Soil Accumulation Research Articles

Soil recalcitrant but not labile organic nitrogen mineralization contributes to microbial nitrogen immobilization and plant nitrogen uptake.

Soil organic nitrogen (N) mineralization not only supports ecosystem productivity but also weakens carbon and N accumulation in soils. Recalcitrant (mainly mineral-associated organic matter) and labile (mainly particulate organic matter) organic materials differ dramatically in nature. Yet, the patterns and drivers of recalcitrant (MNrec) and labile (MNlab) organic N mineralization rates and their consequences on ecosystem N retention are still unclear. By collecting MNrec (299 observations) and MNlab (299 observations) from 57 15N tracing studies, we found that soil pH and total N were the master factors controlling MNrec and MNlab, respectively. This was consistent with the significantly higher rates of MNrec in alkaline soils and of MNlab in natural ecosystems. Interestingly, our analysis revealed that MNrec directly stimulated microbial N immobilization and plant N uptake, while MNlab stimulated the soil gross autotrophic nitrification which discouraged ammonium immobilization and accelerated nitrate production. We also noted that MNrec was more efficient at lower precipitation and higher temperatures due to increased soil pH. In contrast, MNlab was more efficient at higher precipitation and lower temperatures due to increased soil total N. Overall, we suggest that increasing MNrec may lead to a conservative N cycle, improving the ecosystem services and functions, while increasing MNlab may stimulate the potential risk of soil N loss.

Elevated CO2 stimulated glomalin accumulation in soils of black locust seedlings colonized by arbuscular mycorrhizal fungi under cadmium exposure by 13C isotopic tracer technique

Elevated CO2 stimulated glomalin accumulation in soils of black locust seedlings colonized by arbuscular mycorrhizal fungi under cadmium exposure by 13C isotopic tracer technique

Release risk of soil phosphorus under different farming systems: Indoor experiments and in-situ measurement

Agricultural phosphorus (P) application leads to the accumulation and release of soil P, which pose ecosystem risks. Different farming systems carry substantial risks of soil P release. This study evaluated the risk of soil P release in three representative systems of paddy fields in China (rice fields (RF), integrated crayfish-rice fields (CRF), and crayfish fields (CF)) using indoor adsorption and desorption experiments and the diffusive gradient in thin films (DGT) technique, and compared the obtained results. The soils of RF and CRF showed higher levels of redox potential (Eh), free Fe–Al oxides (DCB-Fe, DCB-Al), and amorphous Fe–Al oxides (Ox-Fe, Ox-Al) compared to CF. Additionally, the soils of CRF and CF exhibited higher total organic carbon (TOC) content. The indoor experiments revealed a positive correlation between the contents of Ox-Fe, Ox-Al, bioavailable P (BAP), clay, and soil P adsorption characteristics. Desorption characteristics were primarily influenced by total P, TOC, and Ox-Fe content. Furthermore, the order of soil P release risk followed CRF > RF > CF. According to the in situ DGT measurements, the soil P release fluxes were 0.266 mg·m−2·d−1 for CRF, 0.548 mg·m−2·d−1 for RF, and 0.583 mg·m−2·d−1 for CF. Accordingly, the risk of soil P release followed the order CRF < RF < CF. The contrasting results from these two methods are attributable to the indoor experiments indicating the potential for soil P adsorption under specific experimental conditions and the in situ DGT reflecting natural soil P release in a more effective and suitable manner for evaluating soil P release. The findings improve our understanding of the risk of soil P loss in CRF and provides valuable insights into the two methods.

Critical loads for alkalization in terrestrial ecosystems

Critical loads are a risk assessment approach that has supported large decreases in atmospheric acidic deposition globally. In Canada, SOx emissions fell by approximately 70 % between 1990 and 2021, whereas total particulate matter (TPM) emissions increased by about 40 %, mostly after 2010. Base cations are a major component of TPM, and critical load models consider base cation deposition as beneficial to ecosystems insomuch as it reduces the risk of acidification. However, close to point sources, high levels of alkaline dust deposition have altered soil chemistry and caused an undesirable shift in ecosystem state; something that critical loads are designed to prevent. In this study, the simple mass balance model (SMB) was modified with the objective of preventing base cation accumulation in soil above an acceptable threshold. The concept was applied to a forested site close to large emission sources of sulphur, nitrogen, and base cations in the Oil Sands region of Alberta, Canada. At this site, base cation leaching measured at 25 cm was approximately three times higher than estimated background leaching and exceeded combined SO4 + NO3 leaching. The critical load for alkalization was exceeded under each scenario considered in this study, although the exceedance was marginal if all N in current deposition was assumed to leach from soil. While this framework can easily be applied to regional and national critical load efforts, the main uncertainties of the proposed approach include base cation deposition estimates, assumptions regarding the behavior of N in soil, the selection of an appropriate Alkle(crit) and the long-term immobilization of deposited base cations in soil.

Iron additions accelerate carbon loss from drained soil but promote carbon accumulation in waterlogged soil of Zoige plateau peatland

Iron (Fe), the fourth abundant element in soil, commonly exists as ferrous (Fe(II)) and ferric (Fe(Ⅲ)) forms, playing a crucial role carbon cycling. However, the effect of Fe(II) and Fe(Ⅲ) on soil organic carbon (SOC) remains unclear, especially in carbon-rich peatland soils. Therefore, this study added Fe (Ⅱ) and Fe (Ⅲ) into the drained and waterlogged soils sampled from the Zoige plateau peatland to conduct a 95-day incubation experiment to reveal the role of Fe forms in driving carbon cycling. The dynamics of carbon compositions (phenolics, dissolved organic carbon (DOC), SOC, Fe-bound SOC (Fe–SOC)) and enzyme activity (phenol oxidase and β-glucosidase) were tested along with incubation time. Moreover, soil functional groups and bacteria were determined over the incubation period. The results demonstrated that Fe(II) and Fe(Ⅲ) addition in the drained soil decreased phenolics, DOC and SOC but increased Fe–SOC, soil organic functional groups (i.e., aromatic hydroxyl), and chemical bonds (i.e., C–O bonds); the reduced DOC and phenolics by the increased Fe(III)/Fe(II) ratio (extracted by 0.5 M HCl solution) was the primary reason for SOC loss. In waterlogged soil, Fe(II) and Fe(Ⅲ) addition increased carbon compositions and soil functional groups; the increased DOC and phenolics by the reduced pH was the possible reason for SOC accumulation. It can be known that the wide existence of Fe(II) and Fe(Ⅲ) in peatland may accelerate carbon loss from drained soil but prevent carbon loss from waterlogged soil and enhance SOC stability.

Источники, токсичность и биоаккумуляция редкоземельных элементов в окружающей среде: обзор

The anthropogenic part of the rare earth elements (REE) cycle is becoming increasingly noticeable due to its increasing mining, using, accumulating in wastes. The aim of the work is to summarize current scientific data of the REE effect on living organisms in different habitats, including the mechanisms and specificity of their action, as well as bioaccumulation. Both REE’s natural geochemical anomalies and anthropogenic polluted zones are known. The REE soil accumulation in industrial areas is up to 2.3 µg/kg; in urban snow the REE content varies from 0.411 µg/kg to 1.463 µg/kg. The REE negative molecular mechanism provokes oxidative stress; the latter can be expressed as stimulation of vital functions at low doses of toxicants, and as inhibition of organisms with increasing concentrations. The REE toxic concentrations depends on the chemical element nature, as well as on set of environmental factors and the exposure target, but they are often 2–3 orders of magnitude higher than those of heavy metals. In the early 21th century, this served as a basis to consider REEs environmentally safety. But many sublethal and delayed effects of REEs including endocrine disorders and negative effects on the breeding potential of populations have now been shown. The complexity of REEs study is due to additive, antagonistic, or synergistic effects of their mixtures and combinations with other elements. Thus, a comprehensive study of rare earth elements remains an urgent task with preventive environmental importance. The vulnerable species identification, REEs delayed effects and the REEs co-action with other substances are the most promising scientific issues.

Corrigendum to “Macro- and microplastic accumulation in soil after 32 years of plastic film mulching” [Environ. Pollut. 300, (2022), 118945]

Corrigendum to “Macro- and microplastic accumulation in soil after 32 years of plastic film mulching” [Environ. Pollut. 300, (2022), 118945]

Coriander response to potassium under its medium availability in Typic Haplustepts

Field experiments were carried out with seven levels of potassium (K) (as-1K O ha ) using coriander (var. Ajmer coriander-1) on a medium fertile2sandy loam soil (Typic Haplustepts). These results revealed that plantheight and secondary branches were lower at higher level of K, while thegrowth, yield and associated attributes were statistically (p&lt;0.05) at parwith control. The reduction in seed yield per pot was 4.2 to 8.3 % beyond-1soil application of 40 kg K O ha . There was no significant (p&lt;0.05)2variation in seed nutrient content, except N and K uptake. The N content in-1seed was higher at120 kg K ha , while K content in seed was more beyondthe 60 kg of applied K. Nutrient content in coriander straw increasedmarginally with increase in doses of K. Uptake of nutrients and sodium(Na) content decreased with increase in doses of K. Potassium availability-1was more with higher doses of K; beyond the 40 kg K ha and rest ofnutrient remained at par with doses of K. Soil exchangeable Na wasenhanced slightly with doses of K and soil accumulation was more than itsinitial level. Therefore, it is recommended that there is no need to apply K incoriander, if sufficient availability of K is there in soil and irrigation waterbears an appreciable amount of K. Moreover, higher application of K anddeep irrigations (&gt;50mm) makes coriander susceptible for frost injury, if itoccurs and ultimately reduces crop yield.

Responses of runoff and sediment yield to slope length and gravel content of Lou soil engineering accumulation slope in Guanzhong region, Northwest China.

With the economic development, a large number of engineering accumulation bodies with Lou soil as the main soil type were produced in Guanzhong area, Northwest China. We examined the characteristics of runoff and sediment yield of Lou soil accumulation bodies with earth (gravel content 0%) and earth-rock (gravel content 30%) under different rainfall intensities (1.0, 1.5, 2.0, 2.5 mm·min-1) and different slope lengths (3, 5, 6.5, 12 m) by the simulating rainfall method. The results showed that runoff rate was relatively stable when rainfall intensity was 1.0-1.5 mm·min-1, while runoff rate fluctuated obviously when rainfall intensity was 2.0-2.5 mm·min-1. The average runoff rate varied significantly across different rainfall intensities on the same slopes, and the difference of average runoff rate of the two slopes was significantly increased with rainfall intensity. Under the same rainfall intensity, the difference in runoff rate between the slope lengths of the earth-rock slope was more obvious than that of the earth slope. When the slope length was 3-6.5 m, flow velocity increased rapidly at first and then increased slowly or tended to be stable. When the slope length was 12 m, flow velocity increased significantly. In general, with the increases of rainfall intensity, inhibition effect of gravel on the average flow velocity was enhanced. When rainfall intensity was 2.5 mm·min-1, the maximum reduction in the average flow velocity of earth-rock slope was 61.5% lower than that of earth slope. When rainfall intensity was less than 2.0 mm·min-1, sediment yield rate showed a trend of gradual decline or stable change, while that under the other rainfall intensities showed a trend of rapid decline and then fluctuated sharply. The greater the rainfall intensity, the more obvious the fluctuation. There was a significant positive correlation between the average sediment yield rate and runoff parameters, with the runoff rate showing the best fitting effect. Among the factors, slope length had the highest contribution to runoff velocity and rainfall erosion, which was 51.8% and 35.5%, respectively. This study can provide scientific basis for soil and water erosion control of engineering accumulation in Lou soil areas.

The factors affecting microplastic pollution in farmland soil for different agricultural uses: A case study of China

Microplastics (MPs) accumulation in agricultural soil seriously affects soil quality and grain production, and endangers ecological environment and human safety. The factors contributing to the MPs accumulation in various agricultural land-use soils remain unclear. In this study, a meta-analysis was conducted to analyze the influence of meteorological factors. Furthermore, the accumulation process of MPs pollution in different agricultural land-use soils in China was explored. The conclusions are as follows: (1) The MPs abundance varied from 23 to 41,741 n/kg in Chinese agricultural soil. Especially, the moderate and severe pollution (≥4,000 n/kg) were found in the Yunnan-Kweichow Plateau. (2) The order of MPs abundance in soil was as follows: vegetable > orchard > food crops. Compared to non-mulching, MPs abundance in mulching food crops, vegetable, and orchard soil was approximately 1.4-fold, 11.4-fold, and 1.1-fold, respectively. (3) In orchard and food-crop soils, MPs abundance was negatively associated with rain and wind speed, but positively correlated with altitude and temperature. Whereas MPs abundance in vegetable soil was significantly positively affected with temperature, altitude, sunshine hours, wind speed, and rainfall. (4) The MPs pollution accumulation in soil was mainly dominated by mulching agricultural measures under different agricultural land-use. Meteorological factors have an indirect impact by affecting MPs fragmentation and migration. The results provide theoretical support for soil pollution control, agricultural production safety, and watershed management.

Evaluation of Phosphorus Enrichment in Groundwater by Legacy Phosphorus in Orchard Soils with High Phosphorus Adsorption Capacity Using Phosphate Oxygen Isotope Analysis.

Long-term phosphorus (P) fertilization results in P accumulation in agricultural soil and increases the risk of P leaching into water bodies. However, evaluating P leaching into groundwater is challenging, especially in clay soil with a high P sorption capacity. This study examined whether the combination of PO4 oxygen isotope (δ18OPO4) analysis and the P saturation ratio (PSR) was useful to identify P enrichment mechanisms in groundwater. We investigated the groundwater and possible P sources in Kubi, western Japan, with intensive citrus cultivation. Shallow groundwater had oxic conditions with high PO4 concentrations, and orchard soil P accumulation was high compared with forest soil. Although the soil had a high P sorption capacity, the PSR was above the threshold, indicating a high risk of P leaching from the surface orchard soil. The shallow groundwater δ18OPO4 values were higher than the expected isotopic equilibrium with pyrophosphatase. The high PSR and δ18OPO4 orchard soil values indicated that P leaching from orchard soil was the major P enrichment mechanism. The Bayesian mixing model estimated that 76.6% of the P supplied from the orchard soil was recycled by microorganisms. This demonstrates the utility of δ18OPO4 and the PSR to evaluate the P source and biological recycling in groundwater.

Remediation of imidacloprid and carbamazepine in polluted soil using TiO2 with LED lamps

Imidacloprid and carbamazepine are recognised as emerging contaminants (ECs) due to their ubiquitous presence in environmental compartments and their potential to cause undesirable ecological effects. Wastewater treatment plants are relevant routes for these compounds to enter environment since they are continuously released through treated wastewater. The progressively more extended custom of reusing treated wastewater for agricultural irrigation has also enlarged the risks for ECs accumulation in soil and their translocation to crops, posing a constant threat to both humans and wildlife. This work is aimed to study the behaviour of imidacloprid and carbamazepine and its main transformation products generated in soil during photocatalytic treatments using commercial TiO2 (Degussa P25) and ultraviolet light emitting diode (UV-LED) lamps as light source. Prior to remediation trial, the influence of catalyst load and soil moisture content in ECs degradation was studied. Experiments were performed using a photochemical reactor equipped with LED lamps running at 365 nm, exposing polluted soils to different treatments in presence and absence of photocatalyst. A significant degradation (93.4 and 96.2% for imidacloprid and carbamazepine, respectively) was observed after 4 days of photocatalytic treatment. The main transformation products were identified during the different treatments. Our results suggest that TiO2-photocatalytic treatment combined with UV-LED could be considered a promising technology to remove ECs from soils.

Solar photovoltaic panel soiling accumulation and removal methods: A review

AbstractPhotovoltaic (PV) power generation has become a key area for investment worldwide. Solar PV panels are the core components of PV power generation systems, and the accumulation of soiling on their surfaces has numerous adverse effects on power generation. This paper provides an overview of the soiling accumulation on PV panels and the existing soiling removal methods. Firstly, the sources of soiling particles and the mechanism of soiling fall are analyzed, based on which the accumulation of soiling on the surface of the PV panels is described in detail, and then the effect of the surface soiling on the PV panels is investigated in the order of optics‐thermology‐electrical, with the necessary semiempirical formulas provided to assist in more in‐depth analyses. In addition, the principles, status quo, effects, costs, advantages, and disadvantages of existing soiling removal methods are specifically described, thus providing a reference for the selection of soiling removal methods in different regions. The paper also analyses the soiling accumulation and removal challenges of PV panels in different regions of China. The results of the study are important for the improvement of the effectiveness of soiling removal and the rational optimization of the soiling removal scheme.

Cadmium accumulation in soil resulting from application of biogas digestate and wood ash – Mass balance modelling

This study investigates the impact of substituting conventional NPK fertilizer with wood ash and biogas digestates at an agricultural field site in southwest Sweden. A three-year field experiment, comprising a crop rotation cycle of spring wheat, winter wheat, and oats, was conducted. The obtained results were employed to establish a dynamic mass balance model for the A horizon of the soil at the site. The Cd leaching term in the model was estimated using the Stockholm Humic model (SHM), which was recalibrated to accommodate low Cd concentrations by incorporating Cd complexation to thiol sites. The findings indicate that treatments receiving NPK fertilizer and biogas digestates experienced a net Cd loss, whereas treatments with wood ash demonstrated net Cd accumulation, attributed to its higher Cd content. Harvest yields were highest in the NPK treatment, and lower in two of the wood ash treatments, likely due to lower nitrogen additions in the latter. Cd offtake mirrored this trend, with the highest values in the NPK treatments and the lowest in the wood ash treatments, potentially also influenced by a pH difference of 0.2 units during the last year of the experiment. Geochemical modelling showed that Cd leaching is highly dependent on pH and that geochemically active soil Cd in the A horizon may have doubled between 1950 and 2002, due to elevated atmospheric deposition and fertilizer Cd during this period. Despite significant reductions in anthropogenic Cd fluxes since 2002, soil Cd has only decreased by 4%, showing the slow response of the soil pool to flux changes. Attaining a new steady-state after alterations in input fluxes will require hundreds of years. These results carry significance for determining sustainable application rates for recycled nutrient sources and underscore the crucial role of pH-dependent Cd sorption for Cd leaching.

Influence of nitrogen substitution at an equivalent total nitrogen level on bacterial and fungal communities, as well as enzyme activities of the ditch bottom soil in a rice-fish coculture system.

Rice-fish coculture system (RFS) operates through effectively utilizing water and land resources in a complementary form, but it requires more efficient utilization of fertilizer and feed without compromising rice yield. However, the knowledge of how to regulate the proportion of nitrogen (N) supplied from fertilizer and feed at an equivalent total N levelto improve the benefits of RFS remains limited. Therefore, four treatments (S0: RFS with 0% N fromfertilizer and 100% N from feed; S25: RFS with 25% N from fertilizer and 75% N from feed; S50: RFS with 50% N from fertilizer and 50% N from feed; S75: RFS with 75% N from fertilizer and 25% N from feed) were conducted to assess the variation of ditch bottom soil properties, microbial communities and enzyme activities, as well as to obtain the optimal ratio of N supplied from fish feed and fertilizer. The experiments showed that the contents of soil organic matter, total carbon and total N, and the activities of urease, N-acetyl-β-D-glucosaminidase, protease, β-1,4-glucosidase and catalase in the ditch bottom soil significantly reduced in S25 treatment, compared with the other three treatments. Ammonium N content decreased with increasing percentage of the basal fertilizer, whereas nitrate N content and pH value showed an adverse trend. However, the bacterial and fungal communities were unaffected by the ratio shifts between fertilizer-N and feed-N, but their dominant phyla were influenced by the ditch bottom soil N level. Moreover, the bacterial community composition was positively related to nitrate N, whereas fungal diversity was positively correlated with pH, ammonium N and nitrate N, and urease. We also found that the treatment of N input with 25% N from fertilizer and 75% N from feed can reduce N deposition in the ditch bottom soil in the rice-fish coculture system. Our findings indicate that under the equivalent total N input level, the relative higher ratio of N from fish feed increased (S0 treatment) or reduced (S25 treatment) the deposition of N in the ditch bottom soil, and improved fish production, but decreased rice yield; while the higher ratio of N from basal fertilizer increased the transportation of nutrients into the ditch bottom soil and rice yield, but reduced fish production. So when considering multi-balance and multiple benefits, we recommend that a selective substitution ratio within 50% ~ 75% from fish feed to substitute for the basal fertilizer under the equivalent total N input may achieve a good balance of rice and fish production improvement, and reduce nutrients wastage to the ditch bottom, as well as alleviate the potential of non-point source pollution. This study also provides an evidence for regulating and optimizing the ratio of N supplied from fertilizer and fish feed at an equivalent total N level through monitoring the nutrient accumulation in ditch bottom soil in the rice-fish coculture system. © 2024 Society of Chemical Industry.

Spatial and Seasonal Patterns of Mercury Accumulation in Paddy Soil around Nam Son Landfill, Hanoi, Vietnam

Landfills have the potential to contribute to mercury (Hg) pollution, due to the burial of waste containing mercury. Mercury from domestic waste can enter the soil surrounding landfills through surface runoff and leachate. In this study, we assessed the levels of Hg in the paddy soil around the Nam Son landfill, the largest landfill in the North of Vietnam, during both rainy (September 2021) and dry (January 2022) seasons. The concentration of Hg was in the range of 20.5 to 79.7 μg/kg dry w.t. in Bac Son and Nam Son, and 16.6 μg/kg dry w.t. at a higher reference site. In most of the samples, the rainy season showed higher Hg concentrations than the dry season. Soil samples taken closer to the landfill exhibited higher levels of Hg contamination compared to those in more distant paddy areas, suggesting a decreasing trend of Hg concentration as one moves away from the pollution source. Additionally, Hg concentration was found to decrease vertically from the surface, with the higher value observed in the surface layer (0–5 cm), and the lower in the bottom layer (20–25 cm). The geo-accumulation index showed that all the sampling points were moderately to heavily polluted, indicating that Hg was lost from the waste source in the landfill. This study provides valuable insights into the spatial and vertical distribution of Hg pollution in the topsoil and highlights the importance of managing and assessing the risks of Hg-containing waste.

Modeling soil carbon accumulation in irrigated agricultural systems

In contemporary circumstances characterized by climate change and increased pressure on agricultural ecosystems, determining the impact of irrigation levels on soil carbon dynamics becomes a pertinent task. This study aims to determine the impact of irrigation rates on soil carbon dynamics using agricultural system modeling. The simulations were conducted by LPJ-GUESS Education 3.0. The results were analyzed using the analogy method. Changes in soil carbon accumulation were quantified in three agricultural systems representing the desert, semi-desert, and steppe zones of Russia. Results show an increase in soil carbon accumulation in all biomes and a decrease in ecosystem carbon exchange. These findings suggest that irrigation rates developed for desert, semi-desert, and steppe biomes were effective. The results of this study can be applied to irrigated and rainfed agriculture. The obtained data not only corroborate the positive influence of irrigation levels on carbon accumulation in soil across various biomes but also unveil prospects for the development of sustainable agricultural practices. This study aims at optimizing the utilization of water resources, which may contribute to fostering ecosystem resilience within the agricultural sector.

High spatiotemporal asynchrony between water deficit and nitrate accumulation under apple orchards in deep loess deposits

Understanding the relationship between water and nitrate in soils is critical to agricultural production and aquifer vulnerability assessments, especially in regions with intensive agricultural activities and thick unsaturated zones. Deep soils usually record long-term variations in coupling water and nitrate processes, influenced by multiple environmental factors. As such, this study aims to investigate water and nitrate-nitrogen (NO3–−N) contents and their relationships in soil profiles of 13–23 m deep under farmland and neighboring apple orchards with different ages. Soil properties were considered to explore the individual effect of a single factor or combined effects of multiple factors by wavelet analysis and partial least squares path models. Compared with farmland, apple orchards had large water deficit and NO3–−N accumulation due to root water uptake and synthetic fertilizer inputs, with high spatiotemporal asynchrony in deep unsaturated zones. Specifically, water deficit and NO3–−N accumulation were respectively observed in relatively stable (5–15 m) and active layers (0–5 m, spatial asynchrony), with higher water deficit rates under young apple trees (e.g., 12 and 22 years old) but larger NO3–−N accumulation rates under old apple trees (e.g., 23–32 years old, temporal asynchrony), respectively. Under farmland and orchard, soil texture-organic carbon regulated soil water movement, while soil water-organic carbon affected nitrate transport and transformation processes, which further altered soil pH and electric conductivity conditions in deep vadose zones. The growth of apple trees leads to asynchronous water depletion and fertilizer accumulation in soils, and the > 20 years apple trees are limited by insufficient water despite the excessive fertilizer. The dried soil layers not only reduce potential groundwater recharge, but also prolong the residence time of nitrate bombs in thick unsaturated zones. This study provides essential information for sustainable management of vegetation and water resources, and benefits the complicated hydrological and biogeochemical cycles in thick vadose zones.

Soil nitrogen availability mediates the positive effects of intercropping on soil organic carbon at global scales

Intercropping is an effective cultivation practice to develop sustainable agroecosystems and increase soil organic carbon (SOC) and nitrogen (N) with rich crop diversity. With increased duration, the changes in soil N availability might affect microbial and plant growth and consequently regulate the intercropping effects on SOC sequestration. However, the response of intercropping effects on SOC components to soil N availability has been poorly explored. In this study, we constructed a global database with 939 paired data (intercropping vs. monoculture) from 60 publications. We found that intercropping increased SOC (by 7.94%), microbial biomass carbon (MBC, by 23.73%), particulate organic carbon (POC, by 23.27%), and dissolved organic carbon (DOC, by 16.46%) compared to monoculture. The intercropping effects (percentage change, %) on SOC content strongly depends on soil N availability (soil C: N) and the interactions with duration and crop types. In N-limited soils (soil C: N > 15), intercropping increased SOC and POC contents by 14% and 31%, respectively, which were 2–3 times higher than those in N-rich soils (soil C: N < 15). It implies higher intercropping effects in more N-limited soils. In addition, intercropping increased MBC:SOC by 63% in N-limited but not in N-rich soils, indicating greater contributions of microbial-derived C to SOC storage in N-limited but not in N-rich soils. This might be attributed to that the stimulated microbial decomposition of soil organic matter counterbalanced the microbial-derived C accumulation in N-rich soils. Taken together, these results indicate that soil N availability regulates the intercropping effects on SOC content and the contributions of microbial-derived C to SOC storage. Overall, these findings highlight the importance of soil N availability on SOC content with intercropping, implying that intercropping is a suitable agricultural approach especially in N-limited soils and nutrient management should be carefully considered in long-term intercropping experiments.

Status of Sustainable Balance Regulation of Heavy Metals in Agricultural Soils in China: A Comprehensive Review and Meta-Analysis

To control heavy metal pollution effectively, prevention of heavy metal accumulations in agricultural soils should be the priority rather than remediation of heavy metal contamination. In this research, papers which contained input and output fluxes of Cd, As, Cr, Hg, and Pb in topsoil (the plough layer) of agricultural lands in Hunan, Zhejiang, the Yangtze River Delta, Hainan, and China as a whole were explored. Fluxes of heavy metal species were recalculated, and future trends of pollution were predicted. Also, cases regarding the application of technologies to control the input and output of heavy metals were analyzed. Results indicated that atmospheric decomposition was the dominant input source of heavy metals in all study sites except Hainan. The relative contributions of fertilizers, irrigation water, and straw returning fluctuated greatly among different sites. Cd pollution in all sites was the most serious, followed by Cr and Pb. In Hunan, Cd has already exceeded the maximum limit value and needs to be controlled urgently. The input of heavy metals from irrigation water, fertilizers, and straw returning could be controlled by proposing more policies to manage their quality and application amounts. The amount of heavy metals absorbed by plants could be increased by cultivating crops with hyperaccumulators and high-biomass plants.