Higher Soil Organic Matter Research Articles

Soil chemical properties and wheat yields under different tillage and nitrogen rates in eastern Oregon

AbstractTillage and nitrogen (N) application influence soil‐chemical properties and crop productivity. In a long‐term (76‐yr) wheat (Triticum aestivum L.)–fallow system in northeast Oregon, we assessed the effects of tillage (subsurface‐sweep, sweep; offset‐disk, disk; and moldboard plow, plow) and N application rates (0, 90, and 180 kg N ha−1) on soil organic matter (SOM), soil‐chemical properties in 0‐to‐30‐cm soil profile, and wheat yields. Sweep and disk exhibited more pronounced vertical gradient in soil chemical properties within the 0‐to‐30‐cm soil profile than plow due to shallow soil mixing. Across N rates, at 0‐to‐10‐cm depth, sweep and disk had lower pH (0.60), calcium (Ca; 0.32 g kg−1), magnesium (Mg; 83 mg kg−1), and estimated cation exchange capacity (CECe; 1.8 cmol kg−1), but higher SOM (9 g kg−1) and aluminum (Al; 26 mg kg−1) than plow. Below 10 cm, plow had lower pH (0.67–0.83), Ca (0.29–0.31 g kg−1), and CECe (1.7–1.8 cmol kg−1), but higher Al (13–16 mg kg−1) than disk and/or sweep. Across tillage treatments and depths, pH, Ca, Mg, and CECe generally decreased, whereas phosphorus, potassium, and Al increased with increasing N rates. Wheat yields increased by 14% from N application but did not differ between 90 and 180 kg N ha−1. Sweep and disk produced 9% less wheat yield than plow. Long‐term N application and grain removal of basic cations resulted in surface soil acidification under sweep and disk, which if not remedied, can decrease wheat productivity in this region.

Effect Of Leguminous Winter Cover Crops On Soil Fertility And Yield Of Summer Maize

A field experiment was conducted at IAAS agronomy farm, Rampur, Chitwan, Nepal from Nov. 2012 to Aug. 2013 to improve soil fertility and production of maize through the inclusion of leguminous winter cover crops in the cropping system. The experiment was conducted for two seasons in single factor randomized complete block design (RCBD) with eight treatments and three replications. Five N fixing legume crops: chickpea (Cicer arietinum), garden pea (Pisum sativum var. sativum), field pea (Pisum sativum var. arvense), lentil (Lens culinaris) and grass pea (Lathyrus sativus); one N fixing legume fodder: Berseem (Trifolium alexandrinum); one non-fixing legume: rajma bean (Phaseolus vulgaris); and maize (as a control) were cultivated in the first season and on the following season maize was cultivated in all plots after incorporating former crop residues. Rajma bean covered the highest area at an early stage but field pea and grass pea covered the maximum land area at a later stage. The highest dry matter production (2.32 t/ha) and nitrogen content in residues (2.57%) were obtained from lentil. Cultivation of leguminous winter cover crops had no significant effect on soil parameters. However, the incorporation of legume residues had significant effects on organic matter content, total nitrogen and available phosphorus in soils. The highest soil organic matter (3.03%) and total nitrogen (0.15%) was observed from field pea plots while the highest available phosphorus (36.00 kg/ha) was from berseem plots. Legumes cultivation and their residues incorporation into the soil had significant effects on grain, straw and dry matter yields of succeeding maize crop. Grain (3.92 t/ha), straw (5.39 t/ha) and dry matter (9.31 t/ha) yields were the highest from lentil plots while the lowest grain (2.51 t/ha), straw (3.96 t/ha) and dry matter (6.48 t/ha) from control plots. Total nitrogen uptake by maize was significant and it was the highest (141.90 kg/ha) from lentil plots and the lowest (109.80 kg/ha) from control plots. Cultivation of lentil in the winter produced satisfactory land coverage and incorporation of its residues into the soil was the best for improving soil fertility and succeeding maize yield under the Chitwan condition of Nepal.

Soils Carbon Stocks and Litterfall Fluxes from the Bornean Tropical Montane Forests, Sabah, Malaysia

Tropical forests play an important role in carbon storage, accumulating large amounts of carbon in their aboveground and belowground components. However, anthropogenic land-use activities have increasingly threatened tropical forests, resulting in accelerated global greenhouse gas emissions. This research aimed to estimate the carbon stocks in soil, organic layer, and litterfall in tropical montane forests under three different land uses (intact forest, logged-over forest, and plantation forest) at Long Mio, Sabah, Malaysia. Field data were collected in a total of 25 plots from which soil was randomly sampled at three depths. Litterfalls were collected monthly from November 2018 to October 2019. The results showed that the soil in the study area is Gleyic Acrisol, having pH values ranging between 4.21 and 5.71, and high soil organic matter contents. The results also showed that the total soil carbon stock, organic layer, and litterfall is higher in the intact forest (101.62 Mg C ha−1), followed by the logged-over forest (95.61 Mg C ha−1) and the plantation forest (93.30 Mg C ha−1). This study highlights the importance of conserving intact forests as a strategy to sequester carbon and climate change mitigation.

Természetvédelmi célú botanikai, takarmányozástani és talajtani vizsgálatok a Tapolcai és Káli-medence szürkemarha és bivaly legelőin

In the present work we introduce the coenological and pedological results of examination on the Balaton Upland (Badacsonytördemic, Csobánc, Káptalantóti and Kővágóőrs). Grass management plays an important role in nature conservation, rural development thus in the viability of rural population. Soil and water suffer from extreme degradation and pollution, partly because of agricultural activities, growing settlements and mining activity. We evaluated the changes in species composition and coverage, the possibly occurring regeneration or degradation and the effects of botanical composition changes on forage values, especially in case of economically valuable species. Investigations show strengths and weaknesses of having animals on grasslands. Sample sites were in Balaton Upland National Park, Hungary. Results proved that among the plants there are either weeds and/or poisonous and/or prickly species, too. We examined how important grasses and pulses appeared or disappeared, how did the number of overgrazing tolerant species changed and how did the species composition of the grazed and non-grazed land differed. Based on the results the characteristics of the examined pastures show the effects of overgrazing. With the decrease of the number of the animals, nature conservation and economical values could be increased. The examined areas had totally different soil characteristics, pH, soil thickness and nutrient content varied greatly. In the Gyulakeszi area even a small catena was found on a single pasture. The high soil organic matter and nutrient content ensure the good grass yield thus the areas are suitable for grazing and for grass cutting, too.

Regional mapping of soil organic matter content using multitemporal synthetic Landsat 8 images in Google Earth Engine

Accurate assessment of the spatial distribution of soil organic matter (SOM) is of great significance for regional sustainable development, especially in fertile black soil areas. The present study proposed a regional-scale high spatial resolution (30 m) SOM mapping method based on multitemporal synthetic images. The study area is located on the Songnen Plain of Northeast China. First, all available Landsat 8 surface reflectance (SR) data during the bare soil period (April and May) from 2014 to 2019 in the study area were screened in the Google Earth Engine (GEE), and the cloud mask was constructed. The median, average, maximum, and minimum values of the image set were synthesized according to single-year multimonth, multiyear single-month and multiyear multimonth time ranges, and the spectral index of the synthesized image was constructed. Second, the bands and spectral indices of different synthetic images were used as input to establish a random forest (RF) model of SOM prediction, and the accuracies of different spatial prediction models of SOM were compared to evaluate the optimal regional remote sensing prediction model of SOM. The following results were show. 1) The use of the spectral index combined with the image band as input had a greater improvement in the accuracy of SOM prediction than the use of only the image band. 2) Compared to the average, maximum and minimum synthesized images, the median synthesized image had higher accuracy in SOM prediction. 3) More years of synthesized images provided more robust SOM prediction results. 4) May was the best time window for SOM mapping on the Songnen Plain. This study presents a large-scale and high spatial resolution SOM mapping method that is suitable for black soil areas in Northeast China and extends the application of GEE in digital soil mapping.

Effects of Ca2+ on migration of dissolved organic matter in limestone soils of the southwest China karst area

AbstractThe prospect of carbon sequestration in soils of karst areas remains unclear. The study on migration and transformation of dissolved organic matter (DOM) in limestone soil under the high calcium environment of karst regions has seldom been reported. This study conducted soil column experiments on two surface soils (H1 and S2) and two subsurface soils (H2 and S2) from two limestone soil profiles in the karst region of southwest China and investigated their DOM leaching behaviours under different Ca2+ concentration levels. The results showed that the DOM leaching process can be described by the Elovich equation, including a rapid DOM release stage and the relatively stable DOM release stage. When the Ca2+ concentration of eluent increases from 0 to 2.5 mmol L−1, the percentage of dissolved organic carbon (DOC) loss in H1, H2, S1, and S2 soils decreased from 66.3% to 58.8%, from 76.2% to 72.4%, from 73.0% to 68.8%, and from 52.5% to 46.6%, respectively, and the apparent molecular weight of leached DOM increases, the aromaticity of leach DOM and the contribution of humic‐like components decrease. The results further show that the influence of Ca2+ on easily leaching DOM is stronger than that on the stable DOM, indicating that high Ca2+ runoff can enrich high aromaticity and high molecular weight soil organic matter (SOM) in the limestone soil during the leaching process. This research is helpful to understand the migration and fate of SOM in limestone soils and provides theoretical support for increasing soil carbon sinks in karst areas.

How farmers approach soil carbon sequestration? Lessons learned from 105 carbon-farming plans

Soil carbon sequestration is a recognized climate mitigation method, but it involves changes in the practices of more than 0.5 billion farms worldwide. Regionally customized carbon-farming programs are one way to tailor soil carbon storage to local conditions. We conducted farmer participatory research on 105 Finnish farms to investigate how farmers approach carbon (C) sequestration. We conducted training for farmers in the basics of carbon-farming and instructed them to make a Carbon Farming Plan for one of their fields. The plans were evaluated by a team of experts and through soil C balance calculations. In addition, potential nutrient limitations and the existing C stock were identified from soil tests. Although the existing C stocks were relatively high, an assessment of the plans indicated high potential for additional C storage (median 320 kg C ha−1year−1). The plans did not show any sensitivity to the existing C stock, with similar C inputs planned for low organic matter (OM) and high OM soils. The farmers either did not know their C stock or were not familiar with the C balance concept. Most soil samples showed considerable nutrient deficiencies (P, S, B and Mn), which can limit C storage. The quality of most plans was adequate for research with minor modifications. The largest C storage potential was estimated for measures with large additions of nutrient-poor amendments or in grazing. Most farmers chose measures with relatively low C storage benefits but high potential benefits for soil structure and productivity (cover crops, nutrient-rich amendments, grassland management). The C gain from some measures (subsoiling, diversity in grasslands) could not be estimated with current methodologies. The magnitude of planned C storage over 5 years on most farms was so small (<0.5% OM), that it is challenging to measure it through soil sampling. This finding supports the earlier conclusions that a combination of modeling and soil sampling is needed to verify the C storage.

Accumulation of potentially toxic trace elements (PTEs) by native plant species growing in a typical gold mining area located in the northeast of Qinghai-Tibet Plateau.

Though gold mines provide significant economic benefits to local governments, mining causes soil pollution by potentially toxic trace elements (PTEs) in mining areas, especially in the Qinghai-Tibet Plateau. Screening of native plant species from mining areas is now an effective, inexpensive, and eco-friendly method for the remediation of PTEs in situ. In the present study, we conducted experiments to assess the accumulation of As, Cd, Pb, and Zn in 12 native plant species growing on a typical gold mining area in the Qinghai-Tibet Plateau. Our results showed that rhizosphere soils have high soil organic matter content, high levels of As, and moderate levels of Cd. Geranium pylzowianum accumulated relatively higher As in its shoots and exhibited translocation factor (TF) higher than 1 for As (4.65), Cd (1.87), and Pb (1.36). Potentilla saundersiana had bioconcentration factor of shoot (BCF-S) higher than 1 for Cd (4.52) and Pb (1.70), whereas its TF was higher than 1 for As, Cd, Pb, and Zn. These plant species exhibit strong tolerance to these PTEs. Furthermore, Elymus nutans accumulated low levels of As, Cd, Pb, and Zn in their shoots and exhibited TF values lower than 1 for the four PTEs. Therefore, G. pylzowianum is a promising candidate for the in situ phytoextraction of As, and P. saundersiana can be used as an effective plant for Cd and Pb phytoextraction. E. nutans is better suited for the phytostabilisation of multiple PTEs. This work is of significant importance for screening native plant species that can provide a reference for phytoremediation of PTE-contaminated soils in this area or other place with similar climate, and has a good potential for developing PTE phytoremediation strategies at mining sites.

Small Ruminants Grazing as a Rehabilitative Land Management Tool in the Negev Highland; Soil, Geomorphological and Topographical Perspectives

The ‘wadis’ (ephemeral incised channels in arid regions) concern badlands with low agriculture utilisation that expands to neighbouring cultivated areas. They are noticeable and unique landforms characterised by vegetation patches and seasonal flood flows with scenic beauty that must be conserved. The wadi characteristics have influenced the way of life of their indigenous residents from ancient times until now. The main one is grazing with small ruminants (SR). The authorities and public consider grazing in these areas as a destructive land management practice that should be reduced. To assess the viability of grazing in such regions, we hypothesised that fluvial and biological flows tightly correlate with the wadis’ landforms, channels and slopes. The site of study is located in the Yeroham mountains nearby the Rahma planned Bedouin village. Five different transects of channels and slopes were located over representative wadis, including those exposed to grazing. The finding indicates that a herbaceous vegetation expansion uphill was observed only in grazed transects, while the wadi slope patterns affect its patterns. It contains an increased soil water content (from a similar value of 5% until 13% change in the grazed transect), 1.5% higher soil organic matter, 0.08 mg Kg−1 higher Nitrite content and 1–2% higher clay content in the grazed transects, up to 4 m ahead from the channel. The novelty of this finding suggested that the SR influences the organic matter to reach the wadi channel and facilitate the adherence of aggregated clay and the formed colluvial layer that serves as a substrate to the expanded vegetation growth. Adequate implementation of these grazing patterns may rehabilitate degraded ‘wadis’ and increase their tourism eligibility.

The Distribution of Soil Micro-Nutrients and the Effects on Herbage Micro-Nutrient Uptake and Yield in Three Different Pasture Systems

Pasture micro-nutrient concentrations are often deficient for herbage productivity and the health of livestock. The aim of this study was to investigate soil and herbage micro-nutrient content and the effects on yield on the three pasture systems of the North Wyke Farm Platform (NWFP): high-sugar grass + legume mix minus nitrogen (N) fertilizer (blue/HSG + L); permanent pasture plus N fertilizer (green/P + N); high-sugar grass plus N fertilizer (red/HSG + N). The locations with high soil total micro-nutrient concentrations had a greater slope and higher soil organic matter (SOM) content. Herbage micro-nutrient concentrations were often greater at the locations with high soil total micro-nutrient concentrations. The concentration and uptake of nearly all micro-nutrients was greatest in the herbage of the green/P + N system, which had the highest SOM content, whereas they were often lowest in the red/HSG + N system, which had the lowest SOM and the highest yield, indicating biomass dilution of micro-nutrients in the herbage. At the locations with high soil micro-nutrient concentrations, yield was higher than at locations with low micro-nutrient concentrations, and was equal across the three pasture systems, regardless of fertilizer N treatment. Variation in micro-nutrient uptake/yield in the blue grass–legume system was predominantly explained by the soil molybdenum (Mo) concentration, possibly relating to the requirement for Mo in biological nitrogen fixation. There was, therefore, a trade-off in ploughing and re-seeding for higher yield, with the maintenance of SOM being important for herbage micro-nutrient content.

Influence of organic matter on soil hydrothermal processes in the Tibetan Plateau: Observation and parameterization

AbstractIn the central-eastern Tibetan Plateau (TP) there is abundant organic matter in topsoils, which plays a crucial role in determining soil hydraulic properties that need to be properly described in land surface models. Limited soil parameterizations consider the impacts of soil organic matter (SOM), but they still show poor performance in the TP. A dedicated field campaign is therefore conducted by taking undisturbed soil samples in the central TP to obtain in-situ soil hydraulic parameters and to advance SOM parameterizations. The observed findings are twofold. 1) The SOM pore-size distribution parameter, derived from measured soil water retention curves, has been demonstrated to be much underestimated in previous studies. 2) SOM saturated hydraulic conductivity is overestimated. Accordingly, a new soil hydraulic parameterization is established by modifying a commonly used one based on observations, which is then evaluated by incorporating it into Noah-MP. Compared with the original ones, the new parameterization significantly improves surface soil liquid water simulations at stations with high surface SOM content, especially in the warm season. A further application with the revised Noah-MP indicates that SOM can enhance sensible heat flux but decrease evaporation and subsurface soil temperature in the warm season, and tends to have a much weak effect in the cold season. This study provides insights into the role of SOM in modulating soil state and surface energy budget. Note that, however, there are many other factors at play and the new parameterization is not necessarily applicable beyond the TP.

Impact of Atmospheric Pressure Fluctuations on Nonequilibrium Transport of Volatile Organic Contaminants in the Vadose Zone: Experimental and Numerical Modeling

AbstractAtmospheric pressure fluctuations can induce subsurface airflow, affecting Volatile Organic Compound (VOC) contaminant migration in the vadose zone. When modeling this process, traditional vapor intrusion models have relied on the assumption of local equilibrium conditions and neglected kinetic mass transfer processes among different phases. In this study, a nonequilibrium multiphase flow and transport model was developed to investigate the impact of atmospheric pressure fluctuations on VOC release from groundwater to the atmosphere. Kinetic mass transfer processes between vapor &amp; liquid phases, and between liquid &amp; solid phases were taken into consideration. A series of soil column experiments with downward/upward pumped gas flow were conducted to validate the model. The experimental results imply the necessity to use nonequilibrium models for quantifying the impact of atmospheric pressure fluctuation. The validated model was used to investigate the role of atmospheric pressure fluctuations for various practical hydrogeologic settings under daily pressure fluctuations. It was found that when the soil organic carbon content is relatively large, the nonequilibrium model more accurately represents VOC migration than a traditional equilibrium model. Therefore, this study suggests the need to apply nonequilibrium vapor intrusion models at sites with high soil organic matter content.

Accumulation and relationship of metals in different soil aggregate fractions along soil profiles

Different aggregates vary in their ability to retain or adsorb metals in soil. Five soil profiles were sampled from different soil horizons and grouped, and the concentrations of Al, Mg, Ca, Fe, Mn, Cd, Cu and Pb were determined in six sizes of aggregates (> 2, 2-1, 1-0.6, 0.6-0.25, 0.25-0.053, < 0.053 mm). Significantly high (p < 0.05) structural stability indexes (SSI) and aggregate stability indexes (ASI) were recorded in the topsoil horizon, which may be attributed to the high soil organic matter (SOM) content in aggregates from topsoil. In addition, ASI and SSI were positively correlated (r = 0.569, p < 0.05) with each other, which indicated that the stability of soil aggregates could contribute to the structural stability of bulk soil. Moreover, accumulation factors (AF), principal component analysis (PCA) and Pearson's correlation coefficients were used for metal element assessment. The results indicated that SOM was not a key factor affecting the accumulation of Ca, Mg, Al, Fe, Mn, Pb, Cd and Cu in soil aggregates. In general, AF values for metal elements in microaggregates (< 0.25 mm) were high, which showed that metals preferred to accumulate in fine soil aggregates. The PCA and Pearson's correlation coefficients indicated that soil parent materials primarily controlled the distribution of Al, Ca, Fe, Mg and Mn, while materials derived from technogenic sources have important impacts on the distribution of Cd, Cu and Pb in soil aggregates along the soil profile.

Soil Properties as Affected by Soil Conservation Practices and Soil Depths in Uwite Watershed, Hadero Tunto District, Southern Ethiopia

Soil is a precious natural resource, forming the basis for sustained ecosystem services for the mankind. Its degradation due to the ever-increasing anthropogenic influence is, however, threatening food security and quality of the environment in many regions. The present investigation was, therefore, undertaken with an objective of assessing the effect of soil and water conservation practices of soil bund and Fanya juu terrace compared to no conservation practice on cultivated soils of Uwite watershed in Hadero Tunto District, southern Ethiopia. Soil sampling sites were selected both from the farm fields, where soil conservation structures were raised for the last 10 years, and from fields where there was no conservation practice. A total of eighteen composite soil samples (3 conservation practices × 2 depths, 0–15 and 15–30 cm, ×3 replicates) were collected and analyzed for different physical and chemical soil parameters. The results were subjected to analysis of variance using the General Linear Model of two-way ANOVA by RCBD with factorial arrangement using SAS software. Both practices, statistically similar to each other, indicated significant improvement in soil parameters compared to no conservation practice in higher content of clay, lower bulk density, higher total porosity, higher moisture content, higher pH, higher soil organic matter, higher percent base saturation, higher cation exchange capacity, and higher amounts of macro- (N, P, K, Ca, Mg, and S) and micronutrients (Fe, Zn, and Cu). The surface soil layer (0–15 cm) was significantly superior to the subsurface layer (15–30 cm) in most of these soil parameters. Both practices of soil bund and Fanya juu terrace merit their continuation on the existing lands and upscaling to other degraded areas for sustained land productivity and socioeconomic-environmental stability in the region

Biochar aging alters the bioavailability of cadmium and microbial activity in acid contaminated soils

The effects of biochar aging on heavy-metal bioavailability and microbial activity are not fully understood. This study determined the effect over 270 days of poultry-litter biochar (PBC) and sugar-gum-wood biochar (SBC) on the bioavailability of Cd and microbial activity in acidic soils differing in organic matter content. Soil basal and substrate-induced respirations, microbial properties, Cd bioavailability and plant Cd bioaccumulation were evaluated at 1, 30, 90 and 270 days. The addition of PBC decreased Cd bioaccumulation by 81% and 85% while SBC decreased bioaccumulation by 47% and 56% in high (Chromosol) and low (Sodosol) organic matter soils, respectively, at Day 1. By Day 270, Cd bioaccumulation significantly (P < 0.05) increased in SBC-amended soils but decreased in PBC-amended soils. The addition of PBC increased both basal and substrate-induced microbial respirations compared to the other treatments over 270-day aging. However, SBC increased microbial biomass C compared to the PBC after Day 30. Aging decreased microbial respiration and biomass C in biochar-amended soils. It is concluded that Cd bioaccumulation increased in SBC-amended soils during aging whereas the PBC decreased Cd bioaccumulation and that the selection of biochar is important to enhance remediation efficiency in the long term.

Temporal and microtopographical variations in greenhouse gas fluxes from riparian forest soils along headwater streams

Riparian zones of headwater streams have valuable ecosystem functions and are prevalent across many landscapes. Nevertheless, studies of greenhouse gas (GHG; CO2, CH4, N2O) fluxes from these unique ecosystems, with fluctuating water tables and high soil organic matter, remain limited. Our objectives were to (1) to quantify the effects of local riparian groundwater conditions on soil GHG flux rates, namely to determine if groundwater discharge (DIS) areas in the riparian zone would have higher soil moisture than adjacent non-discharge (ND) areas in the riparian zone, impacting GHG fluxes; and (2) to examine the relationship between GHG fluxes, soil moisture, soil temperature, and groundwater depth. We measured gas fluxes in situ alongside two relatively undisturbed headwater streams over 1 year, using closed static chambers and gas chromatography. We found that, although not significant, DIS areas had on average lower CH4 uptake and lower CO2 emissions than ND areas. We further found that soil temperature explained 30.0% and 26.2% of variation in CO2 and N2O fluxes, respectively, and soil moisture explained 9.8% of variation in CH4 fluxes. Our results provide information on the magnitude and drivers of GHG fluxes in riparian zones to help inform GHG budgets and forest management.

Microbial Respiration and Enzyme Activity Downstream from a Phosphorus Source in the Everglades, Florida, USA

Northeast Shark River Slough (NESS), lying at the northeastern perimeter of Everglades National Park (ENP), Florida, USA, has been subjected to years of hydrologic modifications. Construction of the Tamiami Trail (US 41) in 1928 connected the east and west coasts of SE Florida and essentially created a hydrological barrier to southern sheet flow into ENP. Recently, a series of bridges were constructed to elevate a portion of Tamiami Trail, allow more water to flow under the bridges, and attempt to restore the ecological balance in the NESS and ENP. This project was conducted to determine aspects of soil physiochemistry and microbial dynamics in the NESS. We evaluated microbial respiration and enzyme assays as indicators of nutrient dynamics in NESS soils. Soil cores were collected from sites at certain distances from the inflow (near canal, NC (0–150 m); midway, M (150–600 m); and far from canal, FC (600–1200 m)). Soil slurries were incubated and assayed for CO2 emission and β-glucoside (MUFC) or phosphatase (MUFP) activity in concert with physicochemical analysis. Significantly higher TP contents at NC (2.45 times) and M (1.52 times) sites than FC sites indicated an uneven P distribution downstream from the source canal. The highest soil organic matter content (84%) contents were observed at M sites, which was due to higher vegetation biomass observed at those sites. Consequently, CO2 efflux was greater at M sites (average 2.72 µmoles g dw−1 h−1) than the other two sites. We also found that amendments of glucose increased CO2 efflux from all soils, whereas the addition of phosphorus did not. The results indicate that microbial respiration downstream of inflows in the NESS is not limited by P, but more so by the availability of labile C.

Effect of habitat factors on the understory plant diversity of Platycladus orientalis plantations in Beijing mountainous areas based on MaxEnt model

Habitat factors including topography and soil nutrients affect the formation of understory plant diversity patterns on a small spatial scale. Assessing the combination of suitable habitat factors in areas with abundant understory plant diversity is significant for the management and improvement of plant diversity in the plantations. This study used the maximum entropy model (MaxEnt) to simulate the geographical distribution of the area with abundant understory plant diversity and analyzed the contribution of ten habitat factors to the existence probability of the area with abundant understory plant diversity. The results showed that the regions with medium altitude (292–500 m), gentle slope (13–23 degrees), and high soil organic matter content (>2.3 g/kg) were more likely to breed abundant understory plant diversity. Topographic factors had a dominant effect on the spatial distribution of the understory plant diversity, with the importance of 64.9%. Although the effect of soil nutrient factors on understory plant diversity was less than that of topographic factors, it still made up a large proportion (35.1%). Promoting soil biochemical cycles could be an effective way to increase understory plant diversity. By changing soil organic matter content to 2.3 g/kg, soil available nitrogen to 300 mg/kg, and soil available potassium to 120 mg/kg, the average existence probability of the area with abundant understory plant diversity increased from 0.34 to 0.63. We conclude specific measures including introducing the native broad-leaved tree species such as Cotinus coggygria Scop. and Acer truncatum Bunge into the Platycladus orientalis plantation, logging residue management, and litter management are critical for promoting soil biochemical cycles and thereby increasing understory plant diversity.

Salt crust-assisted thermal decomposition method for direct and simultaneous quantification of polypropylene microplastics and organic contaminants in high organic matter soils

Direct quantitative analysis of soil polypropylene microplastics (MPs) via thermal method is still a challenge due to its sensitivity to the soil matrix during the thermal decomposition. In this work, the impact of soil organic matter (SOM) on MPs decomposition in real soil was estimated, and high SOM contents was found have significantly negative effect on the qualitative and quantitative analysis of PP. To solve this problem, a salt crust-assisted thermal decomposition method was developed to reduce the soil matrix effect. By adding salt solution and heating in appropriate temperature program, salt crust can be formed between MPs and soil matrix to isolate PP MPs and soils during the heating process, and thereby to avoid the influence of SOM. Thermal desorption/decomposition coupling with headspace solid phase microextraction (HS-SPME) was used extraction of MPs decomposition products. All the thermal decomposition products of PP were identified, several alkenes and dialkenes were selected as candidates for quantitative analysis, and 2,4,6,8,10-pentamethyltridec-1-ene with optimal linearity was finally established for quantification. Besides, this method was also established for simultaneous determination of PP MPs and organic contaminants (OCs) including PCBs and PAHs, since it is capable of providing a new approach for investigation of their interaction in real soil environment. A theoretical LOD of 0.002 wt% was obtained for PP MPs, and the LOD of OCs ranges from 0.05 to 1.87 ng/g. Determination of aged soil samples reveal that adsorption of OCs is not a predominating effect of MPs in soil environment, and MPs contaminants may reduce the soil retention capacity. This method provides a new approach for direct quantification of soil PP MPs, and applicable for investigation of the interactions between MPs and OCs in real soils.

Local knowledge and practices towards the ecological restoration of selected landscape in Atok, Benguet, Philippines

Abstract. Landicho LD, Ocampo MTNP, Cabahug RED, Abadillos MG, Cosico RSA, Castillo AKA, Ramirez MAJP, Laruan KA. 2021. Local knowledge and practices towards the ecological restoration of selected landscape in Atok, Benguet, Philippines. Biodiversitas 22: 2785-2794. This study argues that local ecological knowledge and practices contribute to forest conservation and management efforts. This argument is based on the research conducted in upland communities in Atok, Benguet, Philippines. Interviews, farm visits, and focus group discussions revealed that the local communities have been dependent on the forest resources within the watershed in their agricultural production activities. These local communities employed their knowledge and practices towards restoring the ecological state of the watershed. These include the integration of trees on the farm, planting of Alnus japonica for soil and water conservation, the establishment of structural soil and water conservation, maintenance of communal forests, and awareness building among the youth on forest conservation and management. A moderate level of biodiversity and evenness index were in the conservation of giant tree ferns. A very low (0.9718) diversity index and a very high (0.825) evenness index were recorded in the farm lots, while a very low (0.437) diversity index and moderate (0.421) evenness index were measured in the communal forests. On the other hand, high soil organic matter contents of 6.49% and 5.86% were recorded both at the community and farm lots, respectively. Results imply the need to sustain the use of local knowledge and practices in combination with the technological interventions from academia and research institutions to enhance the ecological restoration of forest landscapes.