Abstract:In order to understand in depth the global status and frontier dynamic of the researches on polycyclic aromatic hydrocarbons (PAHs) in soil and to reflect scientific capabilities and influences of relevant countries, institutions and individuals objectively, a bibliometric analysis has been conducted of related literatures published in the period of 1900–2014 and included in the citation database Web of Science of the ISI Web of Knowledge. Results show that the number of related publications displayed a rapidly and steadily rising trend. In terms of number of articles, total citation and H index, the United States ranks first, and China second, but not in average citation per paper. Among the research institutions the world over, the Chinese Academy of Sciences and the University of Lancaster in England are on top of the list in number of articles and H index, and the University of Massachusetts in the United States is the top most one in average citation per paper. Among individuals, Prof. Jones, K. C. of the University of Lancaster is in the lead in number of articles and in H index, too, while Prof. Hawthorne, S. B. of the University of North Dakota is in average citation per paper. Prof. Tao Shu of the Beijing University and Prof. Zhu Lizhong of the Zhejiang University are the most influential scholars in China. In this academic field the journals of “Environmental Science & Technology”, “Chemosphere”, and “Environmental Pollution”, are the leading ones. The researches in this field are mostly focused on degradation and bioremediation of PAHs in the soil, dissolution and adsorption of PAHs in various media, and source apportionment of PAHs. Researches related to “China” hold an important position in the recent 5 years.

Abstract:【Objective】Soil organic matter (SOM) retains and recycles nutrients, improves soil structure and sustains soil microbes. Its content is not only an indicator of soil fertility, but also a direct reflection of soil organic carbon stocks. KeepingSOM content at a relatively high level can mitigate soil degradation, ensure food security and alleviate greenhouse gas emissions. Therefore it is important to dig out what are the factors that can exert influence on SOM content and what are the leading ones. Previous studies in this field used to focus on one or a few factors. Climate, terrain, and land-use data were frequently used in those researches. However, these factors were not adequate enough to reflect impacts of agricultural production on SOM. 【Method】To comprehensively analyze influences of environmental and anthropogenic factors on SOM content in cropland in typical black soil region and paddy soil region, two grain-producing areas, 281 and 193 soil samples were collected, respectively, in the two regions in the autumn of 2011. Field management data, such as cropping system, yield of grains, fertilizer amount and history of residue incorporation of the sampling plots were collected through consulting related farmers. Two-sample Kolmogorov-Smirnov tests were employed to compare the soil samples from the two regions in SOM content and in impact of the affecting factors on SOM. Kendall τ correlation analysis was conducted to screen out factors that were significantly relatedto SOM content for comparative analysis with random forest models established based on environment factors alone, anthropogenic factors aloneor both, and the influence strength of each factor on SOM content was evaluated. 【Result】Results show that all the factors expect for elevation and fertilizer amount, vary sharply in impact on SOM content between the two regions and so does SOM content. Among the environmental factors, mean annual precipitation (MAP) is the one SOM is closely related to in both regions, and mean annual temperature (MAT) and clay content in the Black Soil Region and parent rock and terrain in the Paddy Soil Region are the ones SOM is closely related to, while among the anthropogenic factors, fertilization, tillage and residue incorporation are in both regions and irrigation is not. Random forests models using both environment factors and field management in these two regions perform well in fitting, explaining over 80% of the variances of SOM content in croplands of the two regions. Environment and anthropogenic factors vary between the two regions in explanation of the variation of SOM content. Environment factors explain 84%in the Black Soil Region and52% in the Paddy Soil Region of the variation of SOM, and field management practices do 62% and 72%, respectively. After ruling out the variance which could be explained by both environment factors and field management, environmental factors explain 4.7 times as much as anthropogenic factors the variation of SOM in the Black Soil Region, and 2/7 times as much in the Paddy Soil Region. Therefore SOM content is mainly affected by environmental factors in the Black Soil Region and by anthropogenic factors in the Paddy Soil Region. Relative importance analysis shows that key impact factors are MAT, MAP and clay content in the Black Soil Region and MAP, elevation and fertilizer in the Paddy Soil Region. 【Conclusion】The findings of this study also demonstrate that although SOM content in topsoil could change rapidly as affected by human activities, it is still feasible to predict SOM content quite accurately by using Random forest models with the key lying in the integration of environment factors and field management. Therefore it is of important significance to collect field management data year by year. These data can be used not only to improve performance of the model, but also to analyze trend of spatio-temporal variation of SOM content. The key factors identified in this study affecting SOM may be used to guide field management in study area and soil sampling design for future studies.

Abstract:【Objective】Soil nitrogen is an important indicator of soil fertility of farmland, and also an important component of the nitrogen pool in the terrestrial ecosystem. It is of great significance to exploration of nitrogen circulation in the terrestrial ecosystem and its effect on the environment to study dynamics of the soil nitrogen deposit in farmland. So far, much has been reported both at home and abroad on soil nitrogen deposits on a varying scale, but most of the studies on deposit of total nitrogen in farmland on a regional scale focus on static status of nitrogen deposit of a certain time period, and little has been done on dynamics of soil nitrogen deposit in farmland on a provincial scale based on large volumes of data gathered from huge numbers of sampling sites and spatial database relatively high in accuracy. As a result, it is still very hard for the country to work out proper measures for management of farmland nitrogen on a regional scale in line with variation trend of soil nitrogen content. 【Method】In this research project, with the aid of the ArcGIS 10.2 software and the inverse distance weighting interpolation (IDW) method, based on the data of topsoil attributes collected from 2 021 sample soil profiles during the second soil survey in 1982 and 29 945 sampling sites in extrapolation of soil surfaces of soil testing and fertilizer recommendation in 2008, and the data of average annual nitrogen application rate fertilizer, average annual temperature and average annual precipitation of the past 30 years of Fujian Province, a 1:50,000 high accuracy mapping scaled farmland soil total nitrogen and relevant attribute database of the province was established. This database, containing a total of 462 630 patches, was used to study dynamic changes in soil total nitrogen density and storage in the farmland of the province in the past 30 years.【Result】Results show that the soil total nitrogen density and storage in the farmland of Fujian Province was 0.258 kg m^-2 and 4.26 Tg respectively, in 1982, and rose to 0.262 kg m^-2 and 4.39 Tg, respectively, in 2008, which indicates that soil total nitrogen in the farmland of the province was on a rising or enriching trend. Analysis on a prefectural-level city scale shows that the soil total nitrogen density rose the most or by 0.036 kg m^-2 in Longyan City, but dropped the most or by 0.041 kg m^-2 in Xiamen City. In terms of soil type, it rose the most or by more than 0.015 kg m^-2 in soils of the group of fluvo-aquic soil and the sub-type of gleyed paddy soil, and dropped the most or by more than 0.015 kg m^-2 in soils of the group of calcareous soil and the sub-types of submergenic paddy soil. It is quite clear that as a whole, in the past 30 years, the soil total nitrogen in the farmland of the province varied sharply in density spatially.【Conclusion】Consequently, the province should work out site-specific optimal nitrogen fertilizer management programs for its management of farmland soil nitrogen in future in the light of soil types of the farmland and the degree of nitrogen enrichment in farmland on a prefecture-level city scale. The programs are essential to the control of agricultural non-point source N pollution, protection of eco-environment and realization of agricultural sustainable development.

Abstract:【Objective】Rapid and accurate measurement of soil properties is fundamental to modern precision agriculture. CaCO₃ is a major component of the carbonate in soil and has some important effects on a series of physical, chemical and biological properties of soil, such as soil pH, characteristics of soil colloids, soil nutrition and soil heavy metals absorption capacity. The traditional method for measuring soil CaCO₃ content is mainly based on chemical analysis, which is often rather costly, time-consuming and destructive. Therefore, the method is far from efficient to meet the requirement of modern precision agriculture. The technology of soil reflection spectroscopy can be used to make up the shortages of the traditional method, and provide a new approach for the study of pedology. This paper is oriented to explore feasibility of using visible-near infrared reflection spectra to estimate CaCO₃ content in coastal soil in North Jiangsu, to evaluate impacts of reflection spectra data sets, pre-processing methods on accuracy of the estimation of CaCO₃ content in coastal soil and to compare different modeling methods on estimating CaCO₃ content in coastal soil. 【Method】A total of 142 coastal soil samples were collected from North Jiangsu and analyzed for soil spectra with a portable FieldSpec 3. Soil properties of the soil samples were also determined with chemical methods and characterized, and the characteristics of visible-near infrared reflection spectra of the CaCO₃in the soil were analyzed. On such a basis, reflection spectra data sets of various spectral bands (e.g. seven sensitive bands, 355~2 495 nm, 355~780 nm, 781~2 495 nm and 381~2 459 nm), reflectance (R) and its pre-processing methods (e.g. multiplicative signal correction (MSC), first derivative (FD), standard normal variate (SNV), log(1/R) and 1/log R), and three regressions methods (e.g. partial least squares regression method (PLSR), principal component regression method (PCR) and multiple stepwise linear regression method (SMLR)) were selected to perform modeling analysis. In addition, coefficient of determination (R²), root mean square error (RMSR) and relative percent deviation (RPD) were used to evaluate accuracy of the models. 【Result】Results shows that the coastal soil is quite low in soil organic matter (SOM), but very high in CaCO₃ content; that reflectance of the soil in visible-near infrared bands is positively related to soil CaCO₃ content. Moreover, the response of soil spectral reflectance to change of soil CaCO₃ content is stronger in near infrared bands than in visible bands. The estimation (R²= 0.86, RMSE = 6.48, RPD = 2.66) using the model based on spectral reflectance data sets with bands from 381 nm to 2 459 nm is higher in accuracy than those using the other four data sets; the estimations using the pre-processing methods, R, log(1/R), 1/log R, MSC and SNV are good (0.85 ≤R² ≤ 0.87, 6.55 ≤ RMSE ≤7.13, 2.55 ≤ RPD ≤ 2.77); and the estimation using the model based on SMLR has R²being 0.67, while the estimations using the model based on PLSR and PCR are better than the former (R²≥ 0.81). 【Conclusion】It could be concluded that it is feasible to use visible-near infrared reflection spectra in estimating CaCO₃ content in the coastal soil of North Jiangsu; what kind of reflection spectral data sets, pre-processing methods, and regression methods should be used has a certain impact on precision of the estimation of CaCO₃ content in the soil; and the application of the technology of soil reflection spectroscopy will have a bright prospect in determining properties of coastal soil.

Abstract:【Objective】It is recognized that soil pore size distribution and soil water holding capacity plays an important role in soil aeration and crop root development. This study is to explore changes in water holding capacity and soil pore size distribution induced by the change of land use from paddy field to vegetable field. 【Method】A new method of using the low field nuclear magnetic resonance (LF-NMR) technology was adopted to acquire features of the T₂ spectrum of soil samples collected from the fields full in field moisture capacity, and on such a basis, relationships of amplitude and relaxation time of the signals of the soil samples dehydrating with soil moisture content and pore size distribution were analyzed. 【Result】Results show that pore size distribution did not differ much between paddy soil and facilitated vegetable soil, being quiet scattered, and composed of more small pores than large ones. After paddy field being turned into facilitated vegetable field, soil pores became smaller in diameter and soil structure worse. In the process of the soil losing its water, peak reduction and spectrum shift took place simultaneously. Small peaks disappeared first, with a reduction rate much higher than that of the main peak, indicating that during the process pore shrinkage and water loss of water occurred simultaneously and the water in big pores drained first and then sequentially that in small ones. 【Conclusion】All the findings in the study indicated that the method based on LF-NMR can be used to instantly monitor changes in soil moisture content and more directly and accurately determine soil moisture migration processes and pore distribution rules without disturbing the soil, and hence may serve as new theories and technical support for the study on mechanisms of soil degradation and soil amelioration in facilitated vegetable fields.

Abstract:【Objective】 The problem of vulnerability of soils to compaction damage is getting more and more serious, thus arousing more and more concerns. But for long, researches on mechanical compaction in the black soil region focused mainly on changes in physical structure of the soil. Motivated by the phenomenon that organic matter content in the soil is gradually declining while clay content rising with cultivation going on, this study began to tackle the problem of how the soil responds to the phenomenon in soil mechanics. 【Method】 In order to explore mechanism of the black soil getting compacted under cultivation and factors affecting the compaction and rebound behavior, soil samples were collected from a long-been cultivated black soil field and prepared into test samples different in organic matter content and clay content by spiking humic acid and water. The remolded samples had 3 levels of organic matter content, i.e. 44.93 g kg^-1, 69.13 g kg^-1 and 93.13 g kg^-1, and 2 levels of water content, i.e. 20% and 30%. The samples were incubated for 30 days under 25℃ in temperature and 65% in humidity. Then the samples were analyzed for organic matter content with the total organic carbon analyzer of the German Elementar Corporation. In line with the Stokes principles for precipitation, clay particles were separated from the natural soil, fractionated and blended with the remolded soil samples with known clay content at a required ratio and some water to ensure that the remolded soil samples had 3 levels of clay content, i.e. 18.57%, 29.37% and 56.33%. From the perspective of soil mechanics, an indoor consolidation experiment was conducted with the samples for determination and analysis of compression coefficient, compression index and rebound index and effects of organic matter and clay content on black soil compression - rebound behavior relative to soil moisture content. 【Result】 Results show as follows: (1) Compression index increased with increasing organic matter content. In the treatments high in water content, an extremely significant and positive correlation was found between compression index and organic matter (p<0.001), with the maximum compression index being 0.2463 in the treatments the highest in organic matter. In the initial phase of consolidation (0 ~12.5kPa), compression coefficient also rose with rising organic matter content. Soils higher in organic matter content were higher in potential risk of compaction. The soil compression susceptibility increased significantly with increasing organic matter content, because organic matter was one of the most important cementing substances in soil aggregates, very high in hydrophilicity, and capable of thickening the water film between soil particles, and hence enhanced compressibility of the soil. But no significant correlation between soil organic matter content and rebound index was found in both situations. (2) Clay in the soil was considered as the most active one of the mineral components, and higher than organic matter in cohesive force, so it may affect soil physical and mechanical properties more significantly. Clay content was found significantly and positively related to compression index (p<0.001) in this study, regardless of water content, which means that with increasing clay content, soil compression susceptibility increased, but soil resiliency decreased. In soils low in water content, rebound index was found significantly and negatively related to clay content. The joint effect of clay and water on rebound behavior of black soil was quite obvious. (3) Thickness of the water film between soil particles was not a constant and varied with soil water content, thus affecting plasticity of the soil, and hence causing the effects of organic matter and clay to differ, and the two to interact in affection soil mechanics parameters. Compared to organic matter, clay affected compression and rebound behaviors of the black soil more significantly. Whatever, further work should be done on effect of the interaction of organic matter content, clay content and water content in the initial phase on compaction and rebound behaviors of the soil. 【Conclusion】The compression sensitivity increased with the increase of organic matter content and presented an extremely significant positive correlation under high water content condition, suggesting the higher of organic matter content, the greater risk of compaction. Rebound index showed a decreasing trend with increasing organic matter content. Soil compression sensitivity significantly enhanced with increasing clay content, and there was an extremely significant negative correlation between them under low water content condition, while the resilience gradually weakened. Compared with organic matter, clay content played a more significant role on soil compression – rebound behavior.

Abstract:【Objective】The Shanxi-Shaanxi-Inner Mongolia adjacent region is one of the most important coal energy bases in China, and also one of those the most fragile in ecology. In recent years, the ecological system and the landform therein has been severely and widely destructed as a result of the environment of opencast coal mining, which has also triggered a series of ecological and safety crises. And then how to rapidly and effectively improve the reconstructed soil (especially in soil water holding capacity) on a large scale at overburden disposal sites formed during coal mining has become an important scientific problem to land reclamation and ecosystem restoration. At present, the soil in these sites has some main problems, that is, relatively thin in soil layer (less than 50 cm), and relatively coarse in texture, (over 70%, sands 0.02 ~ 2 mm in particle size), which means that the soil is rather low in water holding capacity. Besides, in the arid and semi-arid region, the precious soil moisture is mostly lost through evaporation and leakage. To save as much as possible soil water from evaporating and leaching, a series of measures are designed and adopted, such as incorporating soft sandstone, which contains about 30% of montmorillonite and weathered coal into the local sandy loess, and spread a layer of soft sandstone or a water-proof plastic sheet underneath the soil to prevent water leaching. 【Method】In order to investigate dynamics of soil moisture content in reconstructed soils relative to composition pattern (sandy loess, soft sandstone, weathered coal) and impervious layer (soft sandstone or plastic sheet), an experiment was carried out, designed to have 6 treatments and 3 replicates for each treatment, making up a total of 18 experimental plots. 【Result】Results show as follows. (1) The overburden disposal sites are subject to a wet season (July- October) and a dry season (November – June) in a year as affected by the climate in the region, and natural rainfall, evapotranspiration and leaching are the main factors affecting the soil moisture content therein; (2) During the wet season when rainfall is rich, the effect of the existence of a impervious layer was significant, raising soil moisture content by 9.65%~13% in the soil body as a whole (p < 0.05, the same below) and by 21.6% in the bottom layer as compared with their respective treatments without the layer, but no significant difference was observed between the treatments with soft sandstone as impermeable layer and the treatments with plastic sheets in the effect. However, on the other hand, the existence of an impervious layer weakened temporal and spatial stability of soil moisture, especially in deep soil layers; (3) Incorporation of weathered coal increased soil water loss through surface evaporation, which is no good to improving soil water holding capacity, while incorporation of soft sandstone affected soil water holding capacity reversely. So in the practice, it still calls for further study on feasibility of the use of weathered coal as soil amendment from the view point of efficient utilization of water sources. Incorporation of soft sandstone increased soil water content by 3.36%~9.57% in the 0~30 cm layer and 11.16%~13.65% in the 30~40 cm layer. In addition, laying of an impervious layer is more effective than incorporation of soft sandstone and/or weathered coal in increasing water content of the artificial soils in the overburden disposal sites. 【Conclusion】To sum up, incorporation of soft sandstone significantly enhances the soil water retention and water holding capacity of the soil, and the impervious layer effectively controls soil water leaching and hence has a positive effect on soil holding water like a reservoir. Besides illustrating the effects of the soil amelioration measures on spatial and temporal variation of soil moisture content and the improvement of soil water regime, the study provides some references for choosing schemes for reconstruction of farmland soil using different components in mining areas.

Abstract:【Objective】How matter recycling matches ecosystem services is always one of the central concerns of the research on ecology, and C:N:P ecological stoichiometry has been an effective tool to link chemical processes on the molecular level with ecological processes in ecosystems. The knowledge about how carbon, N and P is distributed in wetland soils and whether there is a "Redfiled-type" C:N:P ratio in regional or global wetland soils is the basis for understanding fate of carbon, nitrogen and phosphorus and modeling matter circulation in wetland ecosystems. Objectives of this study are to examine whether there is a consistent C:N:P ratio in wetland soils of China and to find its potential influencing factors. 【Method】Based on the data of carbon, nutrient contents, soil properties, vegetation, meteorology and C:N:P ratios of wetland soils of 119 marshes or wetlands published in the “Journal of Marshes of China”, ecological stoichiometric characteristics of C:N:P ratios on a regional scale and their potential affecting factors were analyzed with the mathematical statistics. 【Result】Results show that the average C, N and P content in the wetlands of China was 22.93%, 0.76% and 0.16%, respectively; the average C:N, C:P and N:P ratio (mole ratio) was 18.22, 245.22 and 13.60, respectively, all higher than their respective ones in the soils of the country and the globe; and the average C:N:P ratio was 245:13.6:1. The C:N, C:P and N:P ratio in organic soils was higher than their respective ones in mineral soils. No significant difference was found in soil C:N:P between meadow, peat moss and forest wetlands; However, significant differences were found between inland freshwater, inland saline and tidal wetlands, with the inland freshwater wetlands being the highest and the tidal wetlands the lowest in C:P and N:P ratios, but. no difference in C:N was between the two. Overall, C:N, C:P and N:P ratios were the highest in inland freshwater wetlands and the lowest in tidal wetlands. Pearson analysis shows no significant pairwise relationship was found between the three elements, which implies that there is no “Redfield”-type ratios in the wetland soils of China. Wetland ecosystems were more affected by P than the other soil nutrients. No significant difference in C:N ratio was found between climate zones, but a decreasing order of Tropical Zone > Temperate Zone > Plateau Temperate Zone > Warm Temperate Zone >Mid-subtropical Zone > Northern Subtropical Zone was, while C:P and N:P ratios differed significantly between climate zones, which followed an order of Plateau Temperate Zone > Temperate Zone > Mid-subtropical Zone > Tropical Zone > Warm Temperate Zone > Northern Subtropical Zone in C:P ratio and an order of Plateau Temperate Zone > Mid-subtropical Zone > Temperate Zone > Warm Temperate Zone > Tropical Zone > Northern Subtropical Zone in N:P ratio. Correlation analysis shows that altitude, temperatures (annual mean temperature, mean temperatures in January and July, and active accumulated temperature) and pH are the three main factors determining C:N:P ratios in the wetlands of China. 【Conclusion】In conclusion, C:N:P in the wetland soils of China are highly affected by soil types and climate conditions, and little by plant vegetation. Taking into account the extremely significant correlations of altitude with C:P and N:P, altitude is deemed to be the decisive factor of C:N:P ecological stoichiometry of wetland soils.

Abstract:【Objective】Balance between various elements in the ecosystem has been a focus or a hotspot of the researches on ecology and biogeochemical cycles under global change. Ecological stoichiometry is a science that combines some basic principles of biology, physics and chemistry, explores for balance of energy and balance of various chemical elements in biological systems and provides an integrated approach to investigating rules of the behaviors of various elements in biogeochemical cycling and ecological processes and their stoichiometric relationships. Ecological stoichiometric ratios of C, N and P are important characteristics of the process and function of an ecological system. 【Method】In order to explore variation rules of the contents of organic carbon, nitrogen and phosphorus in shoots and litter of plants and C:N:P stoichiometry characteristics during various enclosure phases of the 30 years of restoration and succession process of natural grasslands in the Yunwu Mountain, typical quadrats of grassland that had been enclosed for restoration for 1, 12, 20 and 30 years were set up for analysis of nutrient contents in shoots and litter of the plants in the grasslands and their relationships with enclosure age in the Loess Plateau. 【Result】Results showed that carbon, nitrogen and phosphorus contents in shoots and little of the plants and their stoichiometry varied sharply with enclosure age. Carbon, nitrogen and phosphorus content varied in the range of 388.1~437.6 mg g^-1, 12.13~15.42 mg g^-1 and 0.78~1.06 mg g^-1, being 418.0 mg g^-1, 13.16 mg g^-1 and 0.92 mg g^-1, on average, respectively in shoots of the plants; and in the range of 402.7~427.2 mg g^-1, 8.58~11.04 mg g^-1 and 0.49~0.56 mg g^-1, being 411.3 mg g^-1, 10.34 mg g^-1 and 0.53 mg g^-1 on average, respectively; and C:N, C:P and N:P ratio in the range of 24.91~37.37, 380.1~562.1 and 12.14~15.86, being 32.51, 473.6 and 14.64, respectively, in shoots of the plants, and in the range of 37.18~47.11, 755.5~885.9 and 16.41~22.31, being 40.71, 819.9 and 20.30, respectively in litter of the plants. In terms of average of the content of nitrogen and phosphorus shoots of the plants was higher than litter of the plants, while in terms of average of the C:N, C:P and N:P ratio a reverse trend was found. It is known that N: P ratio is an important factor that controls litter decomposition and nutrient cycling. Litter, low in P concentration was often high in N and lignin content (or in N: P ratio) and decomposed slowly, while litter low in N:P ratio decomposed easily. As litter of the plants in the grassland of the Yunwu Mountain was low in N:P ratio, it decomposed relatively fast, and kept little nutrients in storage. C, N and P contents in shoots of the plants were extremely significantly correlated with each other (p<0.01); P content in shoots of the plants was in extremely significant negative relationships with the C:N, C:P and N:P ratio (p <0.01), while C and P contents and C:P and N:P ratios in litter were extremely significantly related to P content in shoots of the plants. N:P ratio in the plants of Yunwu Mountain varied between 14 to 16. As plant growth was affected jointly by N and P, it is recommended that application of N and P fertilizers be increased in rate so as to prevent degradation, rationalize exploitation and maintain sustainable development of the grasslands. 【Conclusion】This comprehensive research shows that enclosure can increase vegetation coverage, biomass of the plants, and plant productivity of the grassland and the measure in this area can make the grassland vegetation ecosystem present a trend of comprehensive recovery. The findings of this study help further understand rules and mechanisms of the interactions of carbon, nitrogen and phosphorus on different components of the grasslands in the Yunwu Mountain.

Abstract:【Objective】Nitrous oxide (N₂O) is an important greenhouse gas contributing to global warming and depleting stratospheric ozone. Agricultural soils are the major sources of anthropogenic N₂O emissions. N₂O emitted from natural and cultivated soils is mainly generated through nitrification and denitrification, accounting for about 70% of the global total, but contributions of other processes (such as chemodenitrification) are poorly understood. Hydroxylamine (NH₂OH) and nitrite (NO₂⁻-N) are two main intermediate products of nitrification, and the latter is also an intermediate product of denitrification, both of which can produce N₂O through abiotic processes. However, relative contributions of these two products to N₂O emission in the same soil remain unclear. 【Method】To determine contributions of the two products, NH₂OH and NO₂⁻-N, through abiotic processes in soil to emission of N₂O and to identify related affecting factors, an indoor incubation experiment was designed and carried out, using soil samples collected from a tea garden in Quzhou, an upland field in Yingtan, a vegetable garden in Changshu, an upland field in Hailun, an orchard in Changshu and an upland field in Fengqiu, representing four types of land use. The soil samples, sterilized (autoclaved three times at 121℃ for 1 h before nitrogen fertilization) and unsterilized, were spiked with NH₂OH or NO₂^--N, separately, and incubated. Emissions of N₂O from the soil samples were monitored after 2 hours of incubation. 【Result】Addition of NH₂OH or NO₂^--N increased N₂O emission from each tested soil, with N₂O flux peaking 2 h after the addition of NH₂OH during the observed period, and the highest peak was observed from the soil samples collected from the orchard in Changshu Orchard (1 585 μg kg⁻¹ h⁻¹). N₂O emissions from the soils spiked with NO₂⁻-N varied in the range of 6.42~61.28 μg kg⁻¹ h⁻¹ in flux. In unsterilized or natural soil samples spiked with NH₂OH, N₂O emission coefficients varied from 18.63% to 35.95%, which were 10.03 times~76.46 times that in the soil samples spiked with NO₂^--N. Effect of sterilization on N₂O emission differed between the soil samples spiked with NH₂OH and their respective ones spiked with N₂O⁻-N. Sterilization significantly reduced N₂O emission in all the soil samples spiked with NH2OH, especially in the soil samples from the tea garden in Quzhou, with the reduction reaching, up to 94%, while in the soil samples spiked with NO₂⁻-N, the effect of sterilization was observed only in those from Changshu and Fengqiu, but reverse effects were found in those from Quzhou, Yingtan, Changshu and Hailun. In all the soil samples, abiotic processes of NH₂OH contributed 6%~73% to total of N₂O emission, whereas abiotic process of NO₂⁻-N did 3%~236%. In the soil samples from Quzhou, Yingtan, Changshu and Hailun, all being higher than 7 in pH, abiotic process of NO₂⁻-Ncontributed more than abiotic process of NH₂OH did to N₂O emission but in the soil samples from Changshu and Fengqiu, both being higher than 7 in pH too, reverse trends were found, indicating soil pH is a key factor affecting abiotic N₂O production from NH₂OH or NO₂⁻-N. In the soil samples spiked with NH2OH, the contribution of abiotic process, in terms of proportion, to the total N₂O emission was significantly and positively related to soil pH (p< 0.05), while in the soil samples spiked with NO₂⁻-N, it was negatively related (p< 0.01). 【Conclusion】All the above-describedfindings suggest that the formation of N₂O from NO₂⁻-N is probably mainly attributed to abiotic processes in acid soils and to biotic processes in alkaline soils, while the formation of N₂O from NH₂OH goes just the opposite.

Abstract:【Objective】The middle reaches of the Heihe River is located in the inland arid region of Northwest China and under the continental central temperate arid climate, this area is low in precipitation, high in evaporation and strong in solar radiation. Such climatic environment conditions nurse a unique type of mosaic distribution of farmlands, orchards, wetlands, wastelands, deserts and gobis. This region of the middle reaches of the Heihe River is a sensitive and ecologically fragile area in the course of environmental evolution. So the study on issues related to net ecosystem carbon exchange (NEE) and soil respiration (Rs) relative to land use is of some extremely important theoretical and practical significance in maintaining ecological balance and promoting sustainable development of the region. However, little information is available in the literature on seasonal and spatial distribution of Rs and NEE in different terrestrial ecosystems in this region; and on contribution of Rs to NEE. 【Method】In this study, six different patterns of land use (corn field, orchard, wetland, desert, gobi and wasteland) in this region were cited for observation of Rs and NEE during the crop growing season, using the eddy covariance method and the static chamber/gas chromatograph method, and seasonal dynamics of Rs and NEE and their affecting factors were analyzed, so as to figure out contribution of Rs to NEE relative to pattern of land use. 【Result】It was found that both Rs and NEE during the plant growth season displayed a multi-peaked curve regardless of land use patterns, with highest peaks appearing at the end of July and the beginning of August. Ina terms of numerical value, both Rs and NEE varied sharply between different land use patterns. Relatively low Rs and NEE was found in Gobi, wasteland and desert, varying in the ranges of -69～97, -1.99～122 and -1.65～108 mg m^-2 h^-1, respectively, and in the range of -52～154, -29～82 and -6.3～212 mg m^-2 h^-1, respectively. Comparatively, Rs and NEE was relatively high in corn field, wetland and orchard, varying in the range of 15.1～316, 47.7～710 and 36.9～218 mg m^-2 h^-1, respectively, and in the range of 14.1～2 794, 451～1 622 and 864～1 647 mg m^-2 h^-1, respectively, which shows that the denser the vegetation, the higher the Rs and NEE. Contribution of Rs to NEE also varied with the pattern of land use. It varied in the range of 20%～68% in the former three ecosystems and in the range of 10%～21% in the latters, which indicates that the denser the vegetation, the lower the contribution of Rs to NEE. It was found that Rs and NEE in the terrestrial ecosystems were mainly affected by soil properties, like soil temperature and soil moisture. Soil temperatures in different soil depths were in significant functional relationships with Rs (81%～96%, p<0.05) and NEE (62%～98%, p<0.05), and soil moisture contents in different soil depths in significant exponential function relationships with Rs and NEE (82%～90%, p<0.05). Among soil properties, soil organic carbon content (SOC) was the main factor significantly affecting Rs (i>R ² = 0.91,p<0.05) and NEE (i>R ² = 0.74, p<0.05), and followed by soil bulk density and C / N, which had certain impacts, while soil pH was not a factor that would affect Rs and NEE much in all the ecosystems in the middle reaches of the Heihe River. Significant correlation between Rs and NEE was found in this study (i>R ²=0.48, p<0.05).【Conclusion】 Any minor fluctuation of Rs may potential cause profound changes in NEE in all the terrestrial ecosystems.

Abstract:【Objective】Nitrogen is one of the most important and essential elements for growth of crops. Reasonable application of nitrogen fertilizer may promote crop growth and increase its yield, while excessive N fertilization may not only inhibit crop growth, but also leave a large amount of fertilizer nitrogen (N) in the soil as residue, which disturbs balance of soil nutrients and poses a potential threat to the ecological environment. So, it is necessary to study dynamics and availability to crops of the residual N to provide a theoretical basis for rationalizing N fertilization, improving N use efficiency and reducing fertilizer N loss. 【Method】To that end, a 4-year stationary field experiment was carried out on a winter wheat and summer maize rotation system, using¹⁵N-tracing technique. During the first cycle of the winter wheat and summer maize rotation, 240 kg hm^-2 of nitrogen was applied in the form of ¹⁵N-laballed urea in all the plots before winter wheat was sown, in order to make a background of high N residual, and in the following summer maize season, the plots were divided into two groups applied with 0 and 120 kg hm^-2 of ordinary urea, separately, at the prolonging stage of the crop to explore effect of N fertilizer application on fertilizer N residue in the soil. During the following three cycles of the rotation, no N fertilizer was applied for analysis of dynamic and availability to the crops of the residual fertilizer N in the soil. 【Result】Results show that residue of the ¹⁵N-laballed N fertilizer that was applied before sowing of winter wheat during the first cycle of the rotation, was found throughout the whole soil profiles of 0~200 cm, after the crop was harvested, and most of that accumulated in the 0~40 cm soil layers. The residue amounted to 200.9 kg hm^-2 in total, accounting for 83.7% of the total N fertilizer applied. In the subsequent summer maize growth season, the amount of residual fertilizer N first dropped rapidly, and then declined slowly with the season going on, and eventually leveled off. After for 4 years of rotation, still a considerable amount of ¹⁵N was found in the 0~300 cm soil profile, reaching 47.1 kg hm^-2 and 54.0 kg hm^-2, respectively, in the plots where no or 120 kg hm^-2 N fertilizer was applied to summer maize during the first circle of the rotation. Obviously a part of the fertilizer N was fixed by organic matter in the soil. The recovery rate of residual N by the crop decreased gradually year by years, but the rate varied differed between the two treatments. The total N use efficiency of four years was 46.9% and 50.4%, respectively, in the plots with or without N sidedressing for maize. The total N use efficiency of the winter wheat and summer maize was 41.6% and 42.0%, respectively, in the first year of the rotation, and only 5.3% and 8.4% in the remaining 3 years. During the four years, about 38.1% and 29.7% of the residual fertilizer N was lost, respectively, in the two treatments, with or without N sidedressing, and the loss occurred mainly in the first summer maize growing season. 【Conclusion】It indicates that some of the fertilizer N applied in upland wound inevitably remain in the soil as residue, and this part of residual fertilizer N is low in availability to crops, and has a limited portion being gradually taken up by crops in the late 3 years, a portion remaining in the form of organic N, and the other turning unavailable and lost. Sidedressing of N fertilizer in the summer maize season may promote crop uptake of residual fertilizer N in the soil, while retaining more residual fertilizer, and consequently it reduces the loss of residual N. However, all the effects are attained at the cost of high loss of the N fertilizer per se. Therefore, it is advisable to take into account fertilizer N in the soil when making plans for N fertilizer application.

Abstract:【Objective】Rapeseed is one of the most important oil crops in China, and the Yangtze River Valley is a major oilseed rape production region of the country, accounting for over 20% of the world’s mean of annual rapeseed planting area and total rapeseed yield. Farmers in the Yangtze River Valley plant two or three crops a year to form a rotation system. Rapeseed is planted in winter in rotation with rice, cotton or soybeans. As a result of such an intensive cropping system, the farmlands are quickly deprived of soil nutrients and do not have enough time to get recovered in soil fertility. Besides, farmers apply nitrogen (N), phosphorus (P), potassium (K) and boron (B) fertilizers randomly without taking into account the demands of the crops for nutrients. Consequently, the farmlands vary sharply in soil fertility or soil nutrient content from area to area. In this paper an attempt has been made to explore characteristics of the spatial distribution of soil nutrients and pH as affected by crop rotation system and area in the middle reaches of the Yangtze River Valley with the aid of geostatistics and GIS technology, so as to provide some technical support to the efforts of establishing a region-scaled scientific fertilization system for the crop of rapeseed aiming at high yield, high efficiency and eco-environment safety, and realizing sustainable development of the agriculture in the region. 【Method】Based on the database of the soil survey and sampling carried out in Hubei, Hunan and Jiangxi provinces during the period of 2013-2014, a total of 5463 soil samples collected from these provinces were analyzed for six soil indices, such as soil organic matter (SOM), total N (TN), available P (AP), available K (AK), available B (AB), and soil pH. With the aid of the GIS platform and Kriging method, the farmlands in these provinces were evaluated and sorted into six grades by referring to the standards for grading of the six indices set for the Second National Soil Survey. In the light of complicate topography and high diversity of soil types, the region was divided into four cropping zones, i.e., plain area with double cropping system (PII), mountain area with double cropping system (MII), plain area with triple cropping system (PIII), and mountain area with triple cropping system (MIII). 【Result】Results show that SOM, TN, and AP contents were obviously higher in the areas with triple cropping system than in those with double cropping system, which is attributed to the higher multiple cropping index of the former and resultant higher root residue in the field, increasing SOM. Especially in MIII, SOM, TN and AP reached as high as 28.8 g kg^-1, 1.60 g kg^-1 and 16.2 mg kg^-1, respectively. In terms of SOM, 63.3%~76.1% of the farmlands were sorted into Grade III; in terms of soil TN, about 90.2% or 11 061 000 hm2 were in Grade II (1.5~2.0 g kg^-1) and III (1.0~1.5 g kg^-1); in terms of soil AP, 70.2% or up to 8 601 000 hm² of the farmlands were in Grade III (10~20 mg kg^-1), and 17.5% and 12.3%, in Grade II and Grade IV, respectively. Soil AK did not vary much between zones, ranging from 93.6 to 95.8 mg kg^-1. However, the region still had 182 000 hm²of farmlands deficient in K (<50 mg kg^-1). Soil AB did not either, ranging from 0.42 to 0.47 mg kg^-1. It is quite clear that measures should be taken to raise soil AB content in the region, especially in the areas with triple cropping system, where about 13.6%~20.4% of the farmlands were in Grades V and VI. According to the standard for grading in the Second National Soil Survey, the region was quite high and could be sorted into Grades II and III in SOM, TN, and AP, but quite low and in Grade IV in soil AK and AB. Most of the farmlands in the region were around 6.0 in soil pH, but in areas with triple cropping system, a relatively high proportion or about 35.7% of the farmlands varied in the range of 4.5~5.5 in soil pH. 【Conclusion】To sum up, in the middle reaches of the Yangtze River Valley, soil nutrient status varies from area to area. Especially in the areas with triple cropping system, quite a large proportion of farmlands need to be raised in soil boron content and ameliorated in soil acidity.

Abstract:【Objective】The objective of this study is to obtain fertilizing effects of interplanting forage legumes and corresponding handling modes, which would be lay a basis for fertilizing measures of young orchard in hilly red soil region of south Hunan.【Method】In order to explore effects of interplanting forage legumes and corresponding handling modes on soil fertility in young citrus orchards, a field experiment was carried out interplanting six species of forage legumes, including Trrifoliumrepens, Chamaecradtanictitans, Chamaecristarotundifolia, Chamaecristarotundifolia CPI 86134, Macroptiliumlathyroides, and Lotononisbainesiiwere, separately and designed to have the crops, harvested, laid over or plowed down, in a young citrus plantation in a hilly red soil region of South Hunan. Soil physicochemical properties of all the plots were measured after the experiment for analysis of the effects. 【Result】 Results show as follows. Compared with CK (no crop interplanted), all the plots, on the whole, increased in contents of organic matter, total nitrogen, alkali-hydrolyzable nitrogen, and available phosphorus, and the increasing effects were the highest in the plots with the crops plowed down or incorporated, but decreased in content of readily available potassium and pH, and the decreasing trends were the lowest in the plots with the crops plowed down. Among all the plots, the plot with Chamaecradtanictitans plowed down raised the contents of organic matter, total nitrogen, alkali-hydrolyzable nitrogen, and available phosphorus contents the highest in margin and lowered the content of readily available potassium the least, and the plot with Chamaecristarotundifolia incorporated came the next in the effects. Besides, the plot with Chamaecradtanictitans incorporated lowered soil pH the least. Compared with CK, all the plots increased fruit yield, single fruit weight, and tree height, canopy diameter, and number and length of spring/autumn branches of the orange trees. The effect of the plot with Chamaecradtanictitans incorporated was the most significant and the plot with Chamaecristarotundifolia incorporated came the next. Besides, the plot with Chamaecradtanictitans incorporated was the highest in biomass of the forage legume yielded, and in amount of nitrogen and phosphorus returned into the soil, and in soil microbial biomass carbon, soil microbial biomass nitrogen, and urease activity, too. 【Conclusion】Therefore, it can be concluded that the practice of interplanting Chamaecradtanictitans and then incorporating the crop is the most suitable soil building mode for young citrus orchards, but it needs supplementation of some potassium and phosphorus fertilizers. Besides, it is also necessary to apply some alkaline material, like lime, to offset the effect of interplanting forage legumes lowering soil pH.

Abstract:【Objective】Karst is a landscape formed through dissolution of soluble rocks, including limestone, dolomite and gypsum and characterized by a double-layer structure of surface and underground spaces. This special double layer space structure is the key factor causing development of rocky desertification in karst regions. The non-uniform surface micro-landforms and unique underground hydrogeology in the karst regions complicates the process of soil erosion. As a result, large tracts of bedrocks pop out of the land discontinuing the soil cover, while fissures, ponors, cavities and underground drainage systems are formed underground through dissolution of carbonatite. As large volumes flow through fissures and ponors into underground rivers, water and soil loss in karst regions exists in two forms, surface loss and underground loss, which obviously differ from that in non-karst regions. Guizhou Province, China is one of the largest areas in the world’s wet climate zone concentratedly distributed with karst. It has a total of 109,084 km² of karst, which accounts for 73% of the total area of the province, moreover, about 17.42% of the karst landforms are developed from a large continuous tract of limestone. Under the interaction of natural factors (rainfall, and geology and relief) and human activities, soil erosion in this region is very severe. In recent years, the unique form of underground soil and water loss in the process of karst rocky desertification has aroused more and more concern, but so far little has been reported on the underground soil erosion in karst areas different in rocky desertification degree, and the studies that have been done failed to illustrate either contribution rates of surface and underground soil losses to the total of the area or driving forces and mechanism of karst rocky desertification in the Karst region. Therefore, this study is oriented to determining and analyzing sediment generating process with surface and underground erosion in bare karst areas during the process of karst rocky desertification, and further to exploring effects of outcropping bed rock on soil erosion and effects of soil loss on development of karst rocky desertification. 【Method】For that end, a simulated rainfall experiment was carried out to explore sediment yielding characteristics of surface and underground erosion on bare karst slopes different in rocky desertification degree, by simulating their surface micro topographies and structural characteristics of underground pores and fissures. 【Result】Results show that on bare slopes with no rocky desertification, potential rocky desertification and light rocky desertification, sediment yield was generally higher on the surface than underground when other conditions were the same, and the underground sediment yield varied in the range of 0~100 g in during the initial10 min of rainfall. On bare karst slopes different in rocky desertification strength, both surface and underground sediment yields increased with increasing rainfall intensity. Under rainfalls 30 mm h^-1 ~ 80 mm h^-1 in intensity, the more intense the rocky desertification, the harder for surface erosion to occur, and on slopes with rock desertification reaching a certain degree (40% in bed rock outcropping rate), soil erosion became dominated by underground soil loss; under rainfalls 150 mm h^-1in intensity, surface sediment yield and its contribution rate did not change much with increasing bedrock outcropping rate, while underground sediment yield first increased and then decreased, and peaked on slopes 30% in bedrock outcropping rate. On bare karst slopes, regardless of rocky desertification degree, surface sediment yield and its contribution rate did not vary much while underground sediment yield and its contribution rate increased with increasing underground porosity or fissure density; on slopes 1%~5% in underground porosity or fissure density, surface and underground sediment yields and their respective contribution rates varied sharply with changes in bedrock outcropping rate in the range of 10%~50%. 【Conclusion】All these findings in this study demonstrate that they have some important theoretical and practical significance to understanding mechanism of the development of rocky desertification, revealing characteristics of the soil erosion and controlling surface and underground soil and water losses in Karst regions.

Abstract:【Objective】Eutrophication of the water body is the main environmental problem the operation of the Three Gorge Reservoir (TGR) has to face. Phosphorus in the water body is considered to be the key restrictive factor of eutrophication. During the operation of TGR, the water level in the reservoir rises and falls periodically, thus causing the formation of a hydro-fluctuation zone, where the soil gets inundated and exposed to air periodically, too. The periodical alternation of exposure amd inundation of the soil significantly affects the circulation and migration of phosphorus in the soil, as well as the P loading of the water body. Parts of the hydro-fluctuation zone are used for agricultural production during the low water level period, resulting in an excess accumulation of phosphorus adsorbed in the soil, which becomes a source of phosphorus loading into the overlying water during the flooding period, thus enhancing eutrophication of the water body. 【Method】Therefore, an in-lab incubation experiment was carried out of the purple alluvial soil and grey-brown purple soil, which are widely distributed in the Three Gorges Reservoir area to explore characteristics of the variation of extraneous phosphorous in activity and morphology in the two soils as affected by saturation degree of the nutrient. 【Result】Results show as follows:, (1) Once extraneous phosphorous entered the soils, the content of Olsen-P, which characterizes soil P availability, and soil P releasing ability declined exponentially, which may be described with the equation of C_t = ae^-kt +b, with fitting degree being as high as about 94% for both soils, and the drop was the sharpest during the first 15 days of incubation, and then leveled off; (2) Extraneous phosphorous in different soils differed in decline of availability, equilibrium concentration and release potential. It remained quite higher in the gray-brown purple soil than in the purple alluvial soil in availability and consequently in risk of leaching loss and releasing; (3) The release potential of soil phosphorus was governed by saturation degree of phosphorus in absorption. Fifty percent of Q_m (the maximum adsorption capacity) was the turning-point of Olsen-P and phosphorus equilibrium desorption in both of the soils. When the phosphorus sorption saturation degree reached over the point, availability and leaching risk of the soil phosphorus increased rapidly; (4) A significantly positive relationship was observed between Olsen-P and phosphorus release at the p<0.01 level, and could be well fitted with a linear equation. It is, therefore, feasible to characterize the potential of soil phosphorus release with Olsen-P content; (5) Once extraneous phosphorus entered the soil, about 50%~60% of it transformed into Ca₂-P and Ca₈-P, which were higher in availability, while about 30% turned into Al-P and Fe-P, and O-P (Occluded phosphorus )and Ca₁₀-P did not change much in content; and (6) Ca₂-P was the main form of IP that determined Olsen-P content and soil phosphorus desorption capacity, and the effects on the two were positive and direct. 【Conclusion】Fifty percent of Q_m (the maximum adsorption capacity) was the turning-point of Olsen-P and phosphorus equilibrium desorption in the purple alluvial soil and grey-brown purple soil, The release ability of phosphorus can be predicted by Olsen-P content.

Abstract:【Objective】Heilongjiang Province is the largest grain-producing province of China, and sits at the starting point of the Selenium (Se)-deficient belt of the country. In the light of the physical conditions and soil distribution in various regions of the province, agricultural soil samples, representative of the regions were collected for analysis of Se distribution and exploration of effects of soil physic-chemical properties on it, with a view to providing some providing scientific bases for the survey of environment background and the study of epi-geochemistry of soil selenium as well as human health. 【Method】More than 400 soil samples from the topsoil layers (0~20 cm) of farmlands all over the province and 21 soil profiles of the major types of soils samples (21 of the province, together with 71 soil samples from genetic horizons of the profiles) were gathered and analyzed for content and distribution of soil Se and their relationships with soil properties, such as pH, SOC (Soil organic carbon) and PSD (Particle size distribution). 【Result】Results show that the content of total selenium ranges from 0.008 to 0.660 mg kg^-1 with a mean value of 0.147 mg kg^-1, which means that on the whole the soils are in the category of Se deficiency or potential Se deficiency, with little in the category of high Se or excessive Se (Se-poisoning). Among the types of soils existing in the province, saline-alkali soil is the lowest in Se content (0.097 mg kg^-1), while Peat soil the highest (0.273 mg kg^-1); In most soil profiles Se accumulates mainly in the surface soil, and declines with soil depth, and in a few of them, Se distribution displays two peaks or one peak in the subsoil layer, too. Among the regions of the province, Daxinganling is the lowest in Se content (0.115 mg kg^-1), while Xiaoxinganling the highest (0.198 mg kg^-1). Among the administrative regions, Daxing’anling is the lowest (0.115 mg kg^-1), while Heihe city the highest (0.228 mg kg^-1). Correlation and regression analysis shows that soil Se content is significantly and positively related to soil total organic carbon (SOC) and soil clay content, but negatively to soil pH. 【Conclusion】So SOC content, clay content and soil pH are the main factors affecting selenium content of the topsoils in the studied area. Besides, soil parent material is also an important factor affecting the distribution of selenium in the soil. Whatever, SOC content plays a crucial role in the distribution and accumulation of Se in the profiles.

Abstract:【Objective】 Based on a long-term fertilization experiment on yellow soil typical of Central Guizhou, analysis was done to explore relationship between soil organic carbon (SOC) content and crop yield sustainability in yellow soil and to make case-specific rational fertilization recommendations, because few of the studies in the past did much work on the aspects. 【Method】Therefore, data of the 11 year-long (2004—2014) field experiment that had 10 different treatments, that is CK (no fertilizer), treatment NPK(balanced chemical fertilizer application), treatment N(PK deficiency), treatment PK(N deficiency), treatment NK(P deficiency), treatment NP(K deficiency), treatment M(manure only), treatment MNPK(manure plus balanced chemical fertilizer), treatment 1/2M+1/2NPK(50% manure plus 50% chemical fertilizer) and treatment 1/4M+3/4NPK(25% manure plus 75% chemical fertilizer), were analyzed and compared with the single factor variance analysis, sustainable yield index(SYI) and stability index(CV) methods, with a view to exploring effects of the treatments on SOC content and SOC balance in the yellow soil, their effect on crop yield stability and sustainability, and their interrelationships, clarifying the relationship between SOC and crop yield, and providing some theoretic bases for building of soil fertility, improvement of crop yield, development of sustainable agriculture, expansion of carbon sink and reduction of carbon emission. 【Result】Comparison between the treatments demonstrates that treatments M and MNPK were significantly higher in SOC content than all the others, displaying an order of M > MNPK > 1/2M+1/2NPK > 1/4M+3/4NPK. In treatments M and MNPK, content of SOC was gaining in budgeting, and the higher the application rate of manure, the more significant the gain, while it was losing in all the other treatments, displaying an order of MNPK & M > 1/2M+1/2NPK > 1/4M+3/4NPK > NPK > NK > NP > N & CK > PK. Application of manure plus chemical fertilizers, manure alone or balanced NPK was more conducive to improvement of crop yield than the other patterns of fertilization, and in terms of crop yield, the treatments followed an order of MNPK > 1/4M+3/4NPK & 1/2M+1/2NPK > NPK & M > NP > NK, PK & N > CK. Application of NPK coupled with appropriate of organic manure improved maize yield sustainability (SYI) and yield stability (CV), especially treatment 1/4M+3/4NPK that was the highest in both of the indices, with SYI being > 0.6 and CV being < 0.3. The research also found that annual yield was closely related to balance of SOC content, whereas, yield sustainability and stability was to SOC content. 【Conclusion】To sum up, application of chemical fertilizer coupled with organic manure is conducive to accumulation of SOC content in yellow soil and maintenance of stable and sustainable maize yield, and in response to the fertilizer reducing principle, the application of 1/4M+3/4NPK is recommended to be the optimal practice.

Abstract:【Objective】Photosynthesis of terrestrial vegetation is the major force driving carbon cycling between the soil and the atmosphere. Photosynthetic carbon is a primary source of carbon in the soil and affects significantly biomass and composition of the microbial community in the rhizosphere in the form of rhizodeposit. Therefore, if plants different in variety may have different effect on distribution of photosynthetic carbon, rhizospheric microbe may also vary in community composition and microbial utilization of photosynthetic carbon as affected by plant variety. In order to understand and predict carbon cycling in the plant-soil system, a large volume of research work has been done on how to quantify transportation and distribution of photosynthetic carbon in the system. However, so far little is known about effects of plants different in variety on transportation and distribution of photosynthetic carbon in the plant-soil system and on rhizospheric microbe utilizing photosynthetic carbon. The study on input, distribution and microbial utilization of photosynthetic carbon in the plant-soil system is essential to understanding soil carbon sequestration process and soil biochemical processes. 【Method】To that end, a pot experiment was carried out using the PLFA and ¹³CO₂ labeling technique to quantatively study partitioning of photosynthetic carbon and utilization of newly photosynthesizedby carbon by rhizospheric microbe in two maize-rhizospheric soil systems different in maize variety, Zhengdan 958 (ZD) and Shandan 8806 (SD). The distribution of newly photosynthesized carbon to soil microbe was estimated by analyzing the ¹³C profile of microbial phosphlipid fatty acids (PLFA). This experiment had two groups: one labeled for 7 days with ¹³CO₂ (98 atom% ¹³C) and the other labeled with ¹²CO₂ in natural abundance. Based on the difference between the two groups in abundance of ¹³C, the distribution of photosynthetic ¹³C in the maize-rhizospheric soil systems was calculated. 【Result】Results show that Treatment ZD was 20% and 24% higher than Treatment SD in biomass of shoot and root, respectively, and 260% and 159% higher in ¹³C content in the shoot and root, respectively. In comparison with Treatment SD, Treatment ZD significantly increased ¹³C in the shoot and lowered ¹³C in the root. In addition, Treatment ZD significantly increased organic carbon content, ?¹³C value and ¹³C content in the rhizosphere soil, but decreased ¹³C percentage in the rhizosphere soil, as compared with Treatment SD. These findings indicate that the distribution of photosynthetic carbon in the maize-rhizospheric soil system was influenced by maize varieties. Treatment ZD was significantly higher than Treatment SD in ?¹³C value of 11 types of PLFA among the total of 14. Significant difference in distribution of individual PLFA-C percentage was observed between Treatments ZD and SD, indicating that the microbial communities in the two treatments differed in composition. Besides, Treatment ZD was much higher than Treatment SD in 18:2w6,9c PLFA-¹³C percentage and much lower in a15:0, 18:1w7c and cy19:0 PLFA-13C percentage. Treatment DZ was 89%, 65%, 61%, 629%, and 127% higher than Treatment SD in content of gram-positive bacteria, gram-negative bacteria, fungi and total PLFA-C, respectively, but was 6.4, 3.4, 5.2, 26.2 and 8.6 times higher in ¹³C content in the above-listed microbes, respectively. In Treatment ZD, the PLFA-¹³C content in gram-positive bacteria, gram-negative bacteria, fungi and actinomycetes accounted for 33%, 35%, 2.4%, and 0.3%, respectively, of the total PLFA-¹³C, respectively, while in Treatment SD it accounted for 55%, 11%, 5.9%, and 1.1%, respectively. Treatment ZD was significantly higher than Treatment SD in ratio of fungi to bacteria in PLFA-C and PLFA-¹³C, but much lower in ratio of cyclopropane PLFA to their precursor in PLFA-C and PLFA-¹³C. However, the two treatments did not differ much in ratio of gram-positive bacteria to gram-negative bacteria in PLFA-C and PLFA-¹³C. 【Conclusion】In conclusion, this study demonstrates that maize varieties significantly affect the biomass and photosynthetic carbon distribution in the maize-rhizospheric soil systems, and consequently composition of the microbial community in the rhizosphere and microbial utilization of photosynthetic carbon, and that gram-negative bacteria and fungi communities may be the principal microbial communities that utilize newly photosynthesized carbon in the rhizosphere.

Abstract:【Objective】The aims of this work were to determine 1) whether reduced rates of chemical fertilizer coupled with PGPM inoculants (Trichoderma biofertilizer) would produce cucumber yield and quality equivalent to those obtained using full rates of chemical fertilizer and 2) how this type of fertilization affects the soil fertility of a continuous cropping system. 【Method】Pot trials were conducted 4 times with a reduced application of chemical fertilizer (75% of the recommended application) plus Trichoderma-enriched biofertilizer (BF) or organic fertilizer (OF), with 100% of the recommended chemical fertilizer (CF) as the control. 【Result】The results showed that supplementing 75% of the idiomatic fertilizer with TrichodermaSQR-T037 biofertilizer (BF) produced yield that was statistically equivalent to or higher than the 100% chemical fertilizer (CF) and increased by >21% of yield compared to the OF treatment. This result was consistent across in our previous field experiments, which also indicates that only biofertilizer could be a viable supplementary strategy of fertilizer for maintaining or increasing cucumber yield. Reduced chemical fertilization, both of the BF and OF treatments, resulted in a higher Vitamin C (2%~23% and 35%~54%, respectively) contents in the BF and OF treatments but a lower (32%~46%) accumulation of NO3- in the cucumber fruits compared than those of the control (CF), suggesting that replacing 25% of the chemical fertilizer rates with (bio) organic fertilizer could significantly increase cucumber fruit quality. The application of SQR-T037 biofertilizer (BF) significantly (p<0.05) increased cucumber rhizospheric nutrient availability. Specifically, the highest contents of available P were more frequently observed in the BF treatment. Moreover, the BF treatment maintained at a higher level of available K compared with that of the CF and OF treatments. Also, the BF treatment significantly increased the population of soil microflora, including bacteria and Trichoderma, maintaining the population of actinomycetes, but with the reduced abundance of fungi, compared with the CF treatment. Based on the explanations known in other researches, the relationship between soil nutrients and microflora in this study may be explained as follows: plant growth might initially be improved by enhanced root growth, which occurs in response to a powerful plant-growth-promoting fungus, T.harzianum SQR-T037, as reported in our previous study. Then, better root growth influences soil microbes via the supply of additional root exudates or rhizodeposition, and soil microbes, in turn, alter plant performance through higher microbial abundance and more frequent interactions resulting in more available nutrients. This process continues in a cycle. More bio-available nutrients promote better root growth, which facilitates more microbial colonization in the rhizosphere, and ultimately results in greater nutrient uptake by the inoculated plants. 【Conclusion】The results of this study imply that the excessive use of expensive chemical fertilizer can be significantly avoided without compromising yield (at least in cucumbers) through the application of a Trichoderma -enriched biofertilizer. Additionally, the use of Trichoderma-enriched biofertilizer with lower fertilizer application resulted in enhanced fruit quality and an improvement in soil fertility and the microbial environment. Therefore, biofertilizer such as this could be used in combination with the appropriate rates of chemical fertilizer and should be applied over a long-term period as a component of integrated nutrient management strategies to obtain maximum benefits in terms of the yield, sustainable use of soil and fertilizer savings.

Abstract:【Objective】Nitrous oxide (N₂O) is an important greenhouse gas, which is 298 times higher than carbon dioxide in Global Warming Potential (GWP) over a time scale of one hundred years.With the widespread application of chemical fertilizers and the practice of water management of alternation of drying and wetting, paddy soil has become an important source of nitrous oxide emissions.Researches show that the process of flooding-draining paddy fields can cause emissions of large amounts of nitrous oxide, and variation of the redox potential during the process is closely related to N₂O emission. Iron is a crucial redox element in paddy soil, but its influence on N₂O emission is not clear. The study is oriented to expose impacts of Fe on N₂O emission and denitrifying microorganisms. 【Method】An in-lab soil incubation experiment was carried out using samples of the paddy soil derived from the quaternary red clay. The experiment was designed to have three levels of ferrihydrite amendment (Fe 0, 10 and 40 μmol g^-1 soil) and two levels of soil water content (50% and 80%). The soil samples were air-dried and sifted through a 1mm sieve. According to the designing of the experiment, the pretreated soil samples were fully blended with ferrihydrite, separately, put into 1-L plastic boxes, 200 g soil on a dry weight basis in each box, and then spiked with KNO₃solution to ensure the samples 1.6 μmol g^-1 soil in N content and 50% or 80% in soil water content, separately. The boxes of soil samples were placed into an incubator, 28℃in temperature and kept there for 24h.Air and the soils in the boxes were sampled once every 6 h during the incubation for analysis N₂O concentration in the air sample was determined with a Gas-chromatograph. Soil samples for physical and chemical analysis were stored at 4℃ and analyzed for NH₄+-N and NO₃--N contents with a continuous flow analyzer, while soil samples for microorganism analysis were quick-frozen in liquid nitrogen, and stored at -80℃, and then analyzed for variations of the communities and populations of soil denitrifying microorganisms with a realtime flourescentquantification polymerase chain reaction (qPCR) and a terminal-restricted fragment length polymorphism (T-RFLP). 【Result】Results show that during the process of N₂O emission rate rising to a peak, denitrification was obviously disturbed. In the treatments spiked with extraneous iron, especially at high rates (40 μmol g^-1), nitrate concentrations were much higher than in CK, while N₂O emission rates were significantly lower than in control. However, after the peak, N₂O emission rate decreased markedly in all the treatments, but it did much more slowly in the treatments spiked with high rates of iron than in CK and consequently remained higher than that in CK. Meanwhile, during the first 12 hours of incubation, the abundance of nitrate reductase gene (narG) and nitrous oxide reductase gene (；nosZ) varied significantly, demonstrating that the ferrihydrite spiked apparently inhibited the growth of narG- and ；nosZ-containing communities in population size, and the more ferrihydrite was added and the more obvious was the effect. However, after 12 hours, the inhibition effect was no longer so obvious. The addition of extraneous iron did not have much influence on structure of the denitrifying microorganism community. 【Conclusion】So it is concluded that the effect of Fe (Ⅲ) affecting population of the denitrifying microorganism community is the main cause of extraneous Fe (Ⅲ) inhibiting N₂O emission during the early period of the incubation, and hence nitrate reduction and N₂O production. But in the late period of the incubation, the recovery of denitrifying microorganisms in abundance and the existence of nitrate-containing residues, like NO₃-,pushes the N₂O emission rate higher in the treatments spiked with extraneous iron than in CK.

Abstract:【Objective】Fertilizer, especially chemical fertilizer, contributes significantly to the modern agricultural production. 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 invention and use of water retaining controlled-release fertilizer (WRCRF) is a promising approach to improving utilization of the 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 WRCRF to plants under salt stress. Recently, a study has been done finding that application of WRCRF (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 water use efficiency. 【Method】To validate the finding a pot experiment was carried out on effects of WRCRF on leaf length, leaf temperature, and absorption and translocation of N, P, K, Na 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 the soil up to 4.68 g kg^-1 in salinity. WRCRF was applied at 0, 1, 2 and 4 g kg^-1, separately to the pots. 【Result】Results show as follows. (1) Maximum leaf length of the rice seedlings increased with application rate of WRCRF regardless of salt stress and duration of treatment. WRCRF application decreased leaf surface temperature of the rice plants under salt stress, and the higher the application rate of WRCRF, the higher the effect. However, the plants gradually died of high salinity. (2) The fertilizer increased the contents of N, P and K in the plants under salt stress, but lowered the content of Na. Besides, it increased the translocation factor (N-TF) of N and K from root to shoot in the plants, under low salt stress for 40 d, but lowered that of P and Na, which suggests that application of WRCRF significantly enhanced the plants’ ability of selective adsorption of K and Na (S_K,Na). However, in the plants under low salt stress for 80 d, the application significantly lowered N-TF, P-TF and Na-TF, but raised K-TF and S_K,Na, while in the plants under high salt stress, it did not have much effect on N-TF, but raised P-TF and Na-TF and significantly lowered K-TF and S_K,Na. (3) Na content in the roots was significantly higher than that in the shoot of the plants under salt stress, and Na content in the plants increased very markedly with rising salt stress, especially in the shoot of the rice, indicating that Na-TF increased with rising salt stress. Application of the fertilizer decreased Na content in the plants under salt stress, and Na-TF, too, which suggests that the fertilizer decreased not only Na content in the plants, but also Na translocation to the shoot. However, in the plants under high salt stress, the fertilizer increased Na-TF of the plants, which suggests that the fertilizer decreased Na content in the plants, but enhanced Na translocation to shoot of the plants. And (4) the application of WRCRF increased K and Na selective translocation coefficient (S_K,Na) of the plants under low salt stress, and S_K,Na increasing with rising fertilizer application rate, which suggests that the fertilizer enhanced selective K translocation to shoot under low salt stress. However, the application of WRCRF decreased S_K,Na of the plants under high salt stress, and it did with rising fertilizer application rate. 【Conclusion】To sum up, rice plants applied with WRCRF (ZL 2012 1 0400570.0) under low salt stress significantly increased N, P, K absorption, decreased Na accumulation, enhanced selective K translocation to shoot, and maintained better ion homeostasis, thus, improving their salt tolerance. However, the plants under high salt stress, though applied with WRCRF (ZL 2012 1 0400570.0), significantly lowered their selective K translocation to shoot, and ion homeostasis, and hence gradually withered.

Abstract:Investigations and analyses were done of the data of soil physical-chemical and biological properties of waterlogged paddy fields in seven provinces of South China in an attempt to screen out indices for soil quality assessment of waterlogged paddy fields and build up a minimum dataset for the assessment. Results show as follows. Waterlogged paddy fields differed sharply from non-waterlogged paddy fields and were 26.1%, 11.2% and 12.3% higher respectively in content of soil organic matter, total nitrogen and C/N, and 84.6% lower in available P. The two types of paddy fields did not varied much in content of soil total phosphorus, available nitrogen and available potassium. Besides, the former was 37.6%, 91.5%, 108.1%, 17.0%, 349.5%, 143.1% and 217.9%, respectively, higher than the latter in content of soil moisture, available iron, available manganese, available zinc, Fe²⁺, Mn²⁺, total reducing substance and significantly or 43.8% and 25.2%, respectively, lower in soil microbial biomass carbon and phosphatase activity. However, the former was significantly or 21.2% higher than the latter in soil catalase activity, but did not differ much from the latter in invertase activity. Other than those, the former had a nematode population density of 301.9±78.5 individuals 100g dry soil^-1, which was significantly lower than that in the latter. By means of paired sample T test and principal components analysis, it was found that the minimum data set (MDS) for soil quality assessment of waterlogged paddy fields should encompass the following six indices, that is, pH, total nitrogen, available manganese, Fe²⁺, CN ratio and nematode population, which are significantly lower than their corresponding ones for the non-waterlogged paddy fields. All the findings in this study may be of some important significance to soil quality assessment, soil amelioration of cold waterlogged paddy fields.

Abstract: Dicranopteris dichotoma, Paspalum wetsfeteini, Liquidambar formosanaand Schima superba are four typical species of plants used for soil and water conservation in a rare earth mining area in South China, and were selected as subjects in this study to investigate changes in contents of various forms of nitrogen and organic carbon and pH in the rhizospheres of the plants and in the bulk soil as well. Results show that on average, total nitrogen, ammonium nitrogen and nitrate nitrogen was 79.7%, 34.2% and 30.7%, respectively, higher in the rhizosphere soil than in the bulk soil; soil organic carbon was 164.9% higher and soil pH was 0.13 unit lower. The difference between the rhizosphere soil and the bulk soil was quite obvious except in soil pH. The content of total nitrogen, ammonium nitrogen, nitrate nitrogen and organic carbon was higher in the rhizosphere soil, regardless of plant type, than in the bulk soil. The soil pH in the rhizosphere soil of Paspalum wetsfeteini was higher than that in the bulk soil, but no significant difference was found between soil pH in the rhizosphere and bulk soil of Dicranopteris dichotoma, Liquidambar formosanas and Schima superbas. Soil total nitrogen was positively related to organic carbon both in the rhizosphere soil and the bulk soil, but neither to ammonium nitrogen nor to nitrate nitrogen. All the findings in this study indicate that the all the four types of plants in the rare earth mining area have strong sequestration effects on both carbon and nitrogen, and can be used as main pioneer plants to restore vegetation and ecology of the rare earth mining areas in South China.