Soil Organic Matter Availability Research Articles

Differential degradation dynamics of λ-cyhalothrin in mineral and peat soils: a comparative study under laboratory condition

Dissipation kinetics of λ-cyhalothrin in mineral and peat soils of Semongok (mineral soil) and Sibu (peat soil) farms was investigated in a laboratory incubation experiment under different temperature and moisture conditions at normal and double application dosages. The soil was spiked with λ-cyhalothrin at 5 and 25 µg/g soil, respectively. The soil moisture content was adjusted to 20, 40, and 60% of field capacity and then incubated in three climatic chambers at 15, 25, and 35 °C. Samples were collected at 0, 7, 21, 42, 70, and 105 days and analysed by Gas Chromatography-Electron Capture Detector (GC-ECD). Pesticides from the soil were extracted via a facile-modified QuEChERS method. Recovery studies of λ-cyhalothrin in mineral and peat soils were carried out at 0.05, 0.1, 0.5 and 1.0 µg/g fortification levels. The percentage of recovered amount was in the range of 81.4–95.0% and 81.3–86.5% for mineral and peat soils, respectively which falls within the acceptable recovery range of 70.0–120.0%. Factors i.e., soil carbon content, moisture, temperature, and applied dosage that render the degradation of λ-cyhalothrin in mineral and peat soils were evaluated. Findings showed that faster λ-cyhalothrin degradation took place in soil that contained low organic carbon content (< 12%), low soil moisture (≤ 20%) and incubated under higher temperatures (≤ 35 °C). Degradation of λ-cyhalothrin was described by first-order kinetics in both mineral and peat soils at various conditions. Half-lives of λ-cyhalothrin in mineral soil were shorter compared to peat soil. This is due to its lower carbon content and lower soil organic matter availability. This study provides significant information to the agriculture industry and farmers on the important factors such as soil properties, environmental conditions and application dosage that will influence the fate of pesticides in soil.Graphical abstract

The effect of silicon-based preparation on the amount of humus and essential nutrients in the soil

In today's changing climate, increasing agricultural land use and soil productivity, as well as ensuring the availability of soil organic matter and soil essential nutrients, is becoming increasingly difficult. Farmers can increase crop yields by directly applying many commercial products and various pesticides to the soil, but this is only for this period. Due to the negative impact of such preparations on the basic properties of the soil, they can lead to the destruction of the soil structure in subsequent years. For long-term use of soil, it is very important that the fertilizers or preparations used are environmentally friendly and scientifically based. Today, to improve the relationship between soil and plant, many silicon-containing preparations are processed into the soil. This study examined the effect of silicon-containing Aminosid-Si and other Aminosid-Aton, Bionitrogen preparations on the amount of humus in the soil, the total content of N, P, K and N-NH4, N-NH3, P2O5 and K2O has been studied. Studies have been conducted comparing the effects of silicon-containing preparations with the effects of other preparations. Because of the study, positive results were recorded for the preparation of Aminosid-Si.

Effects of common European tree species on soil microbial resource limitation, microbial communities and soil carbon

Studies of tree species effects on soils have revealed a significant impact on soil organic carbon (SOC) stocks and the carbon (C) distribution between forest floor and mineral soil, but the underlying mechanisms including the roles of litter traits, soil properties, and microbiome remain unclear. To address this challenge, we tested the effect of six common European tree species on the quality and nutrient availability of soil organic matter (SOM) as perceived by the naturally assembled microbial communities and explored the possible links between soil enzyme activities (EAs), microbial resource limitation, and microbial community with SOC stocks. The six studied tree species (Acer pseudoplatanus L., Fraxinus excelsior L, Fagus sylvatica L., Quercus robur L., Tilia cordata L., and Picea abies L.) were planted in common garden monocultures more than 40 years ago at six sites across Denmark. In forest floor, microbial biomass C, fungal and total microbial biomass and fungi to bacteria (F/B) ratios decreased with decreasing litter quality. Ecoenzymatic stoichiometry and relative EAs indicated that microbes in spruce forest floor were more limited by phosphorus (P) than in maple, lime, and beech, while microbes in mineral soils were less P limited in spruce than in other monocultures. Mineral soil under the tree species associated with arbuscular mycorrhizal (AM) fungi had higher microbial C and P limitation, bacterial biomass and total microbial biomass than under tree species associated with ectomycorrhizal (EcM) fungi. Our results indicated that tree species with high-quality litter (i.e. AM-associated trees) had (i) higher microbial biomass and less nutrient limitation that were conducive to higher decomposition rates and lower C stocks in the forest floor, and (ii) such tree species could lead to both greater stabilization of mineral soil C by mineral-associated OM formation and greater microbial mineralization of SOM with higher microbial resource demand. The results suggest that tree species-mediated EA, microbial resource limitation and microbial community composition are important drivers of stocks and vertical distribution of SOC among tree species and between the two types of associated mycorrhiza.

Engineered resistance and risk assessment associated with insecticidal and weeds resistant transgenic cotton using wister rat model

Stacking multiple genes into cotton crop to cop up multiple biotic stresses such as insects and weeds is a promising tool to save crop from losses. Transgenic cotton variety, VH-289, with double Bt and cp4EPSPS genes under the control of 35S promoter was used for the expression analyses and biosafety studies. The transgenic cotton plants were screened through PCR amplification of fragments, 1.7 kb for Cry1Ac, 582 bp for Cry2A and 250 bp for cp4EPSPS; which confirmed the presence of all genes transformed in transgenic cotton. The Cry1Ac + Cry2A and cp4EPSPS proteins were quantified through ELISA in transgenic cotton plants. The Glyphosate assay performed by spraying 1900 mL per acre of glyphosate Roundup further confirmed complete survival of transgenic cotton plants as compared to the non-transgenic cotton plants and all weeds. Similarly, insect infestation data determined that almost 99% insect mortality was observed in controlled field grown transgenic cotton plants as compared to the non-transgenic control plants. Evaluation of effect of temperature and soil nutrients availability on transgene expression in cotton plants was done at two different cotton growing regions, Multan and Lahore, Pakistan and results suggested that despite of higher temperature in Multan field, an increased level of Cry and cp4EPSPS proteins was recorded due to higher soil organic matter availability compared to Lahore field. Before commercialization of any transgenic variety its biosafety study is mandatory so, a 90 days biosafety study of the transgenic cotton plants with 40% transgenic cottonseeds in standard diet showed no harmful effect on wister rat model when studied for liver function, renal function and serum electrolyte.

Vegetative phase of pepper plants on the combination of compost and biochar with the addition of mycorrhiza

Plant growth is strongly influenced by the availability of nutrients in the soil. One factor that influences the availability of nutrients in the soil is the availability of soil organic matter. Soil nutrient content such as C-organic, available nutrients, and soil microorganism diversity are indicators of soil fertility. This research was arranged using a completely randomized design. Data were collected directly in the field and also observations in the laboratory. This study aimed to determine the response of pepper plant growth to the vegetative phase with the application of compost-biochar-mycorrhizae. This study indicates that the best response is shown in the combination application treatment of compost, biochar with mycorrhizal fungi.

The diversity of termite species on natural forest and agroforestry land in Sulawesi tropical forests in Indonesia

The conversion of natural forest to agroforestry causes physical changes in the forest, which affects the availability of organic matter. Therefore, this could influence the diversity of termites which act as decomposers in forest ecosystems. This study aims to determine the effect on the diversity of termite species of changes in tropical forest due to conversion. The study was carried out in the Educational Forest area of Tadulako University, Indonesia. The observations of environmental biophysical conditions include vegetation diversity, biomass, soil physical and chemical properties. Furthermore, using the transect method, the diversity of termite species was monitored. The results showed that the diversity of termite species decreased along with the conversion, because 13 species were found in natural forests, while only seven species were found in agroforestry land. This implies that changes in the biophysical environmental conditions due to forest conversion of tropical rainforests significantly reduced the number and composition of vegetation types at all growth rates, necromass and litter biomass. This decrease affects the availability of soil organic matter and carbon. Furthermore, these changes led not only to the loss of individual species but also to the emergence of previously unrecorded ones such as Microcerotermes dubius .

Sources and priming of nitrous oxide production across a range of moisture contents in a soil with high organic matter.

Adding nitrogen fertilizers to agricultural soils contributes to increasing concentrations of nitrous oxide (N2 O) in the atmosphere. However, the impacts of N addition on soil organic matter (SOM) turnover, SOM availability, and the ensuing SOM-derived N2 O emissions remain elusive. Within this context, the net change in direction and rate of SOM-derived N2 O production triggered by added N is termed the N2 O priming effect. This incubation study examined the sources and priming of N2 O production as a function of urea addition and multiple moisture contents in a soil with high SOM (55g organic C kg-1 ). We assessed four water-filled pore space (WFPS) conditions: 28, 40, 52, and 64%. Relative to controls receiving no N, urea addition increased N2 O production by 2.6 times (P<.001). Cumulative N2 O production correlated well with nitrification rates (r=.75; P=.03). We used 15 N-labeled urea to trace the added urea into N2 O. Of the N added via urea, the recovery as N2 O-N shifted from 0.02 to 0.17% when WFPS increased from 28 to 64% (P<.05). We also partitioned the N2 O production into urea vs. SOM sources. More N2 O was sourced from SOM than urea, with 59 ± 2% N2 O originating from SOM. The magnitude of SOM-derived N2 O under urea was larger than that of the control, revealing that positive N2 O priming was triggered by urea addition. Upon subtracting the controls, the primed N2 O was a consistent 19 ± 2% of the total N2 O produced by urea-amended soils. Nevertheless, the priming magnitude rose sharply with increasing moisture by more than one order of magnitude from 4 to 48μg N2 O-N kg-1 soil and in exponential mode (R2 =.98). Soil moisture, SOM, and nitrification interacted to drive the sources and priming of N2 O.

Drought legacy affects microbial community trait distributions related to moisture along a savannah grassland precipitation gradient

Abstract Ecosystem models commonly use stable‐state assumptions to predict responses of soil microbial functions to environmental change. However, past climatic conditions can shape microbial functional responses resulting in a ‘legacy effect’. For instance, exposure to drier conditions in the field may shape how soil microbial communities respond to subsequent drought and drying and rewetting (DRW) events. We investigated microbial tolerance to low moisture levels (‘resistance’) and ability to recover after a DRW perturbation (‘resilience’) across a steep precipitation gradient in Texas, USA. Although differences in precipitation regime did not result in differences in resistance and resilience of soil microbes, microbial communities appeared to be generally resilient and resistant across the gradient, suggesting that frequent exposure to drought had characterised the trait distributions of microbial communities. Moreover, microbial communities from historically drier sites used carbon more efficiently during a DRW perturbation suggesting that long‐term drought history leaves a legacy effect on microbial functions. This may have been due to an indirect effect of drought caused via precipitation‐induced differences in primary productivity, influencing the availability of soil organic matter to microbes. Alternatively, different exposures to drought might have shaped the microbial ‘readiness’ to cope with the DRW disturbance. Microbial community composition was also linked to drought history, but was unrelated to variation in function. Synthesis. Exposure to drought can have both direct and indirect effects on soil microbial communities, which can result in lasting legacy effects on the functions they control.

Long-term increase in rainfall decreases soil organic phosphorus decomposition in tropical forests

Increased rainfall may affect soil phosphorus (P) cycling in tropical forest ecosystems, yet the key biotic and abiotic factors that govern soil organic P transformations remain unclear. In this study, we conducted a long-term (7 years) rainfall manipulation experiment in the field to examine the effects of increased rainfall (+25%) in the wet season on soil P dynamics in a tropical forest. We found that an increase in rainfall in the wet season enhanced the maximum P adsorption capacity of forest soil as a result of a greater availability of soil organic matter and organic iron (Fe)/aluminum (Al) oxides. Newly formed stable ternary complexes between soil organic matter, metals (Mn, Mg and Ca) and P increased the surface adsorption of soil organic P. Moreover, the alkaline phosphomonoesterase (ALP) activity was reduced under our experimental treatment owing to a decrease in the abundance of both ALP-producing bacteria (Bradyrhizobium and Methylobacterium being the dominant genera) and bacterivores (Rhabditis and Acrobeloides). Our findings demonstrated an overall negative impact of elevated rainfall in wet season on soil organic P decomposition in tropical forests through the enhancement of soil P adsorption capacity and the inhibition of soil ALP activities. Our results implied that a long-term rainfall increase in the wet season could increase soil organic P accumulation, which in turn further reduce soil P availability for plant uptake in the tropical forests.

Changes in fertility parameters of gray forest-steppe soils in garden agricultural landscapes of the south of Russia

Data on the dynamics of changes in fertility parameters of gray forest-steppe soils of the Krasnodar territory under perennial plantings are presented. Significant species diversity of soils, characteristic of these soil and climatic conditions of the region, which are classified according to the recommendations of soil scientists in southern Russia, is noted. Systematic ecological and agrochemical monitoring of the soil was carried out within the boundaries of a 200-hectare test site located in the Seversk district of the Krasnodar territory. The analysis of monitoring data is given for the period from 1993 to 2018. The most detailed analysis was made of the upper part of the soil profile-horizons Aa (0- 25 cm), A (26-43 cm) and AB (43-55 cm). Scientific research was accompanied by generally accepted methods and State standards. In 1993, the soil sections were laid in connection with the laying of fruit plantations. The main parameters of garden suitability and soil fertility were determined. The duration of the first rotation of fruit stands is 16 years. During this period, 12 commercial fruit harvests were received. After the gardens were uprooted, row crops were cultivated on the site for 3 years, and in 2012, perennial plantings were restored within the boundaries of the monitoring site. The leading crop is the apple tree of winter maturation. Already in 2013, as a result of intensive use, a significant decrease in the availability of soil organic matter was found; its losses in the arable horizon (Aa) amounted to 0.18-0.81%, depending on the type of soil. Losses of mobile phosphorus compounds during the study period were in the horizons: Aa – 2.2 mg/kg, A – 7.2 mg/kg, AB – 5.8 mg/kg, which is probably due to its alienation from the crop of row crops for 3 years and non-compliance with the rules for fertilization. The contents of metabolic potassium, the amount of absorbed bases, hydrolytic acidity, soil reaction pHwater over time, and the exploitation of soils for various crops has not changed much. Identified in the dynamics of change in chemical parameters of soil fertility were the basis for the development of erosion control measures, including mechanized tillage across slopes (steepness of slopes on the site does not exceed 3.5°) and regulation of surface runoff by slitting and construction waste channels, and the introduction of high doses of organic fertilizer (50 t/ha manure). In 2016-2017, “traces” of mobile phosphorus and mineral nitrogen (N-NO3) were detected in the soil horizon in areas without organic fertilizers on the background of apple trees entering the commercial fruiting season) determined in the range of 1.0-1.9 mg/kg (Aa); 1.1- 1.2 mg/kg (A) and 1.2 mg/kg (AB). The nitrification capacity of soils in the arable horizon decreased to 11.7-12.0 mg/kg, and in the AB horizon – to 0.1-0.2 mg/kg.

The long-term fate of deposited nitrogen in temperate forest soils

Increased anthropogenic nitrogen (N) inputs can alter the N cycle and affect forest ecosystem functions. The impact of increased N deposition depends among others on the ultimate fate of N in plant and soil N pools. Short-term studies (3–18 months) have shown that the organic soil layer was the dominant sink for N. However, longer time scales are needed to investigate the long-term fate of N. Therefore, the soils of four experimental forest sites across Europe were re-sampled ~ 2 decades after labelling with 15N. The sites covered a wide range of ambient N deposition varying from 13 to 58 kg N ha−1 year−1. To investigate the effects of different N loads on 15N recovery, ambient N levels were experimentally increased or decreased. We hypothesized that: (1) the mineral soil would become the dominant 15N sink after 2 decades, (2) long-term increased N deposition would lead to lower 15N recovery levels in the soil and (3) variables related to C dynamics would have the largest impact on 15N recovery in the soil. The results show that large amounts of the added 15N remain in the soil after 2 decades and at 2 out of 4 sites the 15N recovery levels are higher in the mineral soil than in the organic soil. The results show no clear responses of the isotopic signature to the changes in N deposition. Several environmental drivers are identified as controlling factors for long-term 15N recovery. Most drivers that significantly contribute to 15N recovery are strongly related to the soil organic matter (SOM) content. These findings are consistent with the idea that much of the added 15N is immobilized in the SOM. In the organic soil layer, we identify C stock, thickness of the organic layer, N-status and mean annual temperature of the forest sites as most important controlling factors. In the mineral soil we identify C stock, C content, pH, moisture content, bulk density, temperature, precipitation and forest stand age as most important controlling factors. Overall, our results show that these temperate forests are capable of retaining long-term increased N inputs preferably when SOM availability is high and SOM turnover and N availability are low.

Wildfire effects on BVOC emissions from boreal forest floor on permafrost soil in Siberia

One of the effects of climate change on boreal forest will be more frequent forest wildfires and permafrost thawing. These will increase the availability of soil organic matter (SOM) for microorganisms, change the ground vegetation composition and ultimately affect the emissions of biogenic volatile organic compounds (BVOCs), which impact atmospheric chemistry and climate. BVOC emissions from boreal forest floor have been little characterized in southern boreal region, and even less so in permafrost soil, which underlies most of the northern boreal region. Here, we report the long-term effects of wildfire on forest floor BVOC emission rates along a wildfire chronosequence in a Larix gmelinii forest in central Siberia. We determined forest floor BVOC emissions from forests exposed to wildfire 1, 23 and > 100 years ago. We studied how forest wildfires and the subsequent succession of ground vegetation, as well as changes in the availability of SOM along with the deepened and recovered active layer, influence BVOC emission rates. The forest floor acted as source of a large number of BVOCs in all forest age classes. Monoterpenes were the most abundant BVOC group in all age classes. The total BVOC emission rates measured from the 23- and >100-year-old areas were ca. 2.6 times higher than the emissions from the 1-year-old area. Lower emissions were related to a decrease in plant coverage and microbial decomposition of SOM after wildfire. Our results showed that forest wildfires play an important indirect role in regulating the amount and composition of BVOC emissions from post-fire originated boreal forest floor. This could have a substantial effect on BVOC emissions if the frequency of forest wildfires increases in the future as a result of climate warming.

Understanding the relations between soil organic matter fractions and N2O emissions in a long‐term integrated crop–livestock system

AbstractThe nitrous oxide (N2O) emissions in agricultural systems are influenced by edaphoclimatic conditions, and the availability of soil organic matter (SOM) is a key factor. The objective of this study was to evaluate the accumulation of labile and stable SOM fractions and possible relations with N2O emissions using a multivariate approach in a 24‐year integrated crop–livestock experiment in the Cerrado region. The management systems consisted of: continuous cropping under no tillage (CC‐NT), continuous cropping under annual heavy disc harrow (CC‐CT), an integrated crop–livestock system under no tillage (CLS‐NT) and an adjacent area of native Cerrado as reference. The cumulative N2O emissions were quantified over a period of 146 days throughout the cultivation of sorghum (Sorghum bicolor (L.) Moench). Labile and stable soil carbon (C) fractions and C contents in classes of aggregates (macroaggregates &gt;0.250 mm and microaggregates &lt;0.250 mm) were determined. The cumulative N2O emissions were larger in the CC‐CT system, intermediate in the CC‐NT and CLS‐NT systems, and smaller in the Cerrado. The decomposition of crop residues during the crop succession (first and second crop seasons) and the presence of a grass forage (with grazing and not grazed) in both systems (CLS‐NT and CC‐NT, respectively) explain the differences in N2O fluxes between the land uses. Smaller cumulative N2O emissions were observed in the integrated system (CLS‐NT), which could be attributed to the greatest increase in soil C in its most stable SOM fractions (fulvic acid) and occlusion in microaggregates. This confirms the hypothesis that the accumulation of C in the most stable SOM fractions of the soil, unavailable to the microbiota, results in smaller N2O emissions. Principal component analysis also revealed that aggregation is a key attribute that correlates with soil N2O emissions. Thus, conservation systems such as CLS‐NT had larger average diameter of aggregates and the smallest N2O emissions among the agroecosystems.Highlights Relations between SOM fractions and N2O emissions were studied in integrated systems The accumulation of stabilized C fractions reduces N2O emissions Soil structure (aggregation) and SOM stability partially explain N2O fluxes Integrated crop–livestock promotes better soil conditions, reducing N2O emissions

Soil organic matter availability and climate drive latitudinal patterns in bacterial diversity from tropical to cold temperate forests

Abstract Bacteria are one of the most abundant and diverse groups of micro‐organisms and mediate many critical terrestrial ecosystem processes. Despite the crucial ecological role of bacteria, our understanding of their large‐scale biogeography patterns across forests, and the processes that determine these patterns lags significantly behind that of macroorganisms. Here, we evaluated the geographic distributions of bacterial diversity and their driving factors across nine latitudinal forests along a 3,700‐km north–south transect in eastern China, using high‐throughput 16S rRNA gene sequencing. Four of 32 phyla detected were dominant: Acidobacteria, Actinobacteria, Alphaproteobacteria and Chloroflexi (relative abundance &gt; 5%). Significant increases in bacterial richness and phylogenetic diversity were observed for temperate forests compared with subtropical or tropical forests. The soil organic matter (SOM) mineralisation rate (SOMmin, an index of SOM availability) explained the largest significant variations in bacterial richness. Variation partition analysis revealed that the bacterial community structure was closely correlated with environmental variables and geographic distance, which together explained 80.5% of community variation. Among all environmental factors, climatic features (MAT and MAP) were the best predictors of the bacterial community structure, whereas soil pH and SOMmin emerged as the most important edaphic drivers of the bacterial community structure. Plant functional traits (community weighted means of litter N content) and diversity resulted in weak but significant correlations with the bacterial community structure. Our findings provide new evidence of bacterial biogeography patterns from tropical to cold temperate forests. Additionally, the results indicated a close linkage among soil bacterial diversity, climate and SOM decomposition, which is critical for predicting continental‐scale responses under future climate change scenarios and promoting sustainable forest ecosystem services. A plain language summary is available for this article.

Changes in abundance and community structure of nitrate-reducing bacteria along a salinity gradient in tidal wetlands

Primarily because of their high levels of microbiological activity, wetland soils play a key role in ameliorating nitrogen pollution and reducing nutrient loadings to coastal zones. Saltwater intrusion associated with climate change is expected to dramatically affect the biogeochemistry of these soils and induce changes in the composition of the soil microbial community that may alter their ability to process nitrogen. In this study, the abundance and community structure of microorganisms associated with two key nitrate removal pathways – denitrification and dissimilatory nitrate reduction to ammonium (DNRA) – were assessed for eight tidal wetlands along a naturally-occurring salinity gradient (0–2ppt) in the Chesapeake Bay watershed (USA). Molecular analyses targeted functional genes specific for each pathway (denitrification: nirS and nosZ; DNRA: nrfA). Shifts in abundance and community structure of both groups of nitrate reducers were strongly coupled to changes in salinity, and correlation analyses suggested that the effect of salinity on these organisms may have been mediated, at least in part, by changes in soil organic matter availability. Considering the growing body of evidence that microbial community composition may help regulate ecosystem process rates, an increased understanding of how salinity affects nitrogen cycling microbial communities may help us better predict how wetland soil function will be affected by global change and issues such as sea level rise.

Biochemical quality and accumulation of soil organic matter in an age sequence of Cunninghamia lanceolata plantations in southern China

Biochemical protection is an important mechanism for maintaining the long-term stability of the soil carbon (C) pool. The labile and recalcitrant pools of soil organic matter (SOM) play different roles in regulating C and N dynamics; however, few studies have characterized the capacity of soil C sequestration while considering the biochemical quality of SOM. The aim of the present study was to assess the changes in the soil organic carbon (SOC) and nitrogen (N) pools during a traditional rotation period (25 years) of a Chinese fir (Cunninghamia lanceolata) plantation with an emphasis on SOM biochemical quality. Three different forest stand development stages—young (6 years old), middle-aged (16 years old) and mature (25 years old)—were selected for soil sampling to a depth of 100 cm. Total C and total N of the soil was analysed to determine the changes in the SOC and N stocks among the three development stages using an equivalent soil mass (ESM) approach. Bulk soils were fractionated into labile and recalcitrant fractions using the acid hydrolysis method to identify the quality of SOM. The mineral soil organic carbon pool at a 1-m depth slightly decreased from the young stand to the middle-aged stand and rapidly increased by 28 % to reach a maximum in the mature stand. SOC accumulation in the surface soil predominated the changes in total SOC stocks in all three stands. The increased N was reflected in the entire depth, and the highest soil N accumulation was in the mature stand. The recalcitrant C concentration and SOC were positively correlated. The non-hydrolysable C proportion was lower in the middle-aged stand versus the young stand (8.69 % loss), while the labile C percentage was higher (13.89 % gain). In the mature stand, the recalcitrant C index increased to 39.84 %. The recalcitrant index of C decreased with an increasing soil depth, whereas the recalcitrant index of N dramatically increased. These results highlighted the significant effect of the stand age and the soil depth on the storage and biochemical availability of SOM in Chinese fir plantations of southern China. The recalcitrant index of C changed with the change in SOC concentration, indicating that biochemical protection mechanism plays an important role in soil C sequestration. In addition, more attention should be paid to subsoil C protection in the management of Chinese fir plantations because of low biochemical stability.

Nanoporous clay with carbon sink and pesticide trapping properties

A thorough understanding of the mechanisms and factors involved in the dynamics of organic carbon in soils is required to identify and enhance natural sinks for greenhouse gases. Some tropical soils, such as Andosols, have 3–6 fold higher concentrations of organic carbon than other kinds of soils containing classical clays. In the tropics, toxic pesticides permanently pollute soils and contaminate crops, water resources, and ecosystems. However, not all soils are equal in terms of pesticide contamination or in their ability to transfer pollution to the ecosystem. Andosols are generally more polluted than the other kinds of soils but, surprisingly, they retain and trap more pesticides, thereby reducing the transfer of pesticides to ecosystems, water resources, and crops. Andosols thus have interesting environmental properties in terms of soil carbon sequestration and pesticide retention. Andosols contain a nano porous clay (allophane) with unique structures and physical properties compared to more common clays; these are large pore volume, specific surface area, and a tortuous and fractal porous arrangement. The purpose of this mini review is to discuss the importance of the allophane fractal microstructure for carbon sequestration and pesticide trapping in the soil. We suggest that the tortuous microstructure (which resembles a labyrinths) of allophane aggregates and the associated low accessibility partly explain the poor availability of soil organic matter and of any pesticides trapped in andosols.

Impact of Land Use Management and Soil Properties on Denitrifier Communities of Namibian Savannas.

We studied potential denitrification activity and the underlying denitrifier communities in soils from a semiarid savanna ecosystem of the Kavango region in NE Namibia to help in predicting future changes in N(2)O emissions due to continuing changes of land use in this region. Soil type and land use (pristine, fallow, and cultivated soils) influenced physicochemical characteristics of the soils that are relevant to denitrification activity and N(2)O fluxes from soils and affected potential denitrification activity. Potential denitrification activity was assessed by using the denitrifier enzyme activity (DEA) assay as a proxy for denitrification activity in the soil. Soil type and land use influenced C and N contents of the soils. Pristine soils that had never been cultivated had a particularly high C content. Cultivation reduced soil C content and the abundance of denitrifiers and changed the composition of the denitrifier communities. DEA was strongly and positively correlated with soil C content and was higher in pristine than in fallow or recently cultivated soils. Soil type and the composition of both the nirK- and nirS-type denitrifier communities also influenced DEA. In contrast, other soil characteristics like N content, C:N ratio, and pH did not predict DEA. These findings suggest that due to greater availability of soil organic matter, and hence a more effective N cycling, the natural semiarid grasslands emit more N(2)O than managed lands in Namibia.

The effects of fencing on carbon stocks in the degraded alpine grasslands of the Qinghai-Tibetan Plateau

Quantifying the carbon storage of grasslands under different management strategies can help us understand how this ecosystem responds to different land management practices. To assess the C cycle and the importance of soil microbial biomass carbon, we measured the levels of soil organic carbon, biomass carbon (above- and underground) and soil microbial biomass carbon in areas with different grazing intensities and different management strategy (fenced and unfenced) in the Qinghai-Tibetan Plateau. We also calculated the ratio of soil microbial biomass carbon to soil organic carbon as an indicator of the soil organic matter availability and quality. Results showed that degradation had significant effects on the soil organic carbon, biomass carbon and microbial biomass carbon (P < 0.05). However, fencing only had a significant effect on the non-degraded and moderately degraded grasslands (P < 0.05). We also found that the level of soil microbial biomass carbon was positively correlated with the biomass carbon and soil organic carbon. From our research, we concluded that the level of soil microbial biomass carbon was crucial to the C cycle in the alpine grasslands and that fencing may be an important management strategy for restoring lightly or moderately degraded grassland in the Qinghai-Tibetan Plateau.

Surface Runoff and Soil Organic Matter Availability in Bamboo-Based Agroforestry in Lombok Timur District

Bamboo-based agroforestry is suitable for soils which are poor in nutrient. The characteristics of bamboo and the rapid closure of its canopy improve soil cover, soil nutrient availability and soil moisture content, and prevent erosion by reducing surface runoff. The research was aimed at determining the factors that influenced surface runoff and the availability of soil organic matter (SOM) in the bamboo-based agroforestry in East Lombok. Research was done from March 2010 to March 2011 in Lenek Daya village, Aikmel sub-district, East Lombok district. The research plots were located on slopes of 0-15o, 30-45o, and 45-65o; with bamboo canopy closures of 0-25%, 25-50%, 50-75%, and over 75%. The research involving 12 plots, each in 4 x 12 m size. Measurements included surface runoff, bamboo canopy closure, weeds and bamboo leaves litter weight, rainfall depth and duration, dissolved sediment, and soil physical and chemical properties as well as SOM. Correlation and multiple linear regression tests were used in data analysis. The results of the regression tests showed a change in surface runoff which was influenced by changes in bamboo canopy closure, rain duration, rain intensity and soil sand fraction, each by -0.019, 0.418, 0.049 and -0.065 respectively. Rain duration was the highest influencing variable, whereas bamboo canopy closure significantly decreased surface runoff. Bamboo canopy closure had no correlation with the increase of SOM. But, the increase of SOM had correlation with the increase of soil cation exchange capacity (CEC). The positive impact of bamboo canopy closure on Regosol soil fertility in bamboo-based agroforestry land was determined by land management intensity which could increase the availability of SOM and decrease phosphorus element loss due to leaching of nutrient.