Calcareous soils are characterized by high pH and phosphorus (P) fixation capacity. Increasing application of P fertilizer recently has significantly improved soil P concentration, especially available P (Olsen-P) and inorganic phosphate (Pi) fractions. However, there are few data available on the ability of soils with different initial Olsen-P levels to continuously supply P (i.e., P desorption capacity) to crops without additional P fertilization and on which Pi fraction exerts the greatest influence on P desorption capacity.
Materials and methodsFive soils with different initial Olsen-P levels (0.5, 14.3, 38.4, 55.4, 72.3 mg kg?1, hereafter refer as OP1, OP2, OP3, OP4, and OP5) but similar other soil properties were selected to evaluate the capacity of P desorption and its relationship with Pi fractions. Soil P was sequentially extracted once daily for 16 consecutive days using Olsen solution.
Results and discussionThe content and proportions of dicalcium phosphate fraction (Ca2-P), octacalcium phosphate fraction (Ca8-P), aluminum phosphorus fraction (Al-P), and iron phosphorus fraction (Fe-P) in Pi increased significantly with the increase of initial Olsen-P (P?<?0.01). Applied P fertilizer was mostly stored as Ca8-P in the soil. Soil P desorbed reached an equilibrium after 16 extractions for all soils, and P desorption capacity (12–358 mg kg?1) showed a significant linear relationship with initial Olsen-P (P?<?0.01), with an increase of 4.2 mg kg?1 desorbed P per 1 mg kg?1 increase of initial Olsen-P. Ca2-P exerted the conclusive effect on P desorption in the first four extractions, but Ca8-P played a more important role in the 16 extractions.
ConclusionsCa8-P was the greatest potential pool for P desorption after Ca2-P was depleted. P desorption capacity was significantly linearly related to initial Olsen-P (P?<?0.01). Different fertilizer use strategies were developed based on P desorption capacity for soils with different initial Olsen-P levels. The present study provided basic data on how to reduce effectively the application amount of chemical P fertilizer.
相似文献Being carbon-rich and porous, biochar has the potential to improve soil physical properties, so does conventional farming practice. Here, a field trial was conducted to investigate the combined effects of biochar use and farming practice on the physical properties of a salt-affected compact soil for wheat–maize rotation in the Yellow River Delta region.
Materials and methodsSalix fragilis L. was used as feedstock to produce biochar in the field via aerobic carbonization at an average temperature of 502 °C, terminated by a water mist spray, for use as a soil amendment at 0, 1, 2, and 4 g kg?1 doses (CK, T1, T2, and T3, respectively). Farming practices included rotary tillage/straw returning for wheat sowing, spring irrigation, no-tillage seeding of maize, and autumn irrigation. Both cutting ring and composite samples of the soil were collected at four stages of wheat–maize rotation (22, 238, 321, and 382 d after the benchmark date of land preparation for wheat sowing) for the determination of soil properties by established methods.
Results and discussionRotary tillage/straw returning reduced soil bulk density (BD) from 1.48 to 1.27 g cm?3 (CK) and 1.14 g cm?3 (T3) and increased saturated hydraulic conductivity (Ks) from 0.05?×?10?5 to 0.75?× 10?5 cm s?1 (CK) and 1.25?× 10?5 cm s?1 (T3). This tillage effect on BD and Ks gradually disappeared due to the disturbance from the subsequent farming practice. Biochar use lessened the disturbance. At maize harvest, BD was 1.47 (CK) vs. 1.34 g cm?3 (T3), and Ks was 0.06?×?10?5 (CK) vs. 0.28?×?10?5 cm s?1(T3); in comparison with CK, T3 increased Na+ leaching by 65%, Cl? leaching by 98%, organic carbon content by 40.3%, and water-stable aggregates (0.25–2 mm) by 38%, indicating an improvement in soil properties.
ConclusionsBiochar use and rotary tillage improved soil physical properties (BD, Ks) and favored soil aeration, water filtration, and salt leaching, which further helped the accumulation of soil organic carbon, the formation of water-stable aggregates, and the amelioration of salt-affected compact soil.
相似文献Ammonia oxidation is the limiting step in soil nitrification and critical in the global nitrogen cycle. The discovery of ammonia-oxidizing archaea (AOA) has improved our knowledge of microbial mechanisms for ammonia oxidation in complex soil environments. However, the relative contributions of AOA and ammonia-oxidizing bacteria (AOB) to ammonia oxidation remain unclear.
Materials and methodsIn this study, through large geographical scale sampling in China, totally nine samples representing various types of arable land soils were selected for analyzing the ammonia oxidation activity. The AOA and AOB activities were separately determined by using the dicyandiamide and 1-octyne inhibition method. High-throughput pyrosequencing and DNA stable-isotope probing (DNA-SIP) analysis were applied to investigate the distribution and activity of Candidatus Nitrosocosmicus franklandus in the arable land soils.
Results and discussionIn this study, AOA abundance (3.2?×?107–3.4?×?109 copies g?1) and activity (0.01–1.33 mg N kg?1 dry soil day?1) were evaluated for nine selected arable land soils and accounted for 4–100% of ammonia oxidation. By separately determining AOA and AOB rates, we observed that archaeal ammonia oxidation dominated the ammonia oxidation process in six soils, revealing a considerable contribution of AOA in ammonia oxidation in arable land soils. Based on high-throughput pyrosequencing analysis, the AOA species Ca. N. franklandus with relatively low abundance (0.6–13.5% in AOA) was ubiquitously distributed in all the tested samples. Moreover, according to the DNA-SIP analysis for Urumqi sample, the high activity and efficiency of Ca. N. franklandus in using CO2 suggests that this species plays an important role in archaeal ammonia oxidation in arable land soils.
ConclusionsThrough determining the AOA activity and analyzing the potential predominant functional AOA species, this study greatly improves our understanding of ammonia oxidation in arable land soils.
相似文献Land application of farm dairy effluent (FDE) to pasture soils is the preferred practice in New Zealand. Recently, a new FDE treatment technology has been developed to recycle the water for washing the yard Cameron and Di (J Soils Sediments 2018). Here we report a lysimeter study to compare the leaching losses of Escherichia coli, phosphorus (P), and nitrogen (N) and emissions of greenhouse gases from the treated FDE compared with the untreated original FDE.
Materials and methodsLysimeters were collected from a Balmoral silt loam soil (Typic Dystrudept, USDA) and installed in a field trench facility. Treatments included (1) treated effluent (TE), (2) a mixture of TE and recycled water (M), (3) untreated original FDE (FDE), and (4) water as control. The effluents were applied at a surface application rate of 24 mm on each lysimeter in May and again in September 2017. Measurements included leaching losses of E. coli, total phosphorus (TP), dissolved reactive phosphorus (DRP), total mineral nitrogen (TN), ammonium-N (NH4+-N), and nitrate-N (NO3?-N); emissions of nitrous oxide (N2O), carbon dioxide (CO2), and methane (CH4); herbage yield; and N uptake.
Results and discussionThe results showed that E. coli, TP, and DRP leaching losses from the TE were 1.31?×?1010 cfu/ha, 0.26 kg P/ha, and 0.009 kg DRP/ha and from M treatments were 6.96?×?108 cfu/ha, 0.18 kg P/ha, and 0.004 kg DRP/ha, respectively, which were significantly (P?<?0.05) lower than those from the FDE which were 4.21?×?1010 cfu/ha, 1.75 kg P/ha, and 0.034 kg DRP/ha, respectively. There were no significant differences in NO3?-N leaching losses amongst the different forms of effluents. There were no significant differences in total N2O, CO2 emissions, and CH4 uptakes from the different effluents (P?<?0.05). Herbage dry matter yields and N uptakes were also similar in the different effluent-treated lysimeters.
ConclusionsResults from this research indicate that land application of the treated effluents (TE) or a mixture of TE plus clarified water (M) would result in significant environmental benefits by reducing E. coli and P leaching without increasing greenhouse gas emissions.
相似文献Mercury (Hg) and methylmercury (MeHg) are easily released from sediments to overlying water and cause secondary contamination. In general, Hg concentrations are low in natural aquatic environments, but Hg toxicity is high. Therefore, it is important to assess the mobility and release risks of Hg and MeHg from surface sediment using in situ high-resolution sampling techniques.
MethodsThe profile distribution of Hg and MeHg was obtained for samples from Weishan sub-lake (WL) and Dushan sub-lake (DL) of Nansi Lake, China, by high-resolution dialysis (HR-Peeper probes) and the diffusive gradients in thin films (DGT) technique at mm-resolution. Furthermore, Hg mobility and release risks in sediments were evaluated by combining BCR (European Community Reference Bureau) extraction and DGT-measured data.
ResultsThe soluble concentrations of Hg in surface sediments in WL and DL were 21.70 and 19.38 ng L?1 and the DGT-labile concentration of Hg were 8.21 and 10.30 ng L?1, respectively. The soluble and labile Hg and MeHg concentrations were higher in the surface sediments (from??40 to 0 mm) than in deep sediments. The distribution of the labile-Hg was controlled by the ferrimanganic (hydr)oxide and total nitrogen rather than organic carbon content. The non-residual components accounted for a greater proportion of the interface, which further confirmed Hg was more active on the surface layer of the sediment. The resupply ability indicated that the release of Hg from sediment was insufficient to maintain the initial concentration in the porewater before consumption. The MeHg fluxes in WL (6.18 ng m?2 day?1) were twice those in DL (2.89 ng m?2 day?1), and the risk assessment code revealed a higher risk in the surface layer (25.21–61.88%) than in the deep layer (0–27.75%).
ConclusionsDissolved Hg and MeHg accumulated on the surface of the sediments and were more active than in the deeper sediments. The DGT-labile state can be used for a better understanding of the bioavailability and mobility of Hg. The diffusion direction of Hg and MeHg was from sediment to the overlying water. The release risks of Hg and MeHg from surface sediments (especially in WL) were found to be worthy of concern.
相似文献This study aimed to investigate the benefits of retaining harvest residues on the dynamics of soil C and N pools following clear-cut harvesting of a slash pine plantation in South East Queensland of subtropical Australia.
Materials and methodsImmediately following clear-cut harvesting, macro-plots (10?×?10 m) were established on a section of the plantation in a randomised complete block design with four blocks and three treatments: (1) residue removal (RR0), (2) single level of residue retention (RR1) and (3) double level of residue retention (RR2). Soils were sampled at 0, 6, 12, 18 and 24 months following clear-cutting and analysed for total C and N, microbial biomass C (MBC) and N (MBN), hot water–extractable organic C (HWEOC), hot water–extractable organic N (HWEON), NH4+–N and NOx?–N.
Results and discussionThe study showed that although soil total C decreased in the first 12 months following clear-cutting, harvest residue retention increased soil total C and N by 45% (p?<?0.001) and 32% (p?<?0.001), respectively, over the 12–24 months. NH4+–N, HWEOC, HWEON and MBC showed initial surges in the first 6 months irrespective of residue management, which declined after the 6th month. However, residue retention significantly increased HWEOC and HWEON over the 12–24 months (p?<?0.001).
ConclusionsThis study demonstrated that harvest residue retention during the inter-rotation period can minimise large changes in C and nutrient pools, and can even increase soil C and nutrient pools for the next plantation rotation.
相似文献Currently, the distribution characteristics and transport processes of the radionuclides 137Cs and 239?+?240Pu in the sediments of estuaries are still a controversial issue. Thus, in the present study, we investigated the distribution characteristics, sources and migration path of 137Cs and 239?+?240Pu in sediment cores of the Liao River estuary (LRE), China, and evaluated the relative contributions of the Pacific Proving Grounds (PPG) and riverine sources of Pu for the sediments in this area. We used 137Cs and Pu isotopes for dating the sediments and estimated the sedimentation rates by the two radionuclides in the LRE.
Materials and methodsSeven sediment samples were collected using a box corer from the Liao River estuarine wetland and tidal flat in the LRE in October 2012 and April 2015, respectively. The activities of 137Cs in the various samples were determined by γ spectrometry using HP-Ge detectors with 60% relative counting efficiency. Approximately 2–5 g of sediment were spiked with 242Pu (ca. 1 mBq) as a chemical yield tracer for Pu isotopic analysis at the School of Radiation Medicine and Protection, Soochow University. The measurement of Pu isotopes (239Pu, 240Pu, 242Pu) was performed by a sector field ICP-MS. In order to quantitatively differentiate the relative proportions of global fallout and PPG, we employed a two-end member mixing model to estimate their contributions.
Results and discussionThe average values of 137Cs, 239?+?240Pu activity concentrations, and 240Pu/239Pu atom ratios in the surface sediment samples of the LRE were 6.727?±?0.251 mBq g?1, 0.294?±?0.024 mBq g?1, and 0.188?±?0.049 (1σ), respectively. The average 240Pu/239Pu atom ratios ranged from 0.180?±?0.034 to 0.199?±?0.021 in sediment cores from the east and west sides of the LRE. For core LT-2 values for 137Cs and 239?+?240Pu concentrations were from below the detection limit: 3.380?±?0.414 and 0.036?±?0.007 to 0.105?±?0.007 mBq g?1. The mean 240Pu/239Pu atom ratio 0.217?±?0.050 (1σ) in sediment core LT-2 lies between the global fallout and PPG close-in fallout.
ConclusionsWe found that atmospheric fallout is the main source of Pu in sediment cores from the east and west sides of the LRE. For core LT-2, atmospheric fallout and riverine input (~?73.4%) are the major sources of Pu with the source of the rest of Pu (~?26.6%) attributed to the PPG via the Tsushima Warm Current and the coastal water of the East China Sea. The sedimentation rates (means 0.62–0.8 cm year?1) estimated by the two radionuclides were in good agreement and without any statistically significant difference.
相似文献Crop straw return into arable land is a common method of disposing of excess straw in China and can improve soil dissolved organic matter (DOM) that is known to modify soil zinc (Zn) extractability and mobility.
Materials and methodsWe conducted a soil box (internal dimensions, 160?×?140?×?80 mm3) experiment to evaluate the response of Zn extractability and transfer by diffusion to DOM after maize straw amendment (St, 0 and 15 g kg?1) in calcareous soil treated with ZnSO4·7H2O (Zn, 0 and 20 mg kg?1). Soil treated with St0Zn0 (control), St15Zn0, St0Zn20, or St15Zn20 was isolated in the 10-mm center of the box, and untreated soil was placed in compartments at either side.
Results and discussionResults revealed that addition of St0Zn20 or St15Zn20 increased the concentration of Zn extracted with diethylenetriaminepentaacetic acid (DTPA-extractable Zn) in the central layer compared with control or addition of St15Zn0. Over the course of 45 days, transfer of DTPA-extractable Zn into the adjacent untreated soil was detected at 15–20 mm in soil with St15Zn20 but at 10–15 mm with St0Zn20 and only 0–5 mm with St15Zn0. Additionally, a higher amount of DTPA-extractable Zn transfer into the adjacent untreated soil also occurred in St15Zn20. This increased DTPA-extractable Zn transfer may be associated with the formation of Zn-fulvic acid complexes with the provision of DOM derived from straw.
ConclusionsSoluble Zn combined with straw return may be a promising strategy for improving both Zn mobility and extractability in calcareous soil.
相似文献The purposes of this study were to analyse the spatiotemporal variations in greenhouse gas diffusive fluxes at the sediment–water interface of sewage-draining rivers and natural rivers, and investigate the factors responsible for the changes in greenhouse gas diffusive fluxes.
Materials and methodsGreenhouse gas diffusive fluxes at the sediment–water interface of rivers in Tianjin city (Haihe watershed) were investigated during July and October 2014, and January and April 2015 by laboratory incubation experiments. The influence of environmental variables on greenhouse gas diffusive fluxes was evaluated by Spearman’s correlation analysis and a multiple stepwise regression analysis.
Results and discussionSewage-draining rivers were more seriously polluted by human sewage discharge than natural rivers. The greenhouse gas diffusive fluxes at the sediment–water interface exhibited obvious spatiotemporal variations. The mean absolute value of the CO2 diffusive fluxes was seasonally variable with spring>winter>fall>summer, while the mean absolute values of the CH4 and N2O diffusive fluxes were both higher in summer and winter, and lower in fall and spring. The annual mean values of the CO2, CH4 and N2O diffusive fluxes at the sewage-draining river sediment–water interface were ??123.26?±?233.78 μmol m?2 h?1, 1.88?±?6.89 μmol m?2 h?1 and 1505.03?±?2388.46 nmol m?2 h?1, respectively, which were 1.22, 4.37 and 134.50 times those at the natural river sediment–water interface, respectively. The spatial variation of the N2O diffusive fluxes in the sewage-draining rivers and the natural rivers was the most significant. As a general rule, the more serious the river pollution was, the greater the diffusive fluxes of the greenhouse gases were. On average for the whole year, the river sediment was the sink of CO2 and the source of CH4 and N2O. There were positive correlations among the CO2, CH4 and N2O diffusive fluxes. The main influencing factor for CO2 and N2O diffusive fluxes was the water temperature of the overlying water; however, the key factors for CH4 diffusive fluxes were the Eh of the sediment and the NH4+-N of the overlying water.
ConclusionsRiver sediment can be either a sink or a source of greenhouse gases, which varies in different levels of pollution and different seasons. Human sewage discharge has greatly affected the carbon and nitrogen cycling of urban rivers.
相似文献Large spoil heaps formed during construction projects have caused serious soil erosion and threatened ecological security. The recent researches on soil erosion of spoil heaps are based on one or several soil types, which can only represent the soil texture category within the limited area, but cannot be used in other larger scale areas. Soil texture and gravel are the main factors affecting infiltration and erosion processes of spoil heaps.
Materials and methodsThe runoff plot dimensions were 5.0 m?×?1.0 m?×?0.5 m (length × width × depth). A series of rainfall experiments with a constant rainfall intensity of 1.0 mm min?1 and a slope gradient of 25° were conducted to investigate the effects of soil texture (sandy, loam, and clay) and gravel mass content (GC, 0%, 10%, 20%, and 30%) on the infiltration and erosion processes. The gravels are divided into 3 classes according to particle size 2–14 mm (small), 14–25 mm (medium), 25–50 mm (large), and the mass ratios were 30%, 50%, and 20%. The duration of each rainfall event was 45 min after runoff out of the plot.
Results and discussionResults showed that there was a critical GC (10%) improving or controlling infiltration and soil loss. Infiltration rate of sandy spoil heap (SSH) decreased within 45 min, but it decreased first and then stabilized for loam spoil heap (LSH) and clay spoil heap (CSH). Soil loss rate (SLR) of SSH stabilized first and then increased, while it decreased and then stabilized for LSH and CSH. SLR at early stage (0–18 min) was 0.08–0.23 times than it was at later stage (18–45 min) for SSH, but it was 2.06–5.06 times and 1.46–1.95 times for LSH and CSH, respectively. The soil texture had a more significant effect on SLR (P?< 0.05) than GC did. The effects of gravel on SLRs were dependent on soil texture.
ConclusionsThe greater the GC was, the lower the SLR was for the spoil heaps. Special attention should be paid to the later stage during rainfall events for SSHs and the early stage for LSHs and CSHs when considering erosion protection measures.
相似文献Rare earth elements have been used as sediment tracers in river, estuarine and coastal environments but rarely applied as fluvial tributary tracers. Lanthanides (Ln) and yttrium (Y) were quantified in fluvial sediments of the Minho River lower course (NW Iberian Peninsula), where the catchment contains heterogeneous lithologies, to define the characteristic imprints of tributaries and their relevance in the riverine system.
Materials and methodsSurface sediments were sampled at 36 points in the lower Minho riverbed and its nine main tributaries.The <?2-mm fraction was sieved and ground, and ≈?100 mg was completely acid-digested with HF and aqua regia in closed Teflon bombs at 100 °C for 1 h. The residue was evaporated, re-dissolved with HNO3 and Milli-Q water, heated 20 min at 75 °C and diluted to 50 cm3 with Milli-Q water. Lanthanides and yttrium were determined using a quadrupole ICP-MS equipped with a Peltier impact bead spray chamber and a concentric Meinhard nebuliser. Blanks accounted for less than 1% of the element concentrations in the samples. The precision and accuracy of the analytical procedures were controlled through reference materials AGV-1 and MAG-1.
Results and discussionContents ranged from 22 to 153 mg Ln kg?1 and 1.5–22.9 mg Y kg?1 and ES-normalised light-heavy Ln fractionation, (LN/HN), varied between 0.6 and 2.6. These wide ranges, together with Eu and Ce anomalies and element-by-element Ln, varied with changes in parental rocks of the lower Minho basin. Minho sediments showed negative Ce anomalies (0.81?±?0.29) and positive Eu anomalies (1.23?±?0.18). Sediments received traces of granitic pegmatites and gneissic peralkaline rocks from two tributaries: the Gadanha (22.9 mg Y kg?1; 83 mg Ln kg?1; 0.60 LN/HN; 0.51 Eu/Eu*; 0.88 Ce/Ce*) and the Louro (15.9 mg Y kg?1; 110 mg Lnkg?1; 0.97 LN/HN; 0.69 Eu/Eu*; 1.49 Ce/Ce*). The Tamuxe tributary, flowing through a slate and quartzite fault, provided the lowest source (1.6 mg Y kg?1; 28 mg Ln kg?1; 2.48 LN/HN; 1.01 Eu/Eu*; 0.55 Ce/Ce*).
ConclusionsLanthanide and Y signatures in sediments may be used to trace land-tributary-river influences. The imprints are observed downstream of fluvial confluences but not in all cases, responding to basin lithological changes, particularly for pegmatites and peralkaline rocks. The general REE trend is described using Y contents only. Tributaries, which are responsible for one-fifth of the Minho water load, provide one-half of their sediments. Non-homogeneous sediment patterns may be magnified in dammed rivers such as the Minho.
相似文献Gravity erosion (mass movement) generates an enormous volume of sediments on steep slopes throughout the world, yet its effect on the particle size distribution of suspended sediments (PSDSS) remains poorly understood. The objective of this study is to quantify the effects of gravity erosion on soil loss, especially the changes of particle size distribution of the suspended sediment.
Materials and methodsIn this study, experiments were conducted in a field mobile laboratory in which mass movements were triggered on steep slopes under simulated rainfall. During the experiments, water-sediment samples were collected in polyethylene bottles directly from the gully and channel flows before and during the mass movements. The volumes of each mass failure during and 20 min after the rainfalls were measured by a topography meter. The particle fractions of the samples were analyzed by combining the sieving and photoelectric sedimentometer techniques. A suite of indexes such as median sediment size (d50), sediment heterogeneity (H), fractal dimension (D), and enrichment/dilution ratio (Red) were then used to evaluate the effect of mass movement on PSDSS.
Results and discussion(1) Gravity erosion had a significant influence on PSDSS. After the mass movements occurred, the proportion of sand-sized particles was decreased from 71 to 51%, whereas the proportions of clay and silt were increased from 1 to 7% and 28 to 42%, respectively. (2) The d50, H, and D were significantly correlated with slope failures. The d50 was decreased from 0.084 to 0.051 mm, whereas the H and D were increased from 5.6 to 26.8 and from 2.60 to 2.78, respectively. This implies that mass movements make the PSDSS more nonuniform and irregular. (3) The suspended sediment tended to be enriched in the silt and clay fractions and diluted in the sand fractions after mass movements. Reds for clay, slit, and sand fractions were 13.9, 1.4, and 0.7 respectively.
ConclusionsThe changes of PSDSS after mass movements reflected a combined complex effect of soil sources, erosion types, selective detachment, and deposition processes. Mass movements led to a drastic increase of sediment concentration and the enrichment of fine particles, which developed into hyperconcentrated flows.
相似文献Submerged plants make an important contribution to nitrogen cycling in lakes including in the rhizosphere microenvironment through microbial activities. The main objective of this study was to investigate the abundance of functional genes for nitrogen cycling and the ecological relationship between these genes in the rhizosphere sediment of a freshwater lake in summer.
Materials and methodsSediment from the rhizosphere of four submerged macrophytes (Ceratophyllum demersum, Hydrilla verticillata, Potamogeton maackianus, and Vallisneria spiralis) was sampled in Lake Liangzi, China, in summer. The anammox bacteria community structure and abundance of five functional genes for nitrogen cycling, ammonia monooxygenase (amoA) of ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA), anammox 16S rRNA, and nitrite reductase genes (nirK and nirS) in the sampled sediment, were determined.
Results and discussionA total of 100 anammox gene sequences were grouped into eight operational taxonomic units (OTUs) and genus Ca. Kuenenia was the dominant species in Lake Liangzi in summer. Quantitative polymerase chain reaction (qPCR) revealed that gene copies of AOA amoA (2.42?×?106 copies g?1) were more than one order of magnitude higher than those of AOB amoA (1.98?×?105 copies g?1). The nirS gene (4.13?×?108 copies g?1) was more abundant than the nirK gene (7.28?×?107 copies g?1). There was no significant difference in the abundance of the AOB amoA gene among the rhizosphere of the four macrophytes. Redundancy analysis (RDA) showed a positive correlation between the abundance of the anammox 16S rRNA gene, AOA amoA and AOB amoA, which suggested two of these microbes may have provided a substrate for anammox bacteria in summer.
ConclusionsThe diversity of anammox in the rhizosphere of submerged macrophytes of the freshwater lake in summer was very low, but the plant species could affect the abundance of most nitrogen circulating bacteria, especially for anammox bacteria. Anammox 16S rRNA gene was positively correlated with four other functional genes, indicating that all four genes had significant effects on anammox bacteria.
相似文献Accelerated erosion removes fertile top soil along with nutrients through runoff and sediments, eventually affecting crop productivity and land degradation. However, scanty information is available on soil and nutrient losses under different crop covers in a vertisol of Central India. Thus, a field experiment was conducted for 4 years (2010–2013) to study the effect of different crop cover combinations on soil and nutrient losses through runoff in a vertisol.
Materials and methodsVery limited information is available on runoff, soil, and nutrient losses under different vegetative covers in a rainfed vertisol. Thus, the hypothesis of the study was to evaluate if different crop cover combinations would have greater impact on reducing soil and nutrient losses compared to control plots in a vertisol.
This experiment consisted of seven treatment combinations of crop covers namely soybean (Glycine max) (CC1), maize (Zea mays) (CC2), pigeon pea (Cajanus cajan) (CC3), soybean (Glycine max)?+?maize (Zea mays) ??1:1 (CC4), soybean (Glycine ma x))?+?pigeon pea (Cajanus cajan) ?2:1 (CC5), maize (Zea mays)?+?pigeon pea (Cajanus cajan) ??1:1 (CC6), and cultivated fallow (CC7). The plot size was 10?×?5 m with 1% slope, and runoff and soil loss were measured using multi-slot devisor. All treatments were arranged in a randomized block design with three replications.
Results and discussionResults demonstrated that the runoff and soil loss were significantly (p?<?0.05) higher (289 mm and 3.92 Mg ha?1) under cultivated fallow than those in cropped plots. Among various crop covers, sole pigeon pea (CC3) recorded significantly higher runoff and soil loss (257 mm and 3.16 Mg ha?1) followed by that under sole maize (CC2) (235 mm and 2.85 Mg ha?1) and the intercrops were in the order of maize?+?pigeon pea (211 mm and 2.47 Mg ha?1) followed by soybean?+?maize (202 mm and 2.38 Mg ha?1), and soybean?+?pigeon pea (195 mm and 2.15 Mg ha?1). The lowest runoff and soil loss were recorded under soybean sole crop (194 mm and 2.27 Mg ha?1). The data on nutrient losses indicated that the highest losses of soil organic carbon (SOC) (25.83 kg ha?1), total nitrogen (N), phosphorus (P), and potassium (K) (7.76, 0.96, 32.5 kg ha?1) were recorded in cultivated fallow (CC7) as compared to those from sole and intercrop treatments. However, sole soybean and its intercrops recorded the minimum losses of SOC and total N, P, and K, whereas the maximum losses of nutrients were recorded under pigeon pea (CC3). The system productivity in terms of soybean grain equivalent yield (SGEY) was higher (p?<?0.05) from maize?+?pigeon pea (3358 kg ha?1) followed by that for soybean?+?pigeon pea (2191 kg ha?1) as compared to sole soybean. Therefore, maize?+?pigeon pea (1:1) intercropping is the promising option in reducing runoff, soil-nutrient losses, and enhancing crop productivity in the hot sub-humid eco-region.
ConclusionsStudy results highlight the need for maintenance of suitable vegetative cover as of great significance to diffusing the erosive energy of heavy rains and also safe guarding the soil resource from degradation by water erosion in vertisols.
相似文献Imidacloprid is a widely used seed dressing insecticide in Brazil. However, the effects of this pesticide on non-target organisms such as soil fauna still present some knowledge gaps in tropical soils. This study aimed to assess the toxicity and risk of imidacloprid to earthworms Eisenia andrei and collembolans Folsomia candida in three contrasting Brazilian tropical soils.
Materials and methodsAcute and chronic toxicity assays were performed in the laboratory with both species in a tropical artificial soil (TAS) and in two natural soils (Oxisol and Entisol), at room temperature of 25 °C. The ecological risk was calculated for each species and soil by using the toxicity exposure ratio (TER) and hazard quotient (HQ) approaches.
Results and discussionAcute toxicity for collembolans and earthworms was higher in Entisol (LC50?=?4.68 and 0.55 mg kg?1, respectively) when compared with TAS (LC50?=?10.8 and 9.18 mg kg?1, respectively) and Oxisol (LC50collembolans?=?25.1 mg kg?1). Chronic toxicity for collembolans was similar in TAS and Oxisol (EC50 TAS?=?0.80 mg kg?1; EC50 OXISOL?=?0.83 mg kg?1), whereas higher toxicity was observed in Entisol (EC50?=?0.09 mg kg?1). In chronic assays with earthworms, imidacloprid was also more toxic in Entisol (EC50?=?0.21 mg kg?1) when compared to TAS (EC50?=?1.89 mg kg?1). TER and HQ values indicated a significant risk of exposure of the species to imidacloprid in all soils tested, and the risk in Entisol was at least six times higher than in Oxisol or TAS.
ConclusionsThe toxicity and risk of imidacloprid varied significantly between tropical soils, being the species exposure to this pesticide particularly hazardous in very sandy natural soils such as Entisol.
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