Labile Soil Research Articles

HEAVY METAL ACCUMULATION AND MIGRATION IN SOILS AND PLANTS UNDER CONTAMINATION IN URBAN ENVIRONMENTS

The concentrations of heavy metals (Cu, Zn, Fe, Mn, Pb, Cd) in labile and acidsoluble form in soils and their content in coltsfoot (Tussilago farfara L.) were studied in the surroundings of various industrial enterprises in Tyumen. Soil and plant samples (n=6 each) were collected in a control site and near a highway, an engine plant, an oil refinery, a battery factory, and a steel mill. The involvement of the metals in air-borne migration was estimated by their content in coltsfoot. Heavy metal content in coltsfoot leaves was analyzed in two variants: with and without washing with distilled water. Samples were analyzed by atomic absorption spectroscopy. Cu, Zn, Fe, Mn, and Pb content in soil samples exceeded the control up to 6-fold. Pb content in soils at the battery factory exceeded the MPC 5.8-fold. Heavy metal lability in soils decreased in the following order: Mn > Zn > Cu > Fe. The concentrations of all the metals both in soils and plants were the highest at the battery factory and the steel mill. Metal accumulation by plants decreased in the following order: Fe > Zn > Cu > Mn > Pb > Cd. The bioconcentration factor in washed coltsfoot leaves declined in the Cu > Zn > Cd > Pb > Mn > Fe sequence, while the actual biogeochemical mobility decreased in the Fe > Cu > Zn > Pb > Cd > Mn sequence. The contribution of Cu, Zn, Fe, and Mn air-borne transfer to their accumulation in plants, which was estimated by the difference of metal concentrations before and after washing, ranged from 10 to 73 %. Air-borne migration was the most pronounced at the highway and the steel mill. Iron accumulation in plants showed the greatest connection to airborne industrial pollution as compared to other metals studied. These results indicate the importance of the air-filtering role of plants and prove that plants from urban habitats must not be used for medicinal or agricultural purposes. Accumulation of heavy metals from air-borne industrial pollution by plants is evidence of additional toxic effect of pollutants in the urban environment and suggests that plant samples for ecological research have to be pre-treated.

Soil quality indicators in conventional and conservation tillage systems in the Brazilian Cerrado

Conventional and conservation tillage systems can alter soil aggregation and total and labile soil organic matter (SOM) contents. This study aimed to determine the degree of soil aggregation, quantify total carbon (TC), permanganate oxidizable carbon (POXC), light organic matter (LOM), and potentially mineralizable carbon (CO2-C) contents in soils aggregates, and assess soil quality indexes at sites under conventional and conservation tillage in the Cerrado region of Minas Gerais State, Brazil. Four experimental areas were analyzed: a area under conventional tillage for 20 years, a area under no-till for 6 years, a area under no-till for 18 years, and a reference area of undisturbed Cerrado vegetation. Soil aggregates retained on 8.0–4.0 mm sieves were evaluated for size class distribution and mean weight diameter. TC, POXC, LOM, daily and Total CO2-C emissions were also analyzed. These data were used to calculate the C/N ratio and sensitivity, carbon pool, and lability indexes. The results of SOM compartments were in agreement with those obtained for the soil aggregation status. 6NT and 18NT had a higher proportion of macroaggregates and higher MWD values than CT in both layers. For other classes of aggregates, CT had the highest proportions of mesoaggregates at 0–0.05 m depth and microaggregates at 0–0.10 m depth. At 0–0.05 m depth, TC and LOM contents were highest in 6NT and 18NT aggregates. In comparing the soil indexes of managed areas, we found a similar pattern to that observed for macroaggregates, MWD, TC, and LOM. CA, 6NT, and 18NT aggregates had the largest CO2-C cumulative emissions at the end of the incubation period. Environmental conditions at no-till areas promoted macroaggregate formation and preserved TC and LOM contents, resulting in a high degree of aggregate stability. Soil quality indexes were sensitive to identify changes between the reference area and managed areas. Soil aggregates from no-till areas had higher CO2-C emissions and cumulative emissions than those from the conventional tillage area.

Effect of phosphorus fertilizer form, opener spread and rate of application on biomass yield, P uptake and recovery in a canola-wheat-pea rotation under controlled environment conditions

The form and opener configuration used to apply phosphorus fertilizer can influence its effectiveness and crop response. A growth chamber study was conducted to examine the response of crop (canola, wheat, and pea grown in rotation) and soil to P fertilizer form (monoammonium phosphate and struvite), opener spread (narrow versus wide), and rate treatments of 0, 20, 40, and 60 kg P2O5 ha−1 added to canola (B. napus) in the seed-row, followed by wheat and pea without P fertilization to examine residual effects. Crop emergence, 30 days above ground biomass yield, uptake of P and apparent recovery of fertilizer P were determined, along with labile soil residual P concentrations at the end of the rotation. Both MAP and struvite produced similar crop biomass yield and P uptake response. The narrow opener spread (1”) performed better in canola yield response to added P and in recovery of P fertilizer compared to the wide (3”) spacing and did not appear to reduce canola emergence even at the highest rates of added P fertilizers.

C and N stocks in silvopastoral systems with high and low tree diversity: Evidence from a twenty-two year old field study

This paper aimed to quantify the C and N stocks and the natural abundancy of 13C (δ13C) in organic matter fractions of soil, as well as soil labile C, in a long-term experiment (1997–2019) on silvopastoral systems (SSP) with low and high tree diversity in the Mata Atlântica biome. Disturbed and undisturbed soil samples were collected in transects that were perpendicular to the tree rows every five meters (0, 5, 10, and 15 m of distance), at depths of: 0.0–0.10, 0.10–0.30. 0.30–0.60, 0.60–1.0 m. Litterfall, root density, total organic C and N content, δ13C values for particulate organic matter (POM) fractions as well as mineral-associated organic matter (MAOM) and soil labile C, whilst stocks were calculated afterwards. Litterfall production was higher in the high diversity SSP for all distances, except for 5 m from the tree row. In contrast to litterfall, higher root density was observed for the longest tree distances (15 m) in the low diversity system. The high tree diversity SSP increased TOC stocks in the top soil layer (0.0–0.10 m, distances of 0 and 10 m) only and C-MAOM stocks in the surface (0.0–0.10 m, 10 m distance) and subsurface (0.10–0.30 m, 0 m distance). In contrast, total N stocks or stocks associated with MAOM and POM were higher in the high tree diversity system. The increases were of 37, 36 and 63%, respectively, for total N, N-MAOM, and N-POM up to 1 m depth. The smallest δ13C values found close to the tree row (0 and 5 m distances), especially in the high diversity system, indicate the influence organic residue from leguminous tree species, whilst the C4 grass held the highest contribution at the 15 m distance, also in the high diversity system. In general, the high diversity tree silvopastoral system has shown potential at storing most C in the 0.0–0.10 m soil layers only and N up to 1 m depth. Results showed very little shift in total C stocks, but the increased N stocks with the inclusion the legumes trees, which is reflected in a lower C:N ratio of the SOM. The silvopastoral system containing signal grass both legumes trees can be looked at as a viable strategy towards sustaining existing soil C stocks, whilst increasing N stocks and SOM quality.

Legume cover crop type and termination method effects on labile soil carbon and nitrogen and aggregation

AbstractGrowers use cover crops to provide nutrients for crops and build soil organic matter (SOM). Termination methods may alter the effects of cover crops on soil labile C and N. We examined how two cover crops and three termination methods affected soil microbes, soil aggregates, and C and N pools in an organic grain system. We compared crimson clover (Trifolium incarnatum L.) (CC), hairy vetch (Vicia villosa Roth) (HV), and a control together with disking, mowing, or a roller‐crimper for effects on hot‐water‐extractable carbohydrates, microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN), potentially mineralizable C and N, and aggregation (quantified by mean weight diameter [MWD]). Disking comprised flail mowing plots and then cultivating. Roller‐crimping occurred via a roller with blades. Vetch soil contained 14% higher MBC than no cover crop pretermination, possibly because of enhanced rhizodeposition. Planting CC resulted in 44% higher MBC than no cover crop a week after termination, likely due to its higher biomass C/N ratio. Disking decreased MWD relative to flail mowing in no cover crop soils at 4 wk after termination across both years at 0‐to‐5‐cm depth. In addition, MWD was lower under CC than under no cover crop for both the flail mowed and roller‐crimped treatments at 4 wk after termination across both years from 0 to 5 cm. This is possibly due to enhanced desiccation of the soil in bare plots after termination. Our results indicate that quantity and quality of biomass of different legume species, rather than termination methods, dominated effects on labile C.

Soil labile organic carbon indicating seasonal dynamics of soil organic carbon in northeast peatland

Peatlands have persisted as massive carbon pool in terrestrial ecosystem. Labile organic carbon (LOC) plays a vital role in carbon cycling in high-latitude peatlands, which is an important indicator of seasonal soil organic carbon (SOC) dynamics. However, the contributions of LOC fractions are poorly understood. Here, soil samples were collected at a high-latitude peatland site located in Northeastern China, and SOC and its labile fractions, including dissolved organic carbon (DOC), light-fraction organic carbon (LFOC), easily oxidizable carbon (EOC) and microbial biomass carbon (MBC) were determined, as well as the environmental and microbial parameters. The results presented seasonal variations in SOC with 352.09 ± 4.93 g/kg in July, 357.84 ± 14.02 g/kg in September, 366.74 ± 17.41 g/kg in November, 413.58 ± 7.83 g/kg in January, and 422.17 ± 8.74 g/kg in April. It was shown that DOC and LFOC were to be important indicators in seasonal carbon dynamics from an elastic net regression model. Although DOC and LFOC accounted for only 3.88% ± 0.50% and 0.34% ± 0.21% in this peatland, they might drive the changes in SOC. The redundancy analysis (RDA) model indicated that pH, total nitrogen (TN), precipitation, soil temperature and actinomycetes PLFAs are important driving factors of SOC pools. A structural equation modeling (SEM) was used to part the direct and indirect effects of factors on soil carbon dynamics based on the covariance structures. The results showed that environmental factors influenced SOC pools through different pathways. Soil pH affected carbon pools directly, while soil temperature influenced the carbon cycling indirectly by affecting soil microbes based on the path analysis. This study suggests that DOC and LFOC had the potential to cause the changes of carbon dynamics in northeast crater peatlands.

Nitrogen efficiency by soil quality and management regimes on Malawi farms: Can fertilizer use remain profitable?

• We combine site-specific soil, satellite and management data to estimate 16 regimes for yield response to inorganic nitrogen on farmers’ fields. • Determinants of labile (permanganate oxidizable) carbon is examined to investigate management impacts on soil fertility in the near-term. • Maize response to fertilizer is positively related to labile soil carbon but response estimates are low (negligible to 6 maize kg/nitrogen kg). • Incorporating diverse crop residues and manure consistently for a few years can meaningfully raise labile carbon levels. • Strategies to promote sustainable agricultural intensification and fertilizer use will likely be more successful if soil fertility is addressed holistically. Maize is the primary economic and dietary staple crop for most poor farmers in Southern Africa, yet low yields have persisted in the region for decades. Intensifying maize production in a sustainable way using the same land will be increasingly important as virgin land becomes scarcer and fallowing becomes less common. This study investigates the sustainability of intensification underway in the African smallholder sector using a uniquely detailed panel survey that combines remote sensing data, soil analysis, yield cuts, GPS area measurements, and detailed field management surveys. Specifically, we quantify the on-farm yield response to nitrogen (N) fertilizer in relationship to 16 soil and field management regimes, adding to the scant literature that combines precise and objective measures of inputs, outputs, and ecological conditions on fields managed by farmers. Furthermore, we examine drivers of soil health using a measure of labile carbon that, unlike total carbon, can be responsive to farm management over the observable time period. Results are based on a representative sampling of Malawi’s diverse agroecosystems through a multi-year study for over 1000 fields. We find surprisingly low yield response to N applications, highlighting that fertilizer access alone is not sufficient for sustainable intensification. We find complimentary “good agronomy”, including effective weed management, crop rotations, and organic fertilizer applications are positive influences on maize yield response to inorganic fertilizers. Encouragingly, results show management practices such as incorporating diverse crop residues and manure for a few years can raise labile carbon levels, improving the soil base on which factors jointly determine yields. These findings underscore the importance of education, livestock and crop diversification, and farmer utilization of good agronomy to improve fertilizer use efficiency as a means to promote sustainable agricultural productivity.

Nitrogen Enrichment during Soil Organic Matter Burning and Molecular Evidence of Maillard Reactions.

Wildfires in forested watersheds dramatically alter stored and labile soil organic matter (SOM) pools and the export of dissolved organic matter (DOM). Ecosystem recovery after wildfires depends on soil microbial communities and revegetation and therefore is limited by the availability of nutrients, such as nitrogen-containing and labile, water-soluble compounds. However, SOM byproducts produced at different wildfire intensities are poorly understood, leading to difficulties in assessing wildfire severity and predicting ecosystem recovery. In this work, water-extractable organic matter (WEOM) from laboratory microcosms of soil burned at discrete temperatures was characterized by ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry to study the impacts of fire temperature on SOM and DOM composition. The molecular composition derived from different burn temperatures indicated that nitrogen-containing byproducts were enriched with heating and composed of a wide range of aromatic features and oxidation states. Mass difference-based analysis also suggested that products formed during heating could be modeled using transformations along the Maillard reaction pathway. The enrichment of N-containing SOM and DOM at different soil burning intensities has important implications for ecosystem recovery and downstream water quality.

Effects of Warming and Increased Precipitation on Soil Respiration of Abandoned Grassland in the Loess-Hilly Regions

Clarifying the changing trends and driving factors of soil respiration in fragile habitats under the background of climate change is of great significance for understanding the regional carbon cycle and the conversion of ecosystem carbon source and sink functions. This research focused on grasslands that had been naturally abandoned and restored for 12 years in the loess hilly region of northern Shaanxi, using an open top chamber (OTC) and artificially increased natural rainfall to simulate climate warming and precipitation increase and their interaction. Furthermore, we used a combination of field monitoring and indoor analysis to explore soil water content, temperature, and nutrient characteristics and the response characteristics of soil respiration rate to warming and increased precipitation and further analyzed the key factors driving changes in soil respiration. The results showed that:① warming (W) significantly increased the 5 cm soil temperature, with an average increase of 1.34℃ throughout the sampling year, whereas the increased precipitation (P50%) treatment significantly reduced the 5 cm soil temperature, reducing the average 5 cm soil temperature during the entire sampling year by 0.88℃ and increasing the soil water content (SWC) at the same time. The SWC was 13.12% and 16.45% higher than that in the control (CK), respectively. In addition, compared with that in the CK, the treatment of warming and increased precipitation (WP50%) not only increased soil temperature but also increased SWC; in general, the increase in temperature and precipitation played an antagonistic effect on the influence of soil temperature and humidity. ② P50% significantly increased the content of soil organic carbon, dissolved organic carbon, and labile organic carbon, causing changes in the soil stoichiometric ratio and the distribution characteristics of labile-recalcitrant carbon components, whereas W did not have a significant impact on organic carbon. In addition, soil total nitrogen and phosphorus and available nitrogen and phosphorus nutrients were not significantly different between treatments. ③ P50% significantly increased the Rs rate, and the effect of W on the soil respiration rate mainly depended on the seasonal precipitation and temperature. It was demonstrated that warming in winter and seasons with abundant rainfall had a significant promotion effect on the soil respiration rate. The exponential fitting of soil respiration rate and 5 cm soil temperature found that the soil respiration temperature sensitivity (Q10) was the highest under the precipitation treatment, reaching 1.68, whereas the Q10 was the lowest under the warming treatment (1.50). ④ Linear regression analysis showed that soil organic carbon, dissolved organic carbon, and labile organic carbon were all significantly positively correlated with soil respiration rate. Variation partitioning analysis showed that soil temperature, SWC, and nutrient characteristics explained 64.43% of the variation in soil respiration rate. The soil temperature and SWC were the main controlling factors of the change in soil respiration rate, with an explanation degree of 31.16%. Correlation analysis also showed that there was a significant correlation between SWC, soil temperature and respiration rate, soil organic carbon, dissolved organic carbon, labile organic carbon, C:N, and C:P. In summary, the climate prediction of abandoned grassland tending toward warm temperatures and high humidity in the loess hilly region will significantly affect the regional hydrothermal environment and nutrient characteristics, change the distribution ratio of soil labile and recalcitrant carbon, and promote regional soil carbon emissions. The analysis results showed that the key factor driving the change in soil respiration rate of abandoned grassland in the loess hilly region was soil temperature and SWC characteristics.

A Bayesian approach to understand controls on total and labile soil carbon in cultivated soils of Central and Southern Malawi

Soil degradation on cultivated lands of Sub-Saharan Africa is a threat to food security. Even so, drivers of soil C total and labile pools are little understood for smallholder farms. A unique opportunity to evaluate how environment conditions management drivers was afforded by a systematically representative on-farm study of 1108 cultivated plots in marginal to mesic environments across Central and Southern Malawi. Soil sample collection and analysis and surveys of farmer practice were conducted, and linked to remote-sensed data on environmental and spectral factors. Soil properties included the following ranges (mean values per site), soil clay (6.41% to 17.36%), pH (6.09 to 6.54), soil organic carbon (SOC) (6.31 g C kg soil−1 to 16.17 g C kg soil−1), and two labile soil C assays: permanganate oxidizable carbon (POXC) (291.5 mg C kg soil−1 to 504.5 mg C kg soil−1) and 24-h mineralizable C (Cmin) (28.71 mg C kg soil−1 to 65.34 mg C kg soil−1). Incorporation of domain specialists’ expectation of uncertainty levels is key to carrying out a multiscale assessment of soil total and labile C status, thus a Bayesian linear regression approach was used for determining the influential drivers. Overall, the soil clay content is a strong predictor of SOC (0.479–0.517), POXC (0.139–0.266), and Cmin (0.125–0.223) at the 95% Bayesian credibility level from the Gibbs posterior samples. Vegetative cover, reflected by Normalized Difference Vegetation Index (NDVI), is also a dominant driver for SOC (0.234–0.329), POXC (0.163–0.285), and Cmin (0.249–0.38). Of the management practices studied, crop diversity, residue incorporation, and weed presence are all positive drivers for total soil C, whereas fertilizer N is not. At both regional and local scales, labile soil C pools (as reflected by POXC and Cmin) are not consistently responsive to management. The drivers of SOC are highly consistent, a strong indication of statistical robustness. This contributes to the understanding of patterns of carbon pools in intensively cultivated fields in Sub-Saharan Africa.

Land Use, Landform, and Soil Management as Determinants of Soil Physicochemical Properties and Microbial Abundance of Lower Brahmaputra Valley, India

Due to the shifting course of the Brahmaputra River, the fluvial landforms of the Brahmaputra Valley of Assam, India, are prone to changes in landform and land use. For sustainable soil management under such conditions, it is crucial to have information about soil physicochemical and biological properties for different land uses. Therefore, the present study was conducted to investigate the soil physicochemical properties and soil microbial population across five major land uses under different landforms, such as paddy fields, banana systems, and arecanut cultivations in the alluvial plains; and rubber plantations and sal forests in the uplands, with varying slope gradients and soil depths (0–25 cm and 25–50 cm) in the lower Brahmaputra Valley. The results of the analysis of variance revealed that the effects of different landforms and land uses were found to be statistically significant on very labile soil organic carbon (VLSOC), available K, B, Fe, Mn, Zn, and Cu, and soil moisture content across two different soil depths. Paddy cultivated systems recorded the highest (1.23%) soil organic carbon (SOC), but these levels were statistically at par with other land use scenarios except for banana systems; whereas, forests and rubber plantations showed the highest VLSOC (0.38% and 0.34%, respectively,) and were significantly different from other land use scenarios. All soil microbial populations (bacteria, fungi, and actinomycetes) studied varied significantly in different land uses across varying soil depths. Perennial land uses under arecanut, rubber, and forest cultivations showed significantly higher microbial populations than paddy and banana systems. The principal component analysis (PCA) identified SOC, VLSOC, Cu, K, B, P, and the bacteria count as the major soil quality parameters of the study area. The results showed that landforms, land use, and management practices collectively affect soil properties. Therefore, soil management choices should take into consideration the landforms and land use for maintaining soil health and its sustainability.

Impacts of Elevated Atmospheric CO2 and N Fertilization on N2O Emissions and Dynamics of Associated Soil Labile C Components and Mineral N in a Maize Field in the North China Plain

The elevated atmospheric CO2 concentration (eCO2) is expected to increase the labile C input to the soil, which may stimulate microbial activity and soil N2O emissions derived from nitrification and denitrification. However, few studies studied the effect of eCO2 on N2O emissions from maize field under the free-air CO2 enrichment (FACE) conditions in the warm temperate zone. Here, we report a study conducted during the 12th summer maize season under long-term eCO2, aiming to investigate the effect of eCO2 on N2O emissions. Moreover, we tested zero and conventional N fertilization treatments, with maize being grown under either eCO2 or ambient CO2 (aCO2). We hypothesized that N2O emissions would be increased under eCO2 due to changes in soil labile C and mineral N derived from C-deposition, and that the increase would be larger when eCO2 was combined with conventional N fertilization. We also measured the activities of some soil extracellular enzymes, which could reflect soil C status. The results showed that, under eCO2, seasonal N2O and CO2 emissions increased by 12.4–15.6% (p < 0.1) and 13.8–18.5% (p < 0.05), respectively. N fertilization significantly increased the seasonal emissions of N2O and CO2 by 33.1–36.9% and 17.1–21.8%, respectively. Furthermore, the combination of eCO2 and N fertilization increased the intensity of soil N2O and CO2 emissions. The marginal significant increase in N2O emissions under eCO2 was mostly due to the lower soil water regime after fertilization in the study year. Dissolved organic C (DOC) and microbial biomass C (MBC) concentration showed a significant increase at most major stages, particularly at the tasseling stage during the summer maize growth period under eCO2. In contrast, soil mineral N showed a significant decrease under eCO2 particularly in the rhizospheric soils. The activities of C-related soil extracellular enzymes were significantly higher under eCO2, particularly at the tasseling stage, which coincided with concurrent increased DOC and MBC under eCO2. We conclude that eCO2 increases N2O emissions, and causes a higher increase when combined with N fertilization, but the increase extent of N2O emissions was influenced by environmental factors, especially by soil water, to a great extent. We highlighted the urgent need to monitor long-term N2O emissions and N2O production pathways in various hydrothermal regimes under eCO2.

Climate legacies determine grassland responses to future rainfall regimes.

Climate variability and periodic droughts have complex effects on carbon (C) fluxes, with uncertain implications for ecosystem C balance under a changing climate. Responses to climate change can be modulated by persistent effects of climate history on plant communities, soil microbial activity, and nutrient cycling (i.e., legacies). To assess how legacies of past precipitation regimes influence tallgrass prairie C cycling under new precipitation regimes, we modified a long-term irrigation experiment that simulated a wetter climate for >25years. We reversed irrigated and control (ambient precipitation) treatments in some plots and imposed an experimental drought in plots with a history of irrigation or ambient precipitation to assess how climate legacies affect aboveground net primary productivity (ANPP), soil respiration, and selected soil C pools. Legacy effects of elevated precipitation (irrigation) included higher C fluxes and altered labile soil C pools, and in some cases altered sensitivity to new climate treatments. Indeed, decades of irrigation reduced the sensitivity of both ANPP and soil respiration to drought compared with controls. Positive legacy effects of irrigation on ANPP persisted for at least 3years following treatment reversal, were apparent in both wet and dry years, and were associated with altered plant functional composition. In contrast, legacy effects on soil respiration were comparatively short-lived and did not manifest under natural or experimentally-imposed "wet years," suggesting that legacy effects on CO2 efflux are contingent on current conditions. Although total soil C remained similar across treatments, long-term irrigation increased labile soil C and the sensitivity of microbial biomass C to drought. Importantly, the magnitude of legacy effects for all response variables varied with topography, suggesting that landscape can modulate the strength and direction of climate legacies. Our results demonstrate the role of climate history as an important determinant of terrestrial C cycling responses to future climate changes.

Phosphorus Fractions and Arbuscular Mycorrhizal Fungi Communities in a Tropical Coarse-Textured Soil under Natural Forest and Para Rubber Ecosystems

Soil phosphorus (P) plays an essential role in rubber tree plantations that are rapidly and extensively being established in Southeast Asia. However, available information is quite limited on soil P fractions and arbuscular mycorrhizal fungi (AMF) in the tropical region. Herein, we investigated P fractions and AMF community under natural forest and rubber plantations at different ages of 5 years, 11 years, and 22 years in tropical coarse-textured soils from Thailand. The studied loamy sand soils were acidic (pH=5.0-5.7) with low available P concentrations (1.73-6.48 mg/kg). Data on the P fractions data revealed that the labile P (water-extractable Pi and NaHCO3-extractable Pi) and moderately labile P (NaOH0.1-extractable Po and HCl-extractable Pi) pools in rubber-growing soils were higher than those in the natural forest soil. Elevated values of these properties were substantial with increasing stand ages. The rubber monocropping systems declined in the density and diversity of AMF spores compared to the natural forest site. Glomus badium, Rhizophagus fasciculatus, Acaulospora Laevis, and Ambispora appendiculata were the most dominant and tolerant AMF species across the rubber stands (>50% of the total species). The P fractions and AMF were correlated with soil labile-P forms. Soil labile and moderately P fractions were the important factors affecting the difference in AMF community. This study highlighted that long-term rubber plantations in tropical ecosystems promoted labile P fraction but demoted AMF density and diversity.

Effects of Farmland Conversion to Orchard or Agroforestry on Soil Organic Carbon Fractions in an Arid Desert Oasis Area

In southern Xinjiang province, northwest China, farmland is undergoing rapid conversion to orchards or agroforestry. This has improved land-use efficiency but has also caused drastic ecological changes in this region. This study investigated the effects of farmland conversion to orchard or agroforestry on soil total organic carbon (TOC) and several soil labile fractions: readily oxidizable carbon (ROC), light fraction organic carbon (LFOC), and dissolved organic carbon (DOC). Soil samples were collected from seven cropping treatments: a monocultured wheat field (Mono), a 5-year-old jujube orchard (5 J), a 5-year-old jujube/wheat alley cropping system (5 JW), a 10-year-old jujube orchard (10 J), a 10-year-old jujube/wheat alley cropping system (10 JW), a 15-year-old jujube orchard (15 J), and a 15-year-old jujube/wheat alley cropping system (15 JW). The results show that the ROC concentrations varied from 0.17 ± 0.09 g/kg to 2.35 ± 0.05 g/kg across all land-use types and soil depths studied. It was higher in the 0–10 cm and 10–20 cm layers of treatment 10 JW than in other treatments and significantly greater than in the Mono treatment. The highest value of DOC was reached at 593.04 mg/kg in the 15 JW treatment at 0–10 cm. Labile organic carbon decreased with increasing depth in all treatments. The proportion of ROC and LFOC to TOC decreased with increasing soil depth. In all treatments, the ratio of DOC to TOC generally decreased initially and then increased again with increasing depth. Correlation analysis showed that ROC, LFOC, and DOC were closely correlated with TOC (p < 0.01). The ROC, LFOC, and DOC concentrations were significantly correlated with each other (p < 0.01). Following conversion of farmland to jujube orchard or agroforestry, the content and activity of soil organic carbon tended to increase due to augmentation of plant residues. Thus, jujube orchards and agroforestry systems are effective methods to restore soil organic carbon.

Cropping management in a livestock-pasture-crop integration modifies microbial communities, activity, and soil health score.

Understanding indicators of soil health is crucial for developing agricultural systems that are sustainable and climate resilient. Labile soil carbon (C), microbial properties, and nutrient status are all incorporated into the Haney Soil Health Tool with the goal of summarizing several indicators into one index. Monthly soil samples from an integrated crop-livestock system in Central Texas were collected from 2017 to 2019. Fields represented a range of management practices, including cover crops, no-till, rotational grazing, and a native prairie remnant. Soil samples were analyzed for total C, water-soluble C, macro- and micronutrient content and bioavailability, and phospholipid fatty acids (PLFAs). Microbial activity was determined via a 24-h CO2 incubation. Soil health score, C, and PLFAs were well correlated with each other. The greatest total PLFA (219.5nmol g-1 soil) and organic C (54.3g kg-1 soil) were found in the native prairie, and the lowest were found in the unfertilized continuous-corn system (60.5nmol PLFAs g-1 soil and 24.0g organic C kg-1 soil). Of all agroecosystems, the perennial grazing system (soil health score, 24.7) was most similar to the native prairie (soil health score, 27.4), having high soil C and a large microbial community. Of the row cropping systems, the no-till system approached the perennial systems better than the conventional till and unfertilized conventional till (soil health score, 11.1 vs. 8.0 and 5.3, respectively). This study highlights the value of perennial grass grazing in agroecosystems and appropriate best management practices. Expanding this analysis to other sites may provide additional insight.

Nano and Fine Colloids Suspended in the Soil Solution Regulate Phosphorus Desorption and Lability in Organic Fertiliser-Amended Soils

Nano and Fine Colloids Suspended in the Soil Solution Regulate Phosphorus Desorption and Lability in Organic Fertiliser-Amended Soils

Deadwood mass and microclimate affect labile soil carbon and nitrogen under thinning of a naturally regenerated oak forest

Context Labile soil carbon and nitrogen are important indicators for evaluating carbon sequestration and nutrient availability under forest management such as thinning. Aims This study assessed the effects of thinning on labile soil carbon and nitrogen indices in a naturally regenerated oak forest. Methods Un-thinned control, 15% thinning, and 30% thinning were set up, and labile soil carbon and nitrogen (microbial biomass, permanganate oxidisable carbon, dissolved carbon and nitrogen, and inorganic nitrogen) and C:N balance indices (C:N ratio and threshold element ratio) were measured after 6 years. Key results Thinning generally increased labile soil carbon and nitrogen concentrations (P < 0.01); however, their fraction within the total soil carbon and nitrogen decreased under thinning. Redundancy analysis revealed that the remaining deadwood mass was the most influential factor affecting such differences in labile soil carbon and nitrogen indices across the three treatments (P < 0.01), although soil moisture had an effect as well (P < 0.05). Furthermore, the dissolved C:N ratio was higher than threshold element ratio only in 15% and 30% thinnings, indicating that thinning could shift the limiting factor for microbial growth from carbon to nitrogen by adding deadwoods, which provided carbon-rich substrates. Conclusions Overall, results demonstrate that deadwood retention and soil microclimatic changes could be the significant factors affecting soil carbon and nitrogen storage and the associated microbial affinity in thinned forests. Implications Therefore, sustainable forestry strategies for thinning residue management should be addressed to reinforce soil carbon and nitrogen conditions and the forest ecosystem functions.

Changes in Soil Organic Carbon and Its Labile Fractions after Land Conversion from Paddy Fields to Woodlands or Corn Fields

Land use change could significantly affect soil organic carbon (SOC) and other soil chemical properties. However, the responses of soil labile C fractions at different soil depths to land-use change are not still clear. The aim of this study was to investigate the effect of paddy field conversion on woodlands or corn fields on total soil organic C (TOC) and its labile C fractions including particulate organic C (POC), microbial biomass C (MBC), and potassium permanganate-oxidizable C (KMnO4–C) along a 0–100 cm soil profile. Our results indicate that soil TOC concentrations increased by 3.88 g kg−1 and 3.47 g kg−1 in the 0–5 cm soil layer and 5.33 g kg−1 and 4.68 g kg−1 in the 5–20 cm soil layer during 13 years after the conversion from paddy fields to woodlands and corn fields, respectively. In the 20–40 cm soil layer, the woodlands had the highest TOC concentration (12.3 g kg−1), which was 5.13 g kg−1 and 3.5 g kg−1 higher than that of the paddy and corn fields, respectively. The increase in TOC was probably due to the absence of soil disturbance and greater root residue input into the woodland soil. In corn fields, pig manure addition contributed to the increase in soil organic C concentrations. In addition, the proportion of soil KMnO4–C increased after conversion from paddy fields to woodlands or corn fields in the 0–40 cm soil layer, ranging from 39.9–56.6% for the woodlands and 24.6–32.9% for the corn fields. The soil POC content was significantly higher in woodland and corn field soils than in paddy field soils at lower soil depths (5–40 cm). However, there were no differences in MBC contents in the whole soil profile between the woodlands and paddy fields. The KMnO4–C and MBC was the most important factor affecting the CMI values through the whole 0–100 cm soil profile. Overall, converting paddy fields to woodlands or corn fields increased the TOC and labile C fractions in the 0–40 cm soil layer. Future studies should focus on the response of the deeper soil C pool to land-use change.

Quantifying the immediate response of the soil microbial community to different grazing intensities on irrigated pastures

Grazing is known to affect soil microbial communities, nutrient cycling, and forage quantity and quality over time. However, a paucity of information exists for the immediate changes in the soil physicochemical and microbial environment in response to different grazing strategies. Soil microbes drive nutrient cycling and are involved in plant-soil-microbe relationships, making them potentially vulnerable to plant-driven changes in the soil environment caused by grazing. To test the hypothesis that variable grazing intensities modulate immediate effects on the soil microbial community, we conducted a grazing trial of three management approaches; high-intensity, short-duration grazing (HDG), low-intensity, medium-duration grazing (LDG), and no grazing (NG). Soil and vegetation samples were collected before grazing and 24h, 1 week, and 4 weeks after HDG grazing ended. Soil labile carbon (C) and nitrogen (N) pools, vegetation biomass, and soil microbial diversity and functional traits were determined, including extracellular enzymatic assays and high-throughput sequencing of the bacterial 16S rRNA and fungal ITS2 regions. We found that labile soil C and inorganic N increased following LDG grazing while C-cycling extracellular enzymatic activities increased in response to HDG grazing but both total extracellular enzymatic activity profiles and soil abiotic profiles were mostly affected by temporal fluxes. The soil fungal community composition was strongly affected by the interaction of sampling time and grazing treatment, while the soil bacterial community composition was largely affected by sampling time with a lesser impact from grazing treatment. We identified several key fungal taxa that may influence immediate responses to grazing and modulate plant-soil-microbe interactions. There was strong evidence of temporal influences on soil biogeochemical variables and the soil microbiome, even within our narrow sampling scheme. Our results indicate that the soil ecosystem is dynamic and responsive to different grazing strategies within very short time scales, showing the need for further research to understand plant-soil-microbe interactions and how these feedback mechanisms can inform sustainable land management.