Advances in Greenhouse Gases Emission in Farmland Soils

[Objective] The aim was to overview the emission of greenhouse gases in farmland. [Method] Based on domestic and foreign references, production mechanism, discharging characters and major influential factors of CO2, CH4 and N2O in soils of farmland were overviewed. [Result] Production and discharge of CO2, CH. and N2O played an important role in circulation of carbon and nitrogen in terrestrial ecosystem and constituted a key method for carbon and nitrogen output. It is significant to conduct research on reduction of greenhouse gas and increase of absorption. [Conclusion] The research is beneficial for exploration on discharge rule and influential factors of greenhouse gases, providing theoretical references for reduction of greenhouse gases and study on climate change.

Advances in Cotton Tolerance to Heavy Metal Stress and Applications to Remediate Heavy Metal-Contaminated Farmland Soil

Heavy metal-contaminated soil is one of the major environmental pollution problems of agricultural production and human health in the world.Remediation of heavy metals in soil is one of the most popular research subjects.Different remediation strategies have been reported to remove heavy metals from contaminated soil,among which phytoremediation is the most important one.Compared with other major crops,cotton shows the strongest and most widespread resistance to abiotic stresses,such as heavy metals.Although heavy metal stress adversely affects the growth and development of cotton,cotton possesses a set of sophisticated stress-resistance strategies.As the main product of cotton is nonedible fibers,which have a large biomass and strong heavy metal absorption and enrichment capacities,cotton is an ideal crop to restore heavy metal-contaminated soils and has unique advantages in terms of both ecological and economic benefits,with great application prospects.In this review,based on domestic and foreign research results in recent years,the effects of heavy metals on cotton growth and product quality were analyzed,the heavy metal absorption,accumulation,translocation and enrichment characteristics of cotton plants were summarized,and the adaptation and tolerance mechanisms of cotton to heavy metals were explored.Furthermore,the view that cotton is an effective crop to remediate heavy metal pollution in farmland soil has been proposed,and popularization and application suggestions for planting cotton to repair heavy metal pollution have been put forward to provide a reference for the comprehensive evaluation of the economic feasibility of cotton to repair heavy metal pollution in farmland soil.

Farmland Soil Heavy Metal Pollution and Control Measures

Soil pollution has been considered as one of the main environmental problems in the world nowadays. The source of soil heavy metal pollution in farmland, the effect of heavy metal pollution on soil quality in farmland, growth of crops, quality of agricultural products and the effects of heavy metal pollution on human health were discussed in this paper. The heavy metal pollution control measures were introduced, including physical and chemical regulations, phytoremediation and agroecological restoration measures. The future research perspective was also discussed in this paper.

Distribution Characteristics of Pb and Its Ecological Risk in Different Farmland Soils of Changchun Suburb

Pb in the farmland surface soil of Changchun suburb was taken as the main research object. The field research and laboratory analysis were used to investigate Pb content, spatial distribution characteristics and its ecological risk in different farmland soils. The results showed that Pb content was during 18.85 - 41.34 mg/kg in farmland soil of Changchun suburb, and was higher than the background value of Jilin Province at 90% of the sampling sites. The spatial distribution of Pb content in farmland soil had obvious geographical features, and Pb content in southwest and northeast soils was higher. The high-content areas were relatively concentrated, and Pb content gradually reduced from the high-content island- shape center to its surrounding. The soil Pb contents in paddy field, dry field and vegetable field had insignificant difference with the background value, indicating that Pb accumulations in dry field, paddy field and vegetable field were not significant. The order of Pb content in different land use types was showed as follows： vegetable field 〉 dry field 〉 paddy field. Pb pollution of all samples belonged to light pollution. The average potential ecological risk of soil Pb in different land use types presented the following order： vegetable field 〉 dry field 〉 paddy field.

MONITORING, NURTURE OF THE FARMLAND SOIL & INCREASE OF GRAIN YIELD IN CHINA

In line with the author’s long-time experience on soil reconnaissance, monitoring and scientific probes, this article expounds the vital significance in systematic build-up of pedological data, protection of arable land, employment and renovation of the farmland soil in accordance with the local edaphic setting in a bid to increase the grain yield.

Heavy Metal Contamination in Farmland Soil and Bioremediation Measures: A Case Study of the Mining Area in Shaoguan

With the rapid development of mining,the soil heavy metal contamination is increasingly serious in Shaoguan,directly affecting the production of crops. This paper analyzes the farmland soil heavy metal contamination in the mining area of Shaoguan and the causes of heavy metal contamination in recent years,brings forward the bioremediation measures to control soil heavy metal contamination,and points out the development direction of bioremediation in farmland soil heavy metal contamination in the mining area.

Pool Sizes and Turnover of Soil Organic Carbon of Farmland Soil in Karst Area of Guilin

The three-pool and first-order model separates the mineralizable organic carbon into active,slow,and passive carbon pools.This paper used the model and decomposition curves of the soil organic carbon to fit the active pool and its decomposition rate,slow pool and its decomposition rate.The results showed that the size of the active pool from different profiles accounted for 2.09%-3.08% of the total soil organic carbon and the mean residue time was 3.57-17.21 days.And the size of the slow pool accounted for 3.19%-43.55% and the mean residue time was 1.12-4.94 years.Acid hydrolysis（6M HCl） was used to fractionate the passive organic carbon,which accounted for 50.83%-94.44% of the total soil organic carbon.

Contamination and risk assessment of heavy metals in farmland soils of Baghrash County, Xinjiang, Northwest China

Soil pollution significantly reduces environmental quality.In this study,farmland soil samples were collected from 25 sites in Baghrash County,Northwest China;and the concentrations of eight heavy-metal elements(arsenic,As;cadmium,Cd;chromium,Cr;copper,Cu;manganese,Mn;nickel,Ni;lead,Pb;zinc,Zn)were determined by standard methods.The spatial distribution,contamination level,and ecological risk stature of heavy metals were analyzed based on GIS technology,the Geo-accumulation Index(Igeo),the Pollution Load Index(PLI),and the Potential Ecological Risk Index(RI).Results indicated that(1)The average concentrations of Cd exceeded 12.12 times the allowed national standard for soil environmental quality of China.The average concentrations of Cd,Cr,Ni,Pb,and Zn exceeded the background values of irrigation soils in Xinjiang by 60.58,1.25,1.50,4.95,and 5.10 times,respectively.(2)The pollution order of the average value of Igeo for heavy metals was ranked as Cd>Zn>Pb>Ni>Cr>Cu>As>Mn.The individual potential ecological risk index for heavy metals was ranked in the order of Cd>As>Ni>Cu>Pb>Cr>Zn.The average PLI for the study area showed a heavy pollution level,while the average RI showed a considerable ecological risk stature,as compared to the classification standard.(3)The spatial distribution patterns of eight heavy metal elements were substantially heterogeneous.The moderately polluted areas with moderate potential ecological risks were distributed in the southern parts of the study area,whereas the heavily polluted areas with considerable potential ecological risks were distributed in the northern parts.Overall,it was observed that Cd contributed most to the PLI and RI of the farmland soils in Baghrash County.The pollution risk of Cd should be a major concern,and human activities in the region should be cautious.

Preliminary Study on Heavy Metal Pollution Status of Farmland Soil at Two Sides of Cheng-Guan Expressway

The heavy metal content of the farmland soil at two sides of Cheng-Guan Expressway is measured to make a preliminary evaluation on its heavy metal pollution status.After digestion and volume fixation of the soil samples collected,measure the Cu,Zn,Cd,Pb and Cr content with atomic absorption spectrophotometry and evaluate the measured data according to Level Two of National Soil Environmental Quality Standard to obtain the contamination status.Cu,Zn and Cd content of the farmland soil for sections of Cheng-Guan Expressway goes beyond Level Two of National Soil Environmental Quality Standard,while the Pb and Cr content meets Level Two of National Soil Environmental Quality Standard.Pb and Cr content of the farmland soil at two sides of Cheng-Guan Expressway is in safe state,while the Cu,Zn and Cd content is in a mild contamination state.Cu,Zn and Cd are the main pollution elements.

Research Progress on Remediation Technology Suitable for Farmland Soil Contaminated by Cd

Cd contamination range of farmland soil in China is wide,which has constituted a major threat for food safety and residents＇ health. Via multi-year development,there are more remediation methods suitable for soil contaminated by Cd among the world,but some methods are only suitable for the contaminated sites and indoor research,and can not be applied in large-range contaminated farmland. We analyze the source of Cd in farmland soil. By combining farmland＇s characteristics,three remediation techniques（ low-absorption crops plantation,soil solidification and phytoremediation） and their effects are analyzed,and the existing problems and research prospects of the above techniques are explored. The research could provide reference for restoring farmland soil contaminated by Cd in China,recovering its production function and enhancing food safety standards.

Comparison and Analysis of Estimation Methods for Heavy Metal Pollution of Farmland Soils

Heavy metal pollution of farmland soils is a serious environmental problem. The accurate estimation of heavy metal pollution levels of farmland soils is very crucial for sustainable agriculture. Concentrations of heavy metal elements(As, Cd, Cr, Cu, Mn, Ni, Pb, and Zn) in farmland soils at 186 sampling sites in the Baghrash Lake Basin, NW China, were determined and analyzed based on the pollution index(Pi), the geo-accumulation index(Igeo), the enrichment factor(EF), the ecological risk index(ER), and the environmental risk index(Ier). The results of these five different estimation methods were compared and discussed. The obtained results indicated that the average concentrations of all the heavy metals in the farmland soils of the study area were lower than the Soil Environmental Quality of China(GB 15168–2018) levels, but the average concentrations of Cd, Cr, Ni, Pb, and Zn exceed the corresponding background values. Significant differences in estimation results existed between the five estimation methods. Based on the identified concentrations, the average Pi, Igeo, and EF values of the heavy metals in farmland soils decreased in the order of: Zn > Pb > Cd > Cr > Ni > Cu > As, whereas the average ER values decreased in the order of: Cd > As > Cu > Pb > Ni > Cr > Zn, and the average Ier values decreased in the order of: Cd > Cu > Zn > As = Pb > Cr > Ni. The pollution class values with different estimation methods were ranked as: Pi > Igeo = EF > ER = Ier. The obtained results suggest that the most appropriate estimation method and soil background values of farmlands should be used for better understanding the environmental quality of farmland soils. Overall, the EF and ER methods are recommended for assessing heavy metal pollution risks of farmland soils.

Study on the Major and Trace Elements in Soil of Yunnan Farmland

In order to investigate the distribution of soil available micronutrients, and provide a theoretical basis for management of fertilizing reasonably on crops, the contents of major and trace elements （P, K, Ca, Mg, Cu, Fe, Zn, and Mn） in farm- land soil collected from Yunnan Province were determined by inductively coupled plasma-mass spectrometry （ICP-MS）, the contents and distribution of major and trace elements were also studied. The results showed that the contents of available P, K were balance, available Ca, Mg were deficient, and available Cu, Fe, Zn, Mn were very plentiful. Major and trace elements distribution of different landform areas were obviously different. The contents of trace elements （Fe, Zn and Mn） of central Yunnan Red Plateau were significantly higher than those of Hengduan Mountains in western Yunnan and those of karst plateau in eastern Yunnan. The contents of available P, K, and Ca gradually declined from west to east, while the content of available Cu rose gradually from west to east. The results are reference value to elements determination and agricultural production in farmland soils.

Study on Status quo of Nutrients in Soils of Farmlands in Gonggar County and Related Countermeasures

[Objective] The aim was to analyze nutrients distribution and proportion in soils of farmlands of Gonggar County in Tibet. [Method] According to survey of soils in Tibet, nutrients of farmlands in Gonggar County were analyzed and the countermeasures were proposed to achieve sustainable development of nutrients in soils. [Result] In Gonggar County in Tibet, farmlands with insufficient and less organic matter occupy 58.38%; farmlands with moderate contents of total N occupy 47.71%; farmlands with insufficient and less alkali-hydrolyzable nitrogen represent 82.36%; the farmlands with moderate and rich total P take up 49.40% and 21.59% ; farmlands with insufficient and less rapidly available P represent 67.33%; farmlands with richer and rich total K occupy 76.14% ; farmlands with moderate and insufficient rapidly available K represent 72.21%. [Conclusion] Based on nutrients in soils of farmlands, the countermeasures for sustainable utilization of nutrients in farmlands are proposed, including increase of organic fertilizer, soil testing and formulated fertilization and adjustment of acid-base balance.

Modeling effectiveness and identification of multi-scale objects in farmland soils with improved Yee-FDTD methods

Finite-Difference Time-Domain(FDTD)is the most popular time-domain approach in computational electromagnetics.Due to the Courant-Friedrich-Levy(CFL)condition and the perfect match layer(PML)boundary precision,FDTD cannot simulate soil medium whose surface is connected by multiple straight lines or curves(multi-scale)accurately and efficiently,which greatly limits the application of FDTD method to simulate buried objects in soils.Firstly,this study proposed the absorption boundary and adopted two typical perfect matching layers(UPML and CPML)to compare their absorption effects,and then using the three forms of improved Yee-FDTD algorithm,alternating-direction implicit(ADI-FDTD),unconditionally stable(US-FDTD)and hybrid implicit explicit finite time-domain(HIE-FDTD)to divide and contrast the boundary model effects.It showed that the HIE-FDTD was suitable for inversion of multi-scale structure object modeling,while ADI-FDTD and US-FDTD were ideal for single-boundary objects in both uniaxial perfectly matched layer(UMPL)and convolution perfectly matched layer(CPML)finite element space.After that,all the models were tested by computer performance for their simulated efficiency.When simulating single boundary objects,UPML-US-FDTD and ADI-FDTD could achieve the ideal results,and in the boundary inversion of multi-scale objects,HIE-FDTD modeling results and efficiency were the best.Test modeling speeds of CPML-HIE-FDTD were compared with three kinds of waveform sources,Ricker,Blackman-Harris and Gaussian.Finally,under the computer condition in which the CPU was i5-8250,the HIE-FDTD model still had better performance than the traditional Yee-FDTD forward modeling algorithm.For modeling multi-scale objects in farmland soils,the methods used CPML combined with the HIE-FDTD were the most efficient and accurate ways.This study can solve the problem that the traditional FDTD algorithm cannot construct non-mesh objects by utilizing the diversity characteristics of Yee cell elements.

Heavy metal pollution characteristics and health evaluation of farmland soil in a gold mine slag area of Luoyang in China

The characteristics of eight heavy metals(lead,zinc,copper,nickel,chromium,cadmium,mercury and arsenic)in the surface soil of the historical slag area of the Au ore dressing plant in the South-West of Luoyang City were investigated and evaluated in terms of a pollution index,potential ecological hazards and health risks.The results showed that the average amounts of the heavy metals Pb,Zn and As in the soils of plots S3,S5,S7,S12 and S18 exceeded the soil pollution risk screening values.The Mero comprehensive pollution index in plots S7,S12 and S18 was greater than 3,indicating severe pollution.The severe pollution plot integrated the potential ecological risk index(RI)of each sampling point,which was in the order of RI_(S12)>RI_(S18)>RI_(S7)>RI_(S5)>RI_(S3).Among the heavy metals,Cd poses the greatest threat to ecological and human health.The effects of heavy metals in soil on the single non-carcinogenic health risk index(HQ)and the non-carcinogenic total risk index through three exposure pathways were in the order of HQ_(Hg)<HQ_(Cu)<HQ_(Ni)<HQ_(Zn)<HQ_(Cd)<HQ_(Cr)<HQ_(Pb)<HQ_(As)<1,which meant that the adult and child total carcinogenic risk(TCR)and individual carcinogenic health risk indices CRAs and CRCd were above the maximum acceptable human health level recommended by the USEPA(10^(-6)).TCRAs and TCRCd accounted for 75.65%and 23.94%of the adult TCR,respectively.TCR^(As) and TCR^(Cd) accounted for 75.93%and 23.97%of the child TCR,respectively.Overall,the TCR of children was greater than that of adults.In summary,the soil in the historical slag area of the Au ore dressing plant constitutes a serious threat to the surrounding ecological environment and to residents.

Relationship between soil surface roughness and hydraulic roughness coefficient on sloping farmland

The soil surface roughness and hydraulic roughness coefficient are important hydraulic resistance characteristic parameters. Precisely estimating the hydraulic roughness coefficient is important to understanding mechanisms of overland flow. Four tillage practices, including cropland raking, artificial hoeing, artificial digging, and straight slopes, were considered based on the local agricultural conditions to simulate different values of soil surface roughness in the Loess Plateau. The objective of this study was to investigate the relationship between the soil surface roughness and hydraulic roughness coefficient on sloping farmland using artificial rainfall simulation. On a slope with a gradient of 10°, a significant logarithmic function was developed between the soil surface roughness and Manning＇s roughness coefficient, and an exponential function was derived to describe the relationship between the soil surface roughness and Reynolds number. On the slope with a gradient of 15°, a significant power function was developed to reflect the relationship between the soil surface roughness and Manning＇s roughness coefficient, and a linear function was derived to relate the soil surface roughness to the Reynolds number. These findings can provide alternative ways to estimate the hydraulic roughness coefficient for different types of soil surface roughness.

Investigations on Nitrate Pollution of Soil, Groundwater and Vegetable from Three Typical Farmlands in Beijing Region, China

The aim of this study was to determine the nitrate pollution status of soil, groundwater, and vegetable from three typical farmlands （croplands, vegetable fields, and orchards） in Beijing region. During the investigation, hundreds of the soil, groundwater, and vegetable samples from three typical farmlands were collected and analyzed. In addition, attributes of all samples were recorded for data analysis. The results showed that nitrate was substantially accumulated in soil profiles, while the soil nitrate concentrations of vegetable fields and orchards were higher than those of croplands. Nitrate concentration in 0-30 cm soil of vegetable field and orchard were 3.8 and 1.2 times of that of cropland, respectively. Nitrate content of groundwater in vegetable field was 13.8 mg L-1 （with the over-standard ratio 44.8%）, which was 2.8 folds of that in cropland. Nitrate concentration of groundwater under orchard was 9.3 mg L-1 （with the over-standard ratio 23.5%）, which was 1.9 folds of that in cropland. High concentrations of the nitrate in vegetables were detected, particularly green leafy vegetables ranked first with 2 685.5 mg kg-1, followed by rhizome vegetables, cabbages, and fruit vegetables. The nitrate over-standard ratios of rhizome vegetables, green leafy vegetables, fruit vegetables, and cabbages were 80.9, 37.9, 29.7, and 2.2%, respectively. The results revealed that the high nitrate concentrations of soil, vegetable, and groundwater might result from the high fertilization dose.

Effect of chemical and organic fertilization on soil carbon and nitrogen accumulation in a newly cultivated farmland

Increased food demand from the rapidly growing human population has caused intensive land transition from desert to farmland in arid regions of northwest China. In this developing ecosystem, the optimized fertilization strategies are becoming an urgent need for sustainable crop productivity, efficient resources use, together with the delivery of ecosystems services including soil carbon（C） and nitrogen（N） accumulation. Through a 7-year field experiment with 9 fertilization treatments in a newly cultivated farmland, we tested whether different fertilizations had significant influences on soil C and N accumulation in this developing ecosystem, and also investigated possible mechanisms for this influence. The results showed that applying organic manure in cultivated farmland significantly increased the soil C and N accumulation rates; this influence was greater when it was combined with chemical fertilizer, accumulating 2.01 t C and 0.11 t N ha^（–1） yr^（–1） in the most successful fertilization treatment. These high rates of C and N accumulation were found associated with increased input of C and N, although the relationship between the N accumulation rate and N input was not significant. The improved soil physical properties was observed under only organic manure and integrated fertilization treatments, and the significant relationship between soil C or N and soil physical properties were also found in this study. The results suggest that in newly cultivated farmland, long term organic manure and integrated fertilization can yield significant benefits for soil C and N accumulation, and deliver additional influence on physical properties.

Losses of Soil Organic Carbon and Nitrogen and Their Mechanisms in the Desertification Process of Sandy Farmlands inHorqin Sandy Land

Soil organic carbon(SOC)and total nitrogen(N)concentrations from bulk soils and soil particle size fractions in the different extent of desertified farmlands(potential, light, medium, severe, and most severe desertified farmlands)were examined to quantitatively elucidate losses of carbon and nitrogen and its mechanisms in the desertification process. Particle size fractions(2 -0.1 mm, 0.1 - 0.05 mm, <0.05 mm)were obtained by granulometric wet sieving from 30 sandy soils(0 - 15cm depth)of different desertified extent. It was shown that soil physical stability index(St)in most severe desertified farmlands was 5 -7% and St in other farmlands was less than 5 %, which contributed to very low soil organic matter content. This was the intrinsic cause that sandy farmlands in Horqin sandy land was subject to risk of desertification. Desertification resulted in considerable losses of SOC and N. Regression analysis indicated that SOC and N content reduced 0.169 g kg-1 and 0.0215 g kg-1 respectively with one percent loss of soil silt and clay content. Losses of SOC and N were mostly the removal of fine particle size fractions(silt and clay, and a less extent very fine sand)from the farmlands by wind erosion, which were rich in organic matter and nutrients, as well as the depletion of organic C and N associated with coarse particles(>0. 05 mm)in desertification process. The concentrations of C and N associated with sand(2 - 0.1 mm and 0.1 - 0.05 mm)significantly decreased with increase of desertified extent. Silt and clay associated C and N concentrations, however, were less changed, and in contrast, were higher in soils under most severe desertified extent than in soils under potential and severe desertified extent. The percentage of distribution in sand(>0.05 mm)associated C and N significantly increased with increase of desertified extent, suggesting that stability of SOC decreased in the desertification process.

Effect of farmland shelterbelts on gully erosion in the black soil region of Northeast China

The black soil region of northeast China is one of the most important grain-producing areas in China. Increasingly severe gully erosion in this region has destroyed much farmland and reduced grain production. We analyzed SPOT5 imagery from 2007 and TM imagery from 2008 to describe the distributions of gullies and farmland shelterbelts in Kedong County and to assess the effect of farmland shelterbelts on gully erosion. The ima- gery revealed 2311 gullies with average density of 418.51 m km-2, indicating very serious gully erosion. With increasing slope gradient there was an inverse trend between gully density and shelterbelt density, indicating that farmland shelterbelts can prevent gully erosion. The defense effect of farmland shelterbelts against gullyerosion varied with distance： for distances 〈120 m, the defense effect was consistent and very strong; for distances of 120-240 m, a weak linear decrease was found in the defense effect; and for distances 〉240 m, the defense effect of the shelterbelts was significantly weaker. We recommend an optimal planting density of farmland shel- terbelts for the prevention of gully erosion at 1100-1300 m km-2.