Globally, substantial quantities of organic amendments (OAs) such as plant residues (3.8×109Mg/yr), biosolids (10×107Mg/yr), and animal manures (7×109Mg/yr) are produced. Recycling these OAs in ...agriculture possesses several advantages such as improving plant growth, yield, soil carbon content, and microbial biomass and activity. Nevertheless, OA applications hold some disadvantages such as nutrient eutrophication and greenhouse gas (GHG) emission. Agriculture sector plays a vital role in GHG emission (carbon dioxide— CO2, methane— CH4, and nitrous oxide— N2O). Though CH4 and N2O are emitted in less quantity than CO2, they are 21 and 310 times more powerful in global warming potential, respectively. Although there have been reviews on the role of mineral fertilizer application on GHG emission, there has been no comprehensive review on the effect of OA application on GHG emission in agricultural soils. The review starts with the quantification of various OAs used in agriculture that include manures, biosolids, and crop residues along with their role in improving soil health. Then, it discusses four major OA induced-GHG emission processes (i.e., priming effect, methanogenesis, nitrification, and denitrification) by highlighting the impact of OA application on GHG emission from soil. For example, globally 10×107Mg biosolids are produced annually which can result in the potential emission of 530Gg of CH4 and 60Gg of N2O. The article then aims to highlight the soil, climatic, and OA factors affecting OA induced-GHG emission and the management practices to mitigate the emission. This review emphasizes the future research needs in relation to nitrogen and carbon dynamics in soil to broaden the use of OAs in agriculture to maintain soil health with minimum impact on GHG emission from agriculture.
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► A comprehensive overview for the first time on GHG emission from organic amendments (OAs) ► The amounts of OAs and their carbon and nutrient value are quantified. ► The potential volumes of GHG produced from land application of OAs are quantified. ► The processes by which GHGs are emitted from soil are described. ► Management strategies to mitigate GHG emission from OAs are discussed.
The identification and quantification of the ecological risks, sources and distribution of heavy metals in purple soils are essential for regional pollution control and management. In this study, ...geo-accumulation index (I
), enrichment factor (EF), pollution index (PI), potential ecological risk index (RI), principal component analysis (PCA) model and geographical detector (GD) were combined to evaluate the status, ecological risk, and sources of heavy metals (HMs) in soils from a typical purple soil areas of Sichuan province. The results showed that the average contents of As, Cd, Cr, Cu, Hg, Ni, Pb and Zn in purple soil were 7.77, 0.19, 69.5, 27.9, 0.077, 30.9, 26.5 mg/kg and 76.8 mg/kg, and the I
, EF and RI of topsoil Hg and Cd in designated area was the highest, and the average contents of Hg and Cd in topsoil were obviously greater than respective soil background value in Sichuan province and purple soil. The hot spots for the spatial distribution of 8 HMs were mainly focused in the southwest and northeast of the designated area, and there were also significant differences for 8 HMs distribution characteristics in the profile soil. Cu comes from both anthropogenic and natural sources, Zn, Ni and Cr mainly come from natural sources, but As, Pb, Hg and Cd mainly derived from human activities. GD results showed that soil texture (X
), altitude (X
), total nitrogen (TN), clay content (X
), sand content (X
) and silt content (X
) had the greatest explanatory power to 8 HMs spatial differentiation.This study provides a reference for understanding the status and influencing factors of HM pollution in typical purple soil, and lays a theoretical foundation for the environmental treatment of purple soil in China.
•Change in soil temperature (T10) and moisture depends on the time after thinning and gap size.•Gap formation decreases Rs in the forest, but such effect diminishes with time after thinning.•Decline ...in tree roots and soil labile C drives the decrease in Rs after thinning.•Positive effect of T10 elevation under thinning on Rs is masked by other factors.
Understanding the effects of forest management practices (e.g. thinning) on soil respiration (Rs) is crucial for the accurate estimation of forest carbon budget. However, little is known about the response of Rs to forest thinning in the subalpine region and its linkage to changes in environmental factors induced by thinning. We aimed to quantify the response of Rs rate to various gap sizes following thinning treatments, and to explore the relationships between Rs and soil temperature and moisture and other biophysical factors in the different gap sizes. We applied the thinning by simulating gap formation (four gap sizes at 0, 74, 109 and 196m2) in a 26-year old spruce plantation in the eastern Tibetan Plateau. We measured Rs monthly before (July to November 2008) and after (December 2008 to June 2012) thinning, as well as monthly soil temperature and moisture and other biophysical factors. Thinning tended to decrease fine root biomass, litterfall, soil extractable C, and increased soil temperature and soil moisture. The change in soil temperature and moisture depended on the time after thinning and the size of forest gap. We found that Rs showed an immediate decrease in initial stage after thinning, followed by a gradual increase with understory development towards the level at the control plot. Overall, thinning decreased Rs rate by 14.9%, 15.8% and 25.8% in the small, intermediate and large gap, respectively, as compared to the control. We concluded that the decrease in Rs rates by thinning in a spruce plantation was driven by the decline in tree root biomass and reduction in soil labile C. The positive effect of soil temperature elevation under thinning on Rs was masked by other factors, and the development of understory vegetation after thinning gradually offset the thinning-induced Rs reduction. Our results suggest the need to consider a set of abiotic and biotic factors induced by forest thinning intensity on Rs rates in modeling the response of soil C cycling to forest management practices.
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•Soil microbial biomass, activities and communities change along elevation gradient.•Labile SOM (Cmic/Corg and Nmic/Ntot) was lower at low relative to high elevation.•Microbial ...abundances increased with elevation gradient.•Bacterial and fungal community structure both associated with elevation gradient.•Temperature changes along elevation contributed to soil microbial community.
Moso bamboo (Phyllostachys edulis) is the fastest growing vegetation in the world, and it is widely distributed from low- to medium-elevation mountains in Taiwan. To understand how microbial activity and microbial community change with the elevation in bamboo plantations, we investigated soil microbial biomass, enzymes, and composition of bacteria and fungi in five moso bamboo plantations along an elevation gradient (600, 800, 1000, 1200 and 1400m asl) in central Taiwan. The soil microbial community structure was determined by analysis of the phospholipid-derived fatty acid (PLFA) and denaturing gradient gel electrophoresis (DGGE) profiles. The soil microbial biomass C (Cmic) and biomass N (Nmic) increased along the elevation gradient. Similarly, the activities of soil enzymes, such as cellulase, xylanase and urease, increased along the elevation gradient. The proportion of PLFAs that were attributed to total bacteria, Gram-positive (G+) bacteria, and Gram-negative (G-) bacteria also increased with the increase in elevation. However, the ratio of G+/G- bacteria decreased along the elevation increase, indicating that bamboo plantations at low elevations (600m, 800m and 1000m) contained less active soil organic matter than those at high elevations (1200m and 1400m). The results coincided with the availability of labile organic matter in bamboo plantation soils with lower Cmic/Corg and Nmic/Ntot in lower compared to higher elevations. Principle component analysis of PLFA content separated the low-elevation plantations from the high-elevation plantations. The DGGE analysis revealed that changes in both bacterial and fungal community structures were associated with the elevation gradient. Temperature changes along the elevation gradient contributed to variations in the soil microbial community in the bamboo plantations.
Studying the influence of climatic and/or site-specific factors on soil organic matter (SOM) along an elevation gradient is important for understanding the response of SOM to global warming. We ...evaluated the composition of SOM and structure of humic acids along an altitudinal gradient from 600 to 1400 m in moso bamboo (Phyllostachys edulis) plantations in central Taiwan using NMR spectroscopy and photometric analysis. Total organic C and total nitrogen (N) content increased with increasing elevation. Aromaticity decreased and ΔlogK (the logarithm of the absorbance ratio of humic acids at 400 and 600 nm) increased with increasing elevation, which suggests that SOM humification decreased with increasing elevation. High temperature at low elevations seemed to enhance the decomposition (less accumulation of total organic C and N) and humification (high aromaticity and low ΔlogK). The alkyl-C/O-alkyl-C (A/O-A) ratio of humic acids increased with increasing elevation, which suggests that SOM humification increased with increasing elevation; this finding was contrary to the trend observed for ΔlogK and aromaticity. Such a discrepancy might be due to the relatively greater remaining of SOM derived from high alkyl-C broadleaf litter of previous forest at high elevations. The ratio of recalcitrant C to total organic C was low at low elevations, possibly because of enhanced decomposition of recalcitrant SOM from the previous broadleaf forest during long-term intensive cultivation and high temperature. Overall, the change in SOM pools and in the rate of humification with elevation was primarily affected by changes in climatic conditions along the elevation gradient in these bamboo plantations. However, when the composition of SOM, as assessed by NMR spectroscopy and photometric analysis was considered, site-specific factors such as residual SOM from previous forest and intensive cultivation history could also have an important effect on the humic acid composition and humification of SOM.
•JumpStart of soil organic matter by organic amendment supported higher corn yield.•Soil microbes shift to high C use efficiency after soil organic matter JumpStart.•Soil microbial health improvement ...led to 20% reduction of crop residue CO2 emission.•One-time soil organic matter JumpStart can have 5-decade high soil c sequestration.•Soil organic matter JumpStart can be way for building climate-smart agriculture.
Rebuilding soil organic matter (SOM) to regionally specific targets for high quality soil that are likely maintained in the long term, here defined as “SOM JumpStart”, can unlock soil's potential for increased productivity, enhanced resilience and reduced emission as the main components for climate-smart agriculture (CSA). A field experiment was established in 2013 at Fulton County, western Illinois to use highly stabilized organic amendment (HSOA) at a rate, potentially raising surface SOM of cultivated Alfisol (low quality soil) to the level of cultivated Mollisol (high quality soil for US Midwest). Treatments included one-time application of lagoon-aged air-dried biosolids at 165 Mg ha−1, one-time application of vegetative compost at 165 Mg ha−1, chemical fertilizer at 225–50–85 kg ha−1 yr−1 (N-P-K) as control, and grass fallow as reference. In every year following the HSOA application, fertilizer (N and K) rate was reduced by 25%, and no P was applied for most years. Corn was planted annually. The HSOA JumpStart application dramatically increased SOM, leading to soil organic carbon (SOC) at 2–2.5% after biosolids and about 3% after compost for 2013–2019, as that of Mollisol, while that in chemical fertilizer control remained unchanged at 1–1.2%. For the first seven years, HSOA JumpStart increased corn grain yield by a mean of 19.8% (biosolids) and 7.1% (compost) above the control, with greater increase at precipitations-abnormal (low/high) years. The SOM JumpStart caused the shift of soil microbial physiology to high C utilization efficiency, as evident by reduced microbial metabolic quotient for CO2, leading to the decrease in CO2 emission from agricultural crop residues by 19.6% (biosolids) and 20.0% (compost). Our modeling revealed the promising soil C sequestration (excluding residual C from HSOA) over next 50 years at 10.6 Mg C ha−1 by biosolids application and 13.9 Mg C ha−1 by compost application, higher than 6.8 Mg C ha−1 anticipated by “4 per 1000″ international initiative. A simple but straightforward model suggests JumpStarted soil still contain 50% higher SOC stocks as compared to control after 50 years. Our results suggest the SOM JumpStart by HSOA such as biosolids and compost can transform conventional corn production to CSA.
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Biogeographic separation has been an important cause of faunal and floral distribution; however, little is known about the differences in soil microbial communities across islands. In this study, we ...determined the structure of soil microbial communities by analyzing phospholipid fatty acid (PLFA) profiles and comparing enzymatic activities as well as soil physio-chemical properties across five subtropical granite-derived and two tropical volcanic (andesite-derived) islands in Taiwan. Among these islands, soil organic matter, pH, urease, and PLFA biomass were higher in the tropical andesite-derived than subtropical granite-derived islands. Principal component analysis of PLFAs separated these islands into three groups. The activities of soil enzymes such as phosphatase, β-glucosidase, and β-glucosaminidase were positively correlated with soil organic matter and total nitrogen. Redundancy analysis of microbial communities and environmental factors showed that soil parent materials and the climatic difference are critical factors affecting soil organic matter and pH, and consequently the microbial community structure.
Forest management often results in changes in soil microbial communities. To understand how forest management can change microbial communities, we studied soil microbial abundance and community ...structure in a natural Chamaecyparis (NCP) forest, a disturbed Chamaecyparis (DCP) forest, a secondary (regenerated) Chamaecyparis (SCP) forest and a secondary (reforested) Cryptomeria (SCD) forest. We analyzed soil microbial abundance by measuring phospholipid fatty acids (PLFAs) and microbial community structure by denaturing gradient gel electrophoresis (DGGE) in the studied forest soils. The content of the soil PLFA fungal biomarker decreased from NCP to SCP, DCP and SCD forest soils, associated with the degree of disturbance of forest management. The ratio of soil Gram positive–to-negative bacteria and the stress index (16:1ω7t to 16:1ω7c) increased from NCP to SCP and DCP soils; thus, disturbed forests except for SCD showed increased soil microbial stress. Principal component analysis of soil microbial groups by PLFAs separated the four forest soils into three clusters: NCP, DCP and SCP, and SCD soil. The DGGE analysis showed no difference in the microbial community structure for NCP, DCP and SCP soils, but the community structure differed between SCD and the three other forest soils. In cloud montane forests, disturbance due to forest management had only a slight influence on the soil microbial community, whereas reforestation with different species largely changed the soil microbial community structure.
Continuous research into the availability of phosphorus (P) in forest soil is critical for the sustainable management of forest ecosystems. In this study, we used sequential chemical extraction and ...31P-nuclear magnetic resonance spectroscopy (31P-NMR) to evaluate the form and distribution of inorganic P (Pi) and organic P (Po) in Casuarina forest soils of a subtropical coastal sand dune in Houlong, Taiwan. The soil samples were collected from humic (+2–0 cm) and mineral layers (mineral-I: 0–10, mineral-II: 10–20 cm) at two topographic locations (upland and lowland) with different elevations. Sequential chemical extraction revealed that the NaOH-Po fraction, as moderately recalcitrant P, was the dominant form in humic and mineral-I layers in both upland and lowland soils, whereas the cHCl-Pi fraction was the dominant form in the mineral-II layer. The resistant P content, including NaOH-Pi, HCl-Pi, cHCl-Pi, and cHCl-Po fractions, was higher in the upland than in the lowland. However, the labile P content, NaHCO3-Po, showed the opposite pattern. The content of resistant Pi (NaOH-Pi, HCl-Pi, and cHCl-Pi) increased significantly with depth, but that of labile Pi (resin-Pi and NaHCO3-Pi) and recalcitrant Po (NaHCO3-Po, NaOH-Po, and cHCl-Po) decreased significantly with depth at both locations. 31P-NMR spectroscopy revealed inorganic orthophosphate and monoesters-P as the major forms in this area. The proportions of Pi and Po evaluated by sequential chemical extraction and 31P-NMR spectroscopy were basically consistent. The results indicate that the soils were in weathered conditions. Furthermore, the P distribution and forms in this coastal sand dune landscape significantly differed between the upland and lowland because of the variation in elevation and eolian aggradation effects.
Background
Soil organic carbon (SOC) and carbon (C) functional groups in different particle-size fractions are important indicators of microbial activity and soil decomposition stages under wildfire ...disturbances. This research investigated a natural
Tsuga
forest and a nearby fire-induced grassland along a sampling transect in Central Taiwan with the aim to better understand the effect of forest wildfires on the change of SOC in different soil particle scales. Soil samples were separated into six particle sizes and SOC was characterized by solid-state
13
C nuclear magnetic resonance spectroscopy in each fraction.
Results
The SOC content was higher in forest than grassland soil in the particle-size fraction samples. The O-alkyl-C content (carbohydrate-derived structures) was higher in the grassland than the forest soils, but the alkyl-C content (recalcitrant substances) was higher in forest than grassland soils, for a higher humification degree (alkyl-C/O-alkyl-C ratio) in forest soils for all the soil particle-size fractions.
Conclusions
High humification degree was found in forest soils. The similar aromaticity between forest and grassland soils might be attributed to the fire-induced aromatic-C content in the grassland that offsets the original difference between the forest and grassland. High alkyl-C content and humification degree and low C/N ratios in the fine particle-size fractions implied that undecomposed recalcitrant substances tended to accumulate in the fine fractions of soils.
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