Higher Soil Organic Matter Content Research Articles

Ecological vulnerability: seasonal and spatial assessment of trace metals in soils and plants in the vicinity of a scrap metal recycling factory in Southwestern Nigeria.

The concentrations of selected heavy metals in the soil and vegetation in the immediate vicinity of a metal scrap recycling factory were determined in the dry and wet seasons using the Atomic Absorption Spectrophotometer. The results showed that the soil pH in all the sites indicated slight acidity (from 5.07 to 6.13), high soil organic matter content (from 2.08 to 5.60 %), and a well-drained soil of sandy loam textural composition. Soil heavy metal content in the dry season were 0.84-3.12 mg/kg for Pb, 0.26-0.46 mg/kg for Cd, 9.19-24.70 mg/kg for Zn, and 1.46-1.97 mg/kg for Cu. These values were higher than those in the wet season which ranged from 0.62-0.69 mg/kg for Pb, 0.67-0.78 mg/kg for Cd, 0.84-1.00 mg/kg for Zn, and 1.26-1.45 mg/kg for Cu. Except for cadmium in the dry season, the highest concentrations occurred in the northern side of the factory for all the elements in both seasons. An increase in the concentrations of the elements up to 350 m in most directions was also observed. There was no specific pattern in the level of the metals in the leaves of the plant used for the study. However, slightly elevated values were observed in the wet season (Pb 0.53 mg/kg, Cd 0.59 mg/kg, Cu 0.88 mg/kg) compared with the dry season values (Pb 0.50 mg/kg, Cd 0.57 mg/kg, Cu 0.83 mg/kg). This study showed that the elevated concentrations of these metals might be associated with the activities from the recycling plant, providing the basis for heavy metal pollution monitoring and control of this locality that is primarily used for agricultural purposes.

Reduction of air- and liquid water-filled soil pore space with freezing explains high temperature sensitivity of soil respiration below 0 °C

At temperatures just below 0 °C, the temperature sensitivity of heterotrophic soil respiration (RH) is orders of magnitude higher than above 0 °C. Two primary mechanisms have been proposed for this high sub-zero temperature sensitivity: changes in soil microbial community composition and physiology, or the physical effects of the transition of water between liquid and ice phases. In this study, the effect of soil freezing on RH was modeled using a simple modification of the Dual Arrhenius Michaelis–Menten model, to account for both the reduced liquid water content of the soil pore space and the reduced air-filled pore space as water expands during freezing. Using parameters derived from previous studies, RH was modeled at a range of sites throughout Southeast Wyoming, ranging from prairie to high elevation forest. Across the study region, RH at sub-zero temperatures was low in the prairie (0.002 mg C m−2 h−1 at −1 °C and optimal water content) and sagebrush (5·10−7 to 0.012 mg C m−2 h−1 at −1 °C and optimal water content) sites, with lower organic matter and higher sand content, and much higher in the high sub-alpine forest (0.71 mg C m−2 h−1 at −1 °C and optimal water content) and meadow (3.5 mg C m−2 h−1 at −1 °C and optimal water content) sites with high soil organic matter content. The modeled Q10 (the multiplicative response of RH to a 10 °C increase in temperature) above freezing was ∼3.2, while below freezing the median value ranged from 15 to 255, and the maximum was 1.6·1024. These values capture the range of Q10's described in the literature, suggesting that the model based on changing liquid water contented presented here can explain much of these observed apparent temperature responses. Hence, this model may prove valuable for predicting soil C fluxes in environments that undergo seasonal freezing.

Soil organic matter and salinity affect copper bioavailability in root zone and uptake by Vicia faba L. plants.

Processes that control the mobility, transformation and toxicity of metals in soil are of special importance in the root-developing zone. For this reason, there is a considerable interest in understanding trace elements (TEs) behavior in soil, emphasising the processes by which plants take them up. Increased root-zone salinity can affect plant TEs uptake and accumulation in plant tissue. Furthermore, copper (Cu) complexation by soil organic matter (SOM) is an effective mechanism of Cu retention in soils, controlling thus its bioavailability. Therefore, a greenhouse pot experiment was conducted to study the effects of soil Cu contamination in a saline environment on faba bean (Vicia faba L.) element uptake. Treatment with NaCl salinity was applied (control, 50 mM NaCl and 100 mM NaCl) on faba bean plants grown in a control and in a soil spiked with Cu (250 and 500 mg kg(-1)). Low and high SOM content trial variants were studied. Cu accumulation occurred in faba bean leaf, pod and seed. Cu contamination affected plant element concentrations in leaves (Na, Ca, Mg, Mn), pod (Zn, Mn) and seed (Mn, Mo, Zn). Root-zone salinity also affected faba bean element concentrations. Furthermore, Cu contamination-salinity and salinity-SOM interactions were significant for pod Cu concentration, suggesting that Cu phytoavailability could be affected by these interactions. Future research will be focused on the mechanisms of Cu translocation in plant and adaptation aspects of abiotic stress.

Biodegradation of pyrene by Phanerochaete chrysosporium and enzyme activities in soils: Effect of SOM, sterilization and aging

The impacts of soil organic matter (SOM), aging and sterilization on the production of lignin peroxidase (LiP) and manganese peroxidase (MnP) by Phanerochaete chrysosporium during the biodegradation of pyrene in soils were investigated. The biodegradation of pyrene by P. chrysosporium decreased with increasing SOM content, whereas the maximum activities of LiP and MnP increased, which indicates that SOM outweighed pyrene in controlling enzyme production. Sterilization enhanced the degradation of pyrene due to the elimination of competition from indigenous microbes, whereas aging led to a reduction in the degradation of pyrene primarily through changes in its sorbed forms. Both sterilization and aging could reduce SOM content and alter its structure, which also influenced the bioavailability of pyrene and the enzyme activity. The sterilization and aging processes caused changes in the degradation of pyrene, and the enzyme activities were greater in soils with high SOM contents. MnP was related to the degradation of pyrene to a greater extent, whereas LiP was more related to the decomposition of SOM.

An assessment of the influence of the urban environment on collembolan communities in soils using taxonomy- and trait-based approaches

In this study we investigated collembolan communities using both taxonomy- and trait-based approaches in order to determine: (1) which soil or leaf litter characteristics are the main agents of species distribution and functional trait distribution in collembolan communities, and (2) which functional traits are more prevalent in species tolerant to urban environments. To investigate this, soil and leaf litter were sampled in the urban area of Naples, Italy and the collembolan community was analyzed using taxonomic and functional approaches. The results indicated that collembolan density was negatively affected by site pollution, and that species richness, diversity and evenness were positively affected by the organic matter content of the soil. Folsomia lawrencei was the most abundant species in sites with high metal contamination and low soil organic matter content, whereas Mesaphorura sp. and Parisotoma notabilis were the most ubiquitous taxa overall. The main agents affecting the frequency of functional traits were metal contamination of soil and litter, soil organic matter content, leaf specific mass and thickness of the litter. The species most tolerant to urban environmental conditions were found to have small body size, jumping motion strategy, sexual reproduction and presence of pigmentation.

Pyrosequencing technology reveals the impact of different manure doses on the bacterial community in apple rhizosphere soil

We used DNA-based pyrosequencing to characterize the bacterial community structure of apple rhizosphere soil with different manure ratios. Five percentages of manure (5%, 10%, 15%, 20% and 25%) were examined. More than 10,000 valid reads were obtained for each replicate, and the community was composed of three dominant groups (Proteobacteria, Actinobacteria and Acidobacteria). Principal component analyses revealed that the rhizosphere samples were significantly different among the low manure treatments (control, 5% manure), the 10% manure treatment and the high manure treatments (15%, 20%, 25%). Four Bacillus species and 54 uncultured species showed a decreasing trend with increasing manure ratios. Soil treated with 10% manure showed the highest urease activity, a relatively higher saccharase activity, and the highest plant growth. Our experimental results suggested that although greater manure content leads to higher soil organic matter content, the 10% manure treatment resulted in significantly higher soil enzyme activity and a more diverse bacterial community composition.

Analysis of the coexisting pathways for NO and N2O formation in Chernozem using the 15N-tracer SimKIM-Advanced model

The nitrogen (N) cycle consists of a variety of microbial processes. These processes often occur simultaneously in soils, but respond differently to local environmental conditions due to process-specific biochemical restrictions (e.g. oxygen levels). Hence, soil nitrogen cycling (e.g. soil N gas production through nitrification and denitrification) is individually affected through these processes, resulting in the complex and highly dynamic behaviour of total soil N turnover. The development and application of methods that facilitate the quantification of individual contributions of coexisting processes is a fundamental prerequisite for (i) understanding the dynamics of soil N turnover and (ii) implementing these processes in ecosystem models. To explain the unexpected results of the triplet tracer experiment (TTE) of Russow et al. (Role of nitrite and nitric oxide in the processes of nitrification and denitrification in soil: results from 15N tracer experiments. Soil Biol Biochem. 2009;41:785–795) the existing SimKIM model was extended to the SimKIM-Advanced model through the addition of three separate nitrite subpools associated with ammonia oxidation, oxidation of organic nitrogen (Norg), and denitrification, respectively. For the TTE, individual treatments with 15N ammonium, 15N nitrate, and 15N nitrite were conducted under oxic, hypoxic, and anoxic conditions, respectively, to clarify the role of nitric oxide as a denitrification intermediate during N2O formation. Using a split nitrite pool, this analysis model explains the observed differences in the 15N enrichments in nitric oxide (NO) and nitrous oxide (N2O) which occurred in dependence on different oxygen concentrations. The change from oxic over hypoxic to anoxic conditions only marginally increased the NO and N2O release rates (1.3-fold). The analysis using the model revealed that, under oxic and hypoxic conditions, Norg-based N2O production was the dominant pathway, contributing to 90 and 50 % of the total soil N2O release. Under anoxic conditions, denitrification was the dominant process for soil N2O release. The relative contribution of Norg to the total soil NO release was small. Ammonia oxidation served as the major pathway of soil NO release under oxic and hypoxic conditions, while denitrification was dominant under anoxic conditions. The model parameters for soil with moderate soil organic matter (SOM) content were not scalable to an additional data set for soil with higher SOM content, indicating a strong influence of SOM content on microbial N turnover. Thus, parameter estimation had to be re-calculated for these conditions, highlighting the necessity of individual soil-dependent parameter estimations.

Manure refinement affects apple rhizosphere bacterial community structure: a study in sandy soil.

We used DNA-based pyrosequencing to characterize the bacterial community structure of the sandy soil of an apple orchard with different manure ratios. Five manure percentages (5%, 10%, 15%, 20% and 25%) were examined. More than 10,000 valid reads were obtained for each replicate. The communities were composed of five dominant groups (Proteobacteria, Actinobacteria, Chloroflexi, Acidobacteria and Bacteroidetes), of which Proteobacteria content gradually decreased from 41.38% to 37.29% as manure ratio increased from 0% to 25%, respectively. Redundancy analysis showed that 37 classes were highly correlated with manure ratio, 18 of which were positively correlated. Clustering revealed that the rhizosphere samples were grouped into three components: low manure (control, 5%) treatment, medium manure (10%, 15%) treatment and high manure (20%, 25%) treatment. Venn analysis of species types of these three groups revealed that the bacteria community difference was primarily reflected by quantity ratio rather than species variety. Although greater manure content led to higher soil organic matter content, the medium manure improved soil showed the highest urease activity and saccharase activity, while 5% to 20% manure ratio improvement also resulted in higher bacteria diversity than control and 25% manure ratio treatment. Our experimental results suggest that the use of a proper manure ratio results in significantly higher soil enzyme activity and different bacteria community patterns, whereas the use of excessive manure amounts has negative effect on soil quality.

Chernozem properties of Black Soils in the Baltic region of Germany as revealed by mass-spectrometric fingerprinting of organic matter

Black Soils with dark-coloured, mollic horizons occur in the Baltic region of Germany and their classification as Chernozems was previously discussed. Mollic topsoil horizons are diagnostic for steppe soils. We therefore hypothesized that the molecular characterization of soil organic matter (SOM) by pyrolysis-field ionization-mass spectrometry (Py-FIMS) is suitable to identify similarities between the Black Soils and Chernozems as well as soils from other major soil groups with mollic horizons or otherwise high SOM content. Data were collected from a set of 341 topsoil samples and analysed based on 139 Py-FI mass spectra and thermograms. The OC content in Black Soils reached high values matching those of Haplic Chernozems from Germany and typical steppe climate ecosystems. Arable soil use converted Ah horizons to lighter-coloured Ap horizons that nonetheless had a similar or higher OC content than underlying Ah horizons. Arable soil use led to less stable SOM as indicated by a higher percentage of volatilized organic matter (VM) upon pyrolysis. Furthermore, VM was especially high (21–52%) for redoximorphic soils, whereas it ranged between 5.1 and 15% in the Black Soils, Chernozems and other steppe soils such as Phaeozems or Kastanozems. Assignment of marker signals from Py-FI mass spectra to the compound classes revealed that Black Soils, all Chernozems and other steppe soils had more phenols and N-containing compounds but less sterols and suberin than most of the other soil groups investigated. The percentage of volatilized organic matter (VM) – with low values hinting at SOM stabilization in soil – ranged from 5 to 52%. It was especially high for redoximorphic (21%) and organic soils (52%), whereas it ranged between 5.1 and 15% in the Black Soils, Chernozems and other steppe soils. Principal component analysis unravelled the SOM composition patterns of different soils and showed that the Black Soils clustered together with typical Chernozems, while soils of other units differed. This indicates that sources and especially humification pathways of SOM were different in these soils compared to Black Soils and Chernozems. Notably, this was the case for Colluvic soils (=Colluvic Regosols), redoximorphic soils (e.g. Gleysols, Stagnosols), Luvisols and Phaeozems, although colluviation, influence of ground- or stagnant water, and clay migration were found in several Black Soils as well. Our findings do not support a strong, direct influence of colluviation and perched water on the SOM composition in the mollic horizons of Black Soils. The data also show that the Chernozem-specific SOM formation and clay migration, as in Luvisols and Phaeozems, are temporally discrete processes. The results underline that Chernozem formation in Central Europe is a relic process and is not only due to steppe ecosystem conditions. Rather, it depends on parent substrate properties, especially clay and carbonate content, secondary carbonate input and anthropogenic soil use. These factors preserved or even regraded the relic Chernozems since the Atlantic stage.

Soil organic matter in water-stable aggregates under different soil management practices in a productive vineyard

In a productive vineyard, the influence of different soil management practices on carbon sequestration and its dynamic in water-stable aggregates of Rendzin Leptosol was studied. In 2006, an experiment of different management practices in a productive vineyard was established in the locality of Nitra-Dražovce, in the Nitra winegrowing area of Slovakia. The following treatments were established: (1) control (grass without fertilization); (2) T (tillage); (3) T + FM (tillage + farmyard manure); (4) G + NPK3 (grass + NPK 120–55–195 kg ha−1); and (5) G + NPK1 (grass + NPK 80–35–135 kg ha−1). The results showed that the lowest soil organic matter content (9.70 g kg−1) in water-stable microaggregates was determined in G + NPK3, as well as in T. However, the highest soil organic matter content in the highest size fractions of water-stable macroaggregates (>5 mm) was observed in T + FM (19.7 g kg−1). The highest value for carbon sequestration capacity in water-stable microaggregates was observed in the ploughed farmyard manure treatment. However, the control treatment showed the highest values for carbon sequestration capacity in water-stable macroaggregates, including agronomically favourable size fractions (0.5–3 mm). In all soil management practices under a productive vineyard the most intensive changes in the soil organic matter content were observed in the highest size fractions (>3 mm) of water-stable macroaggregates.

Agricultural management affects the response of soil bacterial community structure and respiration to water-stress

Soil microorganisms are responsible for organic matter decomposition processes that regulate soil carbon storage and mineralisation to CO2. Climate change is predicted to increase the frequency of drought events, with uncertain consequences for soil microbial communities. In this study we tested the hypothesis that agricultural management used to enhance soil carbon stocks would increase the stability of microbial community structure and activity in response to water-stress. Soil was sampled from a long-term field trial with three soil carbon management systems and was used in a laboratory study of the effect of a dry–wet cycle on organic C mineralisation and microbial community structure. After a drying–rewetting event, soil microcosms were maintained wet and microbial community structure and abundance as well as microbial respiration were measured for four weeks. The results showed that the NO-TILL management system, with the highest soil organic matter content and respiration rate, had a distinct bacterial community structure relative to the conventional and the TILL without fertiliser systems. In all management systems, the rewetting event clearly modified microbial community structure and activity. Both returned to their pre-drought state after 28 days. However, the magnitude of variation of C mineralisation was lower (i.e. the resistance to stress was higher) in the NO-TILL system. The genetic structure of the NO-TILL bacterial communities was most modified by water-stress and exhibited a slower recovery rate. This suggests that land use management can increase microbial functional resistance to drought stress via the establishment of bacterial communities with particular metabolic capacities. Nevertheless, the resilience rates of C mineralisation were similar among management regimes, suggesting that similar mechanisms occur, maybe due to a common soil microbial community legacy.

Edge Effects on Soil Acidification in Forests on Sandy Soils Under High Deposition Load

This study investigated how forest soil acidification is affected by edge proximity. We measured pH(KCl) and exchangeable K, Ca, Mg and Al concentrations of the mineral topsoil (0–30 cm) from the exposed edge to the interior (128 m from the edge) of three deciduous and four coniferous forest stands. From the front edge to the interior of the deciduous stands, the pH(KCl) values decreased at 0–5 cm soil depth (from 3.07 to 2.98) but increased at 5–10 cm (from 3.26 to 3.32) and 10–30 cm (from 3.48 to 3.75) depth. In the coniferous stands, pH(KCl) values declined from edge to interior at all soil depths, i.e. from 3.10 to 2.89, from 3.26 to 3.06 and from 3.54 to 3.31 at 0–5, 5–10 and 10–30 cm, respectively. The concentrations of exchangeable cations decreased from edge to interior, with larger differences in the coniferous (of up to 265 %) than in the deciduous stands (up to 99 %). At forest edges, enhanced soil acidification due to higher potentially acidifying deposition could be counteracted in the upper mineral soil by higher base cation throughfall and litterfall, faster litter decomposition, higher soil organic matter content, lower nitrate leaching from the soil and/or lime fertiliser drift. Nonetheless, deeper in the soil of the deciduous stands, these buffer processes seem unable to counteract soil acidification due to potentially acidifying deposition at the edges. Edge effects on soil acidity are important since they can translate into effects on plant communities, soil biota, nitrogen cycling and carbon sequestration.

Process and Mechanism for the Development of Physical Crusts in Three Typical Chinese Soils

To compare the development of physical crusts in three typical cultivated soils of China, a black soil (Luvic Phaeozem), a loess soil (Haplic Luvisol), and a purple soil (Calcaric Regosol) were packed in splash plates with covered and uncovered treatments, and exposed to simulated rainfall. Meshes covered above the surfaces of half of soil samples to simulate the effects of crop residue on crusting. The results indicated a progressive breakdown of aggregates on the soil surface as rainfall continued. The bulk density and shear strength on the surface of the three soil types increased logarithmically as rainfall duration increased. During the first 30 min of simulated rainfall, the purple soil developed a 7–8 mm thick crust and the loess soil developed a 3–4 mm thick crust. The black soil developed a distinguishable, but still unstable, crust after 80 min of simulated rainfall. Soil organic matter (SOM) content, the mean weight diameter (MWD) of soil aggregates, and soil clay content were negatively correlated with the rate of crust formation, whereas the percentage of aggregate dispersion (PAD), the exchangeable sodium percentage (ESP), and the silt and sand contents were positively correlated with crusting. Mechanical breakdown caused by raindrop impact was the primary mechanism of crust formation in the black soil with more stable aggregates (MWD 25.0 mm, PAD 3.1%) and higher SOM content (42.6 g kg−1). Slaking and mechanical eluviation were the primary mechanisms of crust formation in the purple soil with low clay content (103 g kg−1), cation exchange capacity (CEC, 228 mmol kg−1), ESP (0.60%), and SOM (17.2 g kg−1). Mechanical breakdown and slaking were the most important in the loess soil with low CEC (80.6 mmol kg−1), ESP (1.29%), SOM (9.82 g kg−1), and high PAD (71.7%) and MWD (4.6 mm). Simulated residue cover reduced crust formation in black and loess soils, but increased crust formation in purple soil.

Fresh Organic Matter Application to Improve Aggregate Stability of Ultisols under Wet Tropical Region

Ultisol as a marginal soil has become ‘a hope’ by farmers in Indonesia due to land use change, lately. However, the soil is susceptible to degradation since it has low soil aggregate stability (SAS) as affected by low soil organic matter (SOM) content. A pot trial about application of fresh organic matter (FOM) was aimed to improve SAS of Ultisols under wet tropical rainforest. Three types of FOM (Tithonia diversifolia, Chromolaena odorata, and Gliricidia sepium) at different size (8, 6, 4, 2, and 0.5 cm) were applied for 1% (20 g 2 kg-1 soil), then mixed and incubated for three months. The experimental units were allocated in a completely randomized design at a glasshouse. The results showed that FOM generally increased SOM content, percent aggregation, as well as SAS of the Ultisol. Among the organic matter (OM) sources, tithonia gave the highest SOM content after a 3-month incubation. Within the types of OM source, the smallest OM size applied showed the highest SOM content. Tithonia at 0.5 cm in size gave the highest SOM (3.47%) of the Ultisol and SAS increased by 68% compared to the initial soil. Overall, there was a positive correlation (R2 = 0.43) between SOM content and aggregate stability index, but no correlation (R2=0.04) between SOM content and percent aggregation of the Ultisols.[How to Cite : Yulnafatmawita and F Anggriani. 2013. Fresh Organic Matter Application to Improve Aggregate Stability of Ultisols under Wet Tropical Region. J Trop Soils 18 (1): 33-44. doi: 10.5400/jts.2013.18.1.33][Permalink/DOI: www.dx.doi.org/10.5400/jts.2013.18.1.33]

Fate of nitrogen-15 as influenced by soil and nutrient management history in a 19-year wheat–maize experiment

High soil organic matter content may improve synchronization between N supply and crop demand. To test this hypothesis, we compared the fate of 15N-labeled fertilizer in soil with different management history. The soils had received no fertilizer (No-F soil), inorganic N, P, and K fertilizer (NPK soil), or manure plus N, P, and K fertilizer (MNPK soil) as part of a 19-year long-term fertilization trial. The N use efficiency (NUE) of wheat (Triticum aestivum L.) was 62% in the MNPK soil, higher than that in the NPK soil (50% NUE), and in the No-F soil (13% NUE). At wheat harvest, 38% of the fertilizer 15N remained in the 0–100cm depth of the MNPK soil, significantly less that the amount of fertilizer 15N that remained in the NPK soil (45%) or in the No-F soil (88%). More than 50% of the fertilizer 15N in the No-F soil had leached below the 20cm depth by wheat harvest, significantly more than in the NPK or MNPK soils. The amount of immobilized 15N at wheat stem elongation was significantly (P<0.05) greater in the MNPK soil than in the NPK soil. The mineralization of immobilized 15N between stem elongation and flowering was also significantly higher in the MNPK soil than in the NPK soil (P<0.05). The succeeding maize (Zea mays L.) crop took up 9% of the fertilizer 15N in the No-F soil, 6% of the fertilizer 15N in the NPK soil, and 2% of the fertilizer 15N in the MNPK soil. Combined soil profile and crop removal analyses at wheat harvest accounted for nearly 100% of the fertilizer 15N for all three soils. However, only 45% of the fertilizer 15N added to the No-F soil could be accounted for at maize harvest, significantly less than the recovery rate in the NPK (83%) and MNPK (85%) soils (P<0.01). These results indicate that the fertilizer 15N was mainly lost from these soils during the maize growing season. We conclude that the combined application of manure and inorganic fertilizers improves synchrony between N supply and crop demand, thus reducing N losses from agriculture.

Assessing Long Term Effects of Bioremediation: Soil Bacterial Communities 14 Years after Polycyclic Aromatic Hydrocarbon Contamination and Introduction of a Genetically Engineered Microorganism

Environmental contamination by organics such as polycyclic aromatic hydrocarbons (PAHs) generally changes native microbial communities. However our understanding of microbial responses has been limited to short term studies (i.e., less than 2-3 years) so long term community responses are not as well understood. In 1996, the genetically engineered microorganism Pseudomonas fluorescens HK44 was released into polycyclic aromatic hydrocarbon (PAH)-contaminated soil in lysimeters to monitor in situ PAH-biodegradation. The objective of this study was to assess the long term impacts of PAH contamination and addition of HK44 on the indigenous soil bacterial community structure. In 2010, 14 years after the lysimeter experiment initiation, lysimeters were unsealed and sampled. Although PAHs were degraded and PAH concentrations fell below detectable levels within approximately the first two years of this experiment, lysimeters that had received PAHs had significantly higher soil organic matter content (1.30 ± 0.23%) than control lysimeters with clean soils (0.81 ± 0.08%). Pyrosequencing of 16S rRNA gene amplicon libraries revealed a distinct bacterial community structure in the lysimeters that had received PAHs. In contrast, there were no discernible differences in soil chemistry or bacterial community structures in lysimeters where HK44 was inoculated compared to those to which HK44 was not inoculated. These results indicate that although the initial perturbations are no longer detectable, the addition of PAHs had long term influences on the bacterial communities, while the introduction of the genetically engineered microorganism HK44 did not.

Large-scale spatial interpolation of soil pH across the Loess Plateau, China

Soil pH plays an important role in biogeochemical processes in soils. The spatial distribution of soil pH provides basic and useful information relevant to soil management and agricultural production. To obtain an accurate distribution map of soil pH on the Loess Plateau of China, 382 sampling sites were investigated throughout the region and four interpolation methods, i.e., inverse distance weighting (IDW), splines, ordinary kriging, and cokriging, were applied to produce a continuous soil pH surface. In the study region, soil pH values ranged from 6.06 to 10.76, with a mean of 8.49 and a median of 8.48. Land use type had a significant effect (p < 0.01) on soil pH; grassland soils had higher pHs than cropland and forestland soils. From a regional perspective, soil pH showed weak variation and strong spatial dependence, indicated by the low values of the coefficient of variation (0.05) and the nugget-to-sill ratios (<0.25). Indices of cross-validation, i.e., average error, mean absolute error, root mean square error, and model efficiency coefficient were used to compare the performance of the four different interpolation methods. Kriging methods interpolated more accurately than IDW and splines. Cokriging performed better than ordinary kriging and the accuracy was improved using soil organic carbon as an auxiliary variable. Regional distribution maps of soil pH were produced. The southeastern part of the region had relatively low soil pH values, probably due to higher precipitation, leaching, and higher soil organic matter contents. Areas of high soil pH were located in the north of the central part of the region, possibly associated with the salinization of sandy soils under inappropriate irrigation practices in an arid climate. Map accuracy could be further improved using new methods and incorporating other auxiliary variables, such as precipitation, elevation, terrain attributes, and vegetation types.

Different soil fertility conditions depending on different land use methods

In precision nutrient management the most important aspect is adaptation but we should consider the possibility of the long-term improvement of soil fertility within the less fertile landscape zones. This possibility can be evaluated principally by long-term field experiments, which are running on similar soil types. The results of these field experiments can indicate that which soil fertility status should be attained. Some more important soil fertility data, (such as pH, P-, K- and soil organic matter (SOM) content) of a long-term field experiment with increasing farmyard manure(FYM) doses or equivalent NPK fertilizers, set up on an Eutric cambisol, are presented. The yieldincreasing capacity of FYM doses was only 82%, as compared to the equivalent amount of mineral NPK, but long-term FYM treatments resulted in 10% higher SOM content than that of equivalent NPKfertilizer doses. The studies indicate that SOM content is a function of local climate and clay content of the soil, and neither long-term high FYM doses can increase SOM content steadily above a supposed steady-state value. However we have to make efforts to keep the optimum level. The lowest soil reactions developed both with the highest NPK doses and without any fertilization. AL-P2O5 content of soil was increased more by mineral fertilization than by FYM treatments, but in case of AL-K2O content there was no difference between the fertilization variants. However the highest doses of both fertilization variants increased soil nutrient content to an excessive degree. Wecould get very valuable data from the unfertilized control plots as well, where long-term yield data suppose 48 kg ha-1 year-1 air-borne N-input.

Soil organic matter and texture affect responses to dry/wet cycles: Effects on carbon dioxide and nitrous oxide emissions

Soil organic matter (SOM) content and texture are important factors affecting carbon (C) and nitrogen (N) mineralisation under constant soil moisture but their effects on organic matter mineralisation and associated biogenic gas (carbon dioxide (CO2) and nitrous oxide (N2O)) production during dry/wet cycles is poorly understood. A laboratory incubation study was conducted to quantify CO2 and N2O production during sequential dry/wet cycles and under constant soil moisture conditions along a gradient of SOM contents in two soil types representing different texture classes (silt loam vs. clay loam). Three soil moisture treatments were established: wet (WW; field capacity), moderately dry (MD; 120% of soil moisture content (SMC) at wilting point (WP)) and very dry (VD; 80% of SMC at WP). To each of the two ‘dry’ treatments two different dry/wet treatments were applied where the soils were either maintained continuously dry (MD & VD) or subjected to three sequential 20-day long dry/wet cycles (MDW & VDW) during the treatment phase of the experiment. At field capacity soil moisture content, the rate of C mineralisation increased with increases in SOC content and the increase per unit of C was twice as high in silt loam (0.30mgCO2-Cg−1SOCd−1) as in clay loam (0.13mgCO2-Cg−1SOCd−1) soils. N2O-N emissions also increased with increasing in SOC content. However, in contrast to C mineralisation, the effect was four-fold greater for clay loam (1.38μgN2O-Ng−1SOCd−1) than silt loam (0.32μgN2O-Ng−1SOCd−1) soils. Following rewetting, the VDW and MDW soils produced a short-term C mineralisation flush that was, on average, 30% and 15% greater, respectively, than in WW soils. However, the flush of C mineralisation was not sufficient to compensate for the reduction in mineralisation during the drying phase of each cycle, resulting in a lower total C mineralisation from MDW and VDW soils, on average, compared with WW soils over the three sequential dry/wet cycles. The C mineralisation flush also remained a relatively constant proportion of the total C mineralised from both silt loam (23%) and clay loam soils (22%), irrespective of their SOC content. In contrast, the short-term flush of N2O that followed rewetting of dry soil accounted for 62% and 68% of the total N2O emissions from silt loam and clay loam soils, respectively. On average, the total N2O emissions from dry/wet treatments imposed on silt loam and clay loam soils were 33% and 270% greater, respectively, than from the WW treatments, though the effect varied greatly and depended on SOC content. Overall, N2O emissions were highest where we had a combination of fine texture, an adequate supply of available C (i.e. high SOM content), and a water-filled pore space (WFPS) > 0.60 cm cm−3 at field capacity. Prediction of C mineralisation over dry/wet cycles using mineralisation data from soils at constant moisture content is possible, but knowledge of the stress history for the soil would be required to improve accuracy. The prediction of N2O-N emissions during dry/wet cycles using emission data from soils at constant moisture was very inaccurate, due to the inherent spatial variability of N2O emissions.

Does organic farming reduce environmental impacts? – A meta-analysis of European research

Organic farming practices have been promoted as, inter alia, reducing the environmental impacts of agriculture. This meta-analysis systematically analyses published studies that compare environmental impacts of organic and conventional farming in Europe. The results show that organic farming practices generally have positive impacts on the environment per unit of area, but not necessarily per product unit. Organic farms tend to have higher soil organic matter content and lower nutrient losses (nitrogen leaching, nitrous oxide emissions and ammonia emissions) per unit of field area. However, ammonia emissions, nitrogen leaching and nitrous oxide emissions per product unit were higher from organic systems. Organic systems had lower energy requirements, but higher land use, eutrophication potential and acidification potential per product unit. The variation within the results across different studies was wide due to differences in the systems compared and research methods used. The only impacts that were found to differ significantly between the systems were soil organic matter content, nitrogen leaching, nitrous oxide emissions per unit of field area, energy use and land use. Most of the studies that compared biodiversity in organic and conventional farming demonstrated lower environmental impacts from organic farming. The key challenges in conventional farming are to improve soil quality (by versatile crop rotations and additions of organic material), recycle nutrients and enhance and protect biodiversity. In organic farming, the main challenges are to improve the nutrient management and increase yields. In order to reduce the environmental impacts of farming in Europe, research efforts and policies should be targeted to developing farming systems that produce high yields with low negative environmental impacts drawing on techniques from both organic and conventional systems.