Showing papers on "Soil organic matter published in 2019"

Quantitative assessment of microbial necromass contribution to soil organic matter.

Abstract: Soil carbon transformation and sequestration have received significant interest in recent years due to a growing need for quantitating its role in mitigating climate change. Even though our understanding of the nature of soil organic matter has recently been substantially revised, fundamental uncertainty remains about the quantitative importance of microbial necromass as part of persistent organic matter. Addressing this uncertainty has been hampered by the absence of quantitative assessments whether microbial matter makes up the majority of the persistent carbon in soil. Direct quantitation of microbial necromass in soil is very challenging because of an overlapping molecular signature with nonmicrobial organic carbon. Here, we use a comprehensive analysis of existing biomarker amino sugar data published between 1996 and 2018, combined with novel appropriation using an ecological systems approach, elemental carbon-nitrogen stoichiometry, and biomarker scaling, to demonstrate a suit of strategies for quantitating the contribution of microbe-derived carbon to the topsoil organic carbon reservoir in global temperate agricultural, grassland, and forest ecosystems. We show that microbial necromass can make up more than half of soil organic carbon. Hence, we suggest that next-generation field management requires promoting microbial biomass formation and necromass preservation to maintain healthy soils, ecosystems, and climate. Our analyses have important implications for improving current climate and carbon models, and helping develop management practices and policies.

Soil carbon storage informed by particulate and mineral-associated organic matter

Abstract: Effective land-based solutions to climate change mitigation require actions that maximize soil carbon storage without generating surplus nitrogen. Land management for carbon sequestration is most often informed by bulk soil carbon inventories, without considering the form in which carbon is stored, its capacity, persistency and nitrogen demand. Here, we present coupling of European-wide databases with soil organic matter physical fractionation to determine continental-scale forest and grassland topsoil carbon and nitrogen stocks and their distribution between mineral-associated and particulate organic matter pools. Grasslands and arbuscular mycorrhizal forests store more soil carbon in mineral-associated organic carbon, which is more persistent but has a higher nitrogen demand and saturates. Ectomycorrhizal forests store more carbon in particulate organic matter, which is more vulnerable to disturbance but has a lower nitrogen demand and can potentially accumulate indefinitely. The share of carbon between mineral-associated and particulate organic matter and the ratio between carbon and nitrogen affect soil carbon stocks and mediate the effects of other variables on soil carbon stocks. Understanding the physical distribution of organic matter in pools of mineral-associated versus particulate organic matter can inform land management for nitrogen-efficient carbon sequestration, which should be driven by the inherent soil carbon capacity and nitrogen availability in ecosystems. Land management strategies for enhancing soil carbon sequestration need to be tailored to different soil types, depending on how much organic matter is stored in pools of mineral-associated and particulate organic matter, suggests an analysis of soil organic matter across Europe.

Increasing organic stocks in agricultural soils: Knowledge gaps and potential innovations

Abstract: Recent initiatives, such as the United Nations declaring 2015 as the International Year of Soils and the French « 4 per 1000 » initiative call attention on soils and on the importance of maintaining and increasing soil organic matter stocks for soil fertility and food security, and for climate change adaptation and mitigation. We stress that soil organic carbon storage (i.e. an increase of soil organic carbon stocks) should be clearly differentiated from soil organic carbon sequestration, as the latter assumes a net removal of atmospheric CO2. Implementing management options that allow increasing soil organic carbon stocks at the local scale raises several questions, which are discussed in this article: how can we increase SOC stocks, at which rate and for how long; where do we prioritize SOC storage; how do we estimate the potential gain in C and which agricultural practices should we implement? We show that knowledge and tools are available to answer many of these questions, while further research remains necessary for others. A range of agricultural practices would require a re-assessment of their potential to store C and a better understanding of the underlying processes, such as no tillage and conservation agriculture, irrigation, practices increasing below ground inputs, organic amendments, and N fertilization. The vision emerging from the literature, showing the prominent role of soil microorganisms in the stabilization of soil organic matter, draw the attention to more exploratory potential levers, through changes in microbial physiology or soil biodiversity induced by agricultural practices, that require in-depth research.

Global meta-analysis of the relationship between soil organic matter and crop yields

Abstract: . Resilient, productive soils are necessary to sustainably intensify agriculture to increase yields while minimizing environmental harm. To conserve and regenerate productive soils, the need to maintain and build soil organic matter (SOM) has received considerable attention. Although SOM is considered key to soil health, its relationship with yield is contested because of local-scale differences in soils, climate, and farming systems. There is a need to quantify this relationship to set a general framework for how soil management could potentially contribute to the goals of sustainable intensification. We developed a quantitative model exploring how SOM relates to crop yield potential of maize and wheat in light of co-varying factors of management, soil type, and climate. We found that yields of these two crops are on average greater with higher concentrations of SOC (soil organic carbon). However, yield increases level off at ∼2 % SOC. Nevertheless, approximately two-thirds of the world's cultivated maize and wheat lands currently have SOC contents of less than 2 %. Using this regression relationship developed from published empirical data, we then estimated how an increase in SOC concentrations up to regionally specific targets could potentially help reduce reliance on nitrogen (N) fertilizer and help close global yield gaps. Potential N fertilizer reductions associated with increasing SOC amount to 7 % and 5 % of global N fertilizer inputs across maize and wheat fields, respectively. Potential yield increases of 10±11 % (mean ± SD) for maize and 23±37 % for wheat amount to 32 % of the projected yield gap for maize and 60 % of that for wheat. Our analysis provides a global-level prediction for relating SOC to crop yields. Further work employing similar approaches to regional and local data, coupled with experimental work to disentangle causative effects of SOC on yield and vice versa, is needed to provide practical prescriptions to incentivize soil management for sustainable intensification.

Pathways of mineral-associated soil organic matter formation: Integrating the role of plant carbon source, chemistry, and point of entry

Abstract: To predict the behavior of the terrestrial carbon cycle, it is critical to understand the source, formation pathway, and chemical composition of soil organic matter (SOM). There is emerging consensus that slow-cycling SOM generally consists of relatively low molecular weight organic carbon substrates that enter the mineral soil as dissolved organic matter and associate with mineral surfaces (referred to as "mineral-associated OM," or MAOM). However, much debate and contradictory evidence persist around: (a) whether the organic C substrates within the MAOM pool primarily originate from aboveground vs. belowground plant sources and (b) whether C substrates directly sorb to mineral surfaces or undergo microbial transformation prior to their incorporation into MAOM. Here, we attempt to reconcile disparate views on the formation of MAOM by proposing a spatially explicit set of processes that link plant C source with MAOM formation pathway. Specifically, because belowground vs. aboveground sources of plant C enter spatially distinct regions of the mineral soil, we propose that fine-scale differences in microbial abundance should determine the probability of substrate-microbe vs. substrate-mineral interaction. Thus, formation of MAOM in areas of high microbial density (e.g., the rhizosphere and other microbial hotspots) should primarily occur through an in vivo microbial turnover pathway and favor C substrates that are first biosynthesized with high microbial carbon-use efficiency prior to incorporation in the MAOM pool. In contrast, in areas of low microbial density (e.g., certain regions of the bulk soil), MAOM formation should primarily occur through the direct sorption of intact or partially oxidized plant compounds to uncolonized mineral surfaces, minimizing the importance of carbon-use efficiency, and favoring C substrates with strong "sorptive affinity." Through this framework, we thus describe how the primacy of biotic vs. abiotic controls on MAOM dynamics is not mutually exclusive, but rather spatially dictated. Such an understanding may be integral to more accurately modeling soil organic matter dynamics across different spatial scales.

Increasing wildfires threaten historic carbon sink of boreal forest soils

Abstract: Boreal forest fires emit large amounts of carbon into the atmosphere primarily through the combustion of soil organic matter1–3. During each fire, a portion of this soil beneath the burned layer can escape combustion, leading to a net accumulation of carbon in forests over multiple fire events4. Climate warming and drying has led to more severe and frequent forest fires5–7, which threaten to shift the carbon balance of the boreal ecosystem from net accumulation to net loss1, resulting in a positive climate feedback8. This feedback will occur if organic-soil carbon that escaped burning in previous fires, termed ‘legacy carbon’, combusts. Here we use soil radiocarbon dating to quantitatively assess legacy carbon loss in the 2014 wildfires in the Northwest Territories of Canada2. We found no evidence for the combustion of legacy carbon in forests that were older than the historic fire-return interval of northwestern boreal forests9. In forests that were in dry landscapes and less than 60 years old at the time of the fire, legacy carbon that had escaped burning in the previous fire cycle was combusted. We estimate that 0.34 million hectares of young forests (<60 years) that burned in the 2014 fires could have experienced legacy carbon combustion. This implies a shift to a domain of carbon cycling in which these forests become a net source—instead of a sink—of carbon to the atmosphere over consecutive fires. As boreal wildfires continue to increase in size, frequency and intensity7, the area of young forests that experience legacy carbon combustion will probably increase and have a key role in shifting the boreal carbon balance. Soil radiocarbon dating reveals that combusted ‘legacy carbon’—soil carbon that escaped burning during previous fires—could shift the carbon balance of boreal ecosystems, resulting in a positive climate feedback.

Long-term manure application increases soil organic matter and aggregation, and alters microbial community structure and keystone taxa

Abstract: Microbes play pivotal roles in soil organic matter (SOM) turnover: formation and decomposition. Organic fertilizers play crucial role for SOM accumulation, aggregate formation and influence microbial community composition and co-occurrence networks in microhabitats. Here, we investigated prokaryotic and fungal communities and their co-occurrence networks in four aggregate size classes in upland Ultisol following 27 years of mineral and/or organic fertilizer (rice straw, peanut straw, radish, or pig manure) application. Organic fertilizers and aggregate size classes have main and interactive effects on SOM content in aggregates (p 250 μm) than microaggregates (

Evidence for the primacy of living root inputs, not root or shoot litter, in forming soil organic carbon

Abstract: Soil organic carbon (SOC) is primarily formed from plant inputs, but the relative carbon (C) contributions from living root inputs (i.e. rhizodeposits) vs litter inputs (i.e. root + shoot litter) are poorly understood. Recent theory suggests that living root inputs exert a disproportionate influence on SOC formation, but few field studies have explicitly tested this by separately tracking living root vs litter inputs as they move through the soil food web and into distinct SOC pools. We used a manipulative field experiment with an annual C₄ grass in a forest understory to differentially track its living root vs litter inputs into the soil and to assess net SOC formation over multiple years. We show that living root inputs are 2–13 times more efficient than litter inputs in forming both slow‐cycling, mineral‐associated SOC as well as fast‐cycling, particulate organic C. Furthermore, we demonstrate that living root inputs are more efficiently anabolized by the soil microbial community en route to the mineral‐associated SOC pool (dubbed ‘the in vivo microbial turnover pathway’). Overall, our findings provide support for the primacy of living root inputs in forming SOC. However, we also highlight the possibility of nonadditive effects of living root and litter inputs, which may deplete SOC pools despite greater SOC formation rates.

Soil carbon sequestration accelerated by restoration of grassland biodiversity.

Abstract: Agriculturally degraded and abandoned lands can remove atmospheric CO2 and sequester it as soil organic matter during natural succession. However, this process may be slow, requiring a century or longer to re-attain pre-agricultural soil carbon levels. Here, we find that restoration of late-successional grassland plant diversity leads to accelerating annual carbon storage rates that, by the second period (years 13-22), are 200% greater in our highest diversity treatment than during succession at this site, and 70% greater than in monocultures. The higher soil carbon storage rates of the second period (years 13-22) are associated with the greater aboveground production and root biomass of this period, and with the presence of multiple species, especially C4 grasses and legumes. Our results suggest that restoration of high plant diversity may greatly increase carbon capture and storage rates on degraded and abandoned agricultural lands.

The ratio of Gram-positive to Gram-negative bacterial PLFA markers as an indicator of carbon availability in organic soils

Abstract: Despite recent progress in understanding soil microbial responses to carbon (C) limitation, the functional shifts in microbial community structure associated with decreasing soil C availability and changes in organic matter chemistry remain poorly known. It has been proposed that Gram-negative (GN) bacteria use more plant-derived C sources that are relatively labile, while Gram-positive (GP) bacteria use C sources derived from soil organic matter that are more recalcitrant. Because these two groups may differ in how they influence the fate of different C forms in soils, it is important to understand how they vary across ecosystems that differ in their vegetation cover and ecosystem productivity or across environmental gradients. In this study, we used a 19-year plant functional group removal experiment across a long term post-fire chronosequence to assess how microbial community structure (assessed using phospholipids fatty acids; PLFAs) and the association of bacterial functional groups (specifically, the GP:GN ratio) responded to changes in organic matter chemistry (measured via nuclear magnetic resonance; NMR). We found that the GP:GN ratio increased upon removal of shrubs and tree roots and with decreasing ecosystem productivity along the chronosequence, thus showing the greater dependence of GN than GP bacteria on more labile plant-derived C. Overall, GN bacteria were associated with simple C compounds (alkyls) whereas GP bacteria were more strongly associated with more complex C forms (carbonyls). Therefore, we conclude that the GP:GN ratio has potential as a useful indicator of the relative C availability for soil bacterial communities in organic soils, and can be used as a coarse indicator of energy limitation in natural ecosystems.

Large loss of CO2 in winter observed across the northern permafrost region

Abstract: Recent warming in the Arctic, which has been amplified during the winter1–3, greatly enhances microbial decomposition of soil organic matter and subsequent release of carbon dioxide (CO2)4. However, the amount of CO2 released in winter is not known and has not been well represented by ecosystem models or empirically based estimates5,6. Here we synthesize regional in situ observations of CO2 flux from Arctic and boreal soils to assess current and future winter carbon losses from the northern permafrost domain. We estimate a contemporary loss of 1,662 TgC per year from the permafrost region during the winter season (October–April). This loss is greater than the average growing season carbon uptake for this region estimated from process models (−1,032 TgC per year). Extending model predictions to warmer conditions up to 2100 indicates that winter CO2 emissions will increase 17% under a moderate mitigation scenario—Representative Concentration Pathway 4.5—and 41% under business-as-usual emissions scenario—Representative Concentration Pathway 8.5. Our results provide a baseline for winter CO2 emissions from northern terrestrial regions and indicate that enhanced soil CO2 loss due to winter warming may offset growing season carbon uptake under future climatic conditions. Winter warming in the Arctic will increase the CO2 flux from soils. A pan-Arctic analysis shows a current loss of 1,662 TgC per year over the winter, exceeding estimated carbon uptake in the growing season; projections suggest a 17% increase under RCP 4.5 and a 41% increase under RCP 8.5 by 2100.

Manure acts as a better fertilizer for increasing crop yields than synthetic fertilizer does by improving soil fertility.

Abstract: Fertilization is an important management strategy for crop yields by mediating soil fertility. However, rare studies quantitatively assessed the interactions among fertilization, crop yields, and soil fertility. Here, data from a 25-year fertilization experiment in the humid subtropical region of Southern China were used to evaluate and quantify the effect of fertilization on crop yields via soil fertility. Seven treatments were chosen: CK (non-fertilizer); N (synthetic nitrogen); NP (synthetic N and phosphorus); NPK (synthetic N, P and potassium); NPKM1 (synthetic NPK with manure); 1.5NPKM1 (1.5 times of NPKM1); and M2 (manure alone). Overall, the crop yields of wheat and maize under manure (1.36–1.58 and 3.85-5.82 Mg ha−1) were higher than those under CK (0.34 and 0.25 Mg ha−1) and synthetic fertilized treatments (0.27–0.97 and 0.48–2.65 Mg ha−1), as the averaged of 1991–2015. Higher SOC stocks were found under the NPKM1, 1.5NPKM1, and M2 treatments with a pronounced increase in SOC over the first 10 years and stable over the last 15 years. By the boosted regression trees, manure, synthetic fertilizer and soil properties (SOC storage, soil pH, and soil nutrients) accounted for 39%, 21%, and 40% of the variation of the relative yield, respectively. Path analysis identified a network of inter-relations of manure, synthetic fertilizer, and soil properties in the relative yields. Compared to synthetic fertilized treatments, manure application strongly and positively affected the relative yield by increasing SOC storage, soil nutrients, and soil pH (path coefficients: 0.90, 0.88, and 0.76). These factors explained 72% of the crop yields' variance. These results suggest that manure application is a viable strategy for regulating crop yields due to its improvement in soil fertility.

Mycorrhizal Fungi as Mediators of Soil Organic Matter Dynamics

Abstract: Inhabiting the interface between plant roots and soil, mycorrhizal fungi play a unique but underappreciated role in soil organic matter (SOM) dynamics. Their hyphae provide an efficient mechanism f...

Regulation of priming effect by soil organic matter stability over a broad geographic scale.

Abstract: The modification of soil organic matter (SOM) decomposition by plant carbon (C) input (priming effect) represents a critical biogeochemical process that controls soil C dynamics. However, the patterns and drivers of the priming effect remain hidden, especially over broad geographic scales under various climate and soil conditions. By combining systematic field and laboratory analyses based on multiple analytical and statistical approaches, we explore the determinants of priming intensity along a 2200 km grassland transect on the Tibetan Plateau. Our results show that SOM stability characterized by chemical recalcitrance and physico-chemical protection explains more variance in the priming effect than plant, soil and microbial properties. High priming intensity (up to 137% of basal respiration) is associated with complex SOM chemical structures and low mineral-organic associations. The dependence of priming effect on SOM stabilization mechanisms should be considered in Earth System Models to accurately predict soil C dynamics under changing environments. Global soil carbon dynamics are regulated by the modification of soil organic matter (SOM) decomposition by plant carbon input (priming effect). Here, the authors collect soil data along a 2200 km grassland transect on the Tibetan Plateau and find that SOM stability is the major control on priming effect.

Effect of organic matter on phosphorus adsorption and desorption in a black soil from Northeast China

Abstract: Phosphorus (P) adsorption–desorption in soil is an important internal cycle related to soil fertility problems, as well as for determining the environmental fate of P. Soil organic matter (SOM) has been identified as an important factor affecting the adsorption–desorption of soil P through different mechanisms. In this study, humic acids were added to change the SOM content in black soil. Following an incubation period of 30 days, the changes in soil P adsorption–desorption capacity were studied. The results indicated that increased SOM led to increases in the soil available P and the P activation coefficient. All soil treatments fitted well with both Langmuir and Freundlich equations. The P adsorption and desorption characteristics were analyzed using the Langmuir equation as a local isotherm. The maximum adsorption capacity of P increased with the increase in SOM, but the P bonding energy and maximum buffering capacity first decreased, and then increased, with the lowest values obtained with a SOM content of 75.3 mg kg−1. Both the maximum desorption capacity of P and the ratio of soil P desorption showed a fluctuating trend, which were the greatest when the SOM content reached 75.3 g kg−1 in black soil, showing an improved ability to release P. Thus, the addition of organic matter could efficiently enhance P availability by reducing the strength of P adsorption and the maximum phosphate buffering capacity and increasing the desorption of P to some extent, with the greatest P availability obtained at a SOM content of 75.3 g kg−1.

Dynamics and transformations of micronutrients in agricultural soils as influenced by organic matter build-up: A review

Abstract: The dynamics and transformations of micronutrients (Zn, Cu, Fe, Mn, B and Mo) in soils, are governed by various factors like pH, EC, soil organic matter etc. Soil organic matter (SOM) is known to modify different physiochemical reactions that influence the available component of micronutrients. Soil organic matter favors reduced (lower redox potential) environment and enhances the accessibility of micronutrient cations in the soil. Also, SOM has direct and indirect impacts on nutrient transformations. Soil organic matter (SOM) also serves as source of soil organic carbon (SOC) comprising about 60% on a mass basis. Under reduced environment the addition of SOM increased complexed forms of micronutrients. Build-up of SOM in soil converts adsorbed fractions to more plant-accessible forms of micronutrients. Soil organic matter addition increases the water soluble and exchangeable forms of micronutrients in soil which further increase the uptake of micronutrients. High amount of SOM in soils assists the various reactions of micronutrients resulting in formation of more stable complexes of micronutrient. Soil organic matter binds more Zn, Cu, B and Mo compared to Fe and Mn because the former are less sensitive to redox changes. The accretion of organic matter near the soil surface increases transformations (towards adsorbed fractions) of Mn and Fe and possibly decreases the availability of Zn, Cu, B and Mo by causing their redistribution among other complex fractions.

The Effects of Mulch and Nitrogen Fertilizer on the Soil Environment of Crop Plants

Abstract: The demand for food is expected to significantly increase with continued population growth over the next 50 years, indicating that agricultural efficiency should be simultaneously stabilized and enhanced. Here, we discuss the effects of mulching and nitrogen (N) fertilizer on the soil environment and crop yield to inform food security. The use of mulch in agriculture provides many benefits to the soil by reducing evaporation, improving temperatures, adjusting the microbial biomass, maintaining the soil organic carbon balance, increasing nutrient cycling, promoting soil enzyme activity, enhancing soil aggregate stability and suppressing weed infestation. Nitrogen fertilization can markedly improve soil fertility and crop yield. However, nitrogen use efficiency (NUE) and the environment may be negatively affected by the improper application of N fertilizers. The improvement of NUE has been an important focus in field management for the more sustainable use of valuable N fertilizers. A better understanding of the interaction between N and mulch may improve NUE and crop yields. Inorganic mulches more efficiently alter the soil environment to enhance the NUE and crop yield, while organic mulching materials are more environmentally friendly and inexpensive. The selection of appropriate mulching materials should be combined with effective N management strategies, crop species, crop management practices and climatic conditions. In the future, precise nitrogen fertilizer management on farms and the development of relatively high-NUE and high-yielding crops will be highly feasible.

Soil C Sequestration as a Biological Negative Emission Strategy

Abstract: Soil carbon (C) sequestration in one of three main approaches to carbon dioxide removal and storage through management of terrestrial ecosystems. Soil C sequestration relies of the adoption of improved management practices that increase the amount of carbon stored as soil organic matter, primarily in cropland and grazing lands. These C sequestering practices act by increasing the rate of input of plant-derived residues to soils and/or by reducing the rates of turnover of organic C stocks already in the soil. In addition to carbon dioxide removal potential, increases in soil organic matter/soil C content are highly beneficial from the standpoint of soil health and soil fertility Practices to increase soil C stocks include well-known, proven techniques or “best management practices” (BMP) for building soil carbon. A second category includes what we refer to as frontier technologies for which significant technological and/or economic barriers exist today, but for which further R&D and/or economic incentives might offer the potential for greater sequestration over the longer term. We reviewed published estimates of global soil carbon sequestration potential, representing the biophysical potential for managed cropland and/or grassland systems to store additional carbon assuming widespread (near complete) adoption of BMPs. The majority of studies suggests that 4 to 5 GtCO2/y as an upper limit for global biophysical potential with near complete adoption of BMPs. In the longer-term, if frontier technologies are successfully deployed, the global estimate might grow to 8 GtCO2/y. There is a strong scientific basis for managing agricultural soils to act as a significant carbon (C) sink over the next several decades. A two-stage strategy, to first incentivize adoption of well developed, conventional soil C sequestering practices, while investing in R&D on new frontier technologies that could come on-line in the next 2-3 decades, could maximize benefits. Implementation of such policies will require robust, scientifically-sound measurement, reporting, and verification (MRV) systems to track that policy goals are being met and that claimed increases in soil C stocks are real.

Remote Sensing Techniques for Soil Organic Carbon Estimation: A Review

Abstract: Towards the need for sustainable development, remote sensing (RS) techniques in the Visible-Near Infrared–Shortwave Infrared (VNIR–SWIR, 400–2500 nm) region could assist in a more direct, cost-effective and rapid manner to estimate important indicators for soil monitoring purposes. Soil reflectance spectroscopy has been applied in various domains apart from laboratory conditions, e.g., sensors mounted on satellites, aircrafts and Unmanned Aerial Systems. The aim of this review is to illustrate the research made for soil organic carbon estimation, with the use of RS techniques, reporting the methodology and results of each study. It also aims to provide a comprehensive introduction in soil spectroscopy for those who are less conversant with the subject. In total, 28 journal articles were selected and further analysed. It was observed that prediction accuracy reduces from Unmanned Aerial Systems (UASs) to satellite platforms, though advances in machine learning techniques could further assist in the generation of better calibration models. There are some challenges concerning atmospheric, radiometric and geometric corrections, vegetation cover, soil moisture and roughness that still need to be addressed. The advantages and disadvantages of each approach are highlighted and future considerations are also discussed at the end.

Role of Nutrient-Enriched Biochar as a Soil Amendment during Maize Growth: Exploring Practical Alternatives to Recycle Agricultural Residuals and to Reduce Chemical Fertilizer Demand

Abstract: Recycling and value-added utilization of agricultural residues through combining technologies such as anaerobic digestion and pyrolysis could double the recoverable energy, close the nutrient recycle loop, and ensure cleaner agricultural production. This study assessed the beneficial application of biochar to soil to recycle digestate nutrients, improve soil quality, and reduce conventional chemical fertilizer. The addition of digestate-enriched biochar improved soil quality as it provided higher soil organic matter (232%–514%) and macronutrients (110%–230%) as opposed to the unenriched biochar and control treatments. Maize grown in soil amended with digestate-enriched biochar showed a significantly higher biomass yield compared to the control and non-enriched biochar treatments but was slightly lower than yields from chemical fertilizer treatments. The slightly lower yield (20%–25%) achieved from digestate-enriched biochar was attributed to slower mineralization and release of the adsorbed nutrients in the short term. However, digestate-enriched biochar could in the long term become more beneficial in sustaining soil fertility through maintaining high soil organic matter and the gradual release of micronutrients compared to conventional chemical fertilizer. Positive effects on soil micronutrients, macronutrients, organic matter, and biomass yield indicates that enriched biochar could partly replace chemical fertilizers and promote organic farming in a circular economy concept.

Plant Nutrition And Soil Fertility Manual

Abstract: Section I Introduction Management Requirements Productivity Factors Climatic Factors Moving Up the Yield Scale Product Quality Soil Fertility Principles Fertile Soil Defined Making and Keeping a Soil "Fertile" Biological Factors An "Ideal Soil" Soil Fertility Management Concepts Multiple Factor Yield Influence Soil Condition Related to Deficiency in a Major Element and Micronutrient Elemental Content of the Soil and Soil Solution Plant Nutrition Principles Photosynthesis The Function of Plants Determination of Essentiality Essential Element Content in Plants Classification of the Thirteen Essential Mineral Elements Role of the Essential Plant Nutrient Elements Plant Nutrient Element Sources Element Absorption and Translocation Elemental Accumulation Element Absorption and Plant Genetics Diagnostic Plant Symptoms of Essential Plant Nutrient Element Insufficiencies The Plant Root Introduction Root Function Root Hairs Lateral Roots The Rhizosphere Root Ion Absorption Root Crops How to be a Diagnostician The Diagnostic Approach Being a Diagnostician Diagnostic Factors Evaluating Diagnostic Procedures Scouting Weather Conditions Factors Affecting Essential Nutrient Element Concentrations in Plants Plant (Crop) Wilting Summary Certified Crop Advisor Programs Section II: Physical and Physiochemical Characteristics of Soil Soil Taxonomy, Horizontal Characteristics, and Clay Minerals Soil Orders (U.S. System of Soil Taxonomy) Designations for Soil Horizons and Layers Physical Properties of Soils Textural Classification Soil Separates or Primary Soil Separates Soil Separate Properties Soil Texture Characterization Definitions Soil Structure Tillage Practices Water-Holding Capacity Physiochemical Properties of Soil Soil Separate Properties Major Phyllosilicate Minerals in Soils Cation Exchange Capacity (CEC) of a Soil Based on Texture Cation Exchange Capacity (CEC) Determination of a Soil Anion Exchange Capacity Soil pH: Its Determination and Interpretation Definitions Causes of Soil Acidity Water pH Determination of Mineral Soil, Organic Soil, and Organic Soilless Rooting Media pH Determination using a Calibrated pH Meter Other Soil pH Determination Procedure Salt pH Determination for a Mineral Soil pH Interpretation: Mineral Soil pH Interpretation: Organic Soils pH Interpretation: Organic Soilless Medium Soil pH Constancy Plant Root Function Soil Acidity and NPK Fertilizer Efficiency Soil pH Effect on Elemental Availability and/or Soil Solution Composition Soil Buffer pH pH Determination of Water Soil Organic Matter Definitions of Soil Organic Matter and Its Components Humus Soil Organic Matter Characteristics Methods of Soil Organic Matter Determination Management Requirements for High Organic Matter Content Soils Adverse Affects of Organic Matter Additions Section III: Plant Elemental Requirements and Associated Elements Major Essential Plant Elements Terminology Methods of Expression Established Date for Essentiality/Researchers Carbon, Hydrogen, and Oxygen Major Essential Element Properties Micronutrients Considered Essential to Plants Terminology Established Date for Essentiality/Researchers Content and Function Soil and Plant Species Associations Micronutrient Characteristics Micronutrient Properties Possible Additional Essential Micronutrients Elements Considered Beneficial to Plants The A to Z Nutrient Solution Elements Essential for Animals Basis for Essentiality for Beneficial Elements Potential Essential Elements "New" Beneficial Elements Element Substitution Form of Response Summary Elements Considered Toxic to Plants Introduction The Nature of Elemental Toxicity Aluminum and Copper Toxicity Other Elements Plant Species Factor The Heavy Metals Trace Elements Found in Plants Definition Elements Categorized as Trace Elements High Soil Content Elements Availability Factors Accumulator Plants and Elements Symbiotic Element Section IV: Methods of Soil Fertility and Plant Nutrition Assessment Soil Testing Purposes Field Sampling Soil Laboratory Selection Laboratory Soil Testing Procedures Interpretation of a Soil Test Result Soil Test Result Tracking (Monitoring) Liming and Fertilizer Use Strategies Plant Analysis and Tissue Testing Plant Analysis Objectives Sequence of Procedures Sampling Techniques Plant Tissue Handling, Preparation, and Analysis Methods of Interpretation Word Classification of Elemental Concentrations As a Diagnostic Technique Experience Required Data Logging/Tracking of Plant Analyses Utilization of Plant Analyses for Nutrient Element Management Tissue Testing Indirect Evaluation Procedures Section V: Amendments for Soil Fertility Maintenance Lime and Liming Materials Liming Terms Liming Materials Liming Materials and Their Calcium Carbonate Equivalent (CCE) Mesh Size Quality Factor Designation Lime Requirement (LR) Soil Test Ratio of Ca to Mg Determines Form of Limestone to Apply Liming Rate Determined by Acidifying Effect of Fertilizer "Lime Shock" Lime Incorporation Depth of Incorporation Subsoil pH Inorganic Chemical Fertilizers and Their Properties Definitions Fertilizer Terminology Characteristics of the Major Elements as Fertilizer Conversion Factors for the Major Essential Fertilizer Elements Characteristics of the Micronutrients as Fertilizer The Physical and Chemical Properties of Fertilizers Naturally Occurring Inorganic Fertilizers Organic Fertilizers and Their Properties Value Composted Animal Manures Animal Manure Major Element Composition Other Organic Materials Soil and Plant Factors Fertilizer Placement Objectives Methods of Fertilizer Placement Soil Water, Irrigation, and Water Quality Soil Water Terminology Soil Factors Affecting Soil Water-Holding Capacity and Movement Drainage Irrigation Methods Irrigation Water Quality Water Treatment Procedures What is Water? Section VI: Methods of Soilless Plant Production Hydroponics Hydroponics Defined Historical Events Hydroponic Techniques Hydroponic Growing Systems Rooting Media Water Quality The Nutrient Solution Reagents and Nutrient Solution Formulations Concentration Range and Ratios pH Interpretation-Hydroponic Nutrient Solution Reconstitution of the Nutrient Solution Accumulation of Nutrient Elements and Precipitates Soilless Rooting and/or Growing Media Soilless Media Ingredients Soilless Media Formulations Physical Properties Physiochemical Properties Control of pH Use Formulations Bag Culture Systems "Fertility" Determination Procedure for an Organic Soilless Mix Section VII: Miscellaneous Organic Farming/Gardening Chemicalization of Crop Production "Organically Grown" Defined Suitable Inorganic Fertilizer Materials Suitable Organic Fertilizers Organic Soil Fertility Management Soil Physical Properties Food Safety and Quality Issues Weather and Climatic Conditions Definitions Climatic Factors Weather as a Diagnostic Factor Best Management Practices (BMPs) Origin Best Management Practice Application Broadened Best Practice Important Protocol Considerations Precision Farming Section Appendices Glossary Formulation and Use of Soil Extraction Reagents Preparation Procedures and Elemental Content Determination for Plant Tissue Weights and Measures Reference Books and Texts References Index

Uncovering trophic positions and food resources of soil animals using bulk natural stable isotope composition.

Abstract: Despite the major importance of soil biota in nutrient and energy fluxes, interactions in soil food webs are poorly understood. Here we provide an overview of recent advances in uncovering the trophic structure of soil food webs using natural variations in stable isotope ratios. We discuss approaches of application, normalization and interpretation of stable isotope ratios along with methodological pitfalls. Analysis of published data from temperate forest ecosystems is used to outline emerging concepts and perspectives in soil food web research. In contrast to aboveground and aquatic food webs, trophic fractionation at the basal level of detrital food webs is large for carbon and small for nitrogen stable isotopes. Virtually all soil animals are enriched in 13 C as compared to plant litter. This 'detrital shift' likely reflects preferential uptake of 13 C-enriched microbial biomass and underlines the importance of microorganisms, in contrast to dead plant material, as a major food resource for the soil animal community. Soil organic matter is enriched in 15 N and 13 C relative to leaf litter. Decomposers inhabiting mineral soil layers therefore might be enriched in 15 N resulting in overlap in isotope ratios between soil-dwelling detritivores and litter-dwelling predators. By contrast, 13 C content varies little between detritivores in upper litter and in mineral soil, suggesting that they rely on similar basal resources, i.e. little decomposed organic matter. Comparing vertical isotope gradients in animals and in basal resources can be a valuable tool to assess trophic interactions and dynamics of organic matter in soil. As indicated by stable isotope composition, direct feeding on living plant material as well as on mycorrhizal fungi is likely rare among soil invertebrates. Plant carbon is taken up predominantly by saprotrophic microorganisms and channelled to higher trophic levels of the soil food web. However, feeding on photoautotrophic microorganisms and non-vascular plants may play an important role in fuelling soil food webs. The trophic niche of most high-rank animal taxa spans at least two trophic levels, implying the use of a wide range of resources. Therefore, to identify trophic species and links in food webs, low-rank taxonomic identification is required. Despite overlap in feeding strategies, stable isotope composition of the high-rank taxonomic groups reflects differences in trophic level and in the use of basal resources. Different taxonomic groups of predators and decomposers are likely linked to different pools of organic matter in soil, suggesting different functional roles and indicating that trophic niches in soil animal communities are phylogenetically structured. During last two decades studies using stable isotope analysis have elucidated the trophic structure of soil communities, clarified basal food resources of the soil food web and revealed links between above- and belowground ecosystem compartments. Extending the use of stable isotope analysis to a wider range of soil-dwelling organisms, including microfauna, and a larger array of ecosystems provides the perspective of a comprehensive understanding of the structure and functioning of soil food webs.

Crop Residue Management Challenges: A Special Issue Overview

Abstract: The amount of crop residues that can be sustainability removed is highly variable and is a function of many factors including the soil, climatic, and plant characteristics. For example, leaving an insufficient amount of crop residue on the soil surface can be detrimental for soil quality, result in loss of soil organic matter (SOM), and increase soil erosion, whereas leaving excessive amounts can impair soil-seed contact, immobilize N, and/or keep soils cool and wet. This special issue evolved as an outcome of, “Crop Residues for Advanced Biofuels: Effects on Soil Carbon” workshop held in Sacramento, CA, in 2017. The goal of the special issue is to provide a forum for identifying knowledge gaps associated with crop residue management and to expand the discussion from a regional Midwestern U.S. to a global perspective. Several crop residue experiments as well as simulation modeling studies are included to examine effects of tillage, crop rotation, livestock grazing, and cover crops on greenhouse gas (GHG) emissions, crop yield, and soil or plant health. The special issue is divided into 4 sections that include (i) Estimating Crop Residue Removal and Modeling; (ii) Cultural Practice Impact on Soil Health; (iii) Residue Removal Impact on Soil and Plant Health; and (iv) Cultural Practice Impact on Carbon Storage and Greenhouse Gas Emissions.

Global ecological predictors of the soil priming effect

Abstract: Identifying the global drivers of soil priming is essential to understanding C cycling in terrestrial ecosystems. We conducted a survey of soils across 86 globally-distributed locations, spanning a wide range of climates, biotic communities, and soil conditions, and evaluated the apparent soil priming effect using 13C-glucose labeling. Here we show that the magnitude of the positive apparent priming effect (increase in CO2 release through accelerated microbial biomass turnover) was negatively associated with SOC content and microbial respiration rates. Our statistical modeling suggests that apparent priming effects tend to be negative in more mesic sites associated with higher SOC contents. In contrast, a single-input of labile C causes positive apparent priming effects in more arid locations with low SOC contents. Our results provide solid evidence that SOC content plays a critical role in regulating apparent priming effects, with important implications for the improvement of C cycling models under global change scenarios.

Managing for soil carbon sequestration: Let's get realistic.

Abstract: Improved soil management is increasingly pursued to ensure food security for the world's rising global population, with the ancillary benefit of storing carbon in soils to lower the threat of climate change. While all increments to soil organic matter are laudable, we suggest caution in ascribing large, potential climate change mitigation to enhanced soil management. We find that the most promising techniques, including applications of biochar and enhanced silicate weathering, collectively are not likely to balance more than 5% of annual emissions of CO2 from fossil fuel combustion.