Increased Soil Organic Carbon Content Research Articles

Priming of soil organic carbon decomposition induced by exogenous organic carbon input: a meta-analysis

Priming effect (PE) of soil organic carbon (SOC) decomposition induced by exogenous organic C is an important ecological process in regulating the soil C cycle. The objective of this study was to evaluate how the PE varied among different ecosystems at the global scale and explore factors that drive the direction and magnitude of the PE. Using 2048 experimental comparisons compiled from 94 incubation studies with stable (13C) or radioactive (14C) carbon isotopic techniques, we performed a meta-analysis on the effect of exogenous organic C input on native SOC decomposition (i.e., PE) across multiple terrestrial ecosystems. In particular, the linear mixed-effect model was used to examine the relationship between the PE and potential influencing factors. The addition of exogenous organic C significantly enhanced native SOC decomposition by 47.5% (i.e., positive PE), with the highest value in cropland soils (60.9%) and the lowest value in forest soils (26.2%). The intensity of the PE decreased with increasing SOC content, soil total nitrogen content, soil C/N, incubation duration, and incubation temperature, but increased with increasing exogenous organic C addition rate and soil pH. Soil PE was not affected by the complexity of exogenous organic C. Our results indicate that positive PE is a widespread phenomenon in terrestrial ecosystems, and that the magnitude is closely related to soil properties and experimental conditions. These findings may be useful for understanding soil C priming and the effect on soil C balance under climate change scenarios.

Characteristics and Driving Mechanism of Soil Organic Carbon Content in Farmland of Beijing Plain: Implication for the Fate of Engineered Polymers in Soil

Soil organic matter (SOM), as a kind of natural polymers, affects the migration and transport of ions and particles in soil system due to its surface characteristics and interaction and then causes significant changes in soil quality such as soil fertility loss and pollutant transfer. It is of great importance to study the temporal and spatial evolution of soil organic matter and its driving mechanism for soil health management. This study aims to fully reveal the evolution characteristics and driving mechanism of soil organic carbon (SOC) in farmland of the Beijing plain based on a six-year site monitoring. According to the research results, there is a significant difference in the overall soil organic content during the 6-year period. The temporal stability of SOC is moderate, and it is inversely proportional to SOC content in terms of spatial distribution. SOC content increases as organic fertilizer input rises, and an extra unit (15 kg·ha−1) of organic fertilizer input leads to an increase of 0.057 g·kg−1 in SOC content. The soil with higher clay content exhibits higher SOC content. The organic carbon content in different soil texture types increases with time, and there is a significant difference between the increases in medium loam and light loam. The grain field plantation system exhibited declining SOC content, while the protected vegetable fields, open vegetable fields, and orchards all showed an increase in SOC content. According to our results, the SOC content of farmland in the plain areas of Beijing is largely dependent on the input of organic carbon if other conditions remain unchanged or exhibit insignificant changes.

Mechanisms of carbon sequestration and stabilization by restoration of arable soils after abandonment: A chronosequence study on Phaeozems and Chernozems

Abandonment of croplands ongoing on 220 million ha worldwide contributes strongly to soil restoration by improvement of degraded properties and medium- and long-term carbon (C) sequestration in post-agricultural ecosystems. Two interrelated processes – decomposition and stabilization of soil organic carbon (SOC) – govern SOC dynamics and affect the C source or sink functions of former croplands. We investigated how the abandonment of arable soils affects (i) accumulation of SOC, its composition, stability, and turnover during the post-agricultural restoration of soils, and (ii) microbial activity parameters. A chronosequence study was carried in two bioclimatic zones of European Russia: deciduous forest (Luvic Phaeozems, PH-chronosequence) and dry steppe (Calcic Chernozems, CH-chronosequence). Each chronosequence included an arable soil, 3–4 soils abandoned at increasing time periods (up to 35 years), and natural soil: never cropped Phaeozem and completely restored Chernozem. We combined the results of nuclear magnetic resonance (NMR), thermal analysis including Differential Scanning Calorimetry and Derivative Thermogravimetry, long-term incubation for SOC mineralization, and microbiological activity (basal respiration and microbial C content). Degraded Phaeozems with low SOC amount had much higher relative increase in SOC content (134%) during the post-agricultural restoration compared to SOC-rich Chernozems (38%). SOC gains were recorded in all organic compound classes identified by NMR and thermal analysis, but the increase of recalcitrant SOC was more pronounced in the post-agricultural Chernozems than in the Phaeozems. The post-agricultural Chernozems were characterized by higher SOC aliphaticity and aromaticity than Phaeozems. Microbial activity and biodegradable SOC increased gradually during post-agricultural restoration. Being mostly a function of climate and vegetation, the soil type was the primary factor explaining the greatest portion (54–88%) of the total variance for most soil and microbial parameters. Concluding, despite SOC content increased in both Chernozems and Phaeozems during the post-agricultural restoration, the mechanisms of C sequestration and stabilization were dependent on climate, vegetation, and on the degradation intensity during the agricultural use. The accumulation of organic compounds was specific for virgin soils dominating in deciduous forest and steppes, and had direct consequences for microbial activities, C turnover and sequestration.

Impacts of Age and Expansion Direction of Invasive Spartina alterniflora on Soil Organic Carbon Dynamics in Coastal Salt Marshes Along Eastern China

Invasion of Spartina alterniflora has been reported to modify carbon (C) cycling processes and pools of the native salt marsh ecosystems. However, it remains unclear how the invasion age and expansion direction of S. alterniflora impact the soil organic carbon (SOC) dynamics. In this study, by considering the continuous invasion of S. alterniflora into mudflat (seaward) and native species Suaeda salsa (landward) salt marshes over a period of 20 years chronosequence, we quantify their impacts on SOC dynamics along the coastal salt marshes of Yancheng National Nature Reserve of China, based on the extensive field sampling and remote sensing data. The results showed that (1) S. alterniflora invasion increased SOC concentration and density, which averaged 8.39 g C kg−1 and 0.0085 g C cm−3 seaward and 6.26 g C kg−1 and 0.0065 g C cm−3 landward, respectively; (2) soil organic carbon showed a significantly positive relationship with total nitrogen (TN), salinity, and water content and a negative relationship with pH and bulk density for S. alterniflora landward expansion. For seaward expansion, it showed a similar relationship, but there are higher correlations with soil properties except an insignificant relationship with pH; and (3) soil organic carbon and carbon accumulation rate are significantly higher in seaward than in landward. However, for landward expansion, soil organic carbon concentration keeps increasing linearly with invasion time, while for seaward expansion, it increased to a maximum in 11 years of invasion and then decreased. Our results showed that it is very important to assess the effects of invasion on SOC dynamics in salt marsh ecosystems by considering both the expansion direction and invasion age.

Degradation and Mobility of Pesticides in Norwegian Soils

Degradation and Mobility of Pesticides in Norwegian Soils

Soil microbial community structure and enzymatic activity along a plant cover gradient in Victoria Land (continental Antarctica)

In continental Antarctica, autotrophs are exclusively represented by cyanobacteria, algae, lichens and mosses. Consequently, Antarctic soil communities are expected to be rather simple and primarily dominated by microorganisms. Recently, a change in abundance of mosses and lichens has been observed in continental Antarctica in response to an increase of the active permafrost layer, but the implication of this change to soil micro-organisms remains little known. Here we aim to clarify to what extent the abundance of mosses and lichens affects soil biogeochemistry in Victoria Land, with a particular focus on soil microbial abundance and associated soil enzymatic activity. To achieve this aim, we assessed the structure of soil microbiome and the activity of hydrolytic C, N, and P enzymes along a gradient in soil physico-chemical conditions and plant cover. Moss cover strongly relates to the amount of soil organic carbon (SOC), soil water and nutrient content. Soils with higher content of organic carbon were characterized by higher microbial biomass and showed a relatively higher abundance of fungi as compared to bacteria. More specifically, PLFAs biomarkers for Actinomycetes and Gram-positive bacteria were mainly associated to soils with lower SOC. In order to sustain a higher microbial biomass, total activity of hydrolytic enzymes increased with increasing SOC content. Eco-enzymatic stoichiometry, based on C to P and C to N ratios, indicates a higher investment in N- and P-hydrolytic enzymes (ratio < 1), particularly at low SOC content. Oppositely, an increase in C-hydrolytic enzyme activity (ratio ≈ 1) was observed with increasing accumulation of organic carbon. Such a result seems to indicate a stronger role of soil pH at low SOC on enzymatic stoichiometry (abiotic control) whereas with increasing accumulation of organic matter the enzymatic stoichiometry is more affected by microbial metabolism (biotic control).

Carbon sequestration of cropland and paddy soils in China: potential, driving factors, and mechanisms

AbstractThe environmental problems caused by global warming have attracted close attention of governments and scientists all over the world. As the source and sink of atmospheric carbon dioxide, cropland soil plays an important role in the global carbon cycle. Paddy soil is a major component of global cropland, and there is growing research on its carbon sequestration potential. Based on the dynamic characteristics of soil carbon sequestration in cropland, this paper reviews and synthesizes the process and mechanism of soil carbon sequestration in cropland, discusses the driving factors of soil carbon sequestration in cropland from the perspective of crop management practices, and emphatically discusses the knowledge of soil carbon sequestration potential in paddy fields in China. The main conclusions are as follows: (1) The organic carbon content of cropland soil in China is obviously lower than the global average, and the current sequestration rate of paddy soil in China is obviously lower than the potential sequestration rate, which has great potential for carbon sequestration. Since the mid‐1980s, China's agricultural soil organic carbon (SOC) has been gradually increasing, especially the carbon sink effect of rice soil in southern China. (2) Soil and crop management practices such as conservation agriculture, irrigation, integrated nutrition management, straw returning, and crop rotation can improve input efficiency, increase SOC content in the soil carbon pool, and reduce greenhouse gas emissions. (3) The research on SOC fixation mechanism has entered the micro level of soil particles. The chemical protection mechanism of clay, the physical protection mechanism of aggregates, and the biological mechanism interact and influence each other. © 2019 Society of Chemical Industry and John Wiley &amp; Sons, Ltd.

Long-term organic farming on a citrus plantation results in soil organic carbon recovery

It has been shown that soil management under organic farming can enhance soil organic carbon, thereby mitigating atmospheric greenhouse gas increases, but until now quantitative evaluations based on long term experiments are scarce, especially under Mediterranean conditions. Changes in soil organic carbon (SOC) content were examined in response to organic management with cover crops in a Mediterranean citrus plantation using 21 years of survey data. Soil organic carbon increase was more apparent 5 years after a land management change suggesting that, for citrus plantations on Mediterranean conditions, studies should be longer than five years in duration. Soil organic carbon sequestration rate did not significantly change during the 21 years of observation, with values ranging from -1.10 Mg C ha-1 y-1 to 1.89 Mg C ha-1 y-1. After 21 years, 61 Mg CO2 ha-1 were sequestered in long-lived soil C pools. These findings demonstrate that organic management is an effective strategy to restore or increase SOC content in Mediterranean citrus systems.

Effects of organic fertilizer application on accumulation and distribution of assimilates in winter wheat

To understand the effects of organic fertilizer addition on accumulation and distribution of winter wheat assimilates, we compared organic carbon content in soil and wheat plants, photosynthetic characteristics and assimilation transformation under two different fertilizer treatments, CF (chemical fertilizer only) and OF (organic fertilizer with chemical fertilizer), using 13CO2 pulse labeling method. The results showed that OF increased soil organic carbon content and wheat photosynthetic parameters, resulting in higher organic carbon content and total dry biomass accumulation in wheat plants compared with CF treatment. Compared marking to maturity with that on the 7th day after the same marking, the content and distribution rate of 13C in leaves and stems of two treatments decreased; the 13C content in spikes increased at jointing stage and filling stage, decreased at anthesis stage, and the 13C distribution rate increased at all stages. OF treatment was more beneficial for the transportation of photosynthetic product from leaves to spikes at filling stage, with higher 13C distribution rate in spikes compared with CF treatment. The results of correlation analysis showed that dry matter accumulation was significantly positively correlated with the net input of 13C content and its distribution rate, but negatively correlated with organic carbon content in plants. The net input of 13C content was significantly positively correlated with its distribution rate, and negatively correlated with Fv/Fm and Pn. In conclusion, organic fertilizer application could increase the content of organic carbon in soil, improve wheat plants photosynthetic capacity and transportation of photosynthetic product to spikes, and ultimately increase dry matter accumulation in wheat spikes.

Responses of soil carbon sequestration to climate-smart agriculture practices: A meta-analysis.

Climate-smart agriculture (CSA) management practices (e.g., conservation tillage, cover crops, and biochar applications) have been widely adopted to enhance soil organic carbon (SOC) sequestration and to reduce greenhouse gas emissions while ensuring crop productivity. However, current measurements regarding the influences of CSA management practices on SOC sequestration diverge widely, making it difficult to derive conclusions about individual and combined CSA management effects and bringing large uncertainties in quantifying the potential of the agricultural sector to mitigate climate change. We conducted a meta-analysis of 3,049 paired measurements from 417 peer-reviewed articles to examine the effects of three common CSA management practices on SOC sequestration as well as the environmental controlling factors. We found that, on average, biochar applications represented the most effective approach for increasing SOC content (39%), followed by cover crops (6%) and conservation tillage (5%). Further analysis suggested that the effects of CSA management practices were more pronounced in areas with relatively warmer climates or lower nitrogen fertilizer inputs. Our meta-analysis demonstrated that, through adopting CSA practices, cropland could be an improved carbon sink. We also highlight the importance of considering local environmental factors (e.g., climate and soil conditions and their combination with other management practices) in identifying appropriate CSA practices for mitigating greenhouse gas emissions while ensuring crop productivity.

Substitution of mineral fertilizers with biogas digestate plus biochar increases physically stabilized soil carbon but not crop biomass in a field trial

Various organic amendments are scrutinized as potential agricultural management strategies to ensure soil productivity while mitigating climate change due to the accumulation of soil organic matter (OM). The objectives of this experiment were to study the effects of biochar and biogas digestate versus mineral fertilizer on crop aboveground biomass as well as fractions and mineralization of soil organic carbon (SOC). Samples of a sandy Cambisol were taken 14 months after establishment of a field experiment in Germany. Treatments included application of equal nitrogen in the form of mineral fertilizer or liquid biogas digestate without biochar (B0), with 1 Mg biochar ha−1season−1 for two growing seasons (B2), or with 40 Mg biochar ha−1 application (B40). Soil fractionation in water separated water-extractable and free particulate (fPOM) OM, followed by sonification and sieving to isolate occluded particulate (oPOM) and < 20 μm aggregate-occluded and mineral-associated OM. CO2 emissions were measured during 92-day laboratory incubations at 10 and 20 °C. Analysis of variance found digestate lowered (p < 0.05) rye aboveground biomass compared to mineral fertilizer (9.3 vs. 10.6 Mg ha−1), while biochar had no effect. B40 treatments increased C mineralization during incubation by 16% and contained 3.8 times more SOC than B0 treatments. This additional SOC was allocated to fPOM (52%), oPOM (22%), and the <20 μm fraction (26%). Digestate application increased SOC content of oPOM by 11% compared to mineral fertilizer. Furthermore, combined application of 40 Mg biochar ha−1 with digestate resulted in 20% more SOC in the <20 μm fraction than biochar with mineral fertilizer. The lack of a significant fertilizer or biochar-fertilizer interaction effect on C mineralization during incubation demonstrates the stability of SOC from digestate alone or in combination with biochar. The absence of significant differences in SOC content between B0 and B2 treatments demonstrates the difficulty of documenting SOC sequestration in the field at low biochar application rates.

Biochar has little effect on soil dissolved organic carbon pool 5 years after biochar application under field condition

AbstractBiochar application can improve soil properties, such as increasing soil organic carbon content, soil pH and water content. These properties are important to soil dissolved organic carbon (DOC); however, the effects of biochar on DOC concentration and composition have received little research attention, especially several years after biochar application under field conditions. This study was conducted in a long‐term experimental field where the biochar was only applied once in 2009. The purpose of the study was to investigate the effect of different biochar application rates (0, 30, 60 and 90 t ha−1) on the dynamics of soil water content, DOC concentration and DOC compositions (reducing sugar, soluble phenol and aromatics) over nine samplings during a 12‐month period in 2014. Our results showed that soil water content and DOC concentration varied from 7.1% to 14.5% and 59 to 230 mg C kg−1 soil during the 12 months, respectively. However, the biochar application rates did not significantly (p &gt; 0.05) affect soil water content, DOC concentration and DOC composition at the same sampling period. The DOC concentration across the biochar treatments was positively correlated to soil water content. Moreover, the DOC composition (reducing sugar, soluble phenol or aromatics) and their concentrations were positively correlated to the total DOC concentration. In addition, biochar did not affect soil bulk density, pH, saturated hydraulic conductivity and crop yields. The results indicated that some benefits of biochar to soil may not persist 5 years after the application of biochar under a field condition.

Effect of straw amendment modes on soil organic carbon, nitrogen sequestration and crop yield on the North‐Central Plain of China

AbstractWe quantified the effects of different straw return modes on soil organic carbon (SOC), total nitrogen content (TN) and C:N ratios in a wheat/maize double‐cropping agricultural system by analysing their content in different soil aggregate sizes and density fractions under four modes of straw return: (a) no return/retention of wheat and maize straw (Control); (b) retention of long wheat stubble only (Wheat Stubble); (c) retention of long wheat stubble and return of chopped maize straw (Mixed); and (d) return of chopped wheat and maize straw (Both Chopped). The Mixed and Both Chopped straw return modes produced the highest crop yields. Relative to the Control, SOC stock was 9.6% greater with the Mixed treatment and 14.5% greater with the Both Chopped treatment, whereas the Wheat Stubble treatment had no effect on SOC. Mixed and Both Chopped significantly enhanced TN stock relative to the Wheat Stubble and Control treatments. Compared with the Control, the Mixed and Both Chopped treatments increased the mass proportions of large macroaggregates and reduced the silt plus clay fraction; Mixed and Both Chopped caused a significant increase in SOC and TN in large and small macroaggregates; the Mixed treatment significantly increased SOC content in the coarse and fine intra‐aggregate particulate organic matter (iPOM) density fractions of large macroaggregates, whereas Both Chopped increased SOC in the coarse iPOM, fine iPOM and mineral‐associated organic matter (mSOM) density fractions of both large and small macroaggregates; and Mixed and Both Chopped enhanced TN content in coarse iPOM and fine iPOM within small macroaggregates. Although the Mixed treatment was slightly less effective at improving C sequestration in agricultural fields than the Both Chopped treatment, the Mixed treatment may nonetheless be the optimal plant residue management mode in terms of minimizing time and labour due to its ability to improve soil structure, maintain organic carbon levels and provide a means of sustainable crop production in intensive wheat/maize double‐cropping systems.

Effects of Chinese milk vetch intercropped with rape under straw mulching on soil aggregate and organic carbon character

There are severe soil erosion, shallow soil, reduction of soil organic matter, and poor soil and water conservation in purple soil areas in Southwest China, which become the main limiting factors for the sustainable development of agriculture. A series of buckets and field experiments in the field were employed to explore the soil aggregate and soil organic carbon in response to Chinese milk vetch intercropped with rape under straw mulching, aiming to improve soil aggregate structure and increase organic carbon content. Results showed that intercropped Chinese milk vetch increased soil micro-aggregate content in rape rhizosphere, and reduced soil aggregate mean mass diameter. The change of soil macro-aggregate in rape rhizosphere was mainly caused by the change of content of soil aggregate on 10-5 mm and 5-2 mm, while the soil micro-aggregate was mainly caused by soil aggregate on 0.25-0.053 mm. Intercropped Chinese milk vetch and straw mulching significantly increased soil organic carbon content after corn growing season, with increasing the content of soil organic carbon on 10-20 cm and 20-30 cm. Though intercropped Chinese milk vetch and straw mulching had less effect on soil total organic carbon in rape season, more and more significant effect on 0-10 cm, 10-20 cm, and 20-30 cm with rape growing, especially in stem elongation stage, flowering stage, and harvest stage. Our results showed that the characteristic of soil aggregate in rape rhizosphere could be changed by intercropped Chinese milk vetch, and that the content of soil organic carbon could be increased by Chinese milk vetch intercropped with rape under straw mul-ching.

Effects of winter cropping mode on soil organic carbon and carbon management index of double rice paddy

To explore the effects of winter crops recycling into paddy field on soil carbon pool, we cultivated rape, Chinese milk vetch, ryegrass and potato in winter season after harvesting double-season rice, with fallow as control (CK). The contents of soil organic carbon (SOC) and labile organic carbon (LOC) in the harvest of early and late rice were measured, and the stable carbon, activity of carbon pool, carbon pool index, carbon pool activity index and carbon pool management index (CMI) were calculated. Results showed that winter cover crops returning increased SOC content by 1%-8% and 3%-18% after harvest of early rice and late rice, respectively in comparison with CK. Cultivating rape, Chinese milk vetch and ryegrass all increased the LOC content, with enhancement of 16.2%-84.2% and 24.4%-28.1% after harvest of early rice and late rice, respectively. The CMI of all winter crop treatments presented a growth ratio of 1.4%-41.8% compared to CK. In conclusion, the cultivation of winter crop and recycling to field promoted soil carbon fixation and soil quality, among which the ryegrass and Chinese milk vetch showed better comprehensive effect.

Modeling a long-term effect of rice straw incorporation on SOC content and grain yield in rice field

ABSTRACTThe long-term effects of rice straw incorporation on soil organic carbon (SOC) content and rice yield were evaluated from rice cultivation with different treatments: no rice straw (control), rice straw (RS), and rice straw compost (RSC) as a main-plots; five levels of nitrogen (N) fertilizer application: 0, 100, 150, 200, and 250 of N (kg ha−1) as a sub-plots. The denitrification and decomposition (DNDC) model was employed to simulate changes in SOC content and rice grain yield over 35 years. Additionally, scenario analysis on continuous or discontinuous RS incorporation in rice fields was conducted using the DNDC model. The long-term results indicated that RS and RSC treatments played a crucial role in increasing grain yields by 9% and 11% due to the increased SOC contents compared to control treatment. The validated DNDC model on SOC contents and yields showed a good agreement between the observed and simulated values based on the normalized root mean square errors. The model predicted a rapid decline of SOC contents without RS incorporation. Results suggested that incorporating rice straw or amending manure to paddy soils is a preferred practice for maintaining SOC contents.

Impacts of green manure amendment on detritus micro-food web in a double-rice cropping system

Chinese milk vetch (CMV) is widely used as a green manure due to its efficiency for nutrient preservation and soil fertility improvement, as well for providing more organic substances for soil organisms. Detritus micro-food web drives carbon and nutrient cycling and maintains ecosystem productivity. The effects of CMV amendment on detritus micro-food web were investigated in a six-year field experiment. Compared to the mineral fertilizers (NPK) alone, the fertilizers combined with CMV (NPK + CMV) increased soil organic carbon content, and thus enhanced the biomass of microorganisms, as well as protozoa abundance, while did not change micro-feeding nematode abundance (MN). This indicates a substrate-driven bottom-up effect. However, the green manure application increased omnivores-predators (OP) abundance and the OP/MN ratio, suggesting a top-down effect. Higher F/B ratio indicates a shift of the food web energy structure towards to fungi-dominated channel in the manured soil. Here, the green manure amendment should be encouraged to improve soil detritus micro-food web.

Organic fertilizer, but not heavy liming, enhances banana biomass, increases soil organic carbon and modifies soil microbiota

Low soil pH and low soil organic matter content are major factors limiting banana production in acid soils. A pot experiment was conducted to determine whether liming or organic fertilizer is effective in mediating banana growth and soil health. The experiment comprised an unamended control and two treatments, lime and OF (organic fertilizer) and sampling was conducted twice, 65 and 280 days after planting. Soil nutrient concentrations, soil microbial communities and enzyme activities, and banana biomass and nutrient uptake were determined. As expected, the application of lime or organic fertilizer significantly increased soil pH and mineral nutrient concentrations and decreased Al3+ concentration. At both harvests an increase in bacterial and fungal diversity in the lime treatment and a shift in the soil bacterial and fungal communities did not translate into increased plant biomass. Organic fertilizer application significantly increased soil organic carbon content and enzyme activities, root length density down the soil profile, plant biomass and nutrient uptake compared to the lime treatment and the control. Changes in the soil microbial community in the organic fertilizer treatment compared to the control followed the same direction as in the lime treatment. However, the relative abundances of Actinobacteria and Ascomycota increased significantly 280 days after planting and potential pathogenic fungi including Fusarium decreased. Our results indicate that heavy liming alone may not be a viable approach to overcome the growth limiting factors in banana production on acid soils. In addition to the increased soil organic matter and nutrient availability, organic fertilizer may prime microbial activities and act as biologically active agent and/or enhance synergistic interactions within the soil microbiome in enhancing plant biomass. Increased soil biological activities after organic fertilizer application emphasize the importance of soil health in promoting the yield of banana crops.

Arbuscular mycorrhizal fungi ameliorate the chemical properties and enzyme activities of rhizosphere soil in reclaimed mining subsidence in northwestern China

In semi-arid region of northwestern China, underground mining subsidence often results in decreased vegetation coverage, impoverishment of soil fertility and water stress. In addition, the physical-chemical and biological properties of soil also change, resulting in more susceptible to degradation. In particular, subsidence causes disturbance of the symbioses of plant and microbe that can play a beneficial role in the establishment of vegetation communities in degraded ecosystems. The objective of this study was to evaluate the effects of revegetation with exotic arbuscular mycorrhizal fungi (AMF) inoculum on the chemical and biological properties of soil over time in mining subsidence areas. Soils were sampled at a depth up to 30 cm in the adjacent rhizosphere of Amorpha fruticose Linn. from five reclaimed vegetation communities in northwestern China. In August 2015, a field trial was set up with five historical revegetation experiments established in 2008 (7-year), 2011 (4-year), 2012 (3-year), 2013 (2-year) and 2014 (1-year), respectively. Each reclamation experiment included two treatments, i.e., revegetation with exotic AMF inoculum (AMF) and non-AMF inoculum (the control). Root mycorrhizal colonization, glomalin-related soil protein (GRSP), soil organic carbon (SOC), soil nutrients, and enzyme activities were also assessed. The results showed that mycorrhizal colonization of inoculated plants increased by 33.3%–163.0% compared to that of non-inoculated plants (P<0.05). Revegetation with exotic AMF inoculum also significantly improved total GRSR (T-GRSP) and easily extracted GRSP (EE-GRSP) concentrations compared to control, besides the T-GRSP in 1-year experiment and the EE-GRSP in 2-year experiment. A significant increase in SOC content was only observed in 7-year AMF reclaimed soils compared to non-AMF reclaimed soils. Soil total N (TN), Olsen phosphorus (P) and available potassium (K) were significantly higher in inoculated soil after 1–7 years of reclamation (except for individual cases), and increased with reclamation time (besides soil Olsen P). The exotic AMF inoculum markedly increased the average soil invertase, catalase, urease and alkaline phosphatase by 23.8%, 21.3%, 18.8% and 8.6%, respectively (P<0.05), compared with the control. Root mycorrhizal colonization was positively correlated with soil parameters (SOC, TN and soil available K) and soil enzyme activities (soil invertase, catalase, urease and alkaline phosphatase) in both AMF and non-AMF reclaimed soils (P<0.05), excluding available K in non-AMF reclaimed soils. T-GRSP (P<0.05) and EE-GRSP (P<0.05) were significantly correlated with the majority of edaphic factors, except for soil Olsen P. The positive correlation between root mycorrhizal colonization and available K was observed in AMF reclaimed soils, indicating that the AMF reclaimed soil with a high root mycorrhizal colonization could potentially accumulate available K in soils. Our findings concluded that revegetation with exotic AMF inoculum influenced soil nutrient availability and enzyme activities in the semi-arid ecosystem, suggesting that inoculating AMF can be an effective method to improve soil fertility and support restoration of vegetation communities under poor conditions like soil nutrient deficiency and drought.

Water-stable aggregates and carbon accumulation in barren sandy soil depend on organic amendment method: A three-year field study

Organic amendment has proven to reduce resource waste and environmental pollution, in addition to increasing soil quality. However, the effect of different organic amendment methods on water-stable aggregates and soil organic carbon (SOC) accumulation is unknown, especially in barren sandy soil. A field experiment with four organic amendment methods, straw (ST, local practice), biogas residue (BR), manure (PM), and biochar (BC), was designed with the equal amount of nitrogen (N) input in the North China Plain. Soil aggregate distribution, stability, and aggregate-associated C at two depths (0–10 cm and 10–20 cm) were analyzed after a treatment was applied to evaluate soil quality improvement. The main results were as follows: compared to ST treatment, BC treatment enhanced SOC in the 0–10 cm and 10–20 cm layers by 143.8% and 156.5%, respectively (P < 0.05). The mean weight diameter (MWD) of soil aggregates in BR, PM, and BC treatments decreased by 16.2%–31.8%, 10.0%–24.7% (except the 2015 0–10 cm layer), and 18.9%–43.2% compared with ST treatment from 2014 to 2016. BC treatment increased C concentrations in all aggregate fractions compared to ST treatment in 2015–2016 (P < 0.05). The correlations between soil microbial biomass C and MWD (R = 0.7185, P < 0.001) and dissolved organic C and MWD (R = 0.5600, P < 0.001) indicated that soil aggregation is mainly affected by labile organic C in barren sandy soil. All four types of organic amendments increased SOC content; additionally, ST amendment had the highest capacity for aggregate formation. The results indicated that ST amendment is more appropriate for barren sandy soil than BR, PM or BC amendments, and improves soil quality for sustainable soil management.