Abstract:Polycyclic aromatic hydrocarbons (PAHs) are a group of toxic organic pollutants, found widely in the environment. In soil, as they are strongly adsorbed on soil particles, it is hard to remedy the contaminated soil efficiently. To remedy such soils, the technique of using intensified biological methods in combination to intensify the effect may effectively shorten the time the soil needs to get remedied and improve remediation efficiency, so it is considered to be the most promising one with bright future and high application value. Based on field experiments using two kinds of intensified bioremediation methods (plants-microbes and plants-microbes-soil animals), this paper introduces systematically features, mechanisms and effects of the two methods separately, infers immanent factors of the mechanisms and summarizes major factors (such as PAHs concentration, type of root exudates, amount and type of degrading bacteria and soil animals amended into the soil, interspecific competition and some environmental factors). In the meantime, an overall review is presented of the recent studies at home and abroad on intensified bioremediation of PAHs-contaminated soil including addition of surfactants or immobilized microorganisms, and their techniques, principles, applications and problems, and potential factors that may limit the intensified degradation process of PAHs in various conditions are addressed, including amount of surfactant or PAHs immobilizing microorganism added, ratio of different surfactants in mixing, properties of carries, choice of immobilizing pattern, soil water and nutrient contents and so on. In the end, the paper emphasizes that it is essential to pay attention to field application and safety evaluation in practicing the methods, so as to provide some theoretical bases and technical references for future researches on bioremediation of PAH-contaminated soils.

Abstract:The knowledge about impacts of the topography on soil erosion and deposition on hillslope in the typical of the black soil region may serve as a scientific basis for arrangement of soil and water conservation measures in small catchments. However, currently, litter is available in literatures related the effects of topography factors (the slope position, slope gradient, slope length and slope shape) on spatial distribution of soil erosion and deposition on hillslope in the typical black soil region of Northeast China. This paper, based on the ¹³⁷Cs trace technique and Zhang Xinbao’s mass balance model, studied on quantitatively spatial distribution characteristics of hillslope soil erosion and deposition and analyzed influences of topography factors on soil erosion rate. A small catchment, called Dongshangou, located at Bin county, Heilongjiang Province, was selected and a total of 76 soil samples were collected at various position from six typical slopes profiles which located at the upper, middle and down streams, respectively, in additional, 8 background samples, for analysis of 137Cs activity with a gamma-ray spectrometry and for estimation soil erosion-deposition rates with Zhang’s mode. Results show that soil erosion and deposition rates on corn-cultivated hillslopes ranged from -4 685 t km^-2a^-1 to 3 417 t km^-2a^-1 (+ means soil erosion and - means soil deposition) and with a mean of 448 t km^-2a^-1, and the sampling sites where soil erosion and deposition occurred accounted for 60.5% and 39.5% of the total in number, which indicated that the catchment was dominated with soil erosion. Distribution of soil erosion and deposition varied significantly with slope position. The entire hillslope, including the top, upper, middle and lower slopes, were dominated with soil erosion, with erosion rate varying in the range of 38 t km^-2a^-1 to 3 318 t km^-2a^-1; and averaged to be 819, 376, 1 000, and 634 t km^-2a^-1, at the top, upper, middle and lower slope, respectively. Obvious deposition was observed in the foot of a slope, varying in the range of -107 t km^-2a^-1 to -4 685 t km^-2a^-1and averaged to be -1 382 t km^-2a^-1. Moreover, distribution of hillslope soil erosion and deposition also varied with shape of the slope. On convex slopes, soil erosion came first and then followed by deposition; while on the complex slopes, soil erosion and deposition distributed alternatively along the hillslopes. In addition, soil erosion rate exhibited significant power function relationships with slope gradient and slope length; and it increased with increasing slope gradient and slope length. The effect of slope gradient was much greater than that of slope length on soil erosion rate. Therefore, it is essential to mitigate as much as possible the effect of slope gradient erosion on soil erosion in slope farmland in arranging soil and water conservation practices in the black soil region.

Abstract:Soil organic carbon (SOC) and soil nitrogen (TN) are two important elements essential for vegetation growth, and meanwhile the major contributors of greenhouse gases, affecting the entire eco-environmental system. Accurate knowledge of how SOC and TN varies spatially and temporally and their driving factors at a regional scale is of some great significance to extrapolation of balanced fertilization based on soil C and N regulation as well as protection of the ecological environment. Therefore, based on the data gathered during the 2ndNational Soil Survey in 1981 and the measured data of 555 soil samples (0~20cm) collected in 2012, exploration was done of characteristics of the temporal and spatial evolution of organic carbon (SOC) and total nitrogen (TN) and it’s driving factors in the Purple Soil Hilly area of Mid-Sichuan Basin over the past 30 years. With the aid of GS+7.0 and ArcGIS9.3, spatial structure and spatial distribution of the two nutrient elements was analyzed. By means of classic statistics analysis, variance analysis(ANOVA) and regression analysis, comparison was performed of soil parent material, soil type, land use type, topography and vegetation in impact on spatial-temporal evolution of SOC and TN under different. The classical statistical analysis indicates that the mean content of SOC in the topsoil layer was 6.41g kg^-1 in 1981and 13.46 g kg^-1 in 2012, with coefficient of variation being 72.59% and 48.87%, respectively, and the mean content of TN was 0.88 g kg^-1 in 1981and 1.12 g kg^-1 in 2012, with coefficients of variation being 40.04% and 38.75%, respectively. Apparently, the mean content of SOC increased by 109.98% and the mean content of TN by 27.27%, while their coefficients of variation showed a decreasing trend, The spatial structure analysis reveals that over the past 30 years, SOC and TN was affected jointly by structural and random factors, but tended to be more affected by random factors. The ArcGIS9.3 interpolation shows that SOC and TN contents increased in most parts of the study area, especially in areas of low mountains and deep hills. The ANOVA demonstrates that parent material did not have much impact on SOC and TN contents(p>0.05); While soil type, topography, vegetation cover and land use did (p<0.001).The regression analysis indicates that land use type was becoming the dominant factor affecting spatio-temporal variation of SOC and TN, which implies that human cultivation is increasingly important in the spatial variation of both SOC and TN; while soil type was decreasing in its role but still cannot be overlooked as suggested in the structural analysis conducted here. The impact of topography was declining, while that of vegetation cover was rising over the past 30 years. The content of SOC and TN and the soil C/N was increasing, while the correlation coefficient of SOC and TN was decreasing slightly.

Abstract:In the past decades, a large volume of research work has been done on mechanism of rill formation by domestic and foreign scholars. Soil detachment as the main source of rill sediment is also a hot issue of the research on rill erosion. Being an important parameter of rill erosion models, like WEPP, soil detachment rate has also been a focal point in the research on rill erosion. In this article, experimental and analytic methods were proposed and tested for use in calculating rill detachment rate, with a view to defining suitable principles and methods for computing rill detachment ratesin the purplish soil region and enriching the basic research on rill detachment rate in purple soil with theories. The research adopted the in-lab soil flume scouring experiment, using flumes 12m in length each. The flumes were packed with purplish soil to form a sheet of plow layer over a simulated purplish subsoil layer low in permeability. The experiment was designed to have five slope gradients for the flumes (5°, 10°, 15°, 20° and 25°) and three water flow rates (2 Lmin^-1, 4 Lmin^-1 and 8 Lmin^-1). Water flow rates in the experiment were set in the light of the critical intensities of the rainfalls that produce rill erosion in sloping croplands on purple soil. Sediment was collected in a sampling bucket placed at the rill outlet. After a certain period of water scouring, rill erosion occurred, and then the soil flume was adjusted from sloping to horizontal. Plastic film was folded into multiple layers to form eleven thin, waterproof baffle plates the same in width as the rill. The baffle plates were inserted at 0.5 m, 1 m, 2 m, 3 m, 4 m, 5 m, 6 m, 7 m, 8 m, 10 m, and 12m from the rill entrance, thus dividing the erosion rill into the 11 sections: 0～0.5 m, 0.5～1 m, 1～2 m, 2～3 m, 3～4 m, 4～5 m, 5～6 m, 6～7 m, 7～8 m, 8～10m and 10～12 m. The baffle plates were inserted deep enough to prevent water from flowing between the rill sections. Each section of the rill was then filled with water and by calculating volume of the water in the rill, the soil erosion volume was worked out section; then quantity of the soil erosion was figured out from bulk density of the packed soil. Rill erosion was found to be quitelow on a slope 5° in gradient with a flow rate of 8 Lmin^-1, thus excluding the need of running the test with flow rates being lower than 8 Lmin^-1,that is, 2 Lmin^-1or 4 Lmin^-1, on the slope. Similarly, the test with the flow rate of 2 Lmin-1on a slope 10° in gradient, because erosion was already very low with flow rate at 4 Lmin^-1. All the other combinations of gradients and flow rates were tested, forming a total of twelve sets of experimental conditions. Each test had three replicates, thus making up a total of 36 separate trials. A series of process data were obtained through the experiment, and then rill detachment rates were calculated relative to hydraulic condition. On such a basis the relationships of rill detachment rate with rill length distribution process and sediment concentration were simulated. Results of the simulation show that rill detachment rate decreased exponentially with growing rill length, and linearly with rising sediment concentration. In the flumes higher in slope gradient and in flow rate, too, the effect of the simulation was better. Rill detachment rates were calculated with the analytic method and compared with those obtained through the experiment in their relationships with rill length and sediment concentration. It was found that the estimation through the experiment agreed well with the calculation using the analytic method, which indicates that the experimental method used in this research is effective and feasible.

Abstract:Since the special water storage regime in Three Gorge Reservoir, the periodic rise and fall of water table take place within 30m’s elevation difference. So, the different hydrological sections and water level elevations in the water level fluctuating zone of Yangtze River tributaries undergo a different dry-wet alternation. The dry-wet alternation make variable hydrological processes, regional climate, vegetation adaptability and particle size composition of sediment change obviously, which may transfer the role of sediment instead of a nitrogen sink into nitrogen source. The determined total nitrogen (TN) and inorganic nitrogen, such as ammonium-nitrogen (NH₄⁺+-N) and nitrate-nitrogen (NO₃^--N) could reflect background level of nitrogen in sediment, whereas the measured total transformable nitrogen (TF-N), weakly bonded with sediment lattice, was a good indicator for nitrogen cycle. Sediment is composed by different size particles. Since the larger particles are hardly broken down into small size for releasing the dissolved nitrogen into water, the absorbed nitrogen on the surface of the particles and the smaller particles would easily release into water. Frequent dry-wet alternation is a crucial factor affecting soil particle size composition. Sediment plays a key role as a source and pool in nitrogen recycling in water body. So it is important to understand the relationship between sediment particle size composition and nitrogen distribution in the water level fluctuating zone as affected by dry-wet alternation in elaborating mechanism of eutrophication of the water body in tributaries of the Three-Gorge Reservoir. The Pengxi River is a typical tributary of the Yangtze River in the Three-Gorge Reservoir Area. The water level fluctuating zone of the river was selected for the study. Sediment samples were collected, 5 each sampling site, different in depth, at two water level elevations and the sampling sites were distributed at three hydrologic sections of the river, upper, middle and down streams of the river. Particle size composition, TN, TF-N, NH₄⁺-N, NO₃^--N in the sediment samples were determined. Relationships of sediment particle size composition with content and distribution of TN, TF-N, NH₄⁺-N and NO₃^--N were analyzed with the sediment fractal dimension (D_m) theory. Results show that the sediment was composed of sand, silt and clay, accounting for 49.75%, 36.16% and 14.09%, respectively, in the water level fluctuating zone of the Pengxi River. D_m varied in the range of 2.612~2.781, being 2.727 on average. With water level elevation declining, position of the hydrologic section moving downward along the river and sampling going down in depth, the proportions of clay and silt and D_mdecreased and the proportion of sand increased in the sediment. The contents and distributions of TN, TF-N and NO₃^--N were found to be positively related to the proportions of clay and silt in and D_mof the sediment, but negatively to the proportion of sand in the sediment. D_m may serve as an important indicator of sediment structure for evaluating eutrophication risk of the tributary in the Three Gorge Reservoir Area. Generally speaking the sediment in the region is good in textural structure, but the frequent dry-wet alternations decreased the water and nutrient retention capacity of the sediment, while making the sediment sandy in the down stream of the river low in water level elevation, which in turn affected N distribution. TF-N in the sediment in the upper stream during the dry season and in the top layer under high water level elevation increased, thus becoming a source contributing to the eutrophication risk of the water body during the wet season.

Abstract:In China, the pressure of the shortage of land resources is getting more and more intense gradually, so it is very important to develop sustainable utilization and optimal management of the coastal saline soil resources. On the other hand, climate change is intensifying salinization of the inshore saline soil, thus causing a series of ecological environment problems. However, soil, as an important component of the global carbon pool, plays an important role in regulating the carbon cycle. A field experiment was carried out to study effects of various farming practices on electrical conductivity (EC_e), total respiration, organic carbon (OC), microbial biomass C (MBC), and metabolic quotient (q CO₂) in coastal saline soil. In the experiments, maize was cultivated in rotation with wheat in two tracts of saline soil different in salinity, Soil A (slightly salinized soil) and Soil B (moderately salinized soil), and both tracts were subjected to five different treatments or farming practices, that is (1) CK, conventional farming; (2) OF, application of organic fertilizer at a rate of 1.5 t hm^-2; (3) NF, application of a higher rate of nitrogen fertilizer, about 150% of that in CK; (4) S, incorporation of straw at a rate of 5.0 t hm^-2; and (5) NT, no tillage. It was found that after two crops were harvested, EC_e varied in the range from 4.57 to 8.20 dS m^-1 in Soil A, and from 4.89 to 10.13 dS m^-1 in Soil B, and was the lowest in Treatment S and the highest in Treatment NT, which indicates that in corporation of straw and application of organic fertilizer effectively reduced salt content in the surface soil. Compared to Soil B, Soil A was higher in mean soil respiration intensity, 16% higher during the summer maize season and 18% higher during the wheat season. Treatments OF, NF and S were all higher than CK in soil respiration in comparison with CK, and only Treatment NT was a bit lower. In terms of soil respiration intensity measured in the end of the experiment, the treatments followed an order of S > OF > NF > CK > NT, regardless of soil salinity. When soil EC_e got higher than the critical value, soil respiration rate began to slow down. After the crops were harvested, SOC and MBC tended to increase, especially in Treatment OF and S. The treatments varied sharply in SOC and MBC content, which were significantly and positively related to soil respiration. That is to say, with increase SOC content, content of the matrix which soil microbes can decompose into organic carbon increased, thus releasing more CO₂. However, organic carbon did not have any linear relationship with EC_e. Soil A was slightly higher than Soil B in q CO₂ and among the treatments, CK was the highest and NT was the lowest. Comparison of the two groups of treatments in the experiment indicates that the soil electrical conductivity and organic carbon content were the two main factors affecting CO₂ release. All in all, though Treatment NT lowers soil respiration intensity and, increases organic carbon and microbial biomass carbon contents, it increases soil salinity too. This study holds that incorporation of straw and application of organic fertilizer are two optimal farming practices that can be adopted to ameliorate coastal tidal flats, improve soil fertility, promote crop growth, alleviate soil salinity and increase crop yield. Therefore, the practices of organic fertilizer application and straw incorporation have a great potential for extension in coastal polders.

Abstract:Rapid high-prescion determination top soil water content is of vital importance to precise agriculture , precise water resource management and the control of slope land erosion. The technology of low-frequency ground penetrating radar (GPR) currently in use is far from the requirement in precision for determination of topsoil water conteng. It is, therefore, essential to develop and adopt a high-precision detection technology. In this paper, the technology of high frequency (1 GHz and 2 GHz) Ground Penetrating Radar(HFGPR) was tested to determine topsoil water content in a vegetable field of silty clay loam in soil texture in Jiangning of Nanjing, China. HFGPR was used to determine topsoil water content of farmlands under different soil water content, GPR data and images were obtained and electromagnetic spectrum characteristic parameters extracted for analysis of their quantitative relationships with soil water content. Results showed that: The decision coefficient R² of ε~θ model in fitting the soil dielectric constant (ε) obtained by the 1GHz and 2GHz frequency GPR with the soil moisture(θ) measured in the field was 0.94 and 0.97, respectively, which demonstrates that the technology of high frequency GPR is feasible be applied to determine the soil water content in the topsoil of vegetable fields of silty clay loam soil. The new technology is much higher than the old one in precision in determining soil water content in topsoil layers.

Abstract:Soil moisture is predicted with spectroscopy based on the mechanism of moisture affecting characteristics of spectral reflectance of the soil, but most studies took reflectance as an independent variable in moisture predicting models, and paid only a little attention to absorption characteristics. In n this study 8 samples of black soil different in soil organic matter content were collected from its experiment field and prepared them into 102 soil samples using a new soil moisture adjusting method. The samples were then put individually into wide round glass disks. Spectral reflectances of the samples in the visible and near infrared region were measured with an ASD Field Spectroradiometer in the laboratory, yielding 10 spectral curves for each sample, of which a mean was worked out as the actual reflectance of the sample. Since the spectrometer responds unevenly to electromagnetic waves different in wavelength, spectral data need to be pre-processed for smoothing at a regular wavelength interval of 5 nm to diminish noise before data analysis. As the soil samples did not vary much in spectral characteristics, the continuum removal method was used to effectively make the characteristics of spectral adsorption and reflection prominent in the spectral curves. Soil spectral reflectance is comprehensive representation of soil physical and chemical parameters, and hence very sensitive to changes in soil organic matter (SOM) soil moisture, Fe, coarseness, mechanical composition and so on. However, the characteristic parameters of spectral adsorption valleys extracted with the continuum removal method reduced the sensitivities. The continuum removal method was applied with the aid of Software ENVI 4.6. The characteristic parameters of soil spectral adsorption that need to be extracted encompass area, depth and width of a spectral absorption valley. Correlation analysis was used to determine relationships of moisture content of the black soil with reflectance, spectral characteristic parameters and post-continuum-removal values. Based on the Simple Linear Regression, Stepwise Multiple Linear Regression(SMLR) and Partial Least Squares Regression(PLSR) method separately, high-spectrum models for prediction of black soil moisture content were built up using spectral reflectance, post-continuum-removal values and spectral adsorption characteristic parameters as independent variables, and moisture as dependent variable. Determination coefficient and RMSE were used to evaluate prediction accuracy of the models.. The higher the R² and the more stable and accurate the model and the lower the RMSE. Results show that (1) the soil spectral curve of Black soil has five spectral absorption valleys located at 510, 615, 1420, 1920 and 2210 nm, separately; and in predicting soil soil moisture content in black soil, spectral characteristic parameters are higher in correlativity than spectral reflectance, especially at 1420 and 1920 nm; (2) the models based on Simple Linear Regression, Stepwise Multiple Linear Regression (SMLR) and Partial Least Squares Regression (PLSR), separately, are all applicable to prediction of soil moisture content in black soil; and (3) the model based on simple linear regression using the characteristic parameters of the spectral absorption valley at 1 920 nm as independent value is high in prediction accuracy and low in input volume, and hence can be used as the theoretical basis for developing instant soil moisture measuring instruments. The models established in this study are high in stability and accuracy, which may be attributed to their use of just one type of soil and the new soil moisture adjusting method. Therefore, it can be concluded that the soil moisture high-spectrum prediction model based on spectral adsorption characteristic parameters is high in accuracy and stability and can be used for instant prediction of soil water contents.

Abstract:Farmers in Miaofeng Mountain, Mentougou District of Beijing have been growing red rose for over 500 years. The red rose growing there is famous the world over for its bright color, strong flavor taste, high oil content, excellent quality and high economic value. Currently, the area has a total of about 460 hm2 dedicated to rose cultivation and produces about 100 000 kg of roses annually. Fresh roses are used for extraction of rose essential oil and production of rose syrup cordial for export. However, it is very hard to extend control of the rose, because roses were once cultivated in Phoenix Hill, not so high in quality. To explore differences between the soils in Miaofeng Mountain and Phoenix Hill in soil morphological feature, soil slices were prepared out of the soils of the two areas for comparison and analysis with the soil slice image processing and analysis system and the software of image-pro plus 6.0, qualitatively and quantitatively from the aspects of soil microstructure, organic matter, skeleton particles and soil pores. Results show that the soil of the rose gardens in Miaofeng Mountain is better developed in soil structure than that in Phoenix Hill, dominated with bonded matrix and microstructure of moderately separated subangular blocks; The former has rich sources of organic matter and is higher than the latter in distribution frequency of organic matter in all layers, and hence much higher in bio-activity; comparison of the soil profile in Miaofeng Mountain with that in Phoenix Hill shows that the skeleton particles in the former were smaller in particle size, on average < 17 μm, but higher in psephicity than those in the latter; Though the total porocity in the former was lower than the latter in all layers, the former has more stack pores that are well connected and facilitate to storage of water in the soil. Comparison of the two also shows that human activities do not have much effect on soil micromorphology. It is the differentiation between the two areas in geological condition that makes the two different in soil development degree. The bedrock in Miaofeng Mountain is much higher than that in Phoenix Hill in content of Fe, Ca, Mg, Cu, Zn, B and Sr. Consequently, the soil derived from andesite and andesitic volcaniclastic rock is also quite higher in these elements. Researches have shown that elements like Mg, Fe and B can promote synthesis of various enzymes needed for plant growth. In addition, Miaofeng Mountain is a synclinal mountain formed by tectonic movement. The landform, on the one hand, evolved out of the synclinal structure of the mountain improves water holding property of its terrane, and on the other hand, the outstanding mountain facilitates formation of a micrometeorology that favors growth of red roses. All the above-described form a unique natural advantage that gives the red roses in the Miaofeng Mountain unique properties. In order to expand the scale of rose cultivation in Beijing, it is advisable to choose areas similar to Miaofeng Mountain in lithology, geologic structure and landform for cultivation of red roses.

Abstract:In the black soil region of Northeast China, the issue of the soil getting more and more compact due to the extensive use of farming machines has been arousing more and more concerns among the people. Soil compaction has been considered one of the main causes of degradation of agricultural soils worldwide, because it reduces soil porosity and water infiltration, while enhancing soil intensity and soil consistence, which in turn impede root penetration into the soil and consequently reduce land productivity. Despite of this, little has been done on mechanical properties of compression and rebound of black soil typical of Northeast China. It is, therefore, essential to explore compression behavior of the soil for prediction of possible changes in soil structure under the pressure of farming machines. To explore effects of reclamation in mechanical properties of compression and rebound of the black soil, plots of black soil fields different in reclamation history, i.e. 17 (Plot 17), 30 (Plot 30) and 40 (Plot 40) years and un-reclaimed natural secondary forest land (Plot 0), were cited for soil sampling using a ring sampler, 2.00 cm high and 6.12 cm in diameter and the soil samples were analyzed for soil void ratio, compression index, compression coefficient, and rebound index with a fast oedometer. Results show that soil void ratio, compression index, compression coefficient and rebound index all went down with the cultivation going on. During the compression process, Plot 0 was obviously higher than Plots 17, 30 and 40 in soil void ratio (p<0.05); Plot 17 higher than Plots 30 and 40 (p<0.05); and Plot 30 did not differ much from Plot 40. And during the rebound and recompression phase, the four plots displayed a variation pattern similar to that during the compression process. Compression index, compression coefficient and rebound index of the soil varied from 0.252 to 0.426, 0.002 04 to 0.003 70 kPa^-1, 0.041 to 0.070, respectively. Plot 0 was significantly higher than the other three plots (p<0.05), and Plot 17 higher than Plots 30 and 40 in compression index (p<0.05), while no significant difference was found between Plots 30 and 40. However, the plots showed a different trend in soil compression coefficient. Plot 0 and Plot 17 was significantly higher than Plots 30 and 40, but the former two did not differ much. Plot 0 was still significantly higher than all the other three in rebound index (p<0.05), but among the latter three, only Plot 17 was significantly higher than Plot 40 (p<0.05). Besides, it was also found that with farming cultivation going on, soil organic matter content decreased while soil bulk density increased, and both of the indices were found somewhat related to compression index, compression coefficient and rebound index of the soil. Organic matter content was positively related to compression index (r=0.893), compression coefficient (r =0.733) and rebound index (r=0.803), while bulk density was negatively related to compression index (r=-0.884), compression coefficient (r=-0.904) and rebound index (r=-0.840); However, soil clay content did not seem to be related to compression index, compression coefficient and rebound index of the soil. Moreover, both soil compression index and soil rebound index were in significant positive relationship with soil compression coefficient (p <0.05), and soil compression index was in extremely significant positive relationship with soil rebound index (p <0.01). In conclusion, reclamation affects soil compactness significantly, and with mechanical farming cultivation going on, soil compactness increases in degree, while compressibility and rebound capacity of the black soil decrease. Obviously, long-term mechanical farming cultivation decreases soil organic matter content and increases soil bulk density, which is believed to be the major cause leading to the decline of soil compressibility and rebound capacity.

Abstract:Measurement of available potassium (AK) is commonly used to assess potassium (K) status of a soil, and studies in the past have shown that release of AK from 2:1 K-bearing minerals was triggered by chemical extraction methods of exchanging adjacent interlayer K with hydrated cations and the dissolving minerals. However, there is still a great deal of uncertainty in and variation between these batch experiments with respect to respective contribution of the exchange and dissolution to K release budget, which has certain important implications for predicting soil sustainability. Mechanisms of AK released from illite were studied using 2:1 K-bearing mineral dominant in soil, and four extracting methods, i.e. 0.2 mol L^-1 sodium tetraphenylboron (NaTPB), 1 mol L^-1 boiling nitric acid (HNO₃), 2 mol L^-1 cold HNO₃ and 2 mol L^-1 hot hydrochloric acid (HCl) methods. X-ray diffraction (XRD), fourier transform infrared photoacoustic spectroscopy (FTIR-PAS) and atomic force microscopy (AFM) were used to investigate changes in structure and surface morphology of the mineral. Results show that released K accounted for 59.5% of the total K in illite in amount and basically through interlayer exchanging reaction when extracted with NaTPB, but for 1.53% ~ 2.46% when extracted with acid solutions and 88.4% ~ 94.0% of the released K was K released through interlayer exchanging reaction. A very limited amount of structure elements of Fe, Al and Si was released into the solution of NaTPB, but the situations in the acid solutions were just reverse. When NaTPB was used to extract K from illite, the surface of the illite became blurry and the interlayer space was expanded, forming a silicon-rich surface of secondary transition mineral, but did not show any solution phenomena. However, when acid solutions were used to extract K from illite, the mineral did not change much in structure, but lowered in crystallinity and displayed apparent solution phenomena. In the presence of boiling HNO₃ and cold HNO₃, a small number of elliptical dissolution pits were found randomly distributed on the surface of illite. When extracted with hot HCl, the illite showed channel dissolution on the surface, and fine mineral particles attached on large grains were dissolved in the hot HCl solution. All the findings indicate that K is released from illite mainly through cation-exchange reaction in both acid and salt solutions, and interlayer K in the K-bearing minerals is the main pool of K available to plants. The acid extracting methods, on the one hand, may underestimate soil AK supply capacity; on the other hand, they extracte some structural K that is not available to plants. Thus, the 1 mol L^-1 boiling nitric acid (HNO₃), 2 mol L^-1 cold HNO₃ and 2 mol L^-1 hot hydrochloric acid (HCl) methods are not suitable to assessment of soil AK pools.

Abstract:Soil degradation caused by irrational land utilization has greatly threatened sustainable development of the world agriculture. In degraded soil aggregates are readily crushable or breakable and the increasing amount of small-sized aggregates affects stability of the soil structure. In recent years, soil erosion led by soil degradation affects the lives of thousands of millions of people around the world. Biomass ash, a combustion product of agricultural wastes, is low in pH, porous in structure and rich in phosphorus, potassium and other nutrients. Its use as soil amendment can not only improve soil physical and chemical properties and yield of crops but also reduce incidence of crop diseases. Therefore, biomass ash is a new type of green and potentially valuable material that can be used to improve soil quality. In this study, saw-dust ash prepared in an incinerator at 800 ~ 900 ℃ was selected as biomass ash (H). Besides this, other soil amendments including lime (S), lime with zeolite (SF), biological fertilizer (W), plant ash (C), were used, separately, in addition to chemical fertilizer (NPK) in a pot experiment using degraded yellow soil from the Wulong Fairy Hill area in Chongqing for comparison. A lettuce - spinach - lettuce rotation system was adopted to determine effects of the soil amendments on yield and quality of the vegetable and soil fertility as well as on nutrient contents in soil leachate. The aim of this study is to provide scientific basis for comprehensive evaluation of effects of the soil amendments ameliorating degraded yellow soil. Results showed as follows: (1) The effects of the soil amendments varied significantly from one another. Treatments NPKH and NPKW were higher than all the others in lettuce yield. The use of soil amendments in addition to chemical fertilizer helped reduceNO₃^?-N content in lettuce as compared with the use of Chemical fertilizer alone, the content of amino acids in lettuce was the highest in Treatment NPKH; (2) The effects on the degredated soil also differed with type of amendment. The use of soil amendments increased soil organic matter and pH. The content of soil organic matter decreased with the planting going on, but the decrease was the least in Treatment NPKH, which was followed by Treatment NPKC. The effects of the amendments on alkalytic N did not differ much, but the effect of raising soil available P and available K was the highest in Treatment NPKH, with the effect on soil available P in particular, being 190.0% ~ 242.9% higher than that in Treatment NPK. (3) The use of chemical fertilizer alone in degraded soil may easily lead to N loss, which may amount to 22.08 ~ 39.06 mg L^-1 in total N (TN). The leachates from Treatments NPKH, NPKW and NPKC were lower than those from the others in TN concentration. NO₃^?-N was the main form of soil nitrogen lost with leachate, and similar in trend and very closely related to TN (P<0.01, r=0.869). During the pot experiment, Total phosphorus (TP) and disissoluble phosphorus (DP) concentrations in the leachates displayed significant correlationship (P<0.01, r=0.892). DP accounted for more than 60% of TP in concentration. In Treatment NPKH, as ash per se contained a large volume of P, besides the portion absorbed by the crops, a portion was lost with leachate. The concentration of TP and DP in the leachate from Treatment NPKH reached 0.70 ~ 1.35 mg L^-1 and 0.67 ~ 1.27 mg L^-1, respectively, significantly higher than those in the leachates from the other treatments’, thus posing a risk of eutrophying the nearby waterbody.

Abstract:Biogas slurry was known to affect the soil-plant ecosystem when applied as manure, especially in combination with chemical fertilizer. However, little knowledge was available regarding how this combination affects peanut yield and soil fertility in peanut fields of red soil, South China. Therefore, a two-year field experiment, designed to have 6 treatments, except for CK (No fertilizer applied), different in proportion of biogas slurry N to total N input [0% (NPK), 15% (BS15), 30% (BS30), 45% (BS45) and 100% (BS100)] and the same in NPK rate (N-P2O5-K2O, 120-90-135 kg hm-2), was carried out to evaluated synthetically the effects of combined application of biogas slurry and chemical fertilizer on peanut yield, soil organic matter, labile organic matter, carbon management index and soil nutrients (N, P, K et al) in the Red Soil Ecological Experiment Station, Chinese Academy of Sciences. Results show that combined application increased peanut yield by 33.2%～48.3% and 10.2%～22.8% as compared to that in CK and Treatment NPK, respectively, with Treatment BS30 in particular, reaching 3332 kg hm^-2 in peanut yield or being 4.0%～48.3% higher than the other treatments, separately. Meanwhile it also significantly increased soil organic matter, labile organic matter and carbon management index (CMI), and the effect was especially obvious in Treatment BS30. The findings suggest that combined application may increase the content of soil organic matter and improve its quality as well. Treatment BS30 markedly increased soil total nitrogen, ammonium nitrogen, nitrate nitrogen, available phosphorus and potassium in the soil, as compared with CK and Treatment NPK, respectively. Correlation analysis of peanut yield with soil nutrients (N, P, K, etc.) reveals that its correlation coefficient was the highest with available phosphorus, being 0.956**, which indicates that soil available phosphorus is presently the main factor affecting peanut yield in peanut fields of red soil. In addition, peanut yield was also found positively related to labile organic matter with correlation coefficient being 0.826*, but did not have much to do with organic matter. At the same time, labile organic matter was in extremely significant or significant positive relationship with organic matter (0.920**), total nitrogen (0.894*), total phosphorus (0.867*), available phosphorus (0.872*) and available potassium (0.821*), while organic matter was significantly related only to labile organic matter (0.920**), total nitrogen (0.922**) and available phosphorus (0.862*), which suggests that labile organic matter could be better used as indicator of soil quality than organic matter, and, hence, may well be used as a good index for evaluation of soil fertilization efficiency. All the findings in this experiment indicate that the combined application of biogas slurry and chemical fertilizer, 3:7 in ratio can not only significantly increase peanut yield and reduce the use of chemical fertilizer, but also build up the soil nutrient pool with higher labile organic matter and organic matter contents. It is, therefore considered to be an effective way to increase peanut yield, while building up soil fertility in the upland red soil areas of South China.

Abstract:Organic and phenolic acids are the major components of root exudates, and they play important roles in rhizosphere. Studies have demonstrated that root exudates vary with species and nutrient condition of a plant and tillage. However, little work has been done on effect of planting model, especially intercropping, on root exudation, and rhizospheric process. Wheat and faba bean intercropping is a common planting model in Yunnan Province, Southwest China. A number of researchers have found that wheat and faba bean intercropping could significantly improve yields and nutrients use efficiency of the crops, and the beneficial effects of intercropping are partly attributed to the changes it causes in rhizosphere process. In order to explore effects of the intercropping of wheat and faba bean on rhizosphere, a pot experiment was conducted, and HPLC analysis was performed of the rhizospheric soils of the plants for contents of organic and phenolic acids at different growth stages of wheat and faba bean. Results show that intercropping increased the content of organic acids in the rhizosphere of faba bean at the vegetative stage (57~120 d), and especially at the branching and pod setting stages, it did the content of total organic acids in the rhizosphere up to 21.7 and 1.95 times, respectively, as high as in the rhizosphere of mono-cropping faba bean. The effect was reflected particularly on accumulation of citric and fumaric acids. Besides, intercropping also increased the content of organic acids in the rihzosphere of wheat during its reproductive stage (120~169 d), and especially at the booting and filling stages, it did the content of total organic acids up to 3.73 and 2.3 times, respectively, as high as in the rhizosphere of mono-cropping wheat. The effects were particularly apparent on accumulation of lactic, acetic and fumaric acids. In addition, wheat and faba bean intercropping decreased the content of penolic acids and inhibited accumulation of the acid in the rhizosphere of wheat, but did not have any influence on type of penolic acid. However, intercropping altered composition of penolic acids by enhancing the accumulation of vanillic and syringic acids, and reducing the content of ρ-Coumaric acid in the rhizosphere of faba bean. In conclusion, intercropping of wheat and faba bean can alter rhizospheric processes of the plants by affecting the accumulation and composition of organic acids and phenolic acids in the rhizsphere.

Abstract:Every year China produces huge volumes of crop straw, most of which, however, is burnt by the farmers in the fields. Burning of straw in open fields will not only reduce the contents of soil organic matter and soil moisture in the surface soil layer, but also bring about environment pollution and damage human health. To apply corn stover deep into the subsoil layer (20~40 cm), namely “Corn stover deep incorporation” (CSDI), is believed to be able to effectively solve the problem of how to utilize crop residue as resource and a number of other problems caused by burning of crop straw and further on help sequestrate carbon, raise water holding capacity, improve soil fertility and stabilize crop yield. A field experiment was conducted in a mono-cropping corn field at the Experiment Station of the Jilin Agricultural University, with four treatments, that is, CK (no-corn stover incorporated), CS (CSDI), NPK (fertilizers applied only) CS+NPK (CSDI plus fertilizers application) designed to explore effects of corn stover deeply incorporated in addition to fertilizers application on composition of soil humus and structure of humic acid (HA) in the soil. Soil samples were collected from the four treatments for analysis of humus composition with the modified humus component extraction method and for structure of HA with the IHSS method for purification and the infrared spectroscopy for element composition. Results show that treatments CS and CS+NPK were conducive to accumulation of SOC and various humus fractions in all soil layers, but did not affect PQ (percentage of humic acid in humus) much. The two treatments increased the proportion of aromatic-C in HA, and Treatment CS also increased the proportion of aliphatic chain hydrocarbon in HA, while treatment CS+NPK raised the condensation degree and lowered the oxidation degree of HA, which means the two treatments differed in mechanism of making HA stable. Besides their effects of improving the aromaticity of HA in molecular structure, Treatment CS also enhanced hydrophobicity of HA, and Treatment CS+NPK made the structure of HA more complicated.

Abstract:Three commonly observed species of Oniscidea, i.e. Armadillidium vulgare (Latreille, 1804), Porcellionides pruinosus (Brandt, 1833) and Mongoloniscus sinensis (Dollfus, 1901) in a natural farmland soil, which was amended artificially with Cd for the purpose of exploring toxicological effects of the heavy metal on these woodlice. The exploration covered three aspects, that is, acute toxicity of Cd to woodlice, Cd enrichment in woodlice and avoidance behaviors of the woodlice. The test of acute toxicity of Cd on three woodice was done using the filter paper contact method and natural soil method. It was found with the former, the 48 h half lethal concentration (LC₅₀) of Cd to A. vulgare,M. sinensis, and P. Pruinosus was 158, 448 and 238 μg cm^-2, respectively, while with the latter. The 14 h LC₅₀of Cd to these woodlice was 2 489, 5 048 and 2 616 mg kg^-1, respectively. So in terms of LC₅₀ , the three species displayed an order of A. vulgare ＜ P. pruinosus＜ M. sinensis, which indicates that the woodlice vary with species in tolerance and sensitivity to Cd. It was also found that acute toxicity of Cd to the woodlice was closely related to duration of the exposure and concentration of Cd and mortality of the woodlice was positively related to concentration of the heavy metal in the soil, that is, morality of woodlice rises with concentration of Cd. Cd is apparently the decisive factor of the toxicological effect in the test and concentration of Cd significantly affects mortality of woodlice (p<0.01). The findings suggest that morality of woodlice may be used as an effective and sensitive bioindicator to determine Cd pollution in the soil environment. In terms of Cd enrichment in the woodlice, the three species displayed an order of M. sinensis＞P. pruinosus＞ A. vulgare, indicating terrestrial isopods can survive in soils polluted with Cd to certain degree and they vary with species in Cd enrichment capacity. In the case of 15 d-16 mg kg^-1, A. vulgare was the highest in enrichment coefficient, being up to 0.96, in the case of 7 d-48 mg kg^-1, M. sinensis was, reaching 8.37 and in the case of 15 d-48 mg kg^-1, P. pruinosus was, reaching 5.47. Obviously, both M. sinensisand P. pruinosusare capable of enriching Cd, while A. vulgare is not, but just absorbs. Statistical analysis of the enrichment test shows that Cd enrichment in the woodlice is closely related to duration of the exposure or incubation and concentration of the heavy metal. The concentration of Cd effective to cause 80% of A. vulgare to avoid Cd was 32.8 mg kg^-1, with 95% confidence interval being 25.4~42.9 mg kg^-1; the concentration of Cd effective to cause 80% of M. sinensis to avoid Cd was 43.6 mg kg^-1, with 95% confidence interval being 35.9~56.4 mg kg^-1; and the concentration of Cd effective to cause 80% ofP. pruinosus to avoid Cd was 40.5 mg kg^-1, with 95% confidence interval being 33.2~52.6 mg kg^-1. Therefore all the three woodlice displayed obvious avoidance behavior in reaction to Cd pollution in the soil. So, in terms of avoiding ability, the three species displayed an order of A. vulgare ＞ P. pruinosus＞ M. sinensis. Compared with the endpoint LC₅₀ of the acute toxicity test, the endpoint of the avoidance behavior test was more sensitive to heavy mental Cd in the soil. All the findings in the study show that M. sinensis tends to enrich more Cd when Cd concentration rises in soil and hence is much higher than A. vulgare and P. pruinosusin tolerance and enrichment capacity. It is expected that in future studies, M. sinensis may become the animal group of first choice for use as bioindicator of Cd pollution in soil.

Abstract:Excessive application of nitrogen fertilizers in facilitated vegetable fields may easily lead to soil degradation (such as soil salinization，acidification，hardening, etc.), and even further to some serious environmental consequences like pollution of groundwater and emission of large volumes of N₂O, thus seriously affecting sustainable development of the vegetable industry. Recently, a novel soil remediation technology, called RSD(reductive soil disinfestation) has been developed of adding organic substances (e.g., crop straw, molasses, manure, etc.) in flooding water. The RSD method can effectively alleviate the risk of soil degradation, such as removing the nitrate accumulated in the soil, increasing pH, lowering soil electrical conductivity and improving soil structure. However, in strong reducing environments the high amount of nitrate accumulated in the degraded facilitated vegetable fields was rapidly reduced by denitrification, and high nitrous oxide (N₂O) emission was observed in RSD process. N₂O is the third major greenhouse gas, and is 296~310 times as high as CO₂ in global warming potential. It is estimated that N₂O emitted from agricultural soil accounts for 60% of the annual anthropogenic emission into the atmosphere, and the facilitated vegetable soil with high N input is one of the most important agricultural N₂O sources, contributing about 20% to the emission from agricultural soil. Therefore, it is essential to investigate how to mitigate N₂O emission from degraded facilitated vegetable soil, especially in its strong reductive remediation process. In this study, Biochar was selected as soil regulator in evaluating effects of the use of biochar on N₂O emission in degraded vegetable soil and its RSD process relative to rate of its use. Six treatments were designed and conducted, Treatment CK (16% in soil moisture content and no biochar used), Treatment 1% BC(16% in soil moisture content and 1% biochar applied, w/w), Treatment 5% BC (16% in soil moisture content and 5% biochar applied), Treatment RSD (flooded, rice straw incorporated and no biochar used), Treatment RSD + 1% BC (RSD and 1% biochar applied) and Treatment RSD + 5% BC (RSD and 5% biochar applied). By determining the abundance of nitrifying functional genes (norB gene andnosZ gene encoding nitric oxide reductase and nitrous oxide reductase, respectively), activities of denitrifying microorganisms were characterized. Soil samples were collected from the treatments and incubated at 30 ºC in dark for 14 days,and N₂O emission rate was measured during the incubation using the accumulative method. Besides, soil samples were also collected for analysis of inorganic nitrogen contents, soil pH and abundance of denitrifying functional genes. Each sampling had four replicates. Results show that RSD significantly lowered soil nitrate content, raising soil pH and retarded soil degradation, but the cumulative N₂O emission from the RSD-treated soils was over 950 times as high as that from their non-RSD treated counterparts. Application of 5% Biochar reduced the N₂O emission in degraded vegetable soil and its RSD process by 68.7% and 16.0%, respectively. Pearson correlation analysis reveals a negative relationship between N₂O emission rate and soil pH in both degraded vegetable soil and its RSD process, and a positive relationship between N₂O emission rate and soil ammonium content in RSD process. The abundance of norB and nosZ genes was also significantly changed after biochar application. Linear regression analysis shows that soil N₂O emission was mainly related to nosZ gene abundance in degraded vegetable soil, but to norB gene abundance in RSD process. To sum up, the application of 5% biochar in degraded vegetable soil and its RSD process can elevate soil pH and alter abundances of the critical denitrifying functional genes, thus efficiently mitigating N₂O emission. All the findings in this study may serve as experimental evidence for N₂O mitigation in degraded vegetable soil, and also can be regarded as important indices for assessment of environmental effects of the remediation of degraded vegetable soil.

Abstract:Human activities, such as combustion of fossil fuel, production and utilization of chemical fertilizers, intensification of livestock husbandry, etc. have caused atmospheric nitrogen depositionon the globe to increaseby 3 times, which significantly alters nitrogen recycling in forest ecosystems. Subtropical plantations in China are located in the center of the region very high in atmospheric nitrogen deposition on the globe, where the soils, relatively enriched with nitrogen, are very sensitive to input of extraneous nitrogen, in production and emission of soil nitrous oxide (N₂O). However, in the past, the experiments to simulate N deposition used to have only one type of N fertilizer such as NH₄ NO₃ or urea as N source, without taking into account the difference in in-situ effect between oxidized N and reduced N. In this study, a plantation of pinus elliottii at the Qianyanzhou Subtropical Experiment Station, Chinese Academy of Sciences, was selected as an object in an experiment on controlled N addition. This experiment was designed to have two forms of N fertilizers (NH₄Cl and NaN₃O) and three N application rates (0, 40 and 120 kg hm^-2 a^-1) and laid out in plot randomly. Soil-atmospheric N₂O exchanging fluxes, were measured eight times per month using the static chamber-gas chromatography method, and simultaneously, soil temperature and moisture at 0～10 cm depth, dissolved N concentrations (NO₃^--N, NH₄⁺-N, total dissolved N (TDN), and dissolved organic N (DON)) at 0～15 cm depth were determined for analysis of how the N₂O exchanging flux responded to input of extraneous N and its main affecting factors. Results show that N addition did not affect soil temperature and soil moisture in the subtropical plantation, but did increase significantly soil NO₃^--N, NH₄⁺-N and TDN contents, except for soil DON content, of which the potential mechanisms included preferential absorption of NH₄⁺-N by plants, fixation of NH₄⁺-N by soil organic matter/ minerals, and assimilation of inorganic by plants and soil microbes. Also, N addition significantly promoted soil N₂O emission in the subtropical plantation or by 378%~ 847%; and the effect was higher in plots applied with NH₄Cl than in plots applied with Na NO₃. Moreover, soil N₂O flux was found to be positively and significantly related to soil temperature and soil moisture at 0-10cm depth, which indicates that the hydrothermal factors propelled soil N₂O emission in the subtropical plantation. Also, the change in soil N₂O flux (Δsoil N₂O fluxes, the difference between N treatment and control) was significantly and positively related to that in soil NH₄⁺-N and NO₃^--N contents (Δsoil inorganic N contents), and the relationships could well be fitted with linear and exponential growth equations, respectively. The findings of the study indicate that the increase in soilN₂O content in N-enriched soils is mainly attributed to changes in substrates for nitrifier and denitrifier communities, and hint that soil N₂O emission in the subtropical plantations, South China, is very sesitive to input of extraneous N, and more to reduced NH₄⁺ than to oxidized NO₃^-. The sensitivity is higher than the mean of the globe. Therefore, it is advisable to address reduced NH₄⁺ and oxidized NO₃ separately, in assessing influence of atmospheric N deposition on carbon and N recycling and C budget in future studies. Unfortunately, the failure of this study to determine activities of soil nitrifier and denitrifier communities made it hard to assess relative contributions of various processes, separately, to soil N₂O flux. For future studies, it is recommended to apply ¹⁵N tracer and molecular microbiology in in-depth analysis of the relationships between soil N transformation processes and soil N₂O flux, and coupling effects of key microbial functional groups and soil N transformation and emission processes.

Abstract:Agricultural soils have been determined to contribute at present about 60% to the global anthropogenic nitrous oxide (N₂O) emission due to N fertilization. It is a great challenge to guarantee high crop yields while reducing N₂O emissions under continuous application of nitrogen fertilizers. However, few field data sets are available for exploration of effects of fertilizer N regimes on soil N₂O emission in the Sichuan Basin, one of the regions the most intensive in agriculture in China. The main objectives of this research were to screen out optimal N fertilizer management practices which would not only reduce soil N₂O emission, but also maintain high crop yields. Static chamber-gas chromatographic techniques had been used to measure soil N₂O emissions from the purple soil under long-term N fertilization of pure synthetic N fertilizer (N), synthetic NPK fertilizer (NPK), pig manure (OM), pig manure plus synthetic NPK fertilizer (OMNPK) and incorporation of crop residues plus synthetic NPK fertilizer (ICRNPK). A plot with no fertilizer (NF) applied was set as control for emission coefficient calculation. In-situ field measurements were conducted through the wheat-maize rotation season from November 2012 to September 2013. N₂O emission showed a double-peak curve during the season regardless of fertilization regime. The peaks occurred in the first days after fertilization. However, the peak in the maize season was significantly higher than that in the wheat season (p < 0.05). Fertilization regimes influenced cumulative N₂O fluxes and grain yields significantly (p < 0.05). When the total N application rate was the same for all the treatments, 130 kg hm^-2 in the wheat and 150 kg hm^-2 in the maize season, Treatment N, OM, NPK, OMNPK and ICRNPK was 1.93, 1.96, 1.12, 1.50 and 0.79 kg hm^-2, respectively, in cumulative N2O flux, 0.62%, 0.63%, 0.33%, 0.47% and 0.21%, respectively, in emission coefficient, and 4.35, 11.95, 8.39, 9.77, 10.93 t hm^-2, respectively, in total annual grain yield. In comparison with Treatment NPK, Treatment OM enhanced N₂O emission significantly, whereas, Treatment ICRNPK significantly reduced N₂O emission and maintained high crop yields, as well. Therefore, incorporation of crop residues plus synthetic fertilization (ICRNPK) is recommended as an optimal fertilization regime in croplands of purple soil. Content of inorganic N (ammonium and nitrate) was the main controlling factor of soil N₂O emission. Therefore, the difference in N₂O emission flux was attributed to variation of the content of inorganic N induced by fertilization regime. That was also the reason why the fertilization regime, Treatment as ICRNPK, could effectively reduce N₂O emission. Soil water filled pore space (WFPS) might be another important factor affecting soil N₂O emission with a threshold effect. Therefore, it can be concluded that N₂O emissions from upland croplands under the wheat-maize rotation system can be reduced by optimizing timing and rate of N application in the light of crop growth and antecedent soil WFPS.

Abstract:Carbon is the number one of the 17 essential nutrient elements, but over the past 100 years, little has been reported about carbon fertilizer products produced by the chemical fertilizer industry. It is usually believed that the carbon nutrient plants absorb comes from the air in the form of carbon dioxide, which as a matter of fact meets only 1/5 of the demand of a plant. Therefore, plants are always in the state of “hunger for carbon”. Organic carbon used as fertilizer can eliminate plants’ hunger for carbon that is caused by depending mainly on carbon dioxide in the air as carbon source. Water Spinach was cultivated in solutions different in nitrogen level in a batch system in this research. Effects of two kinds of nitrogen-free organic C (α-ketoglutarate and Glycerol) on fresh weight, dry weight, number of branches, carbon and nitrogen metabolism (expressed as water soluble N/ total N or water soluble C/ total C ) and nutrition quality indices (Zinc, Iron and Nitrites) of the water spinaches were analyzed. Results show that foliar spray of organic carbon promoted growth of the Water Spinach regardless of nitrogen level in the solution. However, the effect varied with nitrogen level and source of organic carbon. The effect of foliar spray of Glycerol was the best on the water spinaches growing in the solution moderate in nitrogen level (100 mg kg^-1), raising the fresh weight, dry weight, total carbon and total nitrogen of the plants 12.88%, 15.48%, 7.05% and 8.33% higher than that in CK, respectively. Besides it also increased Fe content in the plant by 16.20% while decreasing Nitrite significantly, which indicates that nutrition quality of the plants was greatly improved. K content in the plant was found decreased significantly, which implies that the spray may help reduce luxury absorption of K in the soil. The effects of foliar spray of α-ketoglutarate was the best on the water spinach growing in the solution high in nitrogen level (120 mg kg^-1), increasing the fresh weight, dry weight, total carbon and total nitrogen by 17.97%, 20.91%,7.97% and 9.56% and the content of Zn, a nutritional quality indicator, by 16.18%, too, while decreasing Nitrite content significantly, which indicates that the plants were greatly improved in nutrition quality. K content was also found decreased in the plants, implying that the spray may help reduce luxury K absorption from the soil. In the experiment, the spray of organic carbon fertilizer, either Glycerol or α-ketoglutarate, lowered WC/TC and WM/TN in leaves of the water spinach, regardless of N content in the solution, which indicates that extraneous organic carbon can promote synthesis and metabolism of carbon and nitrogen in the plants, thus stimulating growth and improving nutritional quality of the Water Spinach. The findings in this study demonstrate that it is organic C, rather than organic N, that raises crop yield and improves quality of the crop. Meanwhile crop yield is found to be related by a certain degree to SN/TN and SC/TC in the plant, which show that these parameters can be used as important physiological indicators for high-yield-oriented fertilization. Currently high yield of a crop is restricted by the crop’s dependence mainly on the air for carbon supply, or hunger for carbon. It is, therefore, quite obvious that how to solve the problem of “Hunger for carbon” is the key to high yield agriculture. This study has found that organic carbon fertilizers may help satisfy crops’ hunger for carbon. So it is feasible to use organic C to balance fertilization, rather than just using NPK in balanced fertilization. Further research in this aspect is of important significance to balanced fertilization and has some profound academic meaning for further developing theories of modern plant nutrition.

Abstract:Fertilizer, especially chemical fertilizer, contributes significantly to the production of modern agriculture. However, in recent years, fertilizer consumption has been increasing exponentially throughout the world, and as a result, causing a series of serious environmental problems. The use of water retaining slowly-release fertilizer (WRSRF) is a promising approach to improving the utilization of water resources and fertilizer nutrients, and pursuing sustainable development of the environment and agriculture. Some fertilizers can also be used to alleviate salt stress of crop plants, such as urea, manure, etc. however, little has been reported on application of water retaining slowly-release fertilizer to plants under salt stress. To fill the gas, a pot experiment was conducted to evaluate effects of WRSRF (ZL 2012 1 0400570.0) on plant morphology, root development, plant dry weight, leaf chlorophyll content, gas exchange parameters and water use efficiency (WUE) of rice seedlings under salt stress for 20, 40 and 80 d, separately. Rice seeds were sown in pots filled with natural soil, 2.68 g kg-1 in salinity. Twenty days later, half of the pots were amended with sodium chloride (NaCl) through irrigation to make 2.0 g kg^-1 in salinity. WRSRF was applied at 0, 1, 2 and 4 g kg^-1, separately to the pots. Results showed that: (1) growth of the rice seedlings applied with WRSRF increased with application rate of the fertilizer regardless of salt stress; (2) total root length, root surface area, root volume and number of root tips were all increased as EPSON scanning reveals, particularly in the treatment applied with WRSRF at 4% and the increase was especially significant in root surface area and root volume; (3) WRSRF application increased dry weight of the rice plants under salt stress, and the effect was more significant when WRSRF was higher in application rate. However, the stimulation effect was more obvious on roots than on shoots; (4) the fertilizer application increased leaf chlorophyll content of the plants under salt stress, and the increase was getting more significant with the experiment going on. However, the increase effect on chlorophyll content in plants under high salt stress was more obvious than that in plants under low salt stress; and (5) application of water retaining and slowly-release fertilizer promoted net photosynthetic rate (Pn), stomatal conductance (Gs), intercellular carbon dioxide concentration (Ci), transpiration rate (Tr) and WUE, and these effects became more significant with increasing WRSFR rate, especially on Pn. However, application of the fertilizer decreased stomatal limitation values (Ls) of the plants, and the decrease became more significant with increasing fertilization rate. To sum up, application of the water retaining and slowly-release fertilizer (ZL 2012 1 0400570.0) may improve salt tolerance of rice seedlings significantly, which may be attributed to its effects on root growth, content of leaf chlorophyll, photosynthesis and WUE.

Abstract:A study was conducted on how activities of plateau pika (Ochotona curzoniae) in Kobresia pygmaea meadows affect the distribution of soil organic carbon and readily available nitrogen in the soil and their coupling relationship in the effect, using the method of counting effective burrows density of the animals in the field as the basis for setting up a disturbance gradient. In the study, the activity or disturbance of the animals was divided into four levels in intensity. In Level I, 112 effective burrows hm^-2 were found, Level II, 192 were, Level Ⅲ, 352 were, and Level Ⅳ, 608 were. Results show that with the activity of the animal getting intensified, the contents of organic carbon in the 0~10 cm and 10~20 cm soil layers of the vegetation-covered land (over 80% of the land covered with vegetation) and bare land (patches of land devegetated by the burrowing animals, with only 10% of the vegetation left growing) rose significantly first and then dropped rapidly, and the contents were the highest in lands of Level Ⅱ or about 21.51% and 46.03% higher than that in lands of Level I. And furthermore, content of organic carbon was much higher in the topsoil layers of vegetation-covered lands than in those of bare lands. The content of readily available N in the bare lands increased significantly first and then declined apparently, and the increase in bare lands of Level II was the biggest or 155.63% higher than that in the vegetation-covered lands, which had significant differences. Under the disturbance of the animals, contents of soil organic carbon, soil available nitrogen and NH₄⁺-N decreased with soil depth in the vegetation-covered lands and were much higher in the 0~10 cm soil layer than in the 10~20 cm soil layer, however, content of NO3--N acted reversely and was lower in the 0~10 cm soil layer than in the 10~20 cm soil layer, where topsoil organic carbon accounted for 69.74% of the total in the soil. In the bare lands 0~10 cm soil layer, the soil available nitrogen and NH₄⁺-N content were significantly lower than in the 10~20 cm soil layer and the NO₃⁻-N content significantly higher than 10~20 cm soil layer, content of organic carbon did not varied much between the two soil layers except of Level I. Under the plateau pika’s disturbance, soil organic carbon was in significantly negative relationships with available nitrogen, NO₃⁻-N and NH₄⁺-N in the vegetation-covered lands, but in significantly positive relationships in the bare lands. It indicates that the activities of the animals changed the coupling relationships of soil C and N and the disturbance of a proper intensity may significantly increase the content of soil organic carbon in the Kobresia pygmaea meadows and cause the formation of bare patches relatively high in nitrogen content, which provides room for expansion, colonization and reproduction of other grasses or opportunistic plant species. Burrowing activities of plateau pika can alter vertical distribution of soil nutrients, which enhances heterogeneity of the soil. All the findings in this study demonstrate that the study to investigate effects of plateau pika disturbing the soil in the alpine meadow should take into account the influence and meaning of the existence of bare patches and the necessity of unified vegetation types, and the population density of plateau pika should be controlled within a reasonable range in the Kobresia pygmaea meadow.

Abstract:During the last decades, long-term fertilization has improved soil fertility in the Huang-Huai-Hai Plain. With increasing soil available P, crop response in yield to phosphorus fertilization has been found declining, while environmental risks of unreasonable fertilization are becoming an hot issue of concern. In recent years, returning straw to fields is a farming practice getting more and more popular in the Huang-Huai-Hai Plain, however, few studies, let alone long-term straw return field experiments, have been carried out to investigate impacts of such changes in field management on fractions of soil inorganic P, soil P availability, yield response as well as potential environmental risks. Therefore, based on the 33-year long-term fertilization field experiment effects of straw return in conjunction with chemical P fertilization on total-P, Olsen-P as well as fractions of inorganic phosphorus in fluvo-aquic soil in the Huang-Huai-Hai Plain were studied. Fractionation of inorganic P was done using the Gu Y-C, Jiang B-F method. In this experiment, the split-plot method was used, and 4 main plots, i.e. N₀S₀, N₁S₁, N₂S₂ and N₃S₃ were laid out. Each main plot was split into 3 sub-plots, applied with straw at a rate of 0, 2250 and 4500 kg hm^-2, separately. This experiment under a winter wheat-summer maize rotation system was initiated in 1981, and designed to have maize straw returned to the field in 1981-1983, 1987-1989, 1993-1995, 1999-2001 and 2005-2013 and winter wheat straw returned in 2000 and on. Results show that among the plots the same in P₂O₅ application rate, (0, 60 or 20 kg hm^-2 in chemical phosphorus), those having maize straw returned for 21 years and those having wheat straw returned for 15 years witnessed soil Ca₈-P significantly increased with rising straw return rate; in plots applied with P₂O₅ at 240 kg hm^-2 in chemical phosphorus, soil total P, available P and inorganic P, such as Ca₂-P, Ca₈-P and Al-P, were all significantly increased with rising straw return rate, but Fe-P, O-P and Ca10-P did not change much in content. Compared to Plot N₀P₀S₀, Plot N₀P₀S₂ (maize straw returned at 4500 kg hm^-2) was 10.2% or 7.33 mg kg^-1 higher in content of soil Ca₈-P; compared to Plot N₁P₁S₀, Plot N₁P₁S₂ was 32.5% or 24.39 mg kg^-1 higher in content of soil Ca₈-P; compared to Plot N₂P₂S₀, Plot N₂P₂S₁ was 10.3% or 10.07 mg kg^-1 and Plot N₂P₂S₂ was 27.3% or 26.71 mg kg^-1 higher in content of soil Ca₈-P; and in comparison with Plot N₃P₃S₀, Plot N₃P₃S₁ and N₃P₃S₂ was 64.5% or 2.47 mg kg^-1and 178.6% or 6.84 mg kg^-1 higher in content of soil Ca₂-P, 42.0% or 80.15 mg kg^-1 and 67.8% or 129.3 mg kg^-1 higher in content of soil Ca₈-P and 37.0% or 15.68 mg kg^-1 and 61.7% or 26.14 mg kg^-1,higher in content of Al-P, respectively. In terms of relative increment (p<0.05) the fractions of inorganic P displayed an order of Ca₂-P＞Ca₈-P＞Al-P. In addition, in the plots the same in straw return rate, impacts of chemical P fertilization rate on soil P were also examined: in comparison with Plot N₀P₀S₀, Plots N₁P₁S₀, N₂P₂S₀ and N₃P₃S₀ had soil total P, inorganic P and Olsen-P increased on average by 154, 164 and 7.24 mg kg^-1(23.1%, 35.9%, 593.2%), respectively, and Ca₂-P, Ca₈-P, Al-P and Fe-P increased on average by 1.53, 49.43, 14.18 and 13.09 mg kg^-1 (242.9%, 68.9%, 59.5% and 40.7%), respectively. Furthermore, in comparison with N₀P₀S₀, Plots N₁P₁S₁, N₁P₁S₂, N₂P₂S₁, N₂P₂S₂, N₃P₃S₁ and N₃P₃S₂ had soil total P, inorganic P and Olsen-P increased on average by 2013, 271 and 9.90 mg kg^-1 (35.1%, 59.1%, 811.7%), and Ca₂-P, Ca₈-P, Al-P and Fe-P increased by 3.67, 97.65, 22.99 and 17.04 mg kg^-1 (581.7%, 136.1%, 96.6% and 53.0%), respectively. In conclusion, in the farmlands under the winter wheat-summer maize rotation system in the Huang-Huai-Hai Plain, when P input falls lower than P output (120 kg hm^-2), the soils would not have much changes in total P, inorganic P, Olsen-P and fractions of inorganic P, regardless of whether straw is returned in addition to fertilization. However, when P input goes beyond P output, soil total P, Olsen-P as well as Ca₂-P, Ca₈-P, Al-P and Fe-P will all increase, and among the P fractions, Olsen-P ranks first in relative increment, and is followed by Ca₂-P, Ca₈-P and Al-P. In addition, balance of soil phosphorus input and output is positively related to contents of the various fractions of soil phosphorus (p<0.05).

Abstract:Biochar is a kind of carbon-rich solid material prepared out of biomass through pyrolysis in an oxygen-limited environment. Recently, it has been attracting more and more attention. Biochar amendment into soil is thought to be a good approach to carbon sequestration, which may in turn improve soil physical and chemical properties, such as nutrient and water holding capacity, soil fertility and crop yield. However, how biochar affects soil microbe is still a topic that needs further study. Soil microbial communities are sensitive to biochar amendment, and microbial community structure varies significantly with type of biochar. However, little is known about effects of the amendment of biochar together with litter on soil microbial communities in artificial forests in Subtropical China. In this paper, an investigation was conducted of impacts of fir (Cunninghamia lanceolata) litter and its biochar on soil properties and microbial community structure in a fir plantation in the Jianou Wanmulin Nature Reserve of Fujian Province, in the hope of providing some valuable information for rational utilization of the biomass resources and management of carbon sequestration in the artificial forest in Subtropical China. The biochar was prepared out of fir litter through pyrolysis at three different temperatures, 350 °C, 550 °C and 750 °C. Soil samples were collected from the plantation, and prepared into eight treatments by amending fir litter, biochar or both, separately, such as: (1) control soil (S); (2) soil+litter (S+L); (3) soil+350 °C biochar (S+BC350); (4) soil+550 °C biochar (S+BC550); (5) soil+750 °C biochar (S+BC750); (6) soil+litter+350 °C biochar (S+L+BC350); (7) soil+litter+550 °C biochar (S+L+BC550); (8) soil+litter+750 °C biochar (S+L+BC750), and the litter and biochar was added both at a rate of 2% of the dry soil mass. All the soil samples were incubated in the dark at 25 °C for 364 d. At the end of the incubation, the soil samples were analysed for soil properties, using conventional methods and for soil microbial biomass and community structure using the phospholipid fatty acid method. Results show that pH was 9.4%~12.7% and 9.6%~12.7% higher in Treatment S+BC and Treatments S+L+BC (regardless of preparation temperature) than Treatment S and C/N ratio was 27.1%~41.8% and 26.3%~41.8% higher, respectively. And the effect was more significant in Treatment S+L+BC750 than in Treatment S+L+BC350. The amendments, regardless of which, increased soil total carbon by 21.7%~94.6%, and total nitrogen by 16.2%~45.7%, but the effect on total carbon was more significant in Treatment S+BC than in Treatment S+L and in Treatment S+BC350 than in Treatment S+BC750. Phospholipid fatty acid analysis shows that Treatment S+L and Treatments S+L+BC were both significantly higher than Treatment S in total PLFAs, fungi abundance and fungi to bacteria ratio, and Treatments S+BC and Treatments S+L+BC were significantly higher than Treatment S in ratio of gram positive bacteria to gram negative bacteria. However, Treatment S+L and Treatments S+L+BC were lower than Treatment S in abundance of actinomycetes, but Treatments S+L+BC were much higher than Treatment S+L in abundance of actinomycetes. Principal component analysis (PCA) shows that microbial community structure varied significantly with type of the amendment. Canonical correspondence analysis (CCA) shows that the amendments changed soil properties, including soil pH, C/N, total carbon, total nitrogen, dissolved organic carbon (DOC) and dissolved organic nitrogen (DON), which in turn affected the soil microbial community structure. The effects of amendment increasing soil total carbon, C/N and soil pH were more significant in Treatment S+BC than in Treatment S+L, but the effect of increasing soil microbial biomass was more in Treatment S+L than in Treatment S+BC, and so was the effect on soil microbial community structure. Treatments S+L+BC may not only improve soil properties, but also stimulate growth and alter community structure of the soil microbe.

Abstract:Soil conservation is an important service function of an ecosystem. Therefore, the study on soil erosion and mass and value of soil conservation of a valley may provide some essential bases for soil-water conservation, regulation of land use patterns,eco-compensation and reservoir management in the areas of the Project of Water Diversion from South to North. For that end, Shangluo, a major water source region of the project, was cited for quantitative evaluation and spatial heterogeneity analysis of the ecological service functions of land retension, soil erosion and soil conservation therein from the angle of hydrology, using the sediment retension sub-model of the InVEST ( Integrated Valuation and Trade offs of Ecosystem Services) model to ensure accuracies of in-situ acquisition, verification, colliberation and input of parameters, and for further exploration of benefits and spatial characteristics of the soil-water conservation pracices of ensuring water quality and desiting in the region, in expectation of providing some theoretical basis and reference to decision-makers.. Results show that (1) the total potential and actual soil erosion rate of Shangluo City was 1.21×10⁹ t and 3.4×10⁷ t, respectively, implying that the region, on the whole, was rated “slight” and “moderate” in soil erosion and had no sign of severe erosion, and the five watersheds (Luo River, Dan River, Jinqian River, Qianyou River and Xun River) in the region were all in the categories of slight and moderate erosion; (2) The total sediment output from the region was 1.61×10⁶ t，whereas the total soil retention rate of the region was approximately 1.17×10⁹ t, of which 2.9×10⁷ t was of sediment, and among the five watersheds, Xun River, Jinqian River and Qianyou River were very high in sediment retention capacity; (3) the total ecological service value of the soil conservation in the region reached 205.5 million yuan and 616.3 million yuan in terms of reduction of sediment accumulation and insurance of water quality and was averaged to be 313.6 yuan hm^-2 a^-1and 824.1 yuan hm^-2 a^-1, excluding the consideration of dead reservoirs; and (4) to prevent and control soil erosion, priorities should be given to optimization of land use, improvement of regional ecological benefit, development of forestry and amelioration of the soil and build-up of soil and water conservation capacity, which should start from small watersheds, with special attention to soil-water management of forest-grass interlaced areas, terrace fields on slopes and ridge-furrow tillage and construction projects.

Abstract:The knowledge of properties and distributions of soils is essential to planning and managing sustainable land use and preventing degradation of the lands, especially lands under Pinus massoniana forest, which are typical degraded lands in red-soil erosion areas of Southern China, reaching 1.42×10⁵ km² in area at the end of the 1980s. Soil is an important material basis for vegetation growth and its distribution and development is subject to the influence of soil erosion. The soil under Pinus massoniana forest in the hilly red soil area of South China is exposed to severe soil erosion, making the eco-environment therein very fragile. It is, therefore, of great significance to vegetation restoration and ecological rehabilitation in such areas, to determine impacts of erosional landform on distribution and properties of the soil. For that end, this study analyzed effects of erosional landform on properties of the soil under Pinus massoniana forests in the region (25°26′～26°17′N，114°42′～115°22′E) in Ganxian County of Jiangxi Province, China. The soil in the studied region is laterite derived from granite with the featured of a calcareous humid ferrisol, coarsein texture (60.8% of sand, 18.7% of silt, and 20.5% of clay). Located under the subtropical hilly humid monsoon climate, the region enjoys a mean annual precipitation of about 1423.4 mm concentrated mainly in the rainy season lasting from April to June. Soil sampling was carried out during the mid- and late-April and mid-October 2013. Four hills were selected typical of the study area. On the ridge, saddle and gully of each hill, a belt transect was laid out at random along the slope and on the upper, mid and lower slope, a sample plot (10 m×10 m)was delineated separately, making up a total of 36 sample plots. In order to keep the samples as consistent as possible in sampling condition, it must be made sure that there had been no rain for 2 weeks before sampling. Soil volumetric water content (SWC) of a sample plot was determined by averaging the soil water contents measured at 9 random sampling points across its topsoil layer (0~15 cm) with TDR-100 (a portable Time Domain Reflectometry), and the soil sample of a sample plot was a mixture of soil samples collected from its topsoil layer at 5 random sampling points. After collection, the soil samples were sieved, separately, to remove plant roots and large stones from the soil with a 2 mm mesh sieve, and then divided into two portions, one stored at 4℃ in an icebox and the other air-dried and sieved again, both ready for analysis of soil texture, enzyme, edaphon and chemical properties, etc. To improve precision of the analysis, each soil sample had three replicates in analysis and then means were worked. Statistics and the grey relational degree analysis were performed of the data obtained in the analysis with the aid of SPSS 19.0 and Excel 2007. In the end of study, the following conclusions were drawn. 1) The soil under Pinus massoniana forests varied significantly with erosional landform in soil properties. Compared with the soils on the ridge and saddle of the hill, the soil in the gully was higher in the most of the soil property indices, in number of soil microbes and in soil enzyme activity; 2) The correlativity between soil physical and chemical properties also varied sharply with erosional landform. Compared with the soils on the ridge and saddle of the hill, the soil in the gully had more soil physical and chemical property indices positively related to the indices of soil microbes and soil enzyme activity, and the relationship between soil properties and gully was the highest in correlativity, reaching 0.93; 3) The micro-environment formed in gullies improved soil properties, providing favorable natural conditions for restoration of vegetation. Therefore, the study on environment of erosional gullies may provide some scientific basis for rapid restoration of soil and vegetation in the hilly red soil areas of south China.