranean rainfed olive grove under conventional tillage: A case study

This study aims to show the effect of conventional tillage (CT) in olive orchards in the medium term (15 years) on carbon (C) storage considering the complete soil profile, on the soil C sequestration and stabilisation capacity and on the viability for the achievement of Objective 4‰. The results obtained showed important losses in soil organic carbon (SOC) and SOC stock (SOC-S), with a significant loss of total SOC-S of 42.3%. Concerning the SOC and the SOC-S linked to the fine soil fraction (<20 μm), the evolution over time led however to a SOC increase in depth (BC and C horizons) of 58.3% and 20.9% and increases in SOC-S of 17.2%, 34.7% and 27.3% for the Ap, BC and C horizons, respectively. Finally, it was seen that the goals set by the 4‰ initiative were not met, as losses of 2.1 Mg C ha^-1 yr^-1 were found when considering the entire soil profile and 0.8 Mg C ha^-1 yr^-1 when considering only the first 40 cm. Therefore, we can affirm that medium-term CT has not only conditioned C storage in the soils studied, but also their capacity for sequestration and stabilisation, which has repercussions not only on the failure to meet the objectives of the 4‰ initiative, but also on the amount of C lost in 15 years.

Arbuscular Mycorrhizal Symbiosis: A Strategy for Mitigating the Impacts of Climate Change on Tropical Legume Crops

Climate change is likely to have severe impacts on food security in the topics as these regions of the world have both the highest human populations and narrower climatic niches, which reduce the diversity of suitable crops. Legume crops are of particular importance to food security, supplying dietary protein for humans both directly and in their use for feed and forage. Other than the rhizobia associated with legumes, soil microbes, in particular arbuscular mycorrhizal fungi (AMF), can mitigate the effects of biotic and abiotic stresses, offering an important complementary measure to protect crop yields. This review presents current knowledge on AMF, highlights their beneficial role, and explores the potential for application of AMF in mitigating abiotic and biotic challenges for tropical legumes. Due to the relatively little study on tropical legume species compared to their temperate growing counterparts, much further research is needed to determine how similar AMF-plant interactions are in tropical legumes, which AMF species are optimal for agricultural deployment and especially to identify anaerobic AMF species that could be used to mitigate flood stress in tropical legume crop farming. These opportunities for research also require international cooperation and support, to realize the promise of tropical legume crops to contribute to future food security.

Rapid improvement in soil health following the conversion of abandoned farm fields to annual or perennial agroecosystems

Incorporating perennial crops into agroecosystems has been shown to mitigate soil degradation and improve soil health by enhancing soil aggregation and soil organic carbon (SOC) accrual. However, our understanding of the ability and timeframe for perennial crop systems to build soil health within the context of conversion from abandoned crop land remains limited. Here, we examined changes in soil health in the first year following the conversion of an abandoned crop field into an agroecosystem planted with various treatments, including: novel perennial grain (intermediate wheatgrass, IWG; Thinopyrum intermedium), IWG/ alfalfa biculture, forage grass, tallgrass prairie, or annual wheat. We analyzed factors considered central to the concept of mitigating soil degradation to improve soil health (soil aggregation, aggregate organic carbon (OC), bulk SOC) and their soil biological and physicochemical correlates throughout the first growing season. Comparisons between treatments showed that both annual and perennial treatments rapidly and significantly improved soil health metrics including aggregation, aggregate stability, and OC levels compared to pre-conversion conditions. Such increases were positively correlated with the abundance of arbuscular mycorrhizal fungi (AMF hyphae, root colonization), labile SOC and microbial activity. Notably, IWG/ alfalfa biculture resulted in significantly higher levels of macroaggregate OC in comparison to other treatments, including tallgrass prairie, supporting the potential of perennial grasses to contribute to soil carbon gains. Overall, the conversion of this abandoned land to an agroecosystem produced rapid and substantial increases in soil health in the first year after planting.

Short-term but not long-term perennial mugwort cropping increases soil organic carbon in Northern China Plain

Perennial cropping has been an alternative land use type due to its widely accepted role in increasing soil carbon sequestration. However, how soil organic carbon (SOC) changes and its underlying mechanisms under different cropping years are still elusive. A chronosequence (0-, 3-, 6-, 20-year) of perennial mugwort cropping was chosen to explore the SOC dynamics and the underlying mechanisms in agricultural soils of Northern China Plain. The results revealed that SOC first increased and then decreased along the 20-year chronosequence. The similar patterns were also found in soil properties (including soil ammonium nitrogen, total nitrogen and phosphorus) and two C-degrading hydrolytic enzyme activities (i.e., α-glucosidase and β-glucosidase). The path analysis demonstrated that soil ammonium nitrogen, total nitrogen, and plant biomass affected SOC primarily through the indirect impacts on soil pH, total phosphorus availability, and C-degrading hydrolytic enzyme activities. In addition, the contributions of soil properties are greater than those of biotic factors (plant biomass) to changes in SOC across the four mugwort cropping years. Nevertheless, the biotic factors may play more important roles in regulating SOC than abiotic factors in the long run. Moreover, SOC reached its maximum and was equaled to that under the conventional rotation when cropping mugwort for 7.44 and 14.88 years, respectively, which has critical implications for sustainable C sequestration of agricultural soils in Northern China Plain. Our observations suggest that short-term but not long-term perennial mugwort cropping is an alternative practice benefiting soil C sequestration and achieving the Carbon Neutrality goal in China.

Management and Utilization of Plant Genetic Resources for a Sustainable Agriculture

Despite the dramatic increase in food production thanks to the Green Revolution, hunger is increasing among human populations around the world, affecting one in nine people. The negative environmental and social consequences of industrial monocrop agriculture is becoming evident, particularly in the contexts of greenhouse gas emissions and the increased frequency and impact of zoonotic disease emergence, including the ongoing COVID-19 pandemic. Human activity has altered 70–75% of the ice-free Earth’s surface, squeezing nature and wildlife into a corner. To prevent, halt, and reverse the degradation of ecosystems worldwide, the UN has launched a Decade of Ecosystem Restoration. In this context, this review describes the origin and diversity of cultivated species, the impact of modern agriculture and other human activities on plant genetic resources, and approaches to conserve and use them to increase food diversity and production with specific examples of the use of crop wild relatives for breeding climate-resilient cultivars that require less chemical and mechanical input. The need to better coordinate in situ conservation efforts with increased funding has been highlighted. We emphasise the need to strengthen the genebank infrastructure, enabling the use of modern biotechnological tools to help in genotyping and characterising accessions plus advanced ex situ conservation methods, identifying gaps in collections, developing core collections, and linking data with international databases. Crop and variety diversification and minimising tillage and other field practices through the development and introduction of herbaceous perennial crops is proposed as an alternative regenerative food system for higher carbon sequestration, sustaining economic benefits for growers, whilst also providing social and environmental benefits.

Perennials as Future Grain Crops: Opportunities and Challenges

Perennial grain crops could make a valuable addition to sustainable agriculture, potentially even as an alternative to their annual counterparts. The ability of perennials to grow year after year significantly reduces the number of agricultural inputs required, in terms of both planting and weed control, while reduced tillage improves soil health and on-farm biodiversity. Presently, perennial grain crops are not grown at large scale, mainly due to their early stages of domestication and current low yields. Narrowing the yield gap between perennial and annual grain crops will depend on characterizing differences in their life cycles, resource allocation, and reproductive strategies and understanding the trade-offs between annualism, perennialism, and yield. The genetic and biochemical pathways controlling plant growth, physiology, and senescence should be analyzed in perennial crop plants. This information could then be used to facilitate tailored genetic improvement of selected perennial grain crops to improve agronomic traits and enhance yield, while maintaining the benefits associated with perennialism.

Exploring the Potential of Straw Biochar for Environmentally Friendly Fertilizers

The pyrolysis of wheat straw in order to produce biochar for soil amendment is a potential strategy for producing environmental friendly fertilizers capable of boosting soil fertility, increasing carbon storage, and lowering greenhouse gas emissions. However, straw biochar’s potential to influence these aspects may vary depending on its properties. Our study sought to investigate biochar from wheat straw from three different regions in Bulgaria. A specially designed set up was used for the biochar production. Three pyrolytic temperatures (300, 400, and 500 °C) were applied, resulting in nine biochar samples. The specific characteristics included moisture content, volatile substances content, ash content, fixed carbon content, and joint ash and carbon content, and they were determined for each sample. The chemical content, resulting in 17 chemical elements and compounds, was measured and analysed. The results obtained showed that the produced straw biochar has the potential to be used as a fertilizer and soil supplement.

Edaphic Response and Behavior of Agricultural Soils to Mechanical Perturbation in Tillage

Mechanical perturbation constrains edaphic functionality of arable soils in tillage. Seasonal soil tool interactions disrupt the pristine bio-physio-mechanical characteristics of agricultural soils and crop-oriented ecological functions. They interfere with the natural balancing of nutrient cycles, soil carbon, and diverse organic matter that supports soil ecosystem interactions with crop rooting. We review soil working in tillage, associated mechanistic perturbations, and the edaphic response of affected soil properties towards cropping characteristics and behavior as soil working tools evolve. This is to further credit or discredit the global transition to minimum and no-till systems with a more specific characterization to soil properties and edaphic crop-oriented goals of soil tooling. Research has shown that improvement in adoption of conservation tillage is trying to characterize tilled soils with edaphic states of native soil agroecosystems rendering promising strategies to revive overworked soils under the changing climate. Soil can proliferate without disturbance whilst generation of new ecologically rich soil structures develops under more natural conditions. Researchers have argued that crops adapted to the altered physio-mechanical properties of cultivated soils can be developed and domesticated, especially under already impedance induced, mechanically risked, degraded soils. Interestingly edaphic response of soils under no-till soil working appeared less favorable in humid climates and more significant under arid regions. We recommend further studies to elucidate the association between soil health state, soil disturbance, cropping performance, and yield under evolving soil working tools, a perspective that will be useful in guiding the establishment of future soils for future crops.

Management of a Mediterranean Forage/Cereal-Based Cropping System: An Ecosystem Service Multisectoral Analysis in the Perspective of Climate Change

Within Mediterranean cropping systems, legume forage crops that last up to 6 years or more (e.g., alfalfa) are replaced with cereal crops (e.g., wheat). The change from forage to cereal crops has negative climate and environmental impacts that must be addressed with mitigation actions. This study evaluated the synergies and tradeoffs between the ecosystem services provided by three management systems after forage legume. A field trial was set up from October 2017 to September 2019 on a 6-year-old alfalfa field subjected to the following management systems: (i) alfalfa termination followed by wheat for 2 years (WW, control); (ii) alfalfa termination followed by single amendment with 60 Mg ha−1 recalcitrant biochar and then by wheat for 2 years (WWB60); and (iii) extension of alfalfa for 2 years (AEXT). A range of regulating, supporting, and provisioning ecosystem services were assessed during the 2018 and 2019 cropping seasons. The results highlight that WWB60 can guarantee carbon sequestration without causing tradeoffs with other services, while AEXT can enhance soil conservation while not increasing soil greenhouse gas emissions. Future policies should support the WWB60 system if the goal is to increase the supporting services. Conversely, the AEXT system should be used if the goal is to increase the regulating and provisioning services.

Biorefinery of Green Biomass─How to Extract and Evaluate High Quality Leaf Protein for Food?

There is a growing need for protein for both feed and food in order to meet future demands. It is imperative to explore and utilize novel protein sources such as protein from leafy plant material, which contains high amounts of the enzyme ribulose-1,5-biphosphate carboxylase/oxygenase (RuBisCo). Leafy crops such as grasses and legumes can in humid climate produce high protein yields in a sustainable way when compared with many traditional seed protein crops. Despite this, very little RuBisCo is utilized for foods because proteins in the leaf material has a low accessibility to monogastrics. In order to utilize the leaf protein for food purposes, the protein needs to be extracted from the fiber rich leaf matrix. This conversion of green biomass to valuable products has been labeled green biorefinery. The green biorefinery may be tailored to produce different products, but in this Review, the focus is on production of food-grade protein. The existing knowledge on the extraction, purification, and concentration of protein from green biomass is reviewed. Additionally, the quality and potential application of the leaf protein in food products and side streams from the green biorefinery will be discussed along with possible uses of side streams from the protein production.

Restoring Soil Fertility on Degraded Lands to Meet Food, Fuel, and Climate Security Needs via Perennialization

A continuously growing pressure to increase food, fiber, and fuel production to meet worldwide demand and achieve zero hunger has put severe pressure on soil resources. Abandoned, degraded, and marginal lands with significant agricultural constraints—many still used for agricultural production—result from inappropriately intensive management, insufficient attention to soil conservation, and climate change. Continued use for agricultural production will often require ever more external inputs such as fertilizers and herbicides, further exacerbating soil degradation and impeding nutrient recycling and retention. Growing evidence suggests that degraded lands have a large potential for restoration, perhaps most effectively via perennial cropping systems that can simultaneously provide additional ecosystem services. Here we synthesize the advantages of and potentials for using perennial vegetation to restore soil fertility on degraded croplands, by summarizing the principal mechanisms underpinning soil carbon stabilization and nitrogen and phosphorus availability and retention. We illustrate restoration potentials with example systems that deliver climate mitigation (cellulosic bioenergy), animal production (intensive rotational grazing), and biodiversity conservation (natural ecological succession). Perennialization has substantial promise for restoring fertility to degraded croplands, helping to meet future food security needs.

Changes in Soil Organic Carbon Concentration and Stock after Forest Regeneration of Agricultural Fields in Taiwan

Afforestation or abandonment of agricultural fields to forest regeneration is a method of sequestering carbon to offset the increasing atmospheric concentration of CO2. We selected 11 sites with altitudes ranging from 14 to 2056 m and with paired forest regenerated and adjacent agricultural fields. Our objectives were to (1) examine the changes in soil organic carbon (SOC) concentration and stock after forest regeneration of agricultural fields and (2) identify the factors related to elevation and adjacent agricultural practices that affect the SOC accumulation rate. Our results demonstrated overall increases in both SOC concentrations and stocks after forest regeneration of the abandoned agricultural fields. The average increase rates of SOC concentrations in the forest regenerated soil samples were 1.65 and 0.95 g C kg−1 at 0–10 and 10–20 cm depths, respectively, representing 101% and 65% increases relative to those in the soil samples from agricultural fields. The average accumulation rates of SOC stocks in the regenerated forests were 13.0 and 6.7 ton C ha−1 at the 0–10 and 10–20 cm depths, respectively, representing 96% and 62% increases relative to those in the agricultural soil samples. The average annual sequestration rate was 1.03 Mg C ha−1 year−1 for the top 0–20 cm soils, which is greater than that observed by previous reviews and meta-analyses. The tropical/subtropical climate, sampling soil depth, forest regeneration period, and tree species in this study are likely to have contributed to the high average SOC accumulation levels. In addition, the SOC stock accumulation rates were higher at low-elevation sites than at middle-elevation sites, which could also be attributed to the favorable climatic conditions at the low-elevation sites. Along with the build-up of carbon sequestration in the forest floor and tree biomass, the afforestation/abandonment of agricultural fields to forest regeneration appears to be a promising carbon offset mechanism.

Patterns and driving factors of biomass carbon and soil organic carbon stock in the Indian Himalayan region

Tree-based ecosystems are critical to climate change mitigation. The study analysed carbon (C) stock patterns and examined the importance of environmental variables in predicting carbon stock in biomass and soils of the Indian Himalayan Region (IHR). We conducted a synthesis of 100 studies reporting biomass carbon stock and 67 studies on soil organic carbon (SOC) stock from four land-uses: forests, plantation, agroforest, and herbaceous ecosystem from the IHR. Machine learning techniques were used to examine the importance of various environmental variables in predicting carbon stock in biomass and soils. Despite large variations in biomass C and SOC stock (mean ± SD) within the land-uses, natural forests have the highest biomass C stock (138.5 ± 87.3 Mg C ha^-1), and plantation forests exhibited the highest SOC stock (168.8 ± 74.4 Mg C ha^-1) in the top 1-m of soils. The relationship between the environmental variables (altitude, latitude, precipitation, and temperature) and carbon stock was not significantly correlated. The prediction of biomass carbon and SOC stock using different machine learning techniques (Adaboost, Bagging, Random Forest, and XGBoost) shows that the XGBoost model can predict the carbon stock for the IHR closely. Our study confirms that the carbon stock in the IHR vary on a large scale due to a diverse range of land-use and ecosystems within the region. Therefore, predicting the driver of carbon stock on a single environmental variable is impossible for the entire IHR. The IHR possesses a prominent carbon sink and biodiversity pool. Therefore, its protection is essential in fulfilling India's commitment to nationally determined contributions (NDC). Our data synthesis may also provide a baseline for the precise estimation of carbon stock, which will be vital for India's National Mission for Sustaining the Himalayan Ecosystem (NMSHE).

Long-term evaluation of the initiative 4‰ under different soil managements in Mediterranean olive groves

The 4‰ initiative implementation has increased the emphasis and interest in soil carbon and nitrogen storage in the last few years. This study evaluated the dynamics of soil organic carbon and total nitrogen under rain-fed olive groves over a long-term period (2004-2019). The management practices associated with achieving the 4‰ initiative objectives and the depth of analysis to measure the effectiveness of the initiative have generated uncertainties and wide debate in the scientific community. To contribute to this debate from a farm level, the objective of this study was to analyse the effects of conventional tillage and no-tillage with bare soil by using herbicides (after land management change from conventional tillage) on carbon and nitrogen stocks in complete soil profiles (depth > 100 cm) over 15 years in a Mediterranean olive grove. Soil samples were collected from each farm and analysed for carbon content and physical-chemical characteristics. This study indicates that management practices evaluated resulted in soil organic carbon and total nitrogen contents decreasing in soil, with a reduction >30% in all horizons. Results highlight a significant depletion of soil organic carbon stock with a significant decarbonisation process (-1.8 Mg C ha^-1 yr^-1) and total nitrogen stock (-0.57 and - 0.41 Mg N ha^-1 yr^-1) on average under both managements (no-tillage no tillage with herbicide and conventional tillage respectively) as compared to the initial situation. Furthermore, it was demonstrated that deep horizons are significant reservoirs of carbon (>50% in all cases) and in woody crops, its analysis within the dynamics of soil organic carbon stocks proposed by the 4‰ initiative was relevant. With these results, no-tillage with bare soil by using herbicides was demonstrated as an unsustainable agricultural practice and it is proposed to change the current soil management to sustainable management that increases the C inputs to achieve the 4‰ targets.

Uncovering the Role of Biophysical Factors and Socioeconomic Forces Shaping Soil Sensitivity to Degradation: Insights from Italy

Following an operational framework derived from earlier research, our study research estimates the specific contribution of biophysical and socioeconomic factors to soil sensitivity to degradation at two-time points (Early-1990s and Early-2010s) in Italy, a Mediterranean hotspot for desertification risk. A total of 34 variables associated (directly or, at least, indirectly) with different processes of soil degradation (erosion, salinization, sealing, contamination, and compaction) and climate change were considered here, delineating the predominant (underlying) cause (i.e., biophysical or socioeconomic). This set of variables represented the largest (quantitative) information available from national and international data sources including official statistics at both national and European scale. Contribution of biophysical and socioeconomic dimensions to soil sensitivity to degradation was heterogeneous in Italy, with the level of soil sensitivity to biophysical factors being the highest in less accessible, natural areas mostly located in hilly and mountainous districts. The highest level of soil sensitivity to socioeconomic drivers was instead observed in more accessible locations around large cities and flat rural districts with crop intensification and low (but increasing) population density. All these factors delineated an enlarged divide in environmental quality between (i) flat and upland districts, and between (ii) Northern and Southern Italian regions. These findings suggest the appropriateness of policy strategies protecting soils with a strong place-specific knowledge, i.e., based on permanent monitoring of local (biophysical and socioeconomic) conditions.

Perennial Staple Crops: Yields, Distribution, and Nutrition in the Global Food System

Staple crops, which have large amounts of carbohydrates, proteins, and/or fats, provide the bulk of calories in people's diets. Perennial plants, which can be productive for many years without the need for replanting, can produce staple foods and environmental benefits, but their agronomic and nutritional properties haven't been considered synthetically in comparison to annual staples. Here we offer a framework to classify perennial staple crops according to their nutritional categories and cultivation status. We assemble literature to report on the yield potential of 51 perennial staple crops, only 15 of which are well-characterized in existing global datasets. We show the extent and distribution of perennial staple crop production in relation to annual crop types, calculate the carbon stocks they hold, and analyze their nutritional content for three macronutrients and nine micronutrients. We found that most perennial staple crops are regional crops (not globally traded) that grow in the subtropics to tropics. At least one perennial staple crop in each of the five nutritional categories has yields over 2.5 t/ha, in some cases considerably higher, competitive with and in many cases exceeding those of nutritionally comparable annual staples. Perennial staple crops only comprise ~4.5% of total cropland. They hold a modest ~11.4 GtC above and below ground, less than one third of the anthropogenic carbon-equivalent emissions for the year 2018, but more than the ~9 GtC held by the same amount of annual cropland. If linear growth in land under perennial staple production continues to 2040, and replaces only annual cropland, an additional ~0.95 GtC could be sequestered. Many perennial crops also had competitive macronutrient density and yield (per unit area) compared to annual staples; moreover, specific perennial staples are abundant in specific micronutrients, indicating that they can be a nutrient-dense part of diets, unlike the most ubiquitous annual staple crops (corn, wheat, rice) that do not appear in the top 85th percentile for any of the nine micronutrients analyzed. Transition of land and diets to perennial staple crops, if judiciously managed, can provide win-win solutions for both food production and ecosystems.