Changes in Organic Carbon Index of Grey Desert Soil in Northwest China After Long-Term Fertilization

Soil organic carbon （SOC）, soil microbial biomass carbon （SMBC） and SMBC quotient （SMBC/SOC, qSMBC） are key indexes of soil biological fertility because of the relationship to soil nutrition supply capacity. Yet it remains unknown how these three indexes change, which limits our understanding about how soil respond to different fertilization practices. Based on a 22-yr （1990-2011） long-term fertilization experiment in northwest China, we investigated the dynamics of SMBC and qSMBC during the growing period of winter wheat, the relationships between the SMBC, qSMBC, soil organic carbon （SOC） concentrations, the carbon input and grain yield of wheat as well. Fertilization treatments were 1） nonfertilization （control）; 2） chemical nitrogen plus phosphate plus potassium （NPK）; 3） NPK plus animal manure （NPKM）; 4） double NPKM （hNPKM） and 5） NPK plus straw （NPKS）. Results showed that the SMBC and qSMBC were significantly different among returning, jointing, flowering and harvest stages of wheat under long-term fertilization. And the largest values were observed in the flowering stage. Values for SMBC and qSMBC ranged from 37.5 to 106.0 mg kg1 and 0.41 to 0.61%, respectively. The mean value rank of SMBC during the whole growing period of wheat was hNPKM〉NPK_M〉NPKS〉CK〉NPK. But there were no statistically significant differences between hNPKM and NPKM, or between CK and NPK. The order for qSMBC was NPKS〉NPKM〉CK〉hNPKM〉NPK. These results indicated that NPKS significantly increased the ratio of SMBC to SOC, i.e., qSMBC, compared with NPK fertilizer or other two NPKM fertilizations. Significant linear relationships were observed between the annual carbon input and SOC （P〈0.01） or SMBC （P〈0.05）, and between the relative grain yield of wheat and the SOC content as well （P〈0.05）. But the qSMBC was not correlated with the annual carbon input. It is thus obvious that the combination of manure, straw with mineral fertilizer may be benefit to increase SOC and improve soil quality than using only mineral fertilizer.     

Spatiotemporal Changes in Soil Nutrients:A Case Study in Taihu Region of China

The accurate assessment of the spatiotemporal changes in soil nutrients influenced by agricultural production provides the basis for development of management strategies to maintain soil fertility and balance soil nutrients. In this paper, we combined spatial measurements from 2 157 soil samples and geostatistical analysis to assess the spatiotemporal changes in soil organic carbon （SOC）, total nitrogen （TN）, available phosphorus （AP） and available potassium content （AK） from the first soil survey （in the 1980s） to the second soil survey （in the 2000s） in the Taihu region of Jiangsu Province in China. The results showed that average soil nutrients in three soil types all exhibited the increased levels in the 2000s （except for AK in the yellow brown soil）. The standard deviation of soil nutrient contents increased （except for TN in the paddy soil）. Agricultural production in the 20 years led to increases in SOC, TN, AP and AK by 74, 82, 89 and 65%, respectively, of the Taihu areas analyzed. From the 1980s to 2000s all the nugget/sill ratios of soil nutrients indices were between 25 and 75% （except for AK in the yellow brown soil in the 2000s）, indicating moderate spatial dependence. The ratio of AP in the yellow brown soil in the 2000s was 88.74%, showing weak spatial dependence. The spatial correlation range values for SOC, TN, AP and AK in the 2000s all decreased. The main areas showing declines in SOC, TN and AP were in the northwest. For AK, the main region with declining levels was in the east and middle of western areas. Apparently, the increase in soil nutrients in the Taihu region can be mainly attributed to the large increase in fertilizer inputs, change in crop systems and enhanced residues management since the 1980s. Future emphasis should be placed on avoiding excess fertilizer inputs and balancing the effects of the fertilizers in soils.     

Total Carbon Storage in Himalaya Rangeland of Milke-Jaljale Area,Eastern Nepal

Rangelands occupy 51% of the terrestrial land surface, 23% total land of Nepal. It contains about 36% of the world＇s total carbon in above and belowground biomass. Rangelands can aid in the mitigation of rising atmospheric carbon dioxide concentrations via carbon storage in biomass and soil organic matter. A study on carbon stock on soil and vegetation at various altitudinal gradients in Milke-Jaljale rangeland area of Eastern Nepal was made. The study was carried out at three altitudinal gradients （above sea levels） Milke （3,000 m）, Gorujure （3,500 m） and Jaljale （4,000 m）. This method required establishing a transect line. Sample points were located by pacing the appropriate distances from the point of origin at a transect line. To determine distribution and quantity of plant carbon and soil organic carbon （SOC）, 45 sample points were established and 15 points were sampled from each study site. Total soil carbon was estimated as follows： 17.65 t/ha at Milke, 17.27 t/ha at Gorujure and 28.33 t/ha at Jaljale. Similarly, total vegetation carbon was estimated 22.68 t/ha at Milke, 29.79 t/ha at Gorujure and 42.54 t/ha at Jaljale. Highest elevation study site with least external disturbance （Jaljale area） had high storage of carbon in both cases vegetation and soil.     

Effects of Long-Term Organic Amendments on Soil Organic Carbon in a Paddy Field A Case Study on Red Soil

Soil organic carbon （SOC） is one of the main carbon reservoirs in the terrestrial ecosystem. It is important to study SOC dynamics and effects of organic carbon amendments in paddy fields because of their vest expansion in south China. A study was carried out to evaluate the relationship between the SOC content and organic carbon input under various organic amendments at a long-term fertilization experiment that was established on a red soil under a double rice cropping system in 1981. The treatments included non-fertilization （CK）, nitrogen-phosphorus-potassium fertilization in early rice only （NPK）, green manure （Astragalus sinicus L.） in early rice only （OM1）, high rate of green manure in early rice only （OM2）, combined green manure in early rice and farmyard manure in late rice （OM3）, combined green manure in early rice, farmyard manure in late rice and rice straw mulching in winter （OM4）, combined green manure in early rice and rice straw mulching in winter （OMS）. Our data showed that the SOC content was the highest under OM3 and OM4, followed by OM1, OM2 and OM5, then NPK fertilization, and the lowest under non-fertilization. However, our analyses in SOC stock indicated a significant difference between OM3 （33.9 t ha^-1） and OM4 （31.8 t ha^-1）, but no difference between NPK fertilization （27 t ha^-1） and nonfertilization （28.1 t ha^-1）. There was a significant linear increase in SOC over time for all treatments, and the slop of linear equation was greater in organic manure treatments （0.276-0.344 g kg-1 yr^-1） than in chemical fertilizer （0.216 g kg^-1 yr^-1） and no fertilizer （0.127 g kg^-1 yr^-1）.     

Soil CO2 Emissions as Affected by 20-Year Continuous Cropping in Mollisols

Long-term continuous cropping of soybean （Glycine max）, spring wheat （Triticum aesativum） and maize （Zea mays） is widely practiced by local farmers in northeast China. A field experiment （started in 1991） was used to investigate the differences in soil carbon dioxide （CO2） emissions under continuous cropping of the three major crops and to evaluate the relationships between CO2 fluxes and soil temperature and moisture for Mollisols in northeast China. Soil CO2 emissions were measured using a closed-chamber method during the growing season in 2011. No remarkable differences in soil organic carbon were found among the cropping systems （P〉0.05）. However, significant differences in CO2 emissions from soils were observed among the three cropping systems （P〈0.05）. Over the course of the entire growing season, cumulative soil CO2 emissions under different cropping systems were in the following order： continuous maize （（829±10） g CO2 m2）〉continuous wheat （（629±22） g CO2 m^2）〉continuous soybean （（474±30） g CO2 m-2）. Soil temperature explained 42-65% of the seasonal variations in soil CO2 flux, with a Q10 between 1.63 and 2.31; water-filled pore space explained 25-47% of the seasonal variations in soil CO2 flux. A multiple regression model including both soil temperature （T, ~C） and water-filled pore space （W, %）, log（]）=a＋bT log（W）, was established, accounting for 51-66% of the seasonal variations in soil CO2 flux. The results suggest that soil CO2 emissions and their Q10 values under a continuous cropping system largely depend on crop types in Mollisols of Northeast China.     

Effects of Rest Grazing on Organic Carbon Storage in Stipa grandis Steppe in Inner Mongolia,China

This study was aimed to evaluate the potential effects of rest grazing on organic carbon storage in Stipa grandis steppe of Inner Mongolia, China. Using potassium dichromate heating method, we analyzed the organic carbon storage of plant and soil in Stipa grand＆ steppe after rest grazing for 3, 6, and 9 yr. The results indicated that as the rest grazing ages prolonged, the biomass of aboveground parts, litter and belowground plant parts （roots） of the plant communities all increased, meanwhile the C content of the biomass increased with the rest grazing ages prolonging. For RG0, RG3a, RG6a, and RG9a, C storage in aboveground vegetation were 60.7, 76.9, 82.8 and 122.2 g C m2, respectively; C storage of litter were 5.1, 5.8, 20.4 and 25.5 g C m^-2, respectively; C storage of belowground roots （0-100 cm） were 475.2, 663.0, 1 115.0 and 1 867.3 g C m^-2, respectively; C storage in 0-100 cm soil were 13.97, 15.76, 18.60 and 32.41 kg C m^-2, respectively. As the rest grazing ages prolonged, the organic C storage in plant communities and soil increased. The C storage ofbelowground roots and soil organic C was mainly concentrated in 0-40 cm soil body. The increased soil organic C for RG3a accounted for 89.8% of the increased carbon in vegetation-soil system, 87.2% for RG6a, and 92.6% for RG9a. From the perspective of C sequestration cost, total cost for RG3a, RG6,, and RG9a were 2 903.4, 5 806.8 and 8 710.2 CNY haq, respectively. The cost reduced with the extension of rest grazing ages, 0.15 CNY kg^-1 C for RG3a, 0.11 CNY kg-~ C for RG6a and 0.04 CNY kg℃ for RG9a. From the growth characteristics of grassland plants, the spring was one of the two avoided grazing periods, timely rest grazing could effectively restore and update grassland vegetation, and was beneficial to the sustainable use of grassland. Organic C storage for RG9a was the highest, while the cost of C sequestration was the lowest. Therefore, spring rest grazing should be encouraged because it was proved to be a very efficient grassland use pattern.     

Effects of Elemental Sulphur and Farmyard Manure on pH and Salinity of Calcareous Sandy Loam Soil and Some Nutrient Elements in Tomato Plant

The objective of this study was to evaluate the effects of elemental sulphur （S） and farmyard manure on soil pH, EC and N, S, P concentrations of tomato grown in a calcareous sandy loam soil. For this purpose, a pot experiment was conducted in greenhouse conditions. Sulphur was applied at 0, 50, 100, 150, 200, 400 mg kg~ and farmyard manure at 0, 3 ton da^-1 to the soil. Three weeks after applications, tomato seedlings were planted and 8 weeks later, the plants were harvested to determine N, S, P concentrations and dry matter yield. Soil pH and EC were determined in the soil samples taken at 3 different periods. Effects of sulphur and farmyard manure applications were not significant on N, P concentrations and dry matter yield of tomato plant. S concentration of tomato plant was increased by sulphur alone. Soil pH was decreased and soil EC was increased in both 2^nd and 3^rd soil sampling period by the sulphur applications. As a result of farmyard manure application, soil pH decreased in the 2^nd soil sampling period but increased in the 3^rd soil sampling period. Also, soil EC was significantly increased in 1^st and 3^rd soil sampling period. Farmyard manure had no significant effect on S supply to tomato plant. The N：S ratio of tomato plant was decreased by sulphur alone. However, the sulphur with farmyard manure applications decreased N：S ratio in lesser extend compared to the S applications.     

Long Term Effects of Farming System on Soil Water Content and Dry Soil Layer in Deep Loess Proifle of Loess Tableland in China

Soil water is strongly affected by land use/cover in the Loess Plateau in China. Water stored in thick loessal soils is one of the most important resources regulating vegetation growth. However, soil water in the deep loess proifle, which is critical for maintaining the function of the“soil water pool”is rarely studied because deep proifle soil samples are dififcult to collect. In this study, four experimental plots were established in 2005 to represent different farming systems on the Changwu Tableland：fallow land, fertilized cropland, unfertilized cropland, and continuous alfalfa. The soil water content in the 15-m-deep loess proifles was monitored continuously from 2007 to 2012 with the neutron probe technique. The results showed that temporal variations in soil water proifles differed among the four farming systems. Under fallow land, the soil water content increased gradually over time, ifrst in the surface layers and later in the deep soil layers. In contrast, the soil water content decreased gradually under continuous alfalfa. The distributions of soil water in deep soil layers under both fertilized and unfertilized cropland were relatively stable over time. Thus farming system signiifcantly affected soil water content. Seven years after the start of the experiment, the soil water contents in the 15-m-deep proifles averaged 23.4%under fallow land, 20.3%under fertilized cropland, 21.6%under unfertilized cropland, and 16.0%under continuous alfalfa. Compared to measurements at the start of the experiment, both fallow land and unfertilized cropland increased soil water storage in the 15-m loess proifles. In contrast, continuous alfalfa reduced soil water storage. Fertilized cropland has no signiifcant effect on soil water storage. These results suggest that deep soil water can be replenished under the fallow and unfertilized farming systems. Dry soil layers （i.e., those which have soil water content less than the stable ifeld water capacity） in the subsoil of the Changwu Tableland region can be classiifed as either temporary dry soil layers or persistent dry soil layers. Temporary dry soil layers, which typically form under annual crops, often disappear during wet years. Persistent dry soil layers generally develop under perennial vegetation. Even after removing the vegetation, persistent dry soil layers remain for several decades. This study provides information useful for the conservation and utilization of soil water resources in the Loess Tableland.     

Crop Yield and Soil Properties in the First 3 Years After Biochar Application to a Calcareous Soil

It remains unclear whether biochar applications to calcareous soils can improve soil fertility and crop yield. A long-term field experiment was established in 2009 so as to determine the effect of biochar on crop yield and soil properties in a calcareous soil. Five treatments were： 1） straw incorporation; 2） straw incorporation with inorganic fertilizer; 3）, 4） and 5） straw incorporation with inorganic fertilizer, and biochar at 30, 60, and 90 t ha-l, respectively. The annual yield of either winter wheat or summer maize was not increased significantly following biochar application, whereas the cumulative yield over the first 4 growing seasons was significantly increased. Soil pH, measured in situ, was increased by a maximum of 0.35 units after 2 yr following biochar application. After 3 yr, soil bulk density significantly decreased while soil water holding capacity increased with adding biochar of 90 t ha^-1. Alkaline hydrolysable N decreased but exchangeable K increased due to biochar addition. Olsen-P did not change compared to the treatment without biochar. The results suggested that biochar could be used in calcareous soils without yield loss or significant impacts on nutrient availability.     

Basic Soil Productivity of Spring Maize in Black Soil Under Long-Term Fertilization Based on DSSAT Model

Increasing basic farmland soil productivity has significance in reducing fertilizer application and maintaining high yield of crops. In this study, we defined that the basic soil productivity （BSP） is the production capacity of a farmland soil with its own physical and chemical properties for a specific crop season under local environment and field management. Based on 22-yr （1990-2011） long-term experimental data on black soil （Typic hapludoll） in Gongzhuling, Jilin Province, Northeast China, the decision support system for an agro-technology transfer （DSSAT）-CERES-Maize model was applied to simulate the yield by BSP of spring maize （Zea mays L.） to examine the effects of long-term fertilization on changes of BSP and explore the mechanisms of BSP increasing. Five treatments were examined： （1） no-fertilization control （control）; （2） chemical nitrogen, phosphorus, and potassium （NPK）; （3） NPK plus farmyard manure （NPKM）; （4） 1.5 time of NPKM （1.5NPKM） and （5） NPK plus straw （NPKS）. Results showed that after 22-yr fertilization, the yield by BSP of spring maize significantly increased 78.0, 101.2, and 69.4% under the NPKM, 1.5NPKM and NPKS, respectively, compared to the initial value （in 1992）, but not significant under NPK （26.9% increase） and the control （8.9% decrease）. The contribution percentage of BSP showed a significant rising trend （P〈0.05） under 1.5NPKM. The average contribution percentage of BSP among fertilizations ranged from 74.4 to 84.7%, and ranked as 1.5NPKM〉NPKM〉NPK〉NPKS, indicating that organic manure combined with chemical fertilizers （I.5NPKM and NPKM） could more effectively increase BSP compared with the inorganic fertilizer application alone （NPK） in the black soil. This study showed that soil organic matter （SOM） was the key factor among various fertility factors that could affect BSP in the black soil, and total N, total P and/or available P also played important role in BSP increasing. Compared with the chemical fertilization, a balanced chemical plus manure or straw fertilization （NPKM or NPKS） not only increased the concentrations of soil nutrient, but also improved the soil physical properties, and structure and diversity of soil microbial population, resulting in an iincrease of BSP. We recommend that a balanced chemical plus manure or straw fertilization （NPKM or NPKS） should be the fertilization practices to enhance spring maize yield and improve BSP in the black soil of Northeast China.     

Soil Quality Assessment of Acid Sulfate Paddy Soils with Different Productivities in Guangdong Province,China

Land conversion is considered an effective measure to ensure national food security in China, but little information is available on the quality of low productivity soils, in particular those in acid sulfate soil regions. In our study, acid sulfate paddy soils were divided into soils with high, medium and low levels based on local rice productivity, and 60 soil samples were collected for analysis. Twenty soil variables including physical, chemical and biochemical properties were determined. Those variables that were significantly different between the high, medium and low productivity soils were selected for principal component analysis, and microbial biomass carbon （MBC）, total nitrogen （TN）, available silicon （ASi）, pH and available zinc （AZn） were retained in the minimum data set （MDS）. After scoring the MDS variables, they were integrated to calculate a soil quality index （SQI）, and the high, medium and low productivity paddy soils received mean SQI scores of 0.95, 0.83 and 0.60, respectively. Low productivity paddy soils showed worse soil quality, and a large discrepancy was observed between the low and high productivity paddy soils. Lower MBC, TN, ASi, pH and available K （AK） were considered as the primary limiting factors. Additionally, all the soil samples collected were rich in available P and AZn, but deficient in AK and ASi. The results suggest that soil AK and ASi deficiencies were the main limiting factors for all the studied acid sulfate paddy soil regions. The application of K and Si on a national basis and other sustainable management approaches are suggested to improve rice productivity, especially for low productivity paddy soils. Our results indicated that there is a large potential for increasing productivity and producing more cereals in acid sulfate paddy soil regions.     

Biomass and Carbon Sequestration Potential of Poplar-Wheat Inter-cropping System in Irrigated Agro-ecosystem in India

An attempt has been made to assess the productivity as well as the carbon sequestration potential of this mixture. The grain as well as straw yields were significantly lower in poplar block plantations than in the open （14 to 64% and 13 to 66% grain and straw yield, respectively under one to six year plantation）. The annual productivity of poplars was recorded maximum after fourth year and later the annual wood increment decreased （42.4, 39.8 and 35.6 m^3/ha/yr after 4^th, 5^th and 6^th year, respectively）. The enrichment of soil through litter and roots enhanced the organic carbon in the surface layer of soil （0-15 cm） under poplar blocks as compared to open fields with wheat crop only. The carbon storage potential in agroforestry system was recorded very high in comparison to sole crop. The carbon storage in agroforestry system increased with the age of the plantation and the major contribution came from the timber, roots and litter （37.30 mg/ha after six years）. However, wheat crop yield decreased under poplar but this may be compensated by the poplar trees in terms of biomass, economic returns and the carbon sequestration potential.     

The Estimation of Soil Trace Elements Distribution and Soil-Plant-Animal Continuum in Relation to Trace Elements Status of Sheep in Huangcheng Area of Qilian Mountain Grassland,China

The purpose of the present study was to survey contents of trace elements of Cu, Mn, Fe, and Zn in the surface layer （0-20 cm） in the soil, pasture and serum of sheep in Huangcheng area of Qilian mountain grassland, China. Also the soil-plantanimal continuum was analyzed. Soil （n=300）, pasture （n=60）, and blood serum samples from sheep （n=480） were collected from Huangcheng area of Qilian mountain grassland, China. The contents of trace element in the samples were analyzed by atomic absorption spectrophotometer after digestion. The soil trace elements density distribution shows a ladder-like pattern distribution. Equations developed in the present study for prediction of Fe （R2=0.943） and Zn （R2=0.882） had significant R2 values.     

Soil Monitoring System as a Basic Tool for Protection of Soils and Sustainable Land Use in Slovakia

The purpose of soil monitoring system in Slovakia is better to protect the soils with regard to sustainable land use. The main objective is the observation of soil properties concerning the main threats to soil： soil contamination, salinisation and sodification, decline in soil organic matter （SOM）, soil compaction and erosion. Soil monitoring system in Slovakia is consistently running since 1993. Its importance consists of providing the information on changing spatial and temporal variations of soil parameters as well as the evolution of soil quality in topsoil and subsoil. Soil monitoring network in Slovakia is constructed using ecological principles, taking into account all main soil types and subtypes, SOM, climatic regions, emission regions, polluted and non-polluted regions as well as various land use. The results of soil monitoring of 318 sites on agricultural land in Slovakia have been presented. Soil properties are evaluated according to the main threats to soil relating to European Commission recommendation for European soil monitoring performance as follows： soil contamination, soil salinization and sodification, decline in SOM, soil compaction and erosion. The most significant change has been determined in physical properties of soils. The physical degradation was especially manifested in compacted and the eroded soils. About 50% of agricultural land is potentially affected by soil erosion in Slovakia. In addition, decline in SOM and available nutrients indicate the serious facts on evaluation and extension of soil degradation processes during the last period in Slovakia. Obtained measured data and required outputs are reported to Joint Research Centre （JRC） in lspra （Italy） and European Environmental Agency （EEA） in Copenhagen （Denmark）. Finally, soil monitoring system thus becomes a basic tool for protection of soils and sustainable land use as well as for the creation of legislatives not only in Slovakia, but in EU, too.     

Soil CO2 and N2O Emissions in Maize Growing Season Under Different Fertilizer Regimes in an Upland Red Soil Region of South China

Upland red soils have been identified as major CO2 and N2O sources induced by human activities such as fertilization. To monitor characteristics of soil surface CO2 and N2O fluxes in cropland ecosystems after continuous fertilizer applications over decades and to separate the respective contributions of root and heterotrophic respiration to the total soil CO2 and N2O fluxes, the measurements of soil surface CO2 and N2O fluxes throughout the maize growing season in 2009 were carried out based on a fertilization experiment （from 1990） through of the maize （Zea mays L.） growing season in red soil in southern China. Five fertilization treatments were chosen from the experiment for study： zero-fertilizer application （CK）, nitrogen-phosphorus- potassium （NPK） fertilizer application only, pig manure （M）, NPK plus pig manure （NPKM） and NPK with straw （NPKS）. Six chambers were installed in each plot. Three of them are in the inter-row soil （NR） and the others are in the soil within the row （R）. Each fertilizer treatment received the same amount of N （300 kg ha-1 yr-1）. Results showed that cumulative soil CO2 fluxes in NR or R were both following the order： NPKS〉M, NPKM〉NPK〉CK. The contributions of root respiration to soil CO2 fluxes was 40, 44, 50, 47 and 35% in CK, NPK, NPKM, M and NPKS treatments, respectively, with the mean value of 43%. Cumulative soil N2O fluxes in NR or R were both following the order： NPKS, NPKM〉M〉NPK〉CK, and soil N2O fluxes in R were 18, 20 and 30% higher than that in NR in NPKM, M and NPKS treatments, respectively, but with no difference between NR and R in NPK treatment. Furthermore, combine with soil temperature at -5 cm depth and soil moisWxe （0-20 cm） together could explain 55-70% and 42-59% of soil CO2 and N2O emissions with root interference and 62- 78% and 44-63% of that without root interference, respectively. In addition, soil CO2 and N2O flUXeS per unit yield in NPKM （0.55 and 0.10 kg C t^-1） and M （0.65 and 0.13 g N t^-1） treatments were lower than those in other treatments. Therefore, manure application could be a preferred fertilization strategy in red soils in South China.     

Determination of Competitive Adsorption and Desorption of Heavy Metals by Isotherm and Sequential Extraction Methods in Different Soil Orders in Erzurum Plain

The objective of this study was to DTPA （complexion agent） and a sequential extraction procedure, and adsorption-desorption isotherm （competitive） evaluate the mobility and distribution of Fe, Zn, Mn, Cu, Cd, Ni, and Pb using the in surface samples of five soil great groups differing in their physicochemical properties. For determining heavy metal adsorption and desorption capacities of soil samples, six different concentrations （0, 2.5, 5, 10, 15 and 20 mg Lt） were used in a laboratory experiment with tree replications. An analytical procedure involving sequential chemical extractions has been used for partitioning of heavy metals into five fractions. Sorption isotherms were characterized using linear, Frendlich and Langmuir equations. The results indicated that the selective sequences of the metal adsorption based on the distribution coefficient was Pb〉Cu〉Ni〉Cd〉Zn〉Mn〉Fe and Pb, Cu, and Ni are the most strongly sorbed metals by these soils, whereas Cd, Zn and Mn are the least sorbed ones. The total adsorbed amount of these metals on the studied soils was well described by Langmuir equation. Calciorthid had the highset Pb, Cu, Ni, Cd, Zn, Mn, and Fe adsorption, and the sequences followed order Fluvaquent〉Argiustoll〉Pellustert〉Haplustept of the studied soil.     

Soil Nitrous Oxide Emissions Under Maize-Legume Intercropping System in the North China Plain

Many studies have focused on various agricultural management measures to reduce agricultural nitrous oxide （N2O） emission. However, few studies have investigated soil N2O emissions in intercropping systems in the North China Plain. Thus, we conducted a ifeld experiment to compare N2O emissions under monoculture and maize-legume intercropping systems. In 2010, ifve treatments, including monocultured maize （M）, maize-peanut （MP）, maize-alfalfa （MA）, maize-soybean （MS）, and maize-sweet clover （MSC） intercropping were designed to investigate this issue using the static chamber technique. In 2011, M, MP, and MS remained, and monocultured peanuts （P） and soybean （S） were added to the trial. The results showed that total production of N2O from different treatments ranged from （0.87＆#177;0.12） to （1.17＆#177;0.11） kg ha-1 in 2010, while those ranged from （3.35＆#177;0.30） to （9.10＆#177;2.09） kg ha-1 in 2011. MA and MSC had no signiifcant effect on soil N2O production compared to that of M （P＆lt;0.05）. Cumulative N2O emissions from MP in 2010 were signiifcantly lower than those from M, but the result was the opposite in 2011 （P＆lt;0.05）. MS signiifcantly reduced soil N2O emissions by 25.55 and 48.84%in 2010 and 2011, respectively （P＆lt;0.05）. Soil N2O emissions were signiifcantly correlated with soil water content, soil temperature, nitriifcation potential, soil NH4＋, and soil NO3-content （R2=0.160-0.764, P＆lt;0.01）. A stepwise linear regression analysis indicated that soil N2O release was mainly controlled by the interaction between soil moisture and soil NO3-content （R2=0.828, P＆lt;0.001）. These results indicate that MS had a coincident effect on soil N2O lfux and signiifcantly reduced soil N2O production compared to that of M over two growing seasons.     

Research on Spatial-Temporal Characteristics and Driving Factor of Agricultural Carbon Emissions in China

Macroscopic grasp of agricultural carbon emissions status, spatial-temporal characteristics as well as driving factors are the basic premise in further research on China’s agricultural carbon emissions. Based on 23 kinds of major carbon emission sources including agricultural materials inputs, paddy ifeld, soil and livestock breeding, this paper ifrstly calculated agricultural carbon emissions from 1995 to 2010, as well as 31 provinces and cities in 2010 in China. We then made a decomposed analysis to the driving factors of carbon emissions with logarithmic mean Divisia index （LMDI） model. The results show：（1） The amount of agricultural carbon emissions is 291.1691 million t in 2010. Compared with 249.5239 million t in 1995, it increased by 16.69%, in which, agricultural materials inputs, paddy ifeld, soil, enteric fermentation, and manure management accounted for 33.59, 22.03, 7.46, 17.53 and 19.39%of total agricultural carbon emissions, respectively. Although the amount exist ups and downs, it shows an overall trend of cyclical rise; （2） There is an obvious difference among regions：the amount of agricultural carbon emissions from top ten zones account for 56.68%, while 9.84%from last 10 zones. The traditional agricultural provinces, especially the major crop production areas are the main source regions. Based on the differences of carbon emission rations, 31 provinces and cities are divided into ifve types, namely agricultural materials dominant type, paddy ifeld dominant type, enteric fermentation dominant type, composite factors dominant type and balanced type. The agricultural carbon emissions intensity in west of China is the highest, followed by the central region, and the east zone is the lowest; （3） Compared with 1995, efifciency, labor and structure factors cut down carbon emissions by 65.78, 27.51 and 3.19%, respectively;while economy factor increase carbon emissions by 113.16%.     

Evaluation of Spatial Variability of Soil Properties in a Long-Term Experimental Tobacco Station in Southwest China

Analysis of the spatial variability of soil properties is important to arrange the experimental treatments in the experimental station. This paper aims to study the spatial structure of soil variables and their distribution in the Pengshui tobacco experiment station in Chongqing, China. Soil samples were taken from 289 soil points on 20 m grid in March 2012. Twenty-two soil chemical and physical properties were analyzed by classical statistical and geo-statistical methods. Soil pH, cation exchange capacity （CEC）, total phosphorus （TP）, available phosphorus （AP）, zinc （Zn）, magnesium （Mg） and sulphur （S） have the strong spatial dependence, with nugget/sill ratios of less than 25%. The others have the moderate dependence with nugget/sill ratios of 26.17% to 71.04%. Ranges of the spatial correlation varied from 51.30 m for chlorine （C1） to 594.90 m for TP. The clearly patchy maps of the nutrients showed the spatial distributions of the soil variables, which can be used for better management of experimental treatments, achieving reliable exoerimental results in the tobacco exnerimental station.Highlight： Scientific experimentation assumes the existence of random variability for soil attributes. This research was to evaluate the spatial variability of soil chemical and physical attributes and to interpolate the spatial distribution of soil properties in the tobacco experimental station in Chongqing. The result of this work can be used for the agricultural management of tobacco cultivation.     

Responses of Plant Community and Soil Properties to Inter-Annual Precipitation Variability and Grazing Durations in a Desert Steppe in Inner Mongolia

Grazing can dramatically affect arid grassland communities that are very vulnerable to environmental changes due to its relatively short and sparse ground coverage, low biomass, sandy soil and inter-annual precipitation found in the desert steppe. The study investigates the effects of different grazing durations on vegetation and soil properties of a desert steppe community. The experiment was conducted in Xisu Banner in Inner Mongolia with ifve treatments：CG （continuous grazing）, 40UG （40 d ungrazed）, 50UG （50 d ungrazed）, 60UG （60 d ungrazed） and UG （ungrazed）. The biomass of both shrub and annual-biennial plant communities were signiifcantly decreased by CG. Continuous grazing and 40UG signiifcantly reduced the ANPP （aboveground net primary productivity） by the end of the three year study. 60UG treatment increased soil organic carbon （OC）, total nitrogen concentration （TN） and total phosphorus concentration （TP） concentrations and 50UG increased the TN and total phosphorus concentration （TK） concentrations, whereas CG, 40UG and 50UG decreased soil OC, TP and available phosphorus concentration （AP） concentrations. The perennial plant species of the desert steppe were generally tolerant for grazing. The annual-biennial plant species had large variability in ANPP because of the inter-annual precipitation. Our results highlight that inter-annual precipitation variations could strongly modify the community responses to grazing in arid ecosystems.