Abstract:In China, Cultivated Land Productivity Evaluation (CLPE) is carrying out country-wide on various scales, e.g. country, province, municipality, city and county, with the《Technical Rules for Productivity Survey and Quality Assessment of Cultivated Lands》 (TRPSQACL) as guidance. In order to minimize negative effects of the modeling based on the subjective evaluation index system, discussion is done in this paper on analytic logic of CLPE, so as to build up a “thought bridge” linking professional knowledge to the physical model of cultivated land productivity. CLPE is just a kind of land productivity evaluation (LPE) and the prevailing LPE methods could be used as reference in forming scientific analytic logic for building a CLPE index system. LPE methods can roughly be sorted into 3 categories. The first one is the category of qualitative classification and grading, such as Land Capability Classification of America (LCC), Soil Fertility Capability Classification of America (FCC), Chinese Land Resource Evaluation Map at 1:100,000 scale. This category of methods is used to classify and grade land resources according to the type and extent of obstacles in land use on all spatial scales, but it does not have a consistent index system. The second is one of quantitative scoring methods, such as Storie Index Soil Rating of America, Soil Quality Rating of Germany (SQR), etc., characterized by explicit index systems and scoring rules, and fast computation with the aid of GIS, but they are only applicable to evaluation on small scales for the sake of accuracy. And the third is one consisting of methods combining classification with scoring, such as Agro Ecological Zone of FAO, Land Potential Productivity suggested by MOSS and Agricultural Land Quality Grading of China. They are characterized by dividing the region to be evaluated into several agricultural zones, for which appropriate evaluation indices are selected zone-specifically, and then calculating potential of phototemperature or climate contributing to land productivity on the large spatial scale as the first step, and modifying the score with soil conditions and site-specific environmental conditions on the small scales as the second step. So they are applicable to evaluation on all spatial scales. Different from the above-listed 3 categories of methods, TRPSQACL specifies a scoring method for CLPE without considering the limitation of this method being unapplicable to evaluation on large scales. So, it has brought about a series of problems in the application, e.g. absence of specific task orientation suitable to all spatio-temporal scales in evaluation, neglect of scale suitability in selecting indices, frequent failure to have the principles of dominance and independence embodied. By utilizing the viewpoints of geoscience, agronomy and system science, this paper has built analytic logic to solve the above-mentioned problems. The paper holds: 1) for CLPE, the implications of task, technical routes and indices to evaluation all possess the feature of spatio-temporal scale. 2) Evaluation indices should be divided into two groups, of which one may directly indicate satisfaction degree of the crop with light, temperature, water and nutrients while the other may indirectly do. It is advisable to choose indices with stability and indirect evaluation indices for CLPE on large scales, which is characterized by long-term effectiveness and low spatial resolution and focus on exposing geographical obstacle and resource constraints in utilizing cultivated land in a region For CLPE on small scales aiming at real-time status of cropland productivity with high spatial resolution, indices featuring instantaneity and directness are recommended. 3) Land-crop-management should be viewed as a holistic system and significances of the indices to cropland productivity should be dialectically analyzed since not only natural and management land conditions but also the match degree of land conditions and crop requirements vary with land system. And 4) the natural and artificial land conditions that jointly indicate nature of a certain aspect, e.g. light, temperature, water and nutrients, should be viewed as a whole, an integrated index, that should not be dissevered in the evaluation index system.

Abstract:Soil is an important source and sink, as well, of greenhouse gases (GHGs). Earthworms are a major component of the soil fauna, and a soil animal the highest in biomass in the soil. Being termed as soil ecosystem engineers, they play an crucial role in formation of soil physical-chemical properties and structure and in recycling of soil matter and nutrients through their feeding, burrowing and casting activities, thus directly or indirectly affecting the generation and emission of GHGs (CO₂, N₂O and CH₄) in the soil. On one hand, the respiration of earthworm is an important part of soil respiration; in micro-environments, like guts, exudate, digesta and feces, anaerobic conditions, proper moisture content and rich C and N supply are favorable to growth and multiplication of denitrifying bacteria, thus greatly increasing biomass and activity of the bacteria, which in turn stimulates the emission of N₂O during the process of denitrification (N₂O 2.5~25 ng h^-1 g^-1 fresh earthworm), as is shown in recent studies. And N₂O emission is higher from earthworm feces than from the soil in its surroundings. On the other hand, through feeding, burrowing and excreting, earthworms also cause changes in soil properties, composition and activity of soil microbes and some other ecological processes (e.g. decomposition, nitrification and denitrification), thus indirectly affecting GHGs emission. The activity of earthworms in the soil helps mix soil with plant residues and reshape soil pores and aggregates, thereby affecting soil moisture dynamics, aeration and content and availability of nutrients. Aerobic and anaerobic micro-environment within earthworm-made aggregates may also have some effect on decomposition and denitrification. Moreover, the macroaggregates formed by earthworms through their activities, in the long run, help C sequestration in microaggregates. Earthworms help blend plant residues with soil in their guts by feeding, thus expanding contact between microbes and organic matter, and alter composition and structure of the microbial community through their digestion and excretion processes. The interactions between earthworms and denitrifying and methanotrophic microbes cause formation of "drilosphere", where N₂O emission increases and CH₄ emission decreases. These effects are usually affected by soil moisture content, organic matter content and earthworm species. Based on their feeding and burrowing behaviors, earthworms are typically divided into three ecological groups: epigeic, endogeic and anecic species. Because of the differences in food accessibility and in distance the gases have to go through from the soil to the atmosphere, the three groups of earthworms differ sharply in ecological function, and the interactions between the groups make the effects on soil GHGs more complex. Besides, earthworm activities may also affect other soil fauna, such as mites, collembola, nematodes, isopods, enchytraeids, etc. in biomass and activity in their habitats. By the above-described indirect means, earthworms alter composition, structure and functions of the soil ecosystem. However, little is known about the effects of earthworm-plant interactions on GHGs balance in the soil. Besides, further researches are needed to fully understand interactions between different ecological groups of earthworms. To sum up, earthworms affect CO₂, CH₄ and N₂O emissions mainly by regulating the ecological processes of carbon and nitrogen, such as decomposition, mineralization, nitrification, denitrification, methanogenesis and methanotrophy. Effects of earthworms on emission of GHGs have attracted more and more attention. Although much research has been done on the impacts of earthworms on soil CO₂ and N₂O emissions, little has been reported on CH₄efflux. In view of the serious soil pollution problems, it is essential to unfold studies on changes in effects and potential role of earthworms in polluted soils. As for research techniques, current studies are still mainly based on short-term indoor incubation and simulation of one-factor environment. As the in-lab manipulated and simplified environments are far from good enough to reflect accurately the real conditions of the nature, it is urgent to start long-term in-situ field experiments and multi-environmental factor interaction experiments, because the functions of earthworm in the soil vary with the seasons; In addition, molecular and isotope tracing techniques have become available as effective tools for studies to expose biological and ecological mechanisms of earthworms’ effects on emissions of GHGs. It is essential, in future, to pay more attention to interactions of the different ecological groups of earthworms with soil properties, composition of soil microbes, other species of soil animals and plants growing on the surface of the soil, to intensify the study on mechanisms with stress on changes in earthworms’ function in polluted soils; to review comprehensively the effects of earthworms on emission of GHGs from the soil and carbon sequestration in the soil; to scientifically evaluate the effects of earthworm activities promoting or mitigating emissions of C and N from the soil.

Abstract:The alpine region in the Tibetan Plateau, characterized by sharp contrasts in topographpy and bioclimate, accounts for about one-fifth of China’s total land area. Due to limited field observation and high spatial heterogeneity, distribution of soil organic and inorganic carbon in the alpine region remains unclear. A better understanding of the distributions of soil organic and inorganic carbon and their controlling factors in this region is critical for accurate assessment of terrestrial carbon storage and important in implication for dealing with global climatic change. In this study, investigations were conducted of vertical distribution of soil organic and inorganic carbon along two toposequences in the middle Qilian Mountains on the northeastern edge of the Tibetan Plateau, one on the shady or north slope, the Hulugou watershed and the other on the sunny or south slope, the Shitougou watershed. Each toposequence consists of five typical soil profiles, and soil samples were collected by soil genetic horizons. The objectives of this study were to examine changes in vertical distribution of soil organic and inorganic carbon along the two toposequences, and to identify main controlling factors for the variations of soil organic and inorganic carboncontent at the slope scale in a relatively small region. Results show that organic carbon content decreased with soil depth in both toposequences, but the rate was much higherin the sunny slope (66% to 91%) than in the shady slope (31% to 77%). In the soil profiles along the shady slope, inorganic carbon was found distributed quite evenly (< 5.0 g kg^-1) due to the strong leaching of carbonate, while in the soil profiles along the sunny slope, inorganic carbon in B horizons was two-fold as high as that in A horizons, which demonstrates that evident enrichment of inorganic carbon in the B horizons of the soil profiles on the sunny slope. Soil carbon in the topmost 1 meter soil layer did not vary much in density between the north and south slopes (16.1 to 33.9 kg m^-2 and 11.8 to 32.8 kg m^-2 respectively), but did in composition. In the north slope, the soil carbon was dominated by organic carbon accounting for 82% to 99% in density, however, the soil organic and inorganic carbon in the south slope varied sharply in density, accounting for 27% to 81% and 19% to 73% of the soil total, respectively. Therefore, it may be concluded that slope aspect plays an important role in the vertical distribution as well as composition of soil carbon in the alpine region. In addition, precipitation and vegetation are also major factors affecting spatial variability of soil carbon along the toposequences. With the mean annual precipitation increasing by 1 mm, soil organic carbon within the 0~20 cm soil layer increased by 0.4 g kg^-1, while inorganic carbon within the 40~80 cm soil layer declined by 0.2 g kg^-1. And vegetation type also had some effect on enrichment of soil organic carbon. All the findings in this study demonstrate that the study on soil carbon cycling and the estimation of soil carbon stocks in the alpine region should take into account the influence of micro-topography, especially slope aspect, on distribution, composition and spatial variation of soil carbon at the slope scale.

Abstract:Six counties, typical of Henan and Jiangsu are selected in a case study on application of the spatial grain size method on a 1 km×1 km grid scale to exploration of soil diversity of dominant and rare soil families (DSF and RSF), type of grain size effects on MSHDAI and MSHDLI, and grain size effects on correlativity and correlations between the four indices and their stabilities. In terms of soil diversity, soil families, the highest in diversity index and in soil patch area as well are deemed as dominant ones. Counties dominated with plains in terrain are the lowest in number of soil families, while those dominated with hills are the highest. For instance, in Rugao County, the water network, being too high in density, plays a unique role in the study on correlativity between pedodiversity and surface water body diversity. With rising spatial grain size, the grain size effects on both DSF and of RSF fall basically into the type of "non-responsive", suggesting that the two indices are not sensitive to changes in spatial grain size, or that they are relatively stable. However, when RSF is located at the edge of the study area, soil patches change in shape with grain size, which in turn affects stability of the pedodiversity. In the research of surface water body diversity, the effects of grain size on MSHDAI and MSHDLI are both of the "declining type". In the study areas, regardless of research period, the relationships in terms of scale effect between MSHDLI and MSHDAI and between their means are all polynomial functions, which indicates that as time goes on, changes of the water bodies in either area or shape do not affect the fitted functional relationship between the two indices. With rising spatial grain size, the correlations between pedodiversity and the surface water body diversity exist in two types, “stable type” (including unchanged significant positive correlationship, unchanged significant negative correlationship and unchanged non-existence of significant correlationship) and “unstable type”. To sum up, of the six counties under study, Xiangcheng of Henan and Wujiang of Jiangsu are the most stable ones, which is attributed to their plain-dominated terrains, while Linzhou and Gushi of Henan and Lishui of Jiangsu are unstable ones, which is attributed to their hill-dominated terrain. Rugao, owing to its high water network density does not show any correlation between pedodiversity and surface water body diversity. It should be pointed out that the distribution of planar lakes in the southwest of Lishui is contributing to a certain extent, to the instability of the correlation, which might be associated with the setting of width and diversity index of lakes. So more efforts should be made in futuring research in this field. The study on effects of grain size on correlation coefficient of related indices in Xiangcheng and Wujiang reveals that in Xiangcheng exists a significant positive correlation between RSF with MSHDAI, and a significant negative one between DSF and MSHDAI and between DSF and MSHDLI, whereas in Wujiang exist significant positive correlations between DSF and MSHDAI and between DSF and MSHDLI. The correlation curve of the correlation coefficients of the two counties remains essentially unchanged, which shows that the soils and surface water bodies are well correlated in the two counties, regardless of regions. Results show that for the effects of grain size of the dominant soil family and rare soil family are basically of the type of "non-responsive", and with rising grain size, the RSF located at the edge of the study area, declines in stability of pedodiversity; The effects of grain size on MSHDLI and MSHDAI are of the type of “Decining”, and when the relationship between the two or their means in scale effect fits the polynomial function, the fitting peaks in degree. During 2000 ~ 2013, the correlations between the indices of pedodiversity and the surface water body diversity in Xiangcheng and Wujiang were of the “Stable type” encompassing both positive and negative ones and never underwent any substantial changes, so they were quite stable while the correlations in Linzhou, Gushi and Lishui were so stable and that in Rugao was almost nil due to its highly dense water network. Therefore, it is quite clear that terrain, shape and density of the water bodies and human activities are the major factors affecting the correlationship between pedodiversity and surface water body diversity.

Abstract:In order to fully understand the spatio-temporal variability of soil available nutrients in cultivated lands of Weibei Tableland, measured data of soil readily available nutrient contents in cultivated lands of Pucheng, a typical agricultural county of Weibei Tableland, in 1980 and 2011 were gathered and analyzed, using traditional statistics and geo-statistics in combination with GIS technology for spatio-temporal variation of alkalytic nitrogen (AN), available phosphorus (AP) and its affecting factors. Significant differences were found between the two years in content of soil nutrients (p < 0.05 ). In 2011, the average content of AN and AP was 75.11 mg kg^-1 and 19.166 mg kg^-1, respectively, or 84.32% and 179.30% higher than their respective one in 1980, but the mean AN/AP was 5.60 in 2011, 22.33% lower than that in 1980, which indicates that their variation coefficients（CV）of the two periods ranged between 35% ~ 77%, and ranked moderate in intensity. However, CVs of the two soil nutrients both increased, with CV of AP in particular, the CV of AN increased by 1.48% and of AP by15.21%. Obviously in the past 30 years the contents of soil AN and AP in the cultivated lands of Pucheng County increased significantly, with widened span between extremes and intensified variability. The semi-variance function and fractal dimension (FD) analyses of the data show that the contents of AN and AP were higher in 2011 than in 1980 in nugget/sill ratio and in fractal dimension, but narrower in spatial correlation distance. Meanwhile, the spatial autocorrelation analysis reveals that the normalized Z scores of Global Moran’s I of AN and AP were higher than 2.58, which indicates that the two were extremely significant in spatial autocorrelationship (p<0.01) and in spatial clustering．Nevertheless, the Z scores of AN and AP in 2011 were lower than those in 1980. The results of the above-mentioned analyses are quite consistent, indicating that in the past 30 years, the spatial structure features of AN and AP weakened and correlationship lowered. Variation of soil nutrient contents is closely related to their initial values (p<0.01). In soils low in initial value, soil available nutrient contents increased drastically, while in soils high in initial value they increased slowly or even decreased somewhat. Quite obviously, initial values of the soil nutrient contents influence their spatial distribution and evolution patterns. Meanwhile, regions high in AN/AP have turned into regions low in the ratio and vice versa. Though in areas the severe imbalance between AN and AP are corrected to a certain extent, they are still not suitable for cultivation. Besides, impacts of geomorphic type, soil type, land use type, irrigation and fertilization on soil nutrient contents were analyzed．It was found that irrigation and fertilization were the main artificial factors affecting spatio-temporal variation of soil AN and AP．Human activities blurred the influence of natural factors and weakened the correlationship between soil organic matter and other nutrients. Moreover, intensity and emphasis of artificial fertilization enhanced differentiation of landforms and soil types, thus intensifying the correlation between soil nutrient and geomorphic types. Therefore, excessive application of N and P fertilizers and improvement of irrigation conditions contributes most to the increase in soil AN and AP．During the process of cultivation management, effective site specific measures should be taken in formula fertilization and soil quality management.

Abstract:Acquisition of the information of soil moisture regime is one of the hotspots in current researches. It is not an easy job to achieve inversion of regional soil moisture content just by depending on soil water estimation models established solely on near-ground hyper-spectra. The study is to explore feasible ways to forecast soil moisture contents by combining the use of narrow-band hyper-spectra and wide-band multi-spectral remote sensing images. Field surveys were conducted and soil samples collected during April 28 to April 30, 2014 in Kenli County, the research area in the Yellow River Delta. Soil water contents were measured in lab using the soil samples and oven-drying method; soil spectra of undisturbed soil samples collected from fields were determined under natural light outdoors with an American ASD Fieldspec4 spectrometer; and the first 7 bands of the OIL sensor were selected and used to collate the Landsat8 remote sensing images of May 1, 2014 for atmospheric radiation correction, geometric precision correction, clipping and other processing. And further on, based on the hyper-spectral narrow-band reflectances measured outdoors LandSat8 wide-band reflectances were simulated with two fitting methods, center wavelength reflectance and band average reflectance methods; by means of band combination in four modes, i.e., ratio, difference, sum dividing reduction, and reduction dividing sum, with sensitive spectral parameters selected according to correlativity; then hyper-spectral single-form band combination and multi-form band combination soil moisture estimation models were established with the multiple stepwise linear regression analysis method, and then screened with the two fitting methods for the best model. Soil information in the remote sensing images was obtained using the linear mixed pixel decomposition method after excluding the vegetation information; the soil information was compared with the measured hyper-spectral reflectance and remote sensing image reflectances were corrected with the ratio and mean method. On this basis, the best hyper-spectral model for estimation of soil moisture contents was applied to the LandSat8 satellite images. Hence, remote sensing inversion of soil moisture contents in the study area was realized; a soil moisture content distribution map based on remote sensing inversion was plotted which was compared with the interpolated soil moisture content map based on measured data at the monitoring sites; Based on spatial distribution and area percentage of each water content level, the results of the inversion were analyzed and verified. Results show that 1）the spectral curves generally proceeded gently in a similar shape; soil reflectance tended to decline with rising water content; and to a certain extent, the 7 bands of Landsat8 OIL were related with soil moisture; 2) the model based on average reflectance of the bands for estimation of soil moisture contents is better than that based on center wavelength reflectance and the model based on multi-form band combination is superior to that based on single-form band combination;3) the outdoor measured reflectance fitted with the band average reflectance method is quite consistent with the remote sensing image reflectance in variation trend with correlation coefficient being 0.989, up to an extremely significant level; and 4) soil moisture content distribution map based on remote sensing inversion and the interpolated soil moisture content distribution map based on measured data are quite consistent and uniform in spatial distribution and numerical statistics, indicating that the estimation of soil moisture contents based on remote sensing inversion is in conformity with the actual situation of study area, displaying good reliability and authenticity. The study explored feasibility of combining hyper-spectral estimation with remote sensing inversion in estimating soil moisture contents in the studied area, and provided some scientific basis and technical reference for quick acquisition of the information of soil moisture regime in the Yellow River Delta.

Abstract:Irrigation and rainfall would make tilled loss soil relatively compact because water makes soil particles cohered to each other, altering the soil structure and erosion resistance. Soil disintegration rate is regarded as a key parameter to evaluating soil’s erodibility. Accurate prediction of disintegration rate of tilled soil is very important to effective management and conservation of soil and water. In this paper, simulation of wet-dry alternation of soil was performed using a soil box to explore effects of the alternation on soil bulk density and soil hydrostatic disintegration rate, and the effect was simulated with the Richards model. Soil wetting process was simulated by immersing the soil in slack water and soil drying process was by oven-drying. The two processes went one after the other forming a round of wet-dry alternation. After the alternation, the soil gradually concreted. Based on soil concretion settling rate and quantity of the soil sample, soil bulk density was calculated. At the same time soil samples were collected with a square ring sampler for determination of soil disintegration rate using the hydrostatic disintegrating method. The soil samples used in the experiment were collected from the topsoil layer of a farmland in Yangling and silt loam in soil texture. The Richards model is a monotone increasing function extensively used to describe growth process. In describing the growth process, the model has two peak values of growth variation rate, which are the two division points of the growth process. However, the cumulative soil disintegration process presents a typical S-curve, so the Richards model can be used to simulate the soil disintegration process and to analyze effect of wet-dry alternation on soil disintegration rate. The paper has come mainly to the following conclusions: With the wet-dry alternation increasing in frequency, bulk density of the soil gradually becomes heavy, but concretion slows down, and disintegration rate declines steadily. The Richards equation can be used to better describe the process of soil disintegration. Based on the characteristic points of soil disintegration displayed in the model, soil disintegration process can be accurately divided into three phases: slow disintegration phase, exponential disintegration phase and disintegration completion. With rising alternation frequency, the slow disintegration phase extends, delaying the exponential disintegration phase, and disintegration rate declines. Especially after three rounds of wet-dry alternation, soil disintegration rate reduces significantly and soil erosion resistance improves. Having experienced wet-dry alternation, soils are much lower in disintegration rate during their soil exponential disintegration phase, of which the proportions to the total are also significantly lowered. After one or two round of alternation, soil disintegration in the exponential disintegration phase accounts for 60% of the total, but after the third round, soil disintegration in that phase accounts only for 29% of the total. Obviously. wet-dry alternation can effectively reduce soil disintegration rate and improve erosion resistance of soil.

Abstract:In order to search for an optimal soil layer structure for constructing an earth dumping site for the open-pit mine at the Jin-Shaan-Meng bordering region, an experiment on soil water percolation through 4 soil columns different in soil layer structure, was carried out. The four soil columns were homogeneously packed with Sandy soil, Pi-sha Sandstone, Loessal soil or Red clay, but different in order, that is, Loessal soil-Sandy Soil-Red clay(L-S-R), Loessal soil-Red clay-Sandy Soil（L-R-S）, Sandy Soil-Loessal soil-Pi-sha Sandstone(S-L-P), and Loessal soil-Pi-sha Sandstone-Sandy Soil(L-P-S). With the aid of an automatic observation system (AOS) attached to the columns to monitor variation of soil water content with time, and at the same time, change in water level in the markov bottles and wetting front movement was recorded. Based on infiltration rate, cumulative infiltration, wetting front movement and change in profile water content, water percolation through the soil columns different in soil layer structure was characterized. Taking into consideration the natural conditions of the region, evaluation of the columns was done for one that was optimal for construction of the earth dumping site. Results show that after water flowing into the second layer of the columns, percolation rate continuously decreased. After water flowing into the third soil layer in Columns L-S-R and S-L-P, percolation rate further decreased. When the wetting front got to the interface between the second and the third soil layers in Columns L-S-R, L-R-S, S-L-P and L-P-S within 169.0, 461.1, 88.6 and 229.1 min, respectively, accumulated percolation reached 19.3, 21.3, 17.8 and 19.6 cm, respectively, in the four columns. In the soil columns the wetting front moved through the 3rd layer of soil at a rate, being 0.34, 0.78, 0.34 and 1.07% of the rate at which it went down through the 2nd layer in Columns L-S-R, L-R-S, S-L-P and L-P-S, respectively. In Column L-S-R, the water content monitored by the probe at the bottom of the sand soil layer was apparently higher than that measured by the other two probes in the layer, while no such phenomenon was observed in the same soil layer in the other columns. Columns L-S-R and S-L-P could hold a large amount of water for a short period of time, and the third layers of soil tended to prevent water from percolating downwards, especially in Column L-S-R, where the effect of the third layer of red clay was very significant. Obviously, these two types of layered soil structure are the ideal ones for construction of earth dumping sites for open pit mines. In Column L-R-S water infiltrated and percolated down the column very slowly. In case of heavy rain storm, rain water could not infiltrate into the soil readily. In Column L-P-S, after wetting front reached the third layer of soil, it kept moving through the layer rapidly. Obviously the soil column could not hold water and instead let the water go further down into deep soil layers. So, these two types of layered soil structure are not fit for use in construction of earth dumping sites. Changes in water content in soil profiles were monitored continuously with the aid of TDR. Soil hydraulic parameters inversed by combining HYDRUS - 1D with water content in infiltration profile of homogeneous soil, after being collated and optimized, were used to simulate variation of the water content and infiltration rate in infiltration profile of layered soil structure. Statistical analysis shows that R2 of measured and simulated infiltration rate and profile water content varied between 0.86 and 0.97, and MEP and SDP of the infiltration rate did between -0.000 4 and -0.009 7, 0.025 and 0.039, respectively, and MEP and SDP of the profile water content did between -0.022 2 and 0.005 7, 0.034 and 0.092, respectively. Statistics also shows that the inversed parameters can be used to better simulate water infiltration processes through the layer-structured soil. The findings in earth this experiment may have some theoretical and practical significance in guiding construction of earth dumping sites for open pit mines.

Abstract:Iron redox cycle is an important microbial process of the degradation of organic matter in anaerobic soil and sediment environment, and it is closely related to transformation of carbon and nitrogen and soil self-purification capacity. As Fe(II) produced anaerobically by dissimilatory iron reduction process could be oxidized by nitrate-reducing/iron-oxidizing bacteria, anoxygenic photosynthetic bacteria or oxygen produced by oxygenic photosynthetic bacteria in wetland soil anaerobically. Furthermore, risk of emission of greenhouse gases, such as CO₂ and biological availability of heavy metals decreases in the process at the same time. Whether oxidation of ferrous generated by dissimilatory iron reduction would occurs or not depends on soil properties, and ferrous oxidation characteristics, including capacity and rate constant are governed by soil pH and contents of water, nitrate, inorganic carbon and other co-substrates. Though upland cinnamon soils belong to oxisol, dissimilatory iron reduction of iron oxide may occur in the semi-luvisol cinnamon soils with adequate water content under non-illuminated incubation as the preliminary study shows, whether the Fe(II) produced anaerobically under non illuminated incubation could be re-oxidized in upland cinnamon soils under illumination incubation is not still clear and neither, are characteristics of the re-oxidation in these soils, not to mention relationship between oxidation characteristics and soil properties. To learn further in-depth about potential microbial iron redox cycle in upland soils, oxidation of ferrous generated by iron reduction, and relationship between ferrous oxidation in upland soils under illuminated incubation and soil properties, soil samples collected from upland farmlands at 7 different locations, and form nearby paddy fields, in which ferrous oxidation occurs under illumination anaerobically, were both prepared into slurry and then put under illuminated anaerobic incubation, to study characteristics of the anaerobic redox of iron oxide in these soils and its influence on contents of water soluble carbon, nitrate and sulfate. Results of the incubation show that iron oxide in upland cinnamon soils could be reduced first and then re-oxidized under light. The amount of iron oxide re-oxidized in these soils ranged from 1.46 to 3.00 mg g^-1, with an average of 2.09 mg g^-1. And the re-oxidation rate constant ranged from 0.23 to 0.80 d^-1, with an average of 0.48 d^-1. The amount of re-oxidation is closely and negatively related to the contents of amorphous iron, water soluble sulphate and cation exchange capacity, and closely but positively related to the contents of total nitrogen and total phosphors, while re-oxidation rate constant is significantly and negatively related to the content of soil organic carbon, but positively to the content of clay. These findings suggest that anaerobic oxidation of ferrous in upland cinnamon soils under illumination is mainly caused by oxygen generated by oxygenic photosynthetic bacteria, and may decrease the content of water soluble inorganic carbon by 52.74%, and the content of water soluble nitrate by 92.15%, but may increase the content of water soluble sulfate by 55.38% in the soil under illuminated anaerobic incubation. The findings may help understand further in-depth the potential microbial iron redox cycle in upland cinnamon soils.

Abstract:To evaluate feasibility of using streaming potential method to characterize interactions between charged particles, change in zeta potential of Al oxide coated quartz (Δζ) induced by colloidal kaolinite was measured with a self-made streaming potential apparatus in studying extent of the interaction between kaolinite and Al oxide coated quartz. The study also covered effects of Al oxide coating degree of quartz, ionic strength and ionic species of supporting electrolyte on the interaction between Al oxide coated quartz and kaolinite colloids. Results show that it is feasible to use the streaming potential method to characterize interactions between oppositely charged particles different in size. When kaolinite suspension flowed through the porous Al oxide coated quartz package, the interaction between oppositely charged particles led to change of zeta potential, which increased with rising Al oxide coating degree and declining ionic strength of electrolyte. These findings suggest that the increase in interaction between the oppositely charged particles with rising Al oxide coating degree may be attributed to the increase in positive charge on the Al oxide coated quartz and the decrease in ionic strength of the electrolyte as a result of the decrease in diffuse layers on the particles. The interaction between kaolinite and Al oxide coated quartz was stronger in the solution containing monovalent ions than in the solution containing divalent ions, causing greater change in zeta potential of Al oxide coated quartz in the former environment. The interaction energy between kaolinite and Al oxide coated quartz can be calculated with the equation derived from the classic DLVO theory. The obtained data could be used to explain the effect of kaolinite on the electrochemical properties at the interface of kaolinite/Al oxide coated quartz. The electrostatic attraction force between the oppositely charged particles was the key factor influencing the interaction between kaolinite and Al oxide coated quartz. Under the effect of electrostatic attraction force, kaolinite induced change in zeta potential of the Al oxide coated quartz through its effect of physical masking when depositing on Al oxide coated quartz and the overlapping of the diffuse layers of electrical double layers on the oppositely charged particles. The higher electrostatic attraction between kaolinite and Al oxide coated quartz, the stronger the influence of kaolinite on the electrochemical properties of the interface. Therefore, the streaming potential method can be used to characterize the interaction between charged particles. The findings in this study may be of some fundamental significance to the studies on the effects of micro-particles on surface electrochemical properties of the bulk soil or other large-scale porous materials during the migration process of colloidal particles and on strategies to reduce soil erosion in tropical and subtropical regions.

Abstract:Application of nitrogen fertilizer is an important approach to ensurance of food security in China. In recent years a large volume of nitrogen fertilizer applied has, though, increased crop yields significantly, it has also at the same time brought about a series of serious environmental problems. So, it is of great importance to get to know well the current situation of nitrogen use efficiency in China, to how to coordinate agricultural benefit with environmental impacts of the use of nitrogen fertilizer in formulating a reasonable fertilization strategy. Therefore, on the basis of the researches accomplished in the 1980s and 2001—2005, nitrogen use efficiencies in the resent 10 years of major grain crops in China were analyzed in this research. The literature research method was used to retrieve all the papers (in Chinese) related to the subject of crop response to nitrogen fertilizer application from the CNKI and VIP databases published after 2004. Results show that currently the basic yields of the three major grain crops without nitrogen fertilization could reach up to 67.9%~75.9% of the maximum yields of the crops with nitrogen fertilization. Yield response of rice, wheat and maize to nitrogen fertilizer application might reach up to 43.0%, 28.2% and 25.8%, respectively. Based on the regression equation of nitrogen application rates and relative yields, the nitrogen application rate for maximum yield of rice, wheat and maize was 246, 250 and 274 kghm^-2, respectively. In the recent 10 years, both the apparent recovery rate (REN) and agronomic efficiency of applied nitrogen(AEN) somewhat increased, reaching up to 39.0%, 34.8% and 29.1%, and 12.7, 9.2 and 11.1 kgkg^-1, respectively, for rice, wheat and maize. Compared with the statistics of the period (2001—2005), REN increased by 6.8%, almost reaching 35% of the level in the 1980s. The relationship between nitrogen application rate and partial factor productivity (PFPN) of nitrogen fertilizer could be well described with the power exponent equation for all the three major crops, with R² for rice, wheat and maize being 0.8489, 0.6575 and 0.7917, respectively. Currently, PFPN is an appropriate index for use in evaluating nitrogen fertilizer utilization efficiency. Taking into overall account target yieldsand nitrogen use efficiencies of the three major grain crops, it is held that 180~240 kghm-2is the proper N application rate for all the three crops in China today, and quite in consistence with the recommendation in the “Fertilizer Formulas and Fertilization Recommendations for Wheat, Maize and Rice in their Major Production Regions” promulgatedand distributed by the Ministry of Agriculture of China.

Abstract:With the termination of national soil test and recommendation initiated in 2005, it is indicated that soil fertility has been improved in different magnitude, especially in the soil phosphorus. Therefore, how to determine reasonable fertilization rates under different soil fertility conditions has become an important issue to maintain or increase yield yet reduce the respective environmental risks. In this study, to examine the current soil fertility, total sampling sites of 851, across 17 counties in the piedmont plain around Taihang Mountain during 2005—2008 (national soil test and recommendation), were determined, where 193 sites were located in Baoding, 401 sites in Shijiazhuang and 257 sites in Handan-Xingtai area. To examine the dynamic changes of soil nutrients of winter wheat-summer maize rotations in the piedmont plain of Taihang Mountain in Hebei Province, historical parameters of soil organic matter (OM), soil total nitrogen (TN), Olsen-P and soil available K in the databases established in 1978 (the second nation soil survey) and 1993 (Changes and control of the arable land top layer in Hebei Province) were extracted. Although the research target of above databases in different period diversified, but large number of investigated sites had same global coordinates, which represented 50% of the total counties within this region. Therefore, the historical correlation between soil nutrient elements and soil fertility can be evaluated. In addition, in order to evaluate the impacts of the changes of soil nutrients on the yield responses of winter wheat and summer maize to the N, P and K fertilization rates, two field experiments during 1996—1999 and 2010—2012 located in the Gaocheng, Shijiazhuang (38°00′N, 114°50′E), a typical winter wheat and summer maize area in the piedmont plain, were selected. Of these two experiments, seven treatments including NPK, -N(PK), -P (NK), -K(NP), 1/2N(1/2NPK), 1/2P (1/2P NK) and 1/2K(1/2K NP) were carried out, where the -N, -P and -K indicated no respective N, P and K fertilizer applied, and 1/2N, 1/2P and 1/2K indicated the application rate of N, P and K were 50% of the respective amount in NPK treatment. Results show that, from 1978 to 2008, the soil organic matter (OM), total nitrogen (TN) and Olsen-P were increased by 7.67 g kg^-1, 0.31 g kg^-1 and 17.77 mg kg^-1, respectively, where the changes during the period of 1993—2008 accounted for 70.8%, 60.0% and 75.5% of their respective totals in 1978—2008. However, soil available K declined by 16.45 mg kg^-1 during 1978—1993 but was characterized with an increase of 13.40 mg kg^-1 during 1993—2008. Meanwhile, spatial variability of OM, Olsen-P and readily available K increased but decreased for TN. In addition, the relative yield productions of -N treatment for winter wheat and summer maize during 1996—1999 were 51.4% and 54.8% of the NPK treatments, respectively, and the relative yields of 1/2N treatments were 91.0% and 85.4% of the NPK treatments, respectively. After about 10-year excessive N application, the relative yields of -N treatments were increased to 89.3% and 72.8% for winter wheat and summer maize, and the relative yields of 1/2N treatments were also increased to 96.2% and 77.3%. For P treatments, the relative yields of winter wheat and summer maize in -P and 1/2P during 1996—1999 were similar to the respective treatment in second experiment. For K treatments however, only the yield reduction was found in the -K treatment between two experimental periods. In conclusion, excessive fertilization in combination with the return of crop residuals during the last three decades has increased the supply capacities of N, P and K in this region, and as a consequence, crop yield response to the N, P and K fertilization is getting less significant and the fertilizer use efficiencies are declining.

Abstract:The study on ecological stoichiometric characteristics of elements in soils is important to revealing mechanisms of the circulation and balance of soil carbon, nitrogen, phosphorus and other elements, and the knowledge of spatial variance of the ecological stoichiometric characteristcs of soil carbon, nitrogen and phosphorus is conducive to soil nutrient management. Spatial distributions of soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP) and stoichiometric characteristcs of soil C, N and P in the topsoil (0～20 cm) were systematically analyzed of a representative small hilly watershed in the subtropical region of China. The watershed studied is the Tuojiahe watershed located in Jinjing Town, Changsha County, Hunan Province. A total of 529 valid soil samples of the watershed were collected by type of land use and of landform, including 21 from vegetable fields, 64 from tea gardens, 262 from rice fields and 182 from woodlands, and averaging about 10 points km-2 in density. The samples were analyzed in lab for total nitrogen, total phosphorus and organic carbon and further for ecological stoichiometric characteristcs and spatial variability of the three indices in the topsoil layer of the watershed with the aid of the GS+Version9 and ArcGIS9.3 softwares. Results show that the mean content of soil organic carbon, total nitrogen and total phosphorus was 13.09 g kg^-1, 1.50 g kg^-1 and 0.51 g kg^-1, with coefficients of variation being 42.4%, 38.5% and 40.8%, and variation range being 2,430m, 5,670m and 570m; respectively; and the mean ratio of C:N, C:P and N:P was 10.42, 72.71 and 7.19, respectively, with coefficients of variation being 35.6%, 46.0% and 37.0%, and variation range being 3,720m, 398m and 450m, respectively. To sum up, the soil C, N and P and their stoichiometric ratios in the watershed are very high in spatial variation and moderate in spatial autocorrelation (C0/(C0 + C) ≤50%). The soils high in soil C:N, C:P and N:P ratio were mainly distributed in areas of woodlands high in altitude, less in human interference and low in fertilization rate, while the soils low in the ratio were mainly in the areas of farmlands, low in elevation, frequent in human activity and high in fertilization rate，which poses a marked contrast to the spatial distribution characteristics of total phosphorus. Soil C: N: P ratio varies sharply with the type of land use (vegetable field, paddy field, tea garden and woodlot). In terms of soil C: N ratio, the four types follow an order of vegetable field > woodland, tea garden > paddy field, in terms of C: P ratio an order of woodland (91.37) > paddy field (66.41) > tea garden (53.74) > vegetable field (48.79), and in terms of N: P ratio, an order of woodland (8.79) > paddy field (6.83) > tea garden (5.25) > vegetable field (4.10). In addition, relationships of the ecological stoichiometric C: N: P ratios of the surface soils with topographic factors were analyzed. Results show that they vary with elevation, Soil C:N ratio is 10.32, 9.84 and 12.54, C:P ratio 66.69, 74.21 and 107.43, and N:P ratio 6.80, 7.61 and 8.57 in soils <100m, 100m ~ 150m and > 100m in elevation, respectively. Soil C:N is significantly higher in areas high in elevation than in areas low in elevation, and similar trends are found of soil C:P and N:P. In the areas high in elevation and steep in slope, soil C:N:P ratios tend to be significantly high, which indicates that the spatial variation of soil C:N:P in the topsoil layer of the study area is closely related to environmental factors, such as land management practices and topography. The findings of the sudy may provide some important information and data basis for scientific management of soil nutrients in small hilly watersheds in the subtropics of China.

Abstract:Carbon (C), nitrogen (N) and phosphorus (P) are the three most important basic elements in soils of arid regions because biogeochemical circulations are closely related to ecological structures, processes and functions of the soils. Ecological stoichiometry combining the first law of thermodynamics, the theory of natural selection during biological evolutions, and the central dogma of molecular biology, has organically integrated biological studies of different scales in the fields of molecules, cells, species groups, communities and ecosystems. As soil is an important component of the terrestrial ecosystem, its elements stoichiometry characteristics plays a substantial role in terrestrial cycling of carbon and nutrients. Four types of soils, i.e. irrigated desert soil, brown desert soil, saline soil and aeolian sandy soil, in the Alar Reclamation Zone at the north edge of the Tarim Basin were selected as objects of the study to explore stoichiometry characteristics soil C, N and P, and to to analyze in-depth their relationships with other physical and chemical factors using the redundancy analysis (RDA) technique of the sorting method. Results show that the mean content of soil C, N and P was 2.97, 0.27 and 0.64 mg g^-1, respectively; and soil C: N, N: P and C: P ratio was 12.14, 0.40 and 4.55, respectively. Soil C and P varied moderately and soil N quite sharply in stoichiometrical characteristics in all the four soils. Correlation analysis of the elements shows that extremely significant correlations exist between C and N, and between C and P (p<0.01) , and between N and P (p <0.05). And C and N were almost synchronous in variation, while P always lagged behind the two. Compared with the average of the global soil (C: N: P=186: 13: 1), the soils in this area, regardless of type of soil, were lower in C: N: P ratio (11: 1: 2.37), thus leading to lower soil nutrient availability. In terms of C, N and P contents, the four soils followed an order of irrigated desert soil > Saline soil > brown desert soil > aeolian sandy soil. Stoichiometrical ratios of the three elements varied somewhat with the type of soil. C: N was more stable than N: P and C: P. In terms of C: N, the four soils followed an order of saline soil > aeolian sandy soil > brown desert soil > irrigated desert soil, and in terms of. N: P and C: P, they did an order of irrigated desert soil > brown desert soil > saline soil > aeolian sandy soil. RDA shows that soil water content is the major factor affecting stoichiometrical properties of soil C, N and P in the study area and soil bulk density followed. However, pH and total salt did not have much significant impact. Soil moisture content was significantly and positively related to C, N and P contents, and also positively to N: P and C: P, but negatively to C: N. Soil bulk density was significantly and negatively related to C, N, N: P and C: P, but positively to P content and C: N. Soil N: P and surface soil C: N are two factors that can be used jointly as a good indicator of soil N supply. Overall consideration of soil C: N and N: P in the region reveals that soil C: N is <30 and N: P <14, which determines variation of stoichiometrical characteristics of C, N and P in the soils of the study area.

Abstract:Selenium(Se) is a kind of trace element in the soil and has three biological functions, that is, as nutrient, toxin and detoxin, it enters the food chain through plants, which absorb Se from the soil. So the content of Se in food depends on the content of Se in the soil, Se content in the soil is governed by a series of geological and geographical factors, while Se concentration in the plant is closely related to species of the plant per se and the environment it grows in. It is, therefore, essential to study soil selenium content. Content and distribution of Soil selenium is an important factor affecting yield and quality of the grain crops in the Northeast China Plain. Surveys and investigations in the past show that the Northeast China Plain is seriously in deficiency of soil and hence a region where endemic diseases prevail because of selenium deficiency. During the period from 2003 to 2006, a Multi-Purpose Regional Geochemical Survey (MPRGS) was performed in the Northeast China Plain, collecting soil samples from the surface (0~20 cm) and deep (150~180 cm) soil layers, 1 sample every 4km² and 1 every 16 km², respectively, for statistic analysis of distribution of soil selenium in the Northeast China Plain and its affecting factors. Results of the analysis show that the content of soil selenium in surface soil of the plain is lower than the average of the country, and its distribution is characterized by a rising trend from the salinized and desertified plain in the west to the low mound-hill region in the east, and strips of selenium-deficient soil and potential selenium-deficient soil alongside the river. About 51.54% of the plain in area is sufficient, 22.63%, potentially deficient, 25.05%, deficient and only less than 1% abundant in soil Se. In deep soils, soil Se content is very low and soils deficient in Se accounts for 80.68% in area. Soil Se content in the surface soil varies significantly with type of soil and pattern of landuse, and does not inherit much from soil parent rock (or deep soil). So the Se content in the surface soil demonstrates an apparent feature of enrichment relative to the content in the deep soil. The soils with apparent Se enrichment amount to 89.01% in area, and the soils depleted in Se are distributed mainly alongside the Songhua River. Correlation analysis shows that clay minerals, ferromanganese oxide and organic matter tend to adsorb Se thus enriching soil Se. Soil selenium enrichment is also quite obvious in farmlands, urban land and lands under some other land use. All the findings show that soil physicochemical properties and recent human activities are the main factors leading to Se enrichment in the soil, but the effects are far from adequate to make the surface soil abundant in selenium. It is, therefore, necessary to rationalize utilization of the land resources in the light of the above characteristics of soil Se distribution, control soil salinization and desertification, and reasonably adjust agricultural planting structure, so as to mitigate the stress of selenium deficiency and the incidence of Se-deficiency caused endemic diseases.

Abstract:Phytolith-occluded organic carbon (PhytOC) is a stable form of organic carbon. PhytOC is a product of silicification of a plant per se and goes back into the soil after the plant dies or withers, thus affecting storage of the stable carbon pool in the forest eco-system. Soil samples were collected from four different soil layers (0~10 cm, 10~30 cm, 30~60 cm and 60~100 cm) in soil profile under five different stands of typical subtropical forestin Qingyuan County, Zhejiang Province for analysis of effects of the forest stands on content of soil phytolith and PhytOC and distribution of PhytOC, and for estimation of total storage of soil PhytOC in these forest soils, separately. In this study phytolith in soil samples was isolated using the microwave digestion method, and complete removal of peripheral organic carbon from phytolith was validated with the Walkley-Black method. The isolated phytoliths were put into a centrifuge tube with a known mass and dried in a forced air oven at 75℃ for 24 h. After cooling down the sample was weighed to determine mass of the phytoliths. Determination of PhytOC was performed using the Alkali Dissolution-Spectrophotometry. At the same time, a portion of standard soil sample (GBW07405) was added to verify accuracy of the measurement. Results show that the content of phytoliths varied with the type of forest soil and the mean content of PhytOC in phytoliths did, too. The content of Phytoliths in the soil was 19.73 g kg^-1 under bamboo groves, 8.14 g kg^-1 under Masson pine forest and 12.24 g kg^-1 under broad-leaved forest, showing sharp difference between the three. The mean content of PhytOC in soil phytoliths was 24.31 g kg^-1 under Masson pine forest and 13.06 g kg-1 under conifer forest, also displaying sharp difference. The content of soil PhytOC under the same forest stand varied with depth in soil profile and the variation trends differed from stand to stand. The content of soil PhytOC decreased with soil depth under Moso bamboo groves and Chinese fir forest and did in a certain degree, too, under the other forest stands. PhytOC/TOC in the soil increased dramatically with soil depth under all the forest stands, except for the stand of Masson pine. The total storage of PhytOC in the soil under Moso bamboo groves, Chinese fir forest, Masson pine forest, broadleaf forest and mixed conifer-broadleaf forest was 1.988×10⁷, 4.025×10⁷, 2.575×10⁷, 2.542×10⁷ and 0.340×10⁷ t. To sum up, soil phytoliths under the five different stands of forest vary in the range between 8.14 and 19.73 g kg^-1, and the content of soil phytoliths is significantly higher under bamboo groves than under the other four stands of forests. The content of PhytOC in phytoliths varies between 13.06~24.31 g kg^-1, and is the highest under the Masson pine forest. The content of soil silicon is positively related to content of soil PhytOC, suggesting that to raise the content of soil silicon is conducive to the content of soil phytoliths and soil PhytOC. The content of Phytoliths decreases with soil depth and on the whole, the content of soil PhytOC decreases with soil depth along a soil profile, while PhytOC/TOC rises dramatically with soil depth but not so obvious in the soil layers of 10~30 cm and 30~60 cm under Chinese fir forest and broadleaf forest.

Abstract:Phenanthrene (Phe), a typical persistent PAHs (polycyclic aromatic hydrocarbons) type organic pollutant, is accumulating step by step in low dosage, posing a potential threat to the soil environment. As one-time Phe pollution of the soil differs in process from gradual accumulation of Phe pollution in low dosage, it is very likely to overestimate environmental risk of the Phe entering the soil in the first manner. Phe entering the soil does not diffuse or translocate in the soil. Therefore, most Phe stays in aqueous phase in the soil due to short soil-Phe contact time. In this paper, a multiple-time addition method was used to simulate of the process of Phe accumulation in the soil. With the multiple-time addition approach, Phe was added into the soil in low dosage 12 times, whereas with the one-time addition method, the same quantity of Phe was added into the soil all at once. Then, bioavailability and toxic effects on enzyme activity in earthworm coelomocytes, chromosome and lysosome membrane of the earthworms exposed to the pollutant at different aging phases (1, 7, 14, 28, and 56 d) were analyzed. It was found that with soil incubation going on, content of available Phe, Phe accumulation in earthworm, activity of SOD and POD in earthworm coelomocytes, content of MDA and micronucleus rates (MNR) all dropped rapidly in the early period (1~28 d) and slowed down their drops gradually in the late period (29~56 d), but neutral red retention time (NRRT) kept rising on steadily, indicating that Phe toxicity to earthworm declined with soil incubation going on. Under the condition of multiple-time overlying pollution and one-time pollution, soil available Phe decreased by 1.12 µg kg^-1 d^-1 and 3.08 µg kg^-1 d^-1, respectively, during the early stage (1~28 d) of incubation and by 0.17 µg kg^-1 d^-1 and 0.39 µg kg^-1 d^-1, respectively, during the late stage (29~56 d) and Phe accumulation in earthworms did by 7.59 µg kg^-1 d^-1 and 21.46 µg kg^-1 d^-1, respectively, during the early stage, and by 0.63 µg kg^-1 d^-1 and 1.91 µg kg^-1 d^-1, respectively, during the late stage. Soil available Phe (Tenax-TA extractable Phe) was in highly significant positive relationship (R²=0.887 9, p<0.01) with Phe accumulation in earthworms and in highly significant relationship, too, with SOD and POD activities, MDA content, micronucleus rate and NRRT in earthworm coelomocytes with the coefficient of determination being 0.893 4, 0.870 9, 0.930 5, 0.893 3 and 0.885 1, respectively. During the 56 days of aging, soil available Phe and Phe accumulation in earthworms was 23.19%~50.15% and 12.64%~57.89% lower, respectively; SOD and POD activities in earthworm coelomocytes 3.40%~47.24% and 6.49%~38.02%, respectively; MDA content 21.30%~57.82% lower; and MNR in earthworm coelomocytes 2.48%~22.99% lower, while NRRT in earthworm coelomocytes was 1.35%~13.97% higher in the soil subjected to multiple-time overlying pollution than in the soil subjected to one-time pollution, which indicates that Phe entering into the soil through multiple-time overlying pollution is lower than that through one-time pollution in toxicity to earthworms. This finding can be cited as theoretic basis for assessment of eco-toxicity of PAHs-type organic pollutants in soil.

Abstract:Fusarium wilt is one of the main soil-borne diseases which are caused by Fusarium oxysporum and may infect a variety of crops. Since it spreads through soil, its traditional controlling methods, such as spraying fungicides, is quite limited in effect. In addition, excessive application of fungicide may not only contaminate the soil, but also affect quality of the agricultural produce. So a pot experiment was conducted to explore effect and mechanism of organic manure controlling Fusarium wilt. In the pot experiment, two types of organic manure, cow dung and bio-manure (bought from market), were used in the experiment. The manures were applied in two ways, base application as solid in soil and leafy application with liquid manure extract. Two sterilization status , sterilized and unsterilized, were also designed for manure and soil, and two sterilization methods were used, high pressure steaming and application of ClO₂, a kind of green fungicide, for manure and soil. A petri dish culture experiment was also carried out to study effect of organic manure controlling Fusarium oxysporum. Manure was also applied in two ways, solid and liquid manure extract. Solid manure was put in the center of the petri dish on the medium in the form of a granule, 0.2 g in weight. Manure extract, absorbed in a filter paper 2.75 cm in diameter, was also applied in the center of the petri dish on the medium. Four treatments in concentration of manure extract were designed. Two sterilization status, unsterilized and sterilized with high pressure steam, were also designed for solid manure and manure extracts. The treatment with no solid manure applied was set as control for comparison with the treatments applied with solid manure and the treatment applied with sterilized demi-water instead of manure extract was as control, too. Results show that organic manure may inhibit incidence of Fusarium wilt, though the effect is affected by a series of factors, such as type, application rate, application method and sterilization of the organic manure used, in an integrative way. The higher the application rate of organic manure, the higher the controlling effect. Application of cow dung and bio-manure at a rate of 1% and 5%, respectively, decreased the incidence of cucumber Fusarium wilt by 34.01%~36.80%, 50 days after seedling emergence. Base application decreased incidence of the disease by 66.82%~78.92% compared with leaf spray. Soil base application and leaf spray all decreased the incidence by 76.65%~81.17% and 17.11%~25.43% compared with the control. The disease controlling effect of organic manure was reduced by sterilization to such an extent that the incidence of cucumber Fusarium wilt increased by 18.27% and 82.82% over the treatments applied with non-sterilized manure at 1% and 5%, respectively and by 36.90% and 29.80% over control. In treatments with soil sterilized with ClO₂ organic manure reduced the disease incidence by 50%. Solid manure and manure extract could directly inhibit the pathogen of Fusarium wilt. A Fusarium oxysporum -free zone appeared like a circle around the manure particle or the filter paper saturated with manure extract. The higher the concentration of the manure extract, the better the controlling effects. The diameter of the pathogen-free zone expanded gradually with the incubation going in the solid manure treatments, but in the manure extract treatments the zone shrank gradually. Having been sterilized, both the solid manure and the manure extract did not show any inhibitory zone, which means that the manure lost its controlling effect on Fusarium oxysporum. The main mechanism of organic manure controlling cucumber Fusarium wilt may be explained as that organic manure enriches micro-organisms in the soil, thus directly inhibiting growth of the pathogen of Fusarium wilt. In addition, the chemicals or micro-organisms in the organic manure may also stimulate plants to improve their disease resistance.

Abstract:In reclaiming or ameliorating salt-affected soils, it is essential to go in-depth studying soil biological activities so as to evaluate variation of soil environmental quality and sustainability of the amelioration measures. Highly saline-sodic takyric solonetz wastelands are distributed mainly in arid regions in Ningxia Plain, Northwest China. This type of soils is characterized by extremely high content of sodium and high pH, varying in the range of 9~10, and consequent poor soil structure and low saturated hydraulic conductivity (K_s< 0.1 mm d^-1). In the 0~40 cm soil layer, the average electrical conductivity of saturated slurry extract (EC_e), pH of saturated slurry (pH) and sodium adsorption ratio of saturated slurry extract (SAR) was 10.3 dS m^-1, 9.4 and 38.9 (mmol L^-1)^0.5, respectively. In the past a lot of measures have been tried to reclaim the wastelands, however, most of them failed primarily because of the very low saturated hydraulic conductivity of the soil. In 2009, this type of wastelands was reclaimed by cultivating wolfberry (Lycium barbarum L.) with drip irrigation. Under the drip emitter near the plant, a pit, 0.2 m in diameter and 0.2 m in depth, was prepared and filled with alien sand for planting wolfberry in. The sand-filled pit was to increase the area of contact between soil and water and the area of water infiltration in takyric solonetz under drip irrigation, thus lowering water supply rate down to or approximately to saturated hydraulic conductivity of the native soil. Besides, the sand pit maight also serve as a reservoir to hold surplus water prior to its infiltrating into the soil and extend water infiltration time, thus ensuring water infiltration into the soil and making reclamation of the soil possible. At the end of the wolfberry growing period in 2011 (October 16^th, 2011), soil samples were collected intensively from soil profiles, perpendicular to the drip irrigation belt, in fields different in wolfberry cultivation history (1 a, 2 a and 3 a), covering a wide gradient of salinity and alkalinity, for analysis of activities of soil urease, alkaline phosphatase and sucrase, which were the enzymes, respectively, key to N, P and C recycling in soil, and of soil physicochemical properties as well. In order to clarify any potential causal-relationships between soil enzyme activities and physicochemical properties, correlation analysis and path analysis were performed. Results show that all the 3 enzymes were very low in activity in uncultivated soils due to the high saline-alkali stress and low organic matter content. After the soil was reclaimed to cultivate wolfberry with drip irrigation, soil enzyme activities increased gradually with the cultivation going on, displaying high spatial variability within the profile. Enzyme activities were found quite high in the root zone under the drip irrigation belt and declined outwards from root zone. Higher soil enzyme activities in the root zone helped the crop absorb soil nutrients. Both correlation analysis and path analysis show that soil pH is always the dominant factor affecting soil enzyme activities, and activities of all the 3 soil enzymes decreased exponentially with pH in the range from 7.38 to 10.00 (p < 0.01). The exponential relationship between them demonstrates that in soils quite low in pH (< 8.5), any rise in soil pH would induce a sharp drop in soil enzymes activities. In a word, the adoption of such a wolfberry cultivation pattern greatly improves soil biological properties of the highly saline-sodic takyric solonetz wasteland.

Abstract:To rationally guide agricultural production, protect ecological environment and explore how much soil temperature responds to climate change, a study was performed to systematically analyze temporal variation and extreme value of shallow soil temperature and their relationships with air temperature based on the observatory data, accumulated during 1961—2013, of the daily shallow soil temperature (0、5、10、15、20 cm) and annual air temperature in the middle (Wuwei) and lower (Minqin) reaches of the Shiyang River Basin, using the linear trend method, variance analysis method, accumulative anomaly method, and correlation coefficient method. Results show that in that region the decade and annual shallow soil temperature displayed a very significant rising trend, particularly, in the first 13 years of the twenty-first century; climate tendency rate was greater in the middle reaches than in the lower reaches, and climate tendency coefficients all passed the α=0.01 significant level test. Annual mean of shallow soil temperature was higher in the middle reaches than in the lower reaches. In the chronology of shallow soil temperature existed 4~6 year paracycles of variation for both middle and lower reaches. Sudden change in shallow soil temperature occurred in 1996 in the middle reaches and in 1985 and 1996 in the lower reaches. Shallow soil temperature was the highest in summer and the lowest in winter in both the middle and lower reaches, and tended to rise in all the four seasons, with climate tendency rate being in the order of spring ＞ summer ＞ autumn ＞ winter. Monthly variation of shallow soil temperature was quite consistent, with an obvious peak in July and an obvious valley in January. The annual mean air temperature was obviously in a rising trend in that region. The climate tendency rate was 0.437 ℃ 10a^-1 in the middle reaches and 0.417 ℃ 10a^-1 in the lower reaches, and climate tendency coefficients all passed the α=0.01 significant level test. Annual shallow soil temperature and annual air temperature were in an extremely significant positive relationship, with correlation coefficients passing the α=0.001significance level test, indicating that air temperature has a positive effect on shallow soil temperature . Annual air temperature and shallow soil temperature showed a similar pattern of variation. It is quite obvious that annual variation of air temperature has a remarkable positive effect on annual variation of shallow soil temperature. The increase in shallow soil temperature may be explained as its response to the rising air temperature, and the response is more sensitive in the lower reaches than in the middle reaches, and in spring and summer than in winter.

Abstract:In selecting and evaluating a new dump site for disposal of high-level radioactive waste (HLW) repository, its hydrogeology condition is one of the most important factors. Moreover, soil permeability of the aeration zone is one of the key issues in the study of hydrogeology, affecting water infiltration, runoff and evapotranspiration in the surface soil layer and their distribution relations. Analysis of soil permeability of the aeration zone helps understand the mechanism of groundwater formation. Beishan in Gansu Province is a preselected priority region for disposal of China’s HLW, while Xinchang-Xiangyangshan is a preselected priority site. For that end, investigations were carried out on soil permeability of the aeration zone in that preselected site, using the double ring method and and a Guelph infiltration meter in-situ. With the aid of software SPSS 19.0, soil organic matter, initial soil water content, soil pH, soil bulk density, soil total ion content and soil particle size distribution were selected as 6 main affecting factors for principal component analysis. This project was aimed at acquiring data for in-depth study on characteristics of soil water movement and formation and circulation of groundwater in the area, so as to provide some scientific basis for site determination and performance evaluation of the preselected area. The following knowledge and results were obtained：(1) horizontal distribution of permeability coefficients of the soil aeration zone of Xinchang-Xiangyangsan was characterized by ① soil permeability varied sharply with the location; ② in terms of soil saturated hydraulic conductivity (K_fs), various geomorphic units followed an order of gully (4×10^-5 m s^-1) > slow slope (1.6×10^-5 m s^-1) > flat land (7.69×10^-6 m s^-1). Therefore，it could be inferred that gullies are the main area where rainwater infiltrates and permeates into deep soil to form groundwater, and an area that should be crossed out from the list of candidates of HLW dump sites, because of its active groundwater; ③ K_fs is higher at the Xinchang fault belt than at the Jijicao fault belt, being on average 2.75×10^-4 m s^-1 and 9.37×10^-5 m s^-1, respectively. So large-scaled fault belts should also be crossed out from the list due to its highly active groundwater; ④ K_fsin clay is very low, being on average only 9.99×10^-7 m s^-1. (2) Soil permeability also varied vertically, with K_fs rising first and declining later down the soil in depth at the four experimental points in the Sishilijing Basin. As the number of soil samples was limited, causes and trend of the change need to be further explored. (3) Analysis of factors affecting K_fs and its mechanism shows that K_fs is closely related to soil physical and chemical properties, and the principal component analysis indicates that K_fs affecting factors may be summarized as follows: the first principal component may be described as soil looseness, which is affected mainly by initial soil water content, organic matter content and soil particle size composition; the second one is basic physical and chemical properties, mainly including soil pH, soil total ion content, soil bulk density and soil particle size (>0.5 mm) composition; and the third one is soil particle size composition, mainly of the particles ranging from 0.1mm to 0.5 mm in size. In a word，among all the affecting factors, the contents of moderate-coarse sands (> 0.5 mm) and clayey silts (< 0.1 mm) are the highest in effect affecting K_fs , while the content of medium-fine sands (0.1 ~ 0.5 mm) is the lowest.

Abstract:Soil samples were collected in the black soil region of Jilin Province and corresponding Landsat TM remote sensing images of the region were acquired. Based on the quantitative relationship between content of soil organic matter (SOM) and soil spectral reflectance, SOM distribution related bands, TM1 and TM5, were screened out and a regional remote sensing-based soil organic matter prediction model was built. Results show that logarithm values of the surface soil organic matter content in study area was in a significantly negative relationship with the DN(Digital Number) values of TM1 and TM5, which met the two polynomial regression. Based on the DN values of TM1 and TM5, the model was used to predict soil organic matter contents in the surface soil layer of the region with sound reliability. The soils with SOM < 15 g kg^-1 in the surface layer were mainly distributed in the eastern part of the region, those with SOM content ranging between 15 and 20 g kg^-1 mainly in the central part, and those between 20 and 25 g kg^-1 mainly in the western part. The investigation indicates that the soils in the eastern and central parts of the region are mainly typical black soils, high in terrain position and hence good in drainage, while those in the western part are mainly meadow black soils, flat in landform, moderate in groundwater table and adequate in soil moisture, and hence high in organic matter content.

Abstract:In order to have a better understanding of soil fertility and fertilizer efficiency of the maize fields in Shaanxi Province after the extension of the technology of soil testing-based formulated fertilization in 2005—2009 in Weibei Plateau, Guanzhong Irrigation Zone and Qinba Mountainous Area of Shaanxi, collected for analysis were data of 7 416 soilsamples and 913 samples of the “3414” fertilizer tests and from sampling surveys of 23492 households in 75 counties involved in the extension.Results show that the content of soil organic matter, alkali-hydrolyzable nitrogen, available phosphorus and readily available potassium in the maize fields of Shaanxi was 15.2 gkg^-1, 72.7 mgkg^-1, 19.7 mgkg^-1 and 153.9 mgkg^-1, respectively, on average. Among the areas surveyed, the Qinba Mountainous Area was the highest in content of soil organic matter and soil alkali-hydrolyzable nitrogen and the Guanzhong Irrigation Zone was in content of soil available phosphorus and soil readily available potassium. In 2000, the inputs of nitrogen (N), phosphorus (P₂O₅) and potassium (K₂O)reached 225.00 kghm^-2, 63.00 kghm^-2and 19.65 kghm^-2, being 114%, 500% and 1 300% higher than that in the 1980s respectively. As a result, the maize fields of Shaanxi still show a nitrogen surplus of 60.0 kghm^-2 and a phosphorus and potassium deficit of 4.5 kghm^-2and 166.5 kghm^-2, respectively.It is, therefore, recommended that the input of nitrogen fertilizer should be properly reduced, and the inputs of phosphorus and potassium fertilizers should be increased in the maize fields of Shaanxi Province.

Abstract:Cosmic-ray Soil Moisture Observing System (COSMOS) is a newly-developed cosmic-ray instrument for measuring average surface soil moisture content over an area with more than 600 m in diameter. A field test was conducted of using this instrument to measure surface soil moisture content in a tract of grassland in the Loess Plateau, and comparison was made of the results of the field test with the results of the oven-drying method, and of the point scale measurement with the HydraProbe II sensors. It was found that the measurements using the COSMOS method were well in agreement with those using the oven-drying method, but differed from those using HydraProbe II sensors in some time spans, suggesting that soil moisture content in the Loess Plateau was subject to spatio-temporal variability. The COSMOS instrument offers an effective approach to measurement of area-average surface soil moisture content in the Loess Plateau with fragmented surface, and a potential tool for studying spatial variability of soil moisture content in the Loess Plateau.