Effect of Initial Concentration on Adsorption-Desorption Characteristics and Desorption Hysteresis of Hexachlorobenzene in Soils

Adsorption and desorption are important processes that influence the transport, transformation, and bioavailability of hexachlorobenzene (HCB) in soils. To examine the adsorption-desorption characteristics of HCB, equilibrium batch experiments were carried out using two soils (red soil and paddy soil) with different initial HCB concentrations (0.25, 0.50, 0.75, 1.00, 1.50, 2.50, 3.50, and 5.00 mg L-1 ) by using 0.01 mol L-1 calcium chloride as the background solution. The successive desorption experiments (48, 96, 144, 192, and 240 h) were conducted after each adsorption equilibrium experiment. The results revealed that adsorption and desorption isotherms of HCB on two soils were nonlinear, which can be best described by the Freundlich equation with the square of the correlation coefficient (r 2 ) ranging from 0.97 to 0.99. Desorption of HCB from the two soils exhibited hysteresis at all HCB concentrations because the Freundlich desorption coefficients were always higher than the Freundlich adsorption coefficients. The hysteretic effect was enhanced with increasing initial HCB concentration, and positive hysteresis was observed at different concentrations.

Effect of Land Cultivation on Soil Nutrient Sedimentation in Water at Southern China

Soil erosion associated with land cultivation exerts a great impact on ecological environment.Such an impact is specific of land,crop,tillage,management and so on.This study aimed to investigate the effects of crop cultivation on water quality by comparing nutrient distribution in the sediment at Southern China.Two sedimentation sites adjacent to the uncultivated(S1)and cultivated upland(S2)were selected and samples were analyzed.Results showed that soil pH decreased with the increasing depth above 20 cm and then kept relatively stable of the both sediments.Soil organic matter,nitrogen and phosphorus contents decreased with the increasing depth.There was no significant difference between two sediments in organic matter and nitrogen contents,but the total phosphorus and extractable phosphorus contents in S2 were much higher than that in S1.The data indicated that soil eroded from S2 could possess much high potential to deteriorate water quality.Nutrient sedimentation can reflect the history of soil erosion and provide useful information for sustainable soil management and water conservation through improving cultivation and tillage measures.

Determination of forest soil organic nitrogen determination using technique of X-ray absorption near-edge structure

The forest soil organic N was investigated using N K-edge X-ray absorption near-edge structure （XANES） to gain an insight into the relationship between N speciation and its transformation in quantity. Soil samples were collected from spruce, hemlock and pine forests in central Taiwan. Results showed that various organic N types could be revealed by XANES spectra. Amide and pyrrolic N are the major parts of the composition in the humic substance, soluble organic nitrogen and original soils. The relative distribution of N speciation differed in treatments and vegetations samples. The spruce had a significant difference from the hemlock in soluble organic nitrogen （SON） spectra at 402.3 eV energy peak. In the A-horizon soils, the relative amount of pyridinic N was much higher than that in the O-horizon soils, indicating N transformation in quantity in the mineral horizon was different from that in the organic horizon, which might play an important role in N cycling of forest ecosystems.

Effect of cultivation time on soil heavy metal accumulation and bioavailability in Phyllostachys praecox stands

Phyllostachys praecox is a bamboo species cultivated for edible shoots under intensive management.However,the potential pollution risk of heavy metals in bamboo soils is not clear under the intensive management for a long term.The objective of this study was to evaluate the effect of cultivation time on soil heavy metal accumulation and bioavailability in bamboo stands subjected to intensive management.Soil samples were collected from a chronosequence of bamboo stands which had been cultivated for 0,1,2,4,8,and 10 years in Lin’an,Zhejiang Province of China.Eight heavy metals(Cu,Zn,Pb,Ni,Cr,Cd,As,and Hg)present in the soil were selected,and their potential pollution risk was evaluated by chemical speciation analysis.Possible heavy metal sources were explored using multivariate and cluster analysis.Our results showed that Zn,Cu,Hg,and Cd contents in the soil increased with the cultivation time,while Ni,Cr,Pb,and As levels were similar among all stands.Furthermore,the bioavailabilities of all analyzed heavy metals increased with the cultivation time.Multivariate and cluster analysis showed that sources of Ni,Cr,Pb,and As were likely lithogenic in origin,whereas input of Zn,Cu,Hg,and Cd was mainly due to cultivation practices.Current bamboo management strategies raised the potential risks of heavy metal pollution in bamboo shoots in the long term.Soil acidification in P.praecox stands induced by intensive cultivation should be controlled since it stimulated and improved the bioavailability of heavy metals.Appropriate management strategies should thus be adopted to ensure safe and sustainable production of bamboo shoots.

Nitrogen Release Characteristics of a Bag Controlled Release Fertilizer

Slow release fertilizers are designed to enhance crop yield and minimizing the loss of nitrogen(N)to environment.However,N release in leaching and loss in ammonia emission from bag controlled release fertilizers have not been previously evaluated under the standardized conditions in soil.Accordingly,a laboratory study was conducted to evaluate the characteristics of N release from a bag controlled fertilizer with 1,3,5 and 7 rows of hole(B-1,B-3,B-5,B-7)and a kraft bag without hole(B-W).The results showed that the amount of N leaching of B-1,B-3,B-5,B-7 and B-W were significantly lower than urea fertilizer without bag(U).The maximum N release from the fertilizers followed the order:U(83.16%)>B-7(54.61%)>B-5(54.02%)>B-W(51.51%)>B-3(48.87%)>B-1(38.60%)during the experimentation.Compared with U treatment,ammonia volatilization losses were significantly decreased by B-1,B-3,B-5,B-7 and B-W treatments.Based on N release and loss,a suitable bag with holes should be considered in practice when using the bag controlled fertilizer to meet an environment good objective.The evaluation method merits further study combined with field experiment.

Effects of biochar amendments on soil water retention characteristics of red soil at south China

Biochar has been extensively used for the improvement of soil water retention.However,the effects of various biochars were not well determined.The objectives of this study were to investigate the effects of three biochars[biochars made from bamboo(Bambusaceae),rice straw(Oryza sativa),and tobacco stem(Nicotiana L.)]on soil physical properties and the water retention characteristics of red soil at southeast China.The air-dried soil samples were mixed with ratios of 2%,5%,and 10%(w w^(−1))BC(bamboo biochar),RC(rice straw biochar),and TC(tobacco biochar),respectively,and evaluated for changes in soil bulk density(BD),soil saturated water content,field capacity,capillary porosity and soil hygroscopic coefficient.The results showed that BD decreased significantly with the application of the three types of biochar,total soil porosity and capillary porosity increased with the increase of the biochar ratio.The soil hygroscopic coefficient,wilting moisture capacity,saturated water content,and field capacity were significantly affected by the application of the three types of biochar.Compared with the other two treatments,the BC showed the best effects on soil water characteristics.BC treatments with addition ratios of 2%,5%,and 10%significantly decreased BD by 6.55%,18.03%,and 36.07%,respectively.Moreover,saturated water content and field capacity were increased by BC.BC treatments significantly increased the readily available water by 32.65%,42.49%,and 50.01%,respectively.However,the increased non-readily available water induced by the high ratio of biochar addition was not easily utilized by plants.Our results suggested that the biochar amendment can improve soil structure,decrease soil BD,boost soil porosity and capillary porosity,and increase soil moisture constant,and 2-5% of BC was recommended in the field condition.

Biochar and organic substitution improved net ecosystem economic benefit in intensive vegetable production

Biochar amendment and substituting chemical fertilizers with organic manure(organic substitution)have been widely reported to increase crop production and decrease reactive nitrogen(Nr)loss including nitrous oxide(N_(2)O),nitric oxide(NO),and ammonia(NH3)emissions,and N runoff and leaching.However,few comprehensive evalua-tions have been performed on the environmental and economic aspects of biochar amendment or organic sub-stitution.Here,we studied the comprehensive effects of biochar amendment,organic substitution,and biochar amendment combined with organic substitution on crop production,Nr loss,and net ecosystem economic benefit(NEEB)in intensive vegetable production by integrating life-cycle assessment for Nr footprints,empirical models for NH3 volatilization and N runoff and leaching derived from peer-reviewed publications and validated by the current measurements and direct field measurement for N_(2)O and NO emissions during 5 consecutive years of vegetable crop rotations.Five fertilization treatments were applied(SN:synthetic fertilizer application;SNB:SN plus 20 t ha^(−1)biochar amendment;SNM:substituting 50%of chemical N fertilizer with organic manure;SNMB:SNM plus 20 t ha^(−1)biochar amendment;and CK:no fertilizer or biochar addition).Compared with the SN,the SNB increased vegetable yield(28.4%,p<0.05;interannually varying from−10 to 74.9%)and nitrogen use efficiency(29.2%,interannually varying from−39.7 to 150.4%),and decreased field Nr loss(45.4%,p<0.01;interannually varying from−40.3 to 78.4%),and thus improved NEEB by 7.1%;meanwhile,the SNM increased vegetable yield(11.6%,interannually varying from−5.4 to 27.1%)and nitrogen use efficiency(45.7%,p<0.05;interannually varying from 2.3 to 154%),reduced field Nr loss(34.9%,p<0.01;interannually varying from 8.4-39.0%),and thus improved NEEB by 17.8%(p<0.05)compared to the SN,being 56.0×10^(3)Chinese Yuan(CNY)ha^(−1)crop^(−1).Due to the high foreground Nr loss during organic manure production and high input costs of biochar production,the SNMB decreased the NEEB by 8.0%as compared to the SN.Moreover,the SNB and SNM improved vegetable qualities by increasing protein,soluble sugar,and vitamin C contents while decreasing nitrate content(p<0.05).Therefore,single application of biochar amendment or organic substitution would achieve better NEEB and product quality in vegetable production.