Abstract:Soil salinization is a critical constraint for agriculture development in arid and semiarid areas, and also one of the most important environmental problems. Therefore, obtaining accurate soil salinization information is crucial to salinization management in those areas. The current study is attempting to derive a relatively straight forward soil salinity index from Landsat TM remote sensing images. First, perform minimum noise fraction (MNF) of the images and calculate their pixel purity index (PPI); select the first three bands that are good to characterize the feature information of a region to construct a MNF spectral eigenspace; then put forward the concept of “vegetation highlight area” by combining field investigations and following the vector space and single line theories and define soil salinization distance index (SDI), so as to enable the multi-dimensional vector space to include the normalized distance from a salinization pixel within the single line to the vegetation highlight area; and in the end verify SDI for precision using the data obtained in field investigations of regions different in salinization level. Results show that in areas low in vegetation coverage, that is, areas moderate and severe in salinization, SDI is more closely related to the average soil salt content in the 0~10 cm soil layer, (R²> 0.83) than in the 0~20 cm soil layer, while in areas high in vegetation coverage, that is, farmland of areas low in soil salinization, it is just the reverse (R²> 0.81), indicating that the overall precision of SDI in prediction of soil salinity in the 0~10 cm soil layer is R²= 0.81, and in the 0~20 cm soil layer R²= 0.72. The findings suggest that the SDI index model is simple and easy- to- construct and yet quite high in precision, so it is of high practical value and can be used to help quantitatively analyze and monitor soil salinization on a large scale in the arid and semiarid areas.

Abstract:A field experiment was carried in Yangling using simulated rainfalls, designed to have two rainfall intensities (1.5 and 2.0mm min^-1), on slopes of Lou soil, different in gradient (10°,15°,20° and 25°), to study characteristics of rill development and distribution of flow velocity along the slopes. Results show that slope gradient is positively related to rill density and average depth of the rills, but with the increase in slope gradient, the increment of total erosion rate tends to level off in amplitude, which implies that there is likely a threshold slope gradient where soil erosion begins to turn from strong into weak. Slope gradient shows extremely significant relationship with to the various indices of soil erosion, indicating that slope gradient is the major factor affecting development of rills. Rill erosion rate is also found to be closely related to total erosion rate, with correlation coefficient being 0.97, indicating that the aggravation of soil erosion on the slope is caused mainly by rill erosion. Flow velocities on the slope, in and in-between rills are all positively related to their distances to the slope top. Rainfall intensity intensifies fluctuation of the trend. However, slope gradient does not have much influence on flow velocities on slopes, in and in-between rills and, moreover, no significant relationship is found between these flows in velocity, which is contradictory to the general conclusion that flow velocity is higher in rills than in-between rills, and remains to be further verified in future experiments.

Abstract:Preferential flow plays an important role in water and contaminants transporting in the soil. The aim of this study is to investigate characteristics of soil preferential flows in different vertical traps in mountains along the Dalaoling-Dengcun section of the Three Gorges of the Yangtze River, using the section staining method coupled with image analysis, and hence to analyze impact of preferential flows on water infiltration in the profile. Results show that the mountain yellow brown earth under evergreen-decidous broadleaf mixed forest in the mid-mountain belt and the mountain yellow earth under low-mountain warm coniferous forests have soil pores large in aperture and extensive in distribution, which is conducive to formation of preferential flows, and water infiltration. In deserted farmland, the large-pored soil structure is damaged by tillage in the past, the paths of preferential flows differ from those in the forest soils, and consequently its water infiltration intensity is low and the color of the stained area is light. Characteristics of preferential flows differ significantly between soil layers. Burrow flows occur frequently in the humus horizon, and soil water percolate down rapidly through macropores, exchanging little with surrounding soil matrix. In the leaching illuvial horizon, burrow flows disappear or weaken, while lateral percolation intensifies. The low-mountain yellow earth under warm coniferous forests is rather coarse in texture, and macropores mainly in the form of crack or fissure appear, making crack flows the preferential flows. In deserted farmland, finger flows dominate in all the genetic horizons with the area of stained section diminishing with soil depth, however, lateral percolation remains basically constant in these horizons. In conclusion, vegetation-soil vertical zonal distribution is the major cause of the difference existing in preferential flow between mountain soils. In eco-environment construction in the maintain regions, it is essential to promote development of preferential flows in the soil.

Abstract:In this study, a total of 136 paddy soil samples were collected from 17 different fertilization treatments of two short-term field experiments in Jintan and Zhangjiagang, the main grain production region in the middle and lower reaches of the Yangtze River for near infrared (350 ～2 500 nm) -partial least squares (NIR-PLS) regression analysis. Based on the analysis coupled with the cross validation method, a model was established for quantitative analysis of the total carbon, total nitrogen, C/N ratio, available potassium, available phosphorus, electro-conductivity and soil pH obtained by near infrared diffuse reflectance spectroscopy and traditional chemical analysis. R², determination coefficient value, and RSC, ratio of SD (standard deviation of chemical analysis)/RMSECV (root mean square error of cross validation) are two criteria for evaluation of the model. Results show that for the total carbon , total nitrogen , C/N ratio and pH, R²was 0.94, 0.95, 0.97 and 0.92 and RSC was 4.31, 4.35, 5.60 and 3.37, respectively, suggesting that the model is good in prediction. For available potassium, R²was 0.81 and RSC was 2.23, indicating that the model is good, however, for available phosphorus and electro-conductivity, R² was 0.22 and 0.37 and RSC was 0.16 and 1.31, respectively, demonstrating that the model is not so ideal. To sum up, for paddy soil, relevant quality indices can be rapidly predicted through NIR-PLS regression analysis.

Abstract:Using a portable Geonics EM38 electromagnetic soil conductivity meter, electrical conductivity of an experiment field at the Yellow River delta was measured in spring, summer and autumn to. Study the temporal-spatial distribution of soil salt .With the help of classical statistics and geostatistics, analysis was performed of the measurements. Results show that the correlation coefficients were all higher than 0.8 and hence in the category of strong correlation, while horizontally, they were in the range of -0.2 ~ 0.2 and the hence in the category of weak correlation. Soil salt was found to be accumulated in the bottom soil layer. Comparisons of coefficients of variation indicate that among the data collected at the same time, the variation was the highest in the surface layer and the lowest in the bottom layer. Semi-variance analysis shows that the nugget/sill ratios of the soil layers were all in the range of 25% ~ 75%. Spatial distribution of salt tended to be moderate in spatial correlation. Spatial interpolation diagrams were formed after values were assigned to cotton growth, and the diagrams of the same season were compared. Soil salinity was sorted into four grades. Proportion of each grade of soil salinity in the grid interpolation of the re-sorted salinity grades was calculated, and shows that the proportion of non-salinized soil has increased from 5.54% to 11.93% in the surface soil layer and that of slightly, salinized soil increased by 40%.

Abstract:Simulated rainfalls, 1.69 mm min^-1 (high), 1.31 mm min^-1 (moderate) and 0.64 mm min^-1 (low) in intensity, were performed on plots of farmland, 2 m×5 m each in area and 10° in average slope gradient, on a red soil hill typical of hilly regions, to study on rules of migration,of sediments and enrichment of organic carbon therein. Results show that soil loss increased with rainfall intensity, and demonstrated a significant cubic relationship with volume of runoff, which is an important factor influencing soil loss on slope farmland; Sediment-bonded soil organic carbon is the mainly form of organic carbon lost with runoff, accounting for more than 84% and even 97.6% of the total loss of organic carbon. Organic carbon enrichment ratio of the sediments decreases gradually with increasing rainfall intensity, and selective migration of organic carbon was more evident in rainfalls low in intensity. In rainfalls, high in intensity, no significant linear relationship was observed between organic carbon enrichment ratio and clay enrichment ratio, but in rainfalls, moderate or low in intensity, an extremely significant or significant positive relationship was observed, respectively. Therefore, it can be concluded that rainfall intensity is an important factor that affects soil loss and migration of organic carbon with sediments.

Abstract:Applying biochar to soil has been suggested as a practice both to improve soil quality and to increase carbon sequestration of the soil. In this study effects of amendment of rice straw and straw biochar on organic carbon in aggregates various in fraction were investigated using the stable carbon isotope technique. 13C-labeled rice straw and straw biochar (prepared at 250℃ or 350℃) was mixed separately with red soil (Ferrosols) for incubation in the experiment. Results show that the effects of rice straw and biochar on fresh carbon and native soil organic carbon were completely different. After 112 days of incubation, the fresh carbon supplied by straw or biochar was mainly found in the 50 ~ 250 μm fraction of soil aggregates, making up 70.3% ~ 75.3% of the total. Compared with CK, amendment of rice straw significantly stimulated decomposition of the native organic carbon in the 250 ~ 2 000 μm fraction of soil aggregates, but had no such significant effect in the 50 ~ 250 μm and <50 μm fractions of aggregates, and the amendment of biochar (either SB250 or SB350) did not affect much decomposition of the native organic carbon in the 250 ~ 2 000 μm and 50 ~ 250 μm fractions of aggregates, but the amendment of biochar SB250 did significantly inhibit decomposition of the native organic carbon in the <50 μm fraction of aggregates, however, no such effect was found with the amendment of biochar SB350. The effects of rice straw and straw biochar on carbon in soil aggregates of the same size fraction differed mainly in distribution of fresh carbon, rather than native soil organic carbon.

Abstract:A two-year stationary field experiment under the crop rotation of wheat-corn was carried out in Shajiang black soil to study effects of incorporation of straws on soil nutrients and labile organic carbon. The experiment was designed to have five treatments, i.e. no fertilizer (CK), chemical fertilizer alone (F), chemical fertilizer + straw (FS), chemical fertilizer + straw + organic matter-decomposing inoculant (FSD), and chemical fertilizer 20% less than Treatment F in terms of P₂O₅ and K₂O + straw + organic matter-decomposing inoculant (F_4/5SD). Soil samples were collected in the plough layer of the field after the crops were harvest, for analysis of contents of nutrients, labile organic carbon and microbial biomass carbon. Results show that the compared with Treatment F, Treatment FS increased alkalystic N, available P, available K, labile organic carbon , ALC and CPMI by 13.0%, 4.6%, 10.7%, 12.0%, 11.1% and 30.6%, respectively, and Treatment FSD did alkalystic N, available P, available K, labile organic C, soluble organic C, A_LC and CPMI by 17.4%, 40.5%, 12.4%, 12.0%, 51.3%, 9.5%, 102.3%, respectively, when compared with F. Correlation analysis shows that CPMI was better related to total N, alkalystic N, available P, available K, microbial biomass C and liable organic C in the soil than total organic C. Quite obvious, incorporating crop straws into the field with organic matter-decomposing inoculant is conducive to increasing soil nutrients, labile fraction of organic carbon, A_LCand CPMI, that is to say, even if the application rate of P and K fertilizers is reduced by 20%, the soil-building effect of this practice will not decline significantly.

Abstract:Soil samples were collected from a long-term field experiment which had four treatments, i.e. compost (CM), half N in compost plus half N in fertilizer (HCM), fertilizer (NPK) and control without any fertilizer or compost(CK) and sifted into macroaggregate (2 000~250 μm), microaggregate (250~53 μm) and silt+clay fraction (<53 μm) suing the wet-sieving method for analysis of molecular structure of the organic matter in the soil and the aggregates on the solid-state ¹³C -nuclear magnetic resonance (¹³C -NMR) spectroscope. It was found that the ratio of alkyl-C/O-alkyl-C increased with decreasing aggregate size, and was also significantly negatively correlated with the C/N ratio（R² = 0.421，p = 0.022）. These findings suggest that the finer the aggregates, the more the organic matter therein decomposed. Compared with CK, treatments HCM and CM increased the ratio of O-alkyl-C or carbonyl-C to total organic C in soil. The increase in the proportion of O-alkyl-C in the soil was mainly attributed to the increase in relative content of methoxyl-C and N-alkyl-C in macroaggregates, and accumulation of carbonyl-C in macroaggregates and microaggregates of the soil. The application of chemical fertilizer increased the ratio of O-alkyl-C and alkyl-C to organic C in the soil. The increase in the proportion of O-alkyl-C was mainly attributed to the increase in methoxyl-C or N-alkyl-C in macroaggregates and O-alkyl-C in microaggregates, whereas that of alkyl-C was mainly observed in macroaggergates. Compared with CK, application of either organic matter or chemical fertilizer reduced the relative content of aryl-C in the soil by 1.8%~4.6%, which was mainly attributed to the decrease in the proportion of aryl-C in macroaggregates and microaggregates; however, in the fraction in the silt+clay the proportion of aryl-C and phenolic-C increased, but that of alkyl-C decreased by 5.9%~7.1%, indicating that fertilization facilitates accumulation of aromatic-C, but weakens that of alkyl-C in fractions small in particle size. All the findings indicate that long-term application of organic manure helps conserve physically the large amount of carbohydrates and organic acids manure carries in in macroaggregates and microaggregates, thus raising the content of organic carbon in soil.

Abstract:A long-term (9 years) field observation was carried out in the Plank Organic Farm in Nanjing to study dynamic changes in soil organic carbon and soil humus composition in vegetable soils different in cultivation mode (organic field, organic greenhouse and conventional field). Results show that the 9 years of vegetable cultivation increased soil organic carbon (SOC) from 11.41 to 15.35 g kg^-1, from 9.29 to 20.90 g kg^-1 and from 9.00 to 10.00 g kg-1, humic acid carbon(C_HA ) from 1.79 to 2.11 g kg^-1, from 1.23 to 3.11g kg^-1 and from 1.14 to 1.31 g kg^-1, and fulvic acid carbon(C_FA) from 2.19 to 2.44 g kg^-1, from 1.88 to 2.68 g kg^-1 and from 1.73 to 1.91 g kg^-1, in the organic field, organic greenhouse and conventional field, respectively. The increases in the soils under organic cultivation either in open field or in greenhouse were significant, but not so in the soil under conventional cultivation. C_HA / C_FAratio and PQ value are two important indicators characterizing quality of soil humus, and were both higher in the soils under organic cultivation than in the soil under conventional cultivation. E₄/E₆ratio and ΔlogK value of soil fulvic acid increased, too, in all the soils, but the increase grew more significant with age of the vegetable cultivation in the former than in the latter. Aromaticity of the soil humic acid displayed a trend of declining first and then rising, which was not so significant in the soil under conventional cultivation. All the findings indicate that long-term organic cultivation may not only be conducive to SOC accumulation, but also promote the process of soil humification.

Abstract:Soil organic matter (SOM) plays a vital role in regulating metal bioavailability. However, the relationship of SOM and its fractions, including water soluble substance (WSS), fulvic acid (FA), humic acid (HA), and soil microbial biomass (SMB), with metal bioavailability to plants has not yet been thoroughly investigated. A pot experiment was carried out to explore effects of exogenous humic acid on soil organic carbon (SOC)，its composition and soil microbial biomass (SMB) in rhizosphere and bulk soils, 6 months after its application, and correlation analysis done of carbon content in each fraction of the soil SOC with Pb content in various parts of the tea plant. The experiment, using yellow-red soil collected from Fuyang, was designed to have three levels of HA application rate (0, 300 and 600 mg kg^-1 DW) and two levels of Pb concentration (0 and 300 mg kg^-1), making up a total of 6 treatments. After the pots, 3 kg of air-dried yellow red soil each, were amended separately with Pb, they were left for aging for 30 days. Then each pot had four uniform seedlings transplanted in. After successful transplantation, three levels (0, 300, and 600 mg kg^-1 DW) of HA were amended separately with irrigation. Six months later, the plants were harvested separately by new leaf, old leaf, new shoot, old shoot and root, for analysis of Pb concentrations in these tissues of the plants. SOC, WSS, FA, HA and SMB in the rhizosphere and bulk soils in the pots were extracted and quantified using a Multi N/C Total Organic Carbon Analyzer. Results show that in the pots that had not been spiked with Pb, the rhizospheric soil was lower than the bulk soil in SOC, whereas in the pots that had, a reverse trend was observed. Amendment of HA significantly increased SOC and SMB both in the rhizospheric and bulk soils, but the effect was affected by Pb spiking. High concentration of HA significantly increased FA in the rhizosphere soil, which was probably attributed to degradation of some of the HA amended. No significant relationship was found between the various fractions of SOC in the bulk soil and Pb concentration in the tea plants, and neither was observed of the SOC and HA in the rhizosphere soil with Pb concentration in various tissues of the plants. However, Pb concentrations in young and old leaves, young and old shoots and roots, were found to be all significantly or extreme significantly and positively related to WSS and FA in the rhizospheric soil, and significantly but negatively related to SMB therein. After all, application of HA in soil changes contents of SOC and its fractions and in turn bioavailability of Pb to and its distribution in the tea plant.

Abstract:The in-situ ¹³CO₂ pulse labeling technique was used to trace the fate of ¹³C in maize-soil system and asses the effect of fertilization and plastic film mulching on the dynamics of photosynthetically fixed carbon by maize planted in the long-term Brown Earth Experiment Station in Shenyang Agricultural University. Results show that the carbons were quickly translocated and distributed unevenly in the maize-soil system on D 1 (the first day after labeling), showing an order of shoots > roots > rhizosphere soil > bulk soil, and unmulched > mulched in δ¹³C value. The δ¹³C values declined in maize plants and rhizosphere soil, but slightly increased in bulk soil with the time passing by from D 1 to D 15. Treatment CK was the highest in ¹³C enrichment with average δ¹³C value in shoots and roots reaching 1 568‰ and 598‰, respectively, on D 1 and 178‰ and 147‰, respectively, on D 15. The ¹³C fixed in the maize plants accounted for 64.01% of the total in the system on D 1 and for 38.65% on D 15. The distribution of ¹³C showed a declining trend in the order of shoots > roots > rhizosphere soil > bulk soil in the plant-soil system. The experiment clearly demonstrated that the treatment of mulching plus organic manure significantly increased photosynthetical fixation of ¹³C and the allocation of ¹³C in maize plant and soil, which means that it is an important practice to improve carbon assimilation and distribution in the maize-soil system.

Abstract:Based on an eight-year long stationary field experiment on Weibei Arid Tableland in Shaanxi Province, China, effects of Nitrogen (N) application rate on grain yield and nitrogen utilization, N residual, nitrate leaching and organic N mineralization in dryland soil were investigated with winter wheat as test crop. The experiment was designed to have 5 N application rates, i.e. 0, 80, 160, 240 and 320 kg hm^-2. Results show that with increasing N application rate, the response of wheat in yield to N application weakened, whereas nitrate N residue in the soil rapidly increased. The nitrate N residue from the current wheat growing season was mainly distributed in the 0 ~ 60 cm soil layers, and when N application rate was raised beyond 160 kg hm^-2, it reached up to 56.8 ~ 211.7 kg hm^-2 in content of which 64% ~ 90% was found derived from the N fertilizer applied before seeding. Depth of the soil layer where leaching of nitrate occurred and amount of the nitrate N leached from the corresponding layer during the summer fallow season were all positively and parabolically related to N fertilizer rate, (r = 0.988 9 and 0.994 0). When N application rate went beyond 160 kg hm^-2, every increment of 100 kg hm^-2 of N would increase the depth of nitrate leaching by 27 cm and the amount of nitrate N leached off by 80.4 kg hm^-2. On average, every 10 mm of rainfall during the summer fallow season would have nitrate N leached 2 ~ 4 mm deeper. However, N application rate did not have much effect on depth of nitrate leaching. During the summer fallow season, soil N mineralization reached 51.8 ~ 160.9 kg hm^-2 of which 31.6 ~ 109.2 kg hm^-2 was found to be N from the fertilizer applied for the current crop, fixed by soil microbes and then remineralized. Based on such findings, it is advisable to suggest that the N application rate for winter wheat in the region should be controlled within the range of 146～163kg hm^-2, so as to guarantee high winter wheat yields, and prevent excessive residue of fertilizer N in the soil and reduce the risk of nitrate N leaching.

Abstract:With its remarkable advantages of rapid growth, high yield, wide application and good economic returns, Phyllostachys edulis has been one of the most extensively cultivated bamboo in China, especially in South China. Soil heat fluxes and meteorological factors of P. edulis ecosystems in Anji were monitored with soil heat flux plates (HFP01) and a meteorological monitoring system. Presently, few works are available on soil heat fluxes in P. edulis ecosystems, but soil heat flux is an important part of ecosystem energy flow. Based on the soil heat flux data measured from Dec. 1st 2010 to Nov. 30th 2011, relationships of soil heat flux with soil temperatures and, soil of water contents in three soil layers and net radiation were analyzed. Results show that soil heat flux varied seasonally with monthly mean flux differing sharply between months, and diurnally, displaying an “S” curve, with one peak and one valley. On an annual scale, soil is the source of heat, providing-7.52 MJ m² a year and contributing, -0.289% to the total net radiation of a year. The maximum positive value appeared in July and the maximum negative one in January. Regression relationship analysis of different temporal scales and different soil depths shows that on a monthly scale, soil heat flux was best related to the soil temperature at 5 cm in soil depth, showing a relationship at the extremely significant level, while on a daily scale, soil heat flux was in an extremely significant relationship with soil water content at 5 cm in soil depth, but the correlation coefficient was not so high. The monthly mean of soil heat fluxes was extremely significantly related with net radiation on a monthly scale and even at a half-an-hour scale, showing no temporal retardation phenomenon.

Abstract:To determine impacts of soil temperature and soil moisture regimes on soil respiration, daily and annual variation patterns of total soil respiration rate and its components, i.e. soil microbial respiration rate, soil root system respiration rate, and litter respiration rate in rubber plantations, 4 a, 12 a and 19 a old separately, were investigated with a Li-6400 portable photosynthesis system. Results show that during a day of observation, the appearance of peak and valley of soil respiration rate varied sharply from plantation to plantation different in age. However, the values obtained between 9:00 and 11:00 were all quite close to the daily mean values of soil respiration.. Although daily variations of the components differed in extent with age of the plantation, the component of litter respiration rate was the lowest in any case. Obvious monthly variations of soil respiration were found in rubber plantations, 4 a, 12 a and 19 a old, with the mean rate being 2.45, 2.63 and 2.96 μmol m^-2 s^-1, respectively, and the maximum value recorded in July or August and the minimum in February or March. No significant difference was observed in monthly variation of soil respiration between rubber plantations different in age. Soil microbial respiration accounted for 43.6% of the total soil respiration, being the highest, and was followed by root system respiration (36.1%) and litter respiration (20.4%). A remarkable exponential relationship was found between soil respiration rate and soil temperature, but not so as such was between soil respiration rate and soil moisture. It is, therefore, concluded that soil respiration is closely related to soil temperature, but may not be directly related to soil moisture in rubber plantations in Hainan.

Abstract:Benzo(a)pyrene (B[a]P) is a typical kind of polycyclic aromatic hydrocarbons (PAHs) often found in soils adjacent to the oil field or in soils irrigated with sewage. Collembolans are often used as sensitive receptors in ecological risk assessment of contaminated soils and in development of soil ecological benchmarks. However, the characteristic indices, such as growth rate, fatality and reproduction rate of their adults, were only responsive to high concentrations of B[a]P in the soil. In the present study, Folsomia candida was used as subject for ecotoxicity test to screen out new characteristic indices sensitive to low concentrations of the substances Besides, comparison was made between two typical zonal soils, i.e. udic-ferrosols and aquic-cambosols in sensitivity of the subject insects. Results show that the index of growth rate of their larva was the most sensitive and even responsive to a low concentration of B[a]P. It is, therefore, suggested that the index be cited as an indicator of the soil B[a]P toxicity. The four indices followed an order of juvenile length > adult length > reproduction rate > survival rate in sensitivity. Significant difference in ecotoxicity of B[a]P to F. candida existed between the two soils with LOEC value being 1 mg kg^-1 in udic-ferrosols and 100 mg kg^-1 in aquic-cambosols, which is likely attributed to the difference in soil physico-chemical property, especially content of organic matter and pH. It is, therefore, necessary to normalize ecotoxicity data of various soils in developing soil ecological benchmarks.

Abstract:BTEXs in water samples were determined with VF-5 ms and CP-8ms capillary-column and Headspace-Gas Chromatography/Mass spectrometer (HS-GC/MS) under modified conditions, especially with the headspace. Results show that when 10 ml flasks with water sample accounting for 60% of each flask in volume were agitated for 20 sec. at a rate of 500 r min ^-1, in the heated shaker, then kept still for 90 sec. mixed with 2.4 g NaCl in each flask and left for equilibrium for 30 min. under 60 ℃, optimal results could be obtained. The BTEXs detection limits of the method varied the range of 0.10~0.13 μg L ^-1; the standard curve correlation coefficient (r) of each BTEXs target was more than or equal to 0.999; and the sample recovery rate lingered in the rang of 98.4%～100.2% with precision being 1.41%~6.52% (n=7). All demonstrate that the method meets the requirements of organic analysis.

Abstract:A field experiment, designed to have six treatments, i.e. CK (no fertilizer and/or manure applied); HF (chemical fertilizer); ZH (composted pig manure and chemical fertilizer); JHB (straw, chemical fertilizer and straw mate); ZHJ (composted pig manure, chemical fertilizer and straw); ZDH (composted pig manure based organic-inorganic complex fertilizer and fertilizer) was conducted to explore effects of application of composted pig manure and straw on population, genera and structure of the soil nematode community in the field. Results show that a total of 22 genera of nematodes of 11 families under 4 orders were found and identified in the six treatments, including 9 genera of bacterivores, 5 genera of fungivores, 4 genera of plant-parasites, 4 genera of omnivores-predators. The total number of nematodes was significantly higher in JHB, ZHJ and ZDH than in CK and HF, while no significant difference between HF and CK. Treatment ZHJ increased the abundance of bacterivores, but inhibited reproduction of phytophagous Tylenchus and Helicotylenchus. All the five treatments, except ZDH, were significantly lower than CK in abundance of plant-parasites. JHB, ZHJ and ZDH were significantly higher than CK in Nematode Channel Ratio (NCR), indicating that in the fields under organic farming, decomposition of the soil detritus food web relies mainly on bacteria. CK, JHB, ZHJ and ZDH was significantly higher than HF in Mature index (MI), indicating that the application of chemical fertilizer only brings about greater disturbance to the soil environment. No significant difference was found between the six treatments in Shannon-Wiener index (H´), Dominance index (λ), Evenness index (J) and Wasilewska index(WI). In all the five fertilized treatments, the c-p 2 group of soil nematodes was the highest in proportion, and was followed by the c-p 3-5 group, and the c-p 1 group the lowest. Comprehensive analysis of nematode trophic groups, community structure and ecological index indicates that JHB and ZHJ were the optimal fertilization modes.

Abstract:Peanut production has been severely repressed by sick soil resulting from long-term monoculture of peanut in red field in Jiangxi Province, China. Phosphorus chemical waste solid, phosphogypsum, was investigated to alleviate the sick soil due to continuous monocropping of peanut in red soil. Mixture of phosphogypsum with chemical nitrogen, phosphate and potassium fertilizer in a different ratio were applied to peanut plots in Yingtan Experimental Station of Agricultural Ecology, Chinese Academy of Sciences to assess their effect on nutrients of red soil and peanut yield and physiological and biochemical properties. The results showed that peanut yield in treatment of phosphogypsum-containing mixed fertilizer was increased by 3.5%~45.1% compared to comventional fertilizer treatments. The soil total nitrogen, available nitrogen and potassium was increased, while plant total N, P, K were raised compared with control. This indicated man-made phosphogypsum-containing mixed fertilizer would effectively relieve sick soil in red soil in the region of continuous monocropping of peanuts.

Abstract:Through field investigation and laboratory analysis, effects of age of tea plantations on distribution of exchangeable base cations in soil aggregates were studied. Results show that (1) content of soil exchangeable K⁺ increased first and then decreased with increasing particle size of the soil aggregates. The distribution of exchangeable Mg²⁺ was relatively even in soil aggregates of all particle sizes, and contents of exchangeable Na⁺ and Ca²⁺ and total exchangeable bases (TEB) increased with decreasing particle size of the soil aggregates. Average contents of the base cations in soil aggregates regardless of particle size show an order of Ca²⁺> Mg²⁺> K⁺> Na⁺. (2) Along with rising age of the tea plantations contents of exchangeable K⁺ and Na⁺ presented a decreasing trend in soil aggregates of all particle sizes. However, contents of exchangeable Ca²⁺ and Mg²⁺ and TEB displayed a rising-and-falling trend, and higher values were found in tea plantations, 23 and 31 years of age. The changes were more evident in the 0～20 cm soil layer than in the 20～40 cm soil layer. (3) In tea plantations regardless of age, the content ratio of (K⁺+Na⁺)/(Ca²⁺+Mg²⁺) increased first and then decreased with decreasing particle size of the soil aggregates and content of soil aggregates showed a decreasing-increasing-decreasing trend with decreasing particle size. Along with rising age of the tea plantations, the content ratios of (K⁺+Na⁺)/(Ca²⁺+Mg²⁺) in soil aggregates of all particle sizes presented a decreasing-first-and-then-increasing trend and were particularly lower in tea plantations 23 and 31 years of age, which was contrary to the variation of the content of >5 mm aggregates, and more evident in the 0～20 cm soil layer. Soil aggregates, different in particle size, differed sharply in exchangeable base cations retaining capacity and supplying capacity. Contents of exchangeable K⁺ and Na⁺ decreased year by year in aggregates of all particle sizes, and contents of exchangeable Ca²⁺ and Mg²⁺ were found to be higher in tea plantations, 23 and 31 years of age, and declined somewhat afterwards. Therefore, in management of tea gardens, it is essential to adopt balanced application of nitrogen and potassium fertilizers, and in tea plantations older than 23 in age, to use organic manure in addition, enhance soil and water conservation and prevent serious soil acidification, so as to reduce leaching loss of exchangeable Ca²⁺ and Mg²⁺.

Abstract:The potential of plants to absorb, translocate and accumulate heavy metals and their biology characteristics makes them one of perfect choices for heavy metal remediation. However, it is important to discover some strengthening measures for phytoremediation, considering its limits of tolerance to heavy metals for practical applications. With the development in natural resources and the technologies, microbial regulation makes phytoremediation more viable and more valuable. Reviewing emerging microbial technology in recent years, plant growth promoting rhizobacteria (PGPR) have been applied as environmentally friendly alternatives and play a significant role in phytoremediation process, due to their abilities to alleviate heavy metal phytotoxicity, to promote plant growth and to influence the migration capacity of metals. Currently, great researches have been done on the screening, identification and application of PGPR. This article aims to review the interactions between plants and PGPR, and their potential mechanisms used to accelerate phytoremediation of heavy metal polluted soils.

Abstract:As a natural phenomenon, soil freeze-thaw processes often occur in the regions of mid- and high latitudes and high altitude. Freeze-thaw can alter the soil physicochemical and biological properties, which thereby results in changes in soil nitrogen transformation and N₂O production and hence emission. Up to now, the impacts of freeze-thaw processes on soil nitrogen transformation found in previous studies remain inconsistent and large discrepancies have been found in the data on the contributions of N₂O losses during freeze-thaw period to annual emissions. In addition, this review also addresses the effects of freezing or a freeze-thaw cycle on major soil nitrogen transformation processes, including mineralization, immobilization, nitrification and denitrification, and possible explanations are discussed. Meanwhile, four potential mechanisms relating to N₂O emission intensity during the freeze-thaw period, such as N₂O trapped in and below the frozen layer and released from thawed soil, N₂O induced by circumstance and substrates, N₂O inhibited by N₂O reductase and N₂O enhanced by chemodenitrification, are systematically analyzed. The implications of global warming for soil freeze-thaw patterns are addressed, as well as the need to investigate alteration of soil nitrogen transformation and N₂O emission as affected by these circumstances. At last, some theoretical problems and perspectives of the study are brought forward.

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