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Global carbon storage in soils is widely discussed today because of climate uncertainty and maintaining sustainable agricultural production. Human intervention in agricultural or energy production poses many changes in soil management, which highly affects soil quality/health. Permanent grasslands fulfil a wide range of ecosystem functions and have a high potential for increasing arable land. Today, grasslands are becoming more and more intensively used, fertilized and disturbed. Optimizing their management is essential to maintain a resilient and stable ecosystem. The produced biomass is used as a forage or for energy production. We aimed at the impact of long-term grassland liming on the total content of soil organic carbon (SOC), humic substances (CHS), and microbial biomass (Cmic). Furthermore, soil reaction and available nutrient content were evaluated. Soil samples were collected from a split-plot field experiment at Mendel University in Brno (locality Kameničky). The soil was classified as Dystric Planosol Siltic, medium textured, strongly acidic, with high soil organic carbon content. The yearly liming rate was 1.4 t/ha CaO. The linkage between the soil pH, SOC, Cmic, and available nutrient content was evaluated by the multivariate exploratory techniques and regression models. Results showed that long-term liming affects both soil biota and carbon storage. [ABSTRACT FROM AUTHOR]

Soil organic carbon (SOC) forms the largest terrestrial organic carbon (C) pool, which is regulated by complex connections between exogenous C input, microbial activity, and SOC conversion. Few studies have examined the changes in natural abundance C due to microbial activity after exogenous C inputs in karst lime soils in China. In this research, the 13C isotope tracer technique was employed to investigate the priming effect of SOC on typical lime soil (0~20 cm) of 13C_litter and 13C_calcium carbonate (CaCO3) through a mineralization incubation experiment. Samples were collected at 5, 10, 20, 40, 60, and 80 days of incubation and analyzed for SOC mineralization, SOC distribution across fractions (>250 μm, 53~250 μm, and <53 μm), and soil microbial diversity. A control consisting of no exogenous C addition was included. SOC mineralization and SOC priming were considerably higher (15.48% and 61.00%, respectively) after litter addition compared to CaCO3. The addition of either litter or CaCO3 reduced the total organic C (TOC) and macroaggregate (>250 μm) and microaggregate (53~250 μm) C fractions by 2150.13, 2229.06, and 1575.06 mg C kg−1 Cbulk on average and increased the mineral particulate C fraction (<53 μm) by 1653.98 mg C kg−1 Cbulk. As the incubation time extended, a significantly positive correlation was apparent between SOC priming and soil fungal diversity, as well as between the mineral particulate C fraction and soil bacterial diversity. The effect of soil fungal diversity on SOC priming (R = 0.40, p = 0.003) significantly exceeded that of bacterial diversity on SOC sequestration (R = 0.27, p = 0.02). Our results reveal that after adding litter or CaCO3, soil fungi stimulate SOC mineralization and decomposition and soil bacteria enhance SOC sequestration, with the effects of fungi being more pronounced. These findings can provide a theoretical basis for understanding C sequestration and emission reduction in karst lime soils. [ABSTRACT FROM AUTHOR]

Forest liming is a management tool that has and continues to be used extensively across northern Europe to counteract acidification processes from anthropogenic sulfur and nitrogen (N) deposition. In this study, we quantified how liming affects soil organic carbon (SOC) stocks and attempt to disentangle the mechanisms responsible for the often contrasting processes that regulate net soil carbon (C) fluxes. Using a paired plot experimental design we compared SOC stocks in limed plots with adjacent unlimed control plots at 28 experimental sites to 60 cm soil depth in mature broadleaf and coniferous forests across Germany. Historical soil data from a subset of the paired experiment plots were analyzed to assess how SOC stocks in both control and limed plots changed between 1990 and 2019. Overall, we found that forest floor C stocks have been accumulating over time in the control plots. Liming however largely offset organic layer buildup in the L/O f layer, and forest floor C stocks remained unchanged over time in the limed plots. This, in turn, meant that nutrients remained mobile and were not bound in soil organic matter complexes. Results from the paired plot analysis showed that forest floor C stocks were significantly lower in limed plots than the control (- 34 %, - 8.4 ± 1.7 MgCha-1) but did not significantly affect SOC stocks in the mineral soil, when all sites are pooled together. In the forest floor layers, SOC stocks exhibited an exponential decrease with increasing pH, highlighting how lime-induced improvements in the biochemical environment stimulate organic matter (OM) decomposition. Nevertheless, for both forest floor and mineral soils, the magnitude and direction of the belowground C changes hinged directly on the inherent site characteristics, namely, forest type (conifer versus broadleaf), soil pH, soil texture, and the soil SOC stocks. On the other hand, SOC stock decreases were often offset by other processes that fostered C accumulation, such as improved forest productivity or increased carbon stabilization, which correspondingly translated to an overall variable response by SOC stocks, particularly in the mineral soil. Lastly, we measured soil carbon dioxide (CO2) and soil methane (CH4) flux immediately after a re-liming event at three of the experimental sites. Here, we found that (1) liming doubles CH4 uptake in the long-term; (2) soil organic matter mineralization processes respond quickly to liming, even though the duration and size of the CO2 flush varied between sites; and (3) lime-derived CO2 contributed very little to total CO2 emissions over the measurement period (determined using stable isotope approaches). [ABSTRACT FROM AUTHOR]

Association of organic carbon (C) with iron (Fe) minerals is one important mechanism for long‐term terrestrial C storage. Yet, specific edaphic variables that directly contribute to Fe‐associated C across diverse soil types are still unclear. Through analyzing soils from the National Ecological Observatory Network (NEON) and other published data, here we show that soil pH primarily controls Fe‐associated C across the globe. Fe‐associated C in most soils ranged from 0 to 20 g kg−1 soil, with a strong increase from pH 4.2 to 3.5, but a small change in soils with pH > 4.2. A microcosm experiment further showed that raising soil pH by liming reduced the formation of Fe‐associated C in an acidic Oxisol. Together, these findings demonstrate the dominant role of soil pH in controlling the abundance of Fe‐associated C. Key Points: Soil pH, rather than reactive iron content, is a primary control on concentration of iron‐associated carbon at the global scaleNeither soil orders nor vegetation types have significant relationships with concentration of iron‐associated carbonIron‐associated carbon represents a relatively small fraction of total soil organic carbon globally [ABSTRACT FROM AUTHOR]

• Silicate-containing amendments increased calcium and available silicate contents. • Silicate-containing amendments moderately increased soil fertility. • Silicate and lime co-application increased the relative change in soil fertility. • Long-term application of silicate and lime reduced C stratification. • Carbon stocks reduced in lime and silicate amended soils. Most agricultural soils are unproductive due to soil acidity which limits crop growth and yield. To ameliorate soil acidity constraints and enhance the ecosystem services the soil renders to achieve optimum crop yields, lime, and silicate are mostly used. However, there are few studies reporting the impacts of the combined application of silicate and lime on soil properties, soil fertility and carbon stocks and stratification in long-term experiments. This study evaluated the impacts of the combined application of silicate and lime on soil fertility indicators (pH, soil organic matter (SOM), available phosphorus, exchangeable potassium, magnesium, and calcium, and available SiO 2), carbon stratification and stocks in comparison to sole lime and sole silicate applied to a Fluvaquentic Eutrudepts over a 67-year period. Each treatment's rate of application was calculated to raise the soil pH to 6.5. Incorporation of the treatments increased the soil pH by 1.30, 1.22, and 1.35 folds in the sole silicate, sole lime, and combined silicate and lime-treated soils, respectively, relative to the baseline soil pH (5.5). The combined application of silicate and lime resulted in significant decreases in C stratification and C stocks. The significant reduction in the C stocks in the silicate and lime-treated soils implies that its long-term application could potentially reduce carbon sequestration and increase the carbon footprint of rice cultivation. This information is crucial to develop sustainable soil management interventions to curtail the environmental footprint in rice paddy ecosystems. Comparatively, the combined silicate and lime treatment caused an increase in the relative change of soil fertility by 65.7% and the average annual growth rate in the soil fertility improvement by 0.0115, as compared to the untreated soil. Among the soil variables, soil pH, exchangeable calcium, and available silicate contributed most to the variation the soil fertility. The obtained results could serve as a guide in revising the lime and silicate fertilization programs instituted by the Korean Government and reviewing national soil fertility management systems in temperate paddy ecosystems. [ABSTRACT FROM AUTHOR]

Lime application is the most common method to improve crop production in acid soils and has been shown to change soil organic C content. However, the impact of liming history on the priming effect on soil organic C is not well understood. This study examined the effect of liming history on C priming in response to the addition of crop residues of different qualities. Soils with pH ranging from 4.7 to 7.4 were collected from two adjacent field experiments whereby lime was applied at different rates, 6 and 35 years ago. A 90-day incubation study was conducted by applying C-labelled wheat (C/N 42) and field-pea (C/N 29) residues at a rate of 5 g kg soil. Residue application to soils yielded the positive priming effect in all pH levels with the magnitude of C priming being the greatest at initial soil pH 6.6. In comparison, the optimal pH for residue decomposition (7.3) was higher than that for priming. The overall priming effect was about 17% greater with field-pea than wheat residue. However, cumulative decomposition of added field-pea residue was 15% lower than that of wheat residue. Furthermore, C priming was greater in soils from the 35-year-old than the 6-year-old limed plots, indicating that a longer history of liming did not enhance the protection of indigenous C from mineralization. The results suggest that increases in soil pH by liming enhanced native C priming through greater microbial biomass and activity and that the magnitude and dynamics of the priming effect largely depended on residue quality and its consequent nutrient supply to decomposer organisms. The study implies that over-liming would likely have negative impacts on the long-term C sequestration. [ABSTRACT FROM AUTHOR]

Limited information is available on the C stabilization mechanism of tropical soils under different management practices including long-term organic manuring, mineral fertilization alone, or in combination with lime. Hence, to understand the effect of continuous application (for 60 years) of organic manure, fertilizer, and lime alone or in combination on an acidic Alfisol, stabilization of soil organic carbon (SOC) was evaluated under maize (Zea mays L.) wheat (Triticum aestivum L.) cropping. There were eight treatments that included farmyard manure (FYM) and nitrogen (N) applied in terms of FYM, additional dose of phosphorus (P) and potassium (K) applied in terms of inorganic fertilizer (FYM + P'K'), FYM + P'K' with liming (FYM + P'K' + L) and NPK alone. These treatments were laid in a randomized block design with three replications. Results indicated that FYM + P'K' plots had maximum amount of SOC inside large macroaggregates. The value was 33 and 92% greater than only minerally fertilized (NPK) and unfertilized control plots, respectively, whereas microaggregate-associated C was highest in plots with FYM + P'K' and lime (FYM + P'K' + L), which was 48 and 183% more than unfertilized control and NPK plots, respectively. Inside soil microaggregates, plots under FYM + P'K' had highest labile C, while NPK + L plots had highest recalcitrant C. Plots with organic amendments contained higher glomalin in large macroaggregates. Plots treated with FYM + P'K' had maximum intra-aggregate particulate organic matter within microaggregates inside macroaggregates (iPOM_mM), which was 28 and 74% higher than NPK and unfertilized control plots, respectively. Total C stock inside the protected microaggregates within macroaggregates was maximum for FYM + P'K' plots. It had 38, 67, and 171% higher C stock than NPK, FYM, and unfertilized control plots, respectively. Interestingly, despite estimated C input in FYM-treated plots was much higher than NPK plots, FYM-treated plots had less C stabilization within microaggregates and within microaggregates inside macroaggregates. Microaggregates within macroaggregates accounted for ~54% of the recalcitrant C content. Thus, macroaggregates stabilization through occlusion of microaggregates was accountable for sequestration of SOC and only FYM application did not promote that mechanism compared to NPK. Carbon stabilization within macroaggregates under FYM plots was mainly governed by amorphous iron oxide. [ABSTRACT FROM AUTHOR]

This study used two field trials with 5 and 34 years of liming histories, respectively, and aimed to elucidate the long-term effect of liming on soil organic C (SOC) in acid soils. It was hypothesized that long-term liming would increase SOC concentration, macro-aggregate stability and SOC concentration within aggregates. Surface soils (0-10 cm) were sampled and separated into four aggregate-size classes: large macro-aggregates (>2 mm), small macro-aggregates (0.25-2 mm), micro-aggregates (0.053-0.25 mm) and silt and clay fraction (<0.053 mm) by wet sieving, and the SOC concentration of each aggregate-size was quantified. Liming decreased SOC in the bulk soil and in aggregates as well as macro-aggregate stability in the low-input and cultivated 34-year-old trial. In contrast, liming did not significantly change the concentration of SOC in the bulk soil or in aggregates but improved macro-aggregate stability in the 5-year-old trial under undisturbed unimproved pastures. Furthermore, the single application of lime to the surface soil increased pH in both topsoil (0-10 cm) and subsurface soil (10-20 cm) and increased KSO-extractable C, microbial biomass C (C) and basal respiration (CO) in both soil layers of both lime trials. Liming increased the percentage of SOC present as microbial biomass C (C/C) and decreased the respiration rate per unit biomass (qCO). The study concludes that despite long-term liming decreased total SOC in the low-input systems, it increased labile C pools and the percentage of SOC present as microbial biomass C. [ABSTRACT FROM AUTHOR]

Liming is a common agricultural practice worldwide, used for increasing productivity in acid agricultural soils. Liming reduces Al saturation and toxicity and/or increases pH up to values where the availability of nutrients is higher. The effect of this practice on soil properties has been extensively studied, with focus of most studies upon pH, exchangeable cations and productivity. In turn, the effects of liming on soil organic C (SOC) stocks still remain poorly known. The net effect on SOC can be the result of several factors: first, liming increases the soil biological activity, thus favoring the mineralization of organic matter, which should result in CO 2 losses and a decrease of the SOC stocks. Second, liming ameliorates soil structure, increasing the stability of clay assemblages and clay-organic matter bonds, which should bring an increase in SOC physical and physicochemical protection. Finally, as liming ameliorates soil conditions to plant growth, plant productivity increases and also the return of C inputs to soil, thus potentially increasing SOC concentrations. The net effect of these processes is not well understood yet. Still, some overall trends can be deduced from data currently available in the literature. Liming does modify SOC stocks, increasing them in most cases, what seems to be caused by higher C inputs to limed soils due to increased productivity. Reductions in SOC have also been reported, probably in connexion with increased mineralization, whereas the role of improved soil structure remains unclear. Overall, these insights are deduced from published data which are still scarce, so we encourage the scientific community to synthesize unpublished SOC data from existing in situ experiments, in order to enlarge the span of experimental conditions and gain knowledge about the role of such a widespread agricultural practice on SOC stocks. [ABSTRACT FROM AUTHOR]

Agroforestry systems have been recognized as a potential greenhouse gas mitigation strategy under the Kyoto Protocol because of their ability to absorb carbon dioxide from the atmosphere and store carbon mainly in the soil. Soil particle size and land management practices are known to have a considerable influence on carbon storage in soils. This study evaluated changes in soil chemical and physical properties, and quantified and compared the amount of C stored in the bulk soil and in three different soil fractions (250–2000, 53–250 and <53 μm) at each of four soil depths (0–25, 25–50, 50–75 and 75–100 cm) in a silvopastoral system located on an acidic forest soil under Pinus radiata D. Don. Areas of this system were subjected ten years ago to one of nine fertilization treatments: three different doses of sewage sludge or no fertilization, all with or without the addition of lime, and mineral fertilizer with no liming. Seventeen years after reforestation and seven years after canopy closure, strong gradients with soil depth were found regarding soil bulk density, pH and carbon storage. Intense soil management (high doses of sewage sludge and liming) generally reduced soil carbon storage, mainly in coarse aggregates, but this could be compensated by the increase in tree and pasture development observed in soils subject to intermediate sewage sludge doses. [ABSTRACT FROM AUTHOR]

Abstract: The stabilisation of soil organic matter (SOM) is the result of the simultaneous action of three mechanisms: chemical stabilisation, biochemical stabilisation and physical protection. The objectives of this study were (i) to evaluate carbon-protection mechanisms in different SOM pools in soil aggregates and (ii) to identify the association of Ca2+ with total organic carbon (TOC) under the influence of surface liming in a medium-textured Oxisol in a long-term experiment under no-till system (NTS) in southern Brazil (25° 10′ S, 50° 05′ W). The treatments consisted of application of zero or 6tons ha−1 of dolomitic lime on the soil surface in 1993 and a reapplication of zero or 3tons ha−1 of dolomitic lime in 2000 to plots with or without previous lime application. Soil samples collected at depths of 0–2.5, 2.5–5, 5–10 and 10–20cm were separated into seven aggregate classes. In each of these classes, TOC, particulate organic carbon (POC) and mineral-associated organic carbon (MAOC) were analysed. The 8–19mm sized aggregates from the 0–2.5cm layer were assessed by energy-dispersive X-ray spectroscopy (EDS) for the elemental analysis of carbon (C) and calcium (Ca). The liming caused an accumulation of TOC in the aggregates, mainly at a depth of 0–2.5cm. The aggregates from soils treated with lime had a higher mean weight diameter (MWD) that resulted in the accumulation of TOC, especially in the 8–19mm aggregate class, that was linear and closely related with C input (R2 =0.99). The proportion of large aggregates in the treatments with lime was closely correlated with the TOC content of the whole sample. The largest dose of lime (9tons ha−1) resulted in higher TOC, POC and MAOC values, mainly in the 8–19mm aggregate class. The elemental analyses for C and Ca revealed similar spectra between them for the surface-liming treatments in the clay fraction found in the centres of the 8–19mm aggregates. The surface application of lime to NT fields provided greater stability and protection of the intra-aggregate C, presumably due to Ca2+ acting as a cationic bridge between OC and the kaolinite in the clay fraction. [Copyright &y& Elsevier]

The suitability of pH buffer methods that determine lime requirement (L.R.) of acid soils of the eastern region of Botswana has not been determined, and the soil physiochemical properties that influence L.R. are not known. As a result, a number of laboratory pH buffer methods for determining L.R. were evaluated by using acid soils from that region. The methods evaluated were the Yuan double buffer (Yuan–DB) method, Shoemaker, McLean, and Pratt double, and single buffer (SMP–DB and SMP–SB) methods, and the Adams, and Evans single buffer (AE–SB) method. The evaluation was based on the ability of the methods to predict the actual L.R. to pH 6.5 determined by the soil–CaCO3–moist–incubation (SCMI) method. The incubation, physiochemical properties, and L.R. by laboratory pH buffer methods were determined in triplicates. All the pH buffer methods were (P < 0.001) significantly correlated (0.79 < r < 0.94) with the SCMI method. The performance was in the order of Yuan–DB method > SMP–DB method > SMP–SB method > AE–SB. However, the SMP–SB has been recommended for routine analysis of soils of eastern Botswana, because it is simple and rapid. The relationship between SCMI method actual L.R. and the physiochemical properties (0.55 < r < 0.71) reveals that the buffer capacity, organic carbon, exchangeable acidity, and extractable aluminum are the most important soil properties influencing L.R. of soils in eastern Botswana. [ABSTRACT FROM AUTHOR]

Investigates the lime-induced loss of soil organic carbon in New South Wales. Effect of the carbon loss to the aggregate stability of the soil; Increased aggregate stability in limed soils suggested formation of bonding involving calcium bridges.

Highlights: [•] Combining no-tillage with a Ca-amendment was the best practice in acid degraded soils. [•] In some cases tillage suppressed the positive effects of liming. [•] Carbon and glomalin-related soil proteins seem to play a role in the alleviation of Al toxicity. [Copyright &y& Elsevier]

Soil organic matter (SOM) has long been recognized as an important indicator of soil productivity. The SOM refers to the organic fraction of the soil exclusive of undecayed plant and animal residues. It plays a crucial role in maintaining sustainability of cropping systems by improving soil physical (texture, structure, bulk density, and water-holding capacity), chemical (nutrient availability, cation exchange capacity, reduced aluminum toxicity, and allelopathy), and biological (nitrogen mineralization bacteria, dinitrogen fixation, mycorrhizae fungi, and microbial biomass) properties. The preservation of SOM is crucial to ensure long-term sustainability of agricultural ecosystems. Improvement/preservation of soil organic matter can be achieved by adopting appropriate soil and crop management practices. These practices include conservation tillage, crop rotation, use of organic manures, increasing cropping intensity, use of adequate rate of chemical fertilizers, incorporation of crop residues, liming acidic soils, and keeping land under pasture. Organic matter can adsorb heavy metals in the soils, which reduce toxicity of these metals to plants and reduce their escape to ground water. Similarly, SOM also adsorbs herbicides, which may inhibit contamination of surface and ground water. Furthermore, SOM also functions as a sink to organic carbon and mitigates carbon dioxide (CO2) gas escape to the environment. Globally, soil organic matter contains about three times as much carbon as found in the world's vegetation. Hence, organic matter plays a critical role in the global carbon balance that is thought to be the major factor affecting global warming. Overall, adequate amounts of soil organic matter maintain soil quality, preserve sustainability of cropping systems, and reduce environmental pollution. [ABSTRACT FROM PUBLISHER]

Soil pH and the availability of carbon (C) substrate and nutrients to microorganisms are well recognized to influence C priming. However, the mechanisms underpinning such interplay so far remain elusive. Given that liming acid soils, residue retention and fertilization are common agricultural practices, small changes in SOC content by these practices could have a big impact on the global C budget. This study aimed to gain insight into the impact of initial pH and mineral N availability on the priming effect of two C substrates with contrasting biodegradability. Stable 13 C-labelled substrates, glucose and lignocellulose, were applied at the rate of 0.5 mg C g −1 soil with or without NH 4 NO 3 to the same soil matrix with three different initial pH levels; pH 4.1 (strongly acidic), 4.7 (moderately acidic) and 6.6 (slightly acidic). The N treatment was based on a C:N of 10 of the added substrate (0.05 mg N g −1 soil) to ensure N was non-limiting. Interestingly, the priming effect was not linearly related to soil pH; greatest at pH 4.1, followed by pH 6.6 and lowest at pH 4.7. The greater net increase in microbial biomass upon C supply in strongly acidic soils compared to the moderately and slightly acidic soils would have enhanced co-metabolic decomposition of native soil organic C (SOC). The cumulative amount of primed SOC during the 30-day incubation period was greater in glucose- (21 μg C g −1 ) than lignocellulose-amended soils (13 μg C g −1 ). Nitrogen application reduced the C priming effect of both C substrates at all pH levels. This reduction was more prominent with lignocellulose and in the moderately acidic soils. The results suggest that maintaining optimal soil pH for nutrient availability and N application that exceeds the microbial N requirements in agricultural fields may minimize SOC loss via the priming effect in the short term. [ABSTRACT FROM AUTHOR]

Purpose: Substituting chemical fertilizers with organic manure may alleviate soil acidification in vegetable fields, but the optimum organic manure substitution ratio (SR, the ratio of organic nitrogen (N) rate to total N application rate) may vary due to different climatic conditions (mean annual precipitation (MAP), mean air temperature, and climate zone), initial soil properties (soil texture, initial soil pH, and soil organic carbon content), and management practices (vegetable type, cultivation type, planting season, growth cycle, planting years, and N application rate). Methods: Based on a meta-analysis of 348 pairwise observations collected from 74 studies in Chinese vegetable fields, we quantified the responses of topsoil (0–20 cm) pH and vegetable yields to various organic manure (commercial and farmyard manure) substitution ratios (low, SR ≤ 35%; medium, 35% < SR ≤ 70%; and high, SR > 70%) with chemical fertilizer alone as the control. Results: The soil pH increased overall with the increase of SRs. Compared with the control, low, medium, and high SRs increased the soil pH by 2.6%, 5.6%, and 9.0% and the vegetable yield by 11.0%, 12.6%, and 3.2%, respectively. The soil pH in open (33.7%) and greenhouse (66.3%) vegetable fields under medium SR increased by 6.3% and 5.0%, respectively. The initial soil pH, MAP, and climate zone are the key factors affecting soil pH in the vegetable field, and their total contribution ratio on soil pH change accounted for 32.1% of all variables. When the initial soil pH ≤ 6, the soil pH increased with the increase of SRs. Conversely, when the initial soil pH > 8, all SRs decreased the soil pH. The soil pH also tended to increase with increasing MAP and subtropical climate zone. The contribution rate of the N application rate on soil pH change was 7.5%. The growth cycle, planting season, and vegetable type had the least impact on soil pH change. Conclusion: In general, manure substitution can significantly improve the soil pH and vegetable yield. The optimal SR ranges from 35 to 70%. However, the interactions (among factors) and trade-offs during the process remain complicated, which requires further validation based on local conditions. [ABSTRACT FROM AUTHOR]

Soil organic carbon (SOC) and mineral nitrogen (Nmin), especially nitrates (NO3−) in agroecosystems have attracted much attention over the past few decades due to their crucial roles in soil fertility, crop productivity, environmental quality, and/or climate change mitigation and adaptation. The aim of the study was to evaluate the contents of organic carbon, ammonium, and nitrate in soils under differentiated pH, texture, and fertilization rates. A large-scale environmental study was conducted in Polish arable lands. The spatial distribution of the sampling points reflected agricultural production conditions, variability of soil properties, and representativeness of textures that are characteristic of Poland. Our results indicated that SOC content was significantly affected by the soil pH and texture as well as mineral and organic fertilization. The same factors, except organic amendments, significantly supported mineral nitrogen concentration in the present study. The most important factors controlling SOC in the study were ranked as follows: soil pH > pre-crop N fertilization > crop N fertilization > N applied with manure > soil texture. In the case of N-NH4 and N-NO3, mineral fertilization was the most critical variable. The carbon and nitrogen governance in agroecosystems should consider the ranks of factors controlling their contents. [ABSTRACT FROM AUTHOR]

The soil inorganic carbon (SIC) pool is a major component of soil carbon (C) pools, and clarifying the predictors of SIC stock is urgent for decreasing soil C losses and maintaining soil health and ecosystem functions. However, the drivers and their relative effects on the SIC stock at different soil depths remain largely unexplored. Here, we conducted a large-scale sampling to investigate the effects and relative contributions of abiotic (climate and soil) and biotic (plant and microbe) drivers on the SIC stock between topsoils (0–10 cm) and subsoils (20–30 cm) across Tibetan alpine grasslands. Results showed that the SIC stock had no significant differences between the topsoil and subsoil. The SIC stock showed a significant increase with altitude, pH and sand proportion, but declined with mean annual precipitation (MAP), plant aboveground biomass (PAB), plant coverage (PC), root biomass (RB), available nitrogen (AN), microbial biomass carbon (MBC), and bacterial abundance (BA) and fungal gene abundance (FA). For both soil layers, biotic factors had larger effects on the SIC stock than abiotic factors did. However, the relative importance of these determinants varied with soil depth, with the effects of plant and microbial variables on SIC stock weakening with soil depth, whereas the importance of climatic and edaphic variables increased with soil depth. Specifically, BA, FA and PC played dominant roles in regulating SIC stock in the topsoil, while soil pH contributed largely to the variation of SIC stock in the subsoil. Our findings highlight differential drivers over SIC stock with soil depth, which should be considered in biogeochemical models for better simulating and predicting SIC dynamics and its feedbacks to environmental changes. [ABSTRACT FROM AUTHOR]

Intensive crop production systems worldwide, particularly in China, rely heavily on nitrogen (N) fertilization, but left more than 50% of fertilizer N in the environment. Nitrogen (over) fertilization and atmospheric N deposition induce soil acidification, which is neutralized by soil inorganic carbon (SIC; carbonates), and carbon dioxide (CO2) is released to the atmosphere. For the first time, the loss of SIC stocks in response to N‐induced soil acidification was estimated for Chinese croplands from 1980 to 2020 and forecasts were made up to 2100. The SIC stocks in croplands in 1980 were 2.16 Pg C (16.3 Mg C/ha) in the upper 40 cm, 7% (0.15 Pg C; 1.1 Mg C/ha) of which were lost from 1980 to 2020. During these 40 years, 7 million ha of cropland has become carbonate free. Another 37% of the SIC stocks may be lost up to 2100 in China, leaving 30 million ha of cropland (37.8%) without carbonates if N fertilization follows the business‐as‐usual (BAU) scenario. Compared to the BAU scenario, the reduction in N input by 15%–30% after 2020 (scenarios S1 and S2) will decrease carbonate dissolution by 18%–41%. If N input remains constant as noted in 2020 (S3) or decreases by 1% annually (S4), a reduction of up to 52%–67% in carbonate dissolution is expected compared to the BAU scenario. The presence of CaCO3 in the soil is important for various processes including acidity buffering, aggregate formation and stabilization, organic matter stabilization, microbial and enzyme activities, nutrient cycling and availability, and water permeability and plant productivity. Therefore, optimizing N fertilization and improving N‐use efficiency are important for decreasing SIC losses from acidification. N application should be strictly calculated based on crop demand, and any overfertilization should be avoided to prevent environmental problems and soil fertility decline associated with CaCO3 losses. [ABSTRACT FROM AUTHOR]

To limit warming to well below 2°C, most scenario projections rely on greenhouse gas removal technologies (GGRTs); one such GGRT uses soil carbon sequestration (SCS) in agricultural land. In addition to their role in mitigating climate change, SCS practices play a role in delivering agroecosystem resilience, climate change adaptability and food security. Environmental heterogeneity and differences in agricultural practices challenge the practical implementation of SCS, and our analysis addresses the associated knowledge gap. Previous assessments have focused on global potentials, but there is a need among policymakers to operationalise SCS. Here, we assess a range of practices already proposed to deliver SCS, and distil these into a subset of specific measures. We provide a multidisciplinary summary of the barriers and potential incentives towards practical implementation of these measures. First, we identify specific practices with potential for both a positive impact on SCS at farm level and an uptake rate compatible with global impact. These focus on: (a) optimising crop primary productivity (e.g. nutrient optimisation, pH management, irrigation); (b) reducing soil disturbance and managing soil physical properties (e.g. improved rotations, minimum till); (c) minimising deliberate removal of C or lateral transport via erosion processes (e.g. support measures, bare fallow reduction); (d) addition of C produced outside the system (e.g. organic manure amendments, biochar addition); (e) provision of additional C inputs within the cropping system (e.g. agroforestry, cover cropping). We then consider economic and non‐cost barriers and incentives for land managers implementing these measures, along with the potential externalised impacts of implementation. This offers a framework and reference point for holistic assessment of the impacts of SCS. Finally, we summarise and discuss the ability of extant scientific approaches to quantify the technical potential and externalities of SCS measures, and the barriers and incentives to their implementation in global agricultural systems. [ABSTRACT FROM AUTHOR]

This paper examined the contribution of various soil components to pH buffering capacity (pHBC) of haplic Acrisols in an upland area of Southeastern Vietnam. Sampling was conducted in 2016 in Tan Bien district, Tay Ninh province at seven sites from the surface to 60-cm depth. Soils were very acidic (pHH2O 4.53 ± 0.05). The pHBC were very low, 0.46 ± 0.04 and 0.44 ± 0.05 cmol H+ kg−1 pH−1, respectively, for original samples and those from which soil organic carbon (SOC, 0.52 ± 0.09%) were removed. The contribution of Al3+ to pHBC was remarkable while that of SOC was of little significance. The contribution of clay minerals to pHBC was unclear due to the low (9.37 ± 0.76%) and kaolinite-dominated clay content. The current soil conditions indicated a potential for further soil acidification. Liming would be one of the measures to remediate soil acidity in the research area. [ABSTRACT FROM AUTHOR]

A proper understanding of variability of soil chemical properties over an area is important for identifying the soil nutrients related production constraints. The suggestions for remedial measures and execution of appropriate nutrient management strategies are also based on the good knowledge of variation in soil nutrients. A case study was undertaken with an objective of assessing spatial variability of selected soil chemical properties of agricultural land. Soil samples from the surface (0 to 15 cm) were collected from farmers' field in the central part of Kavrepalanchowk district of Nepal in February 2018. Soil samples were analyzed for soil pH, total organic carbon (TOC), total nitrogen (N), phosphorous (P), and potassium (K). Descriptive statistics revealed that the soil in the study area was slightly acidic and contained the low status of TOC, P, and K, while the N content was medium. Coefficient of variation (CV) indicated that soil pH was the least variable (CV= 9.37% with values ranging from 5.3 to 7.7) among the investigated soil samples while N was the most variable (CV= 98.81% with content values ranging from 0.03% to 0.67%). Other selected properties (TOC, P, and K) were found to be highly variable (CV= 49.94%, 94.89%, and 57.53% respectively). These variations in soil chemical properties were mostly related to the different cropping systems and soil management practices, including nutrient management carried out in the study area. Owing to the higher variability of nutrients, the results suggested to take into account various soil and nutrient management practices for sustained soil fertility and enhanced productivity. [ABSTRACT FROM AUTHOR]

Soil fertility is the basis for production of high green mass, which has numerous essential benefits in urban areas. This study aimed to investigate the soil fertility of urban land. This was done by comparing soils from a vegetable garden and its surrounding arable land. A local brickwork dump was included. The soils were Hortisols, slightly stagnogleyic Luvisols, and a Regosol from sandy loamy silt. The location of the study was in the center of one of the world’s largest urban, hard-coal mining and heavy industry areas, the Ruhr area in Germany. The investigations for identifying the characteristic features of the soil fertility involved determination of the profile horizons, texture, pH, bulk density, C/N ratio, content and stocks of organic carbon, total nitrogen, available phosphorus and potassium, and soil water by field capacity. As they are expected to become construction land, the sites were already in a derelict state. The results show that all three soil types had high fertility characteristics. However, the fertility of the garden soils was much greater than that of the local arable land. This was due to the strong and deep accumulation of organic carbon due to compost application. The available phosphorus and potassium contents and field capacity were also distinctly increased in the garden soils. The spatial distribution and distribution with depth of pH, bulk density, organic carbon, nitrogen, available phosphorus, and potassium were extremely heterogeneous among the individual garden soils. In contrast, in the arable land, they were uniform. The organic carbon accumulation in the dump was in the range of that of the garden soils, but the nutrient contents were lower. These results show that the diversity of properties of urban soils is much higher than that of arable soils. The dereliction of arable, garden, and dump soil and vegetation by bushes and trees also affect the soil properties. There should be greater awareness of the high fertility of urban soils, such as vegetable garden soils. Vegetable garden soils have a high potential for contributing to solving urban problems by producing high volumes of biomass and storing water. Therefore, it should be demanded that vegetable garden soils receive a high protection status, and they should not be used for the establishment of construction. [ABSTRACT FROM AUTHOR]

Soil quality is recognised as being a key parameter of sustainable agricultural management. Existing methods of life cycle impact assessment (LCIA) do not include any soil quality indicators other than soil organic matter content. This paper rectifies this omission by presenting Swiss Agricultural Life Cycle Assessment for Soil Quality (SALCA-SQ), a LCIA conform method, to assess effects of agricultural management practices on soil quality. SALCA-SQ characterises all major types of impacts of land management practices on the quality of arable soils by means of nine indicators covering soil physical, chemical and biological aspects: rooting depth of soil, macropore volume, aggregate stability, organic carbon content, heavy metal content, organic pollutants, earthworm biomass, microbial biomass and microbial activity. Since these indicators are not measured directly, the impacts of agricultural management activities are assessed via impact class modelling to determine the most probable changes in soil quality indicators as a result of on-farm agricultural practices. To illustrate the application and results of SALCA-SQ, treatment effects of a long-term field trial on soil quality were assessed and compared against measured field data. The data generated by SALCA-SQ revealed the important influence of fertiliser regime on soil quality. Field measurements generally confirmed SALCA-SQ assessments, but small differences between measured data in different treatments could not be predicted. Case studies on theoretical scenarios covering a broad spectrum of site conditions and management practices demonstrated the potential of SALCA-SQ to assess the effects of the major impact classes on the nine soil quality indicators, thus giving a refined picture of the potential effects of a farming system on soil quality. In principle, these results support the assumption that SALCA-SQ has the potential to assess effects of agricultural management practices on soil quality, but validity in a strict scientific sense remains to be substantiated. In addition, SALCA-SQ can be used by agricultural advisory services and farmers to analyse agricultural management effects on soil quality and move soil management in a more sustainable direction. [ABSTRACT FROM AUTHOR]

Discusses long-term experiments on soil carried in Sweden. Factors influencing Nitrogen mineralization; Decline in carbon content in soils; Significance of carbon metabolism of heterophic microflora.

• Interactions between sward management and liming reduced soil organic carbon. • Nitrogen increased and C:N ratio decreased under liming and hay cutting. • Changes to soil organic matter dynamics did not affect soil carbon stocks. • Upland grasslands can be managed using known methods without reducing soil carbon. • Regular organic matter input by livestock can help maintain soil carbon stocks. Soils in less favoured areas, (LFA's) defined as areas where unfavourable environmental conditions allow only extensive farming systems such as livestock rearing, are relatively stable, being rarely ploughed or disturbed, and cover extensive upland regions of the UK and Europe. Under low intensity management these soils have the potential to act as long-term carbon stores, mitigating the effects of climate change and potentially acting as a source of income for rural economies. However, upland grasslands are sensitive to management decisions, and careful planning is needed to ensure that they continue to provide a range of ecosystem services. Using the long-term grassland experimental plots at Brignant, Wales, management and liming effects on soil organic carbon and related soil parameters under long-term permanent pastures were explored. Results showed that interactions between management and liming could significantly influence carbon storage potential, making a difference of up to 0.45 kg C m−2 in Hay-cut swards. The greatest reductions were found under pastures that had been cut (rather than grazed) and limed, probably due to a combination of enhanced soil microbial activity, increased root production and a lack of fresh biomass. These results indicate that while the potential to further increase soil organic carbon may be limited, grazing for all or part of the year can reduce losses by providing regular organic matter inputs. [ABSTRACT FROM AUTHOR]