Most metal(loid)s do not undergo degradation and persist long after their introduction into the environment. With greater public awareness of the implications of contaminated soils on human and animal health, the development of technologies for the management (remediation) of contaminated sites has attracted increasing interest amongst scientists and engineers. Remediation options for ensuring a diffuse distribution of metal(loid)s generally include amelioration of soils to minimise metal(loid) bioavailability. This can be accomplished through chemical and biological immobilisation of metal(loid)s using a range of inorganic compounds, such as lime and phosphate (P) compounds, as well as organic compounds. More localised metal(loid) contamination can be remediated by increasing bioavailability through mobilisation processes such as bioremediation (including phytoremediation) and chemical washing. A number of amendments are used either to mobilise or immobilise heavy metal(loid)s in soils. The basic principle underlying mobilisation techniques is the release of metal(loid)s into soil solution, which are subsequently removed by soil washing or uptake by higher plants. In contrast, immobilisation techniques entail the removal of metal(loid)s from soil solution either through adsorption, complexation or precipitation reactions, thereby rendering the metal(loid)s less bioavailable for plant uptake and leaching into groundwater. In this paper, the role of various inorganic and organic soil amendments in controlling the interactions of metal(loid)s and their subsequent (im)mobilisation in soils is examined with regard to the remediation of metal(loid)-contaminated soils.

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Food insecurity, affecting more than 1 billion people worldwide, and the risks associated with the projected climate change are among the serious global issues that must be addressed. The terrestrial biosphere in general and world soils in particular, have been sources of greenhouse gases throughout human history, but especially since the beginning of settled agriculture. Most agricultural soils have lost 25% to 75% of their original soil organic carbon (SOC) pool, with a technical sink capacity of 30 to 40Mg C/ha over a 40- to 50-year period. The magnitude of C depletion is exacerbated by soil degradation caused by erosion and other physical (compaction, drought) and chemical (salinization, acidification, nutrient imbalance) processes. Conversion to restorative land use and adoption of recommended management practices that create positive C and nutrient (N, S, P) budgets would enhance the SOC pool while also improving soil quality and the agronomic productivity. Estimates of the technical potential of C storage in the terrestrial biosphere correspond to a reduction in atmospheric CO_2 in the range of 50 to 100ppm over about 100 years.

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The effects of irrigation over a two-year period with shallow groundwater were evaluated for two typical areas of the Great Hungarian Plain. The site at Kunmadaras has light-textured soil, and the site at Karcag has heavy-textured soil. No adverse effects of irrigation with groundwater were evident at the Kunmadaras site with light-textured soil. An increase in subsoil alkalinity but not soil salinity was found at the Karcag site with heavy-textured soil.

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In Japan, rapid industrialization during the 1960s brought about dangerous pollution of soil by heavy metals such as cadmium (Cd). Similar heavy metal pollution may occur in other Asian countries that are undergoing rapid development and economic growth, which suggests that these countries will need to regulate heavy metals and institute countermeasures against heavy metal pollution. In this paper we present an overview of soil contamination by heavy metals across Asia, including Japan, paying particular attention to Cd contamination. We present standard values for heavy metal pollution set by various Asian countries. We also describe sources of heavy metal pollution in agricultural soils and summarize the chemical forms of heavy metals in soils. In addition, we discuss two promising soil chemistry based remediation methods for minimizing the risk of Cd contamination: (1) water management practices to reduce the bioavailability of soil Cd to rice plants and (2) remediation of Cd-contaminated soil by soil washing with solutions of chemicals such as iron salts.

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Field measurements of soil respiration were carried out under various bioclimatic conditions in Eurasia. The data were simultaneously analyzed to identify factors that control the in situ soil respiration and its temperature and moisture dependence, together with the laboratory incubation data to support the analysis of field data. We obtained the following results: 1) In the stepwise regression analysis for estimating the in situ total soil respiration and microbial soil respiration using soil temperature and moisture as explanatory variables, activation energy (E), which is a temperature-dependent factor, was preferentially selected in the temperate plots, whereas the coefficient for moisture dependence (b) was primarily selected for the tropical plots. 2) Both the incubation and field experiments suggested that E was higher in the tropical zone than in the temperate zones; however, there was some uncertainty in the microbial soil respiration determined in the field. Therefore, we speculate that the direct influence of climatic change (i.e., global warming) on the acceleration of soil organic matter (SOM) decomposition and the accompanying decrease in its stock would be more conspicuous in the tropics than in other zones. 3) The moisture coefficient b and decomposition rate constant k are often higher in cropland than forest or grassland. The conversion of land-use from natural vegetation to cropland can, therefore, accelerate SOM decomposition, owing to the increase in the decomposition rate constant in addition to the decrease in litter incorporation into the soil after reclamation. 4) A close relationship was found between annual microbial respiration (AMR) and annual total soil respiration (ATR): AMR=0.550(ATR)-0.015; (R^2=0.81^<**>, n=19). That is, approximately 55% of the total soil respiration originates from the activity of soil microbes and the remaining 45% from plant roots. 5) Positive correlation was found between the decomposition rate constant k determined from the incubation experiment and that based on field measurements. The laboratory incubation experiment, therefore, was demonstrated to be useful for simulating the in situ dynamics of SOM and analyzing the temperature and moisture dependence of the SOM dynamics.

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Phosphate compounds have been used for the immobilization of heavy metals in contaminated environments. In this study, phosphate-solubilizing bacteria (PSB) were isolated from phosphate-amended and lead (Pb)-contaminated soils, and their effects on phosphate-induced immobilization of Pb were examined. Two isolated PSB strains, CS2-B1 and SM1-B1, which were putatively identified as Pantoea sp. and Enterobacter sp., respectively, were able to solubilize phosphorous (P) from insoluble P sources through the release of organic acids. Strains CS2-B1 and SM1-B1 solubilized 479mg/L and 293mg/L, respectively, of P from tricalcium phosphate. The addition of either CS2-B1 or SM1-B1 and various P amendments into Pb-contaminated soil reduced the NH_4NO_3-extractable Pb concentration, with a 51% increase in the immobilization of Pb observed in rock phosphate-amended soil containing SM1-Blover control soil lacking added PSB. This study indicates that PSB increase the solubility of P in soil, thereby leading to effective immobilization of Pb in contaminated soils.

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The Rothamsted carbon (RothC) model, which is one of leading soil organic matter (SOM) models, was validated against data collected in long-term field experiments in Japan and Thailand. The unmodified model simulated well the changes in soil organic carbon (SOC) with time in Japanese non-volcanic soils. For Andisols and paddy soils, however, the model required modifications taking into account the unique SOC dynamics of these soils. With respect to tropical soils in Thailand, the model performed well for plots with low organic matter inputs, but poorly for plots with high organic matter inputs.

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The phytoavailability of cadmium (Cd), lead (Pb) and Zinc (Zn) in soils from Bangladesh was assessed. The uptake by Ipomea aquatica and Oryza sativa was measured and a range of extractants tested on soils and plant tissue samples. Extractants tested were distilled H_2O, 1M NH_4Cl, 0.01M CaCl_2, 0.005M diethylenetriamine pentaacetic acid (DTPA), 0.1M ethylenediamine tetraacetic acid (EDTA), 0.1M HCl and 1M HCl. The extractability of metals varied depending on the metal species, the crop and the extractant used. The best extractant was 1M HCl, which extracted the highest amount of heavy metals and correlated most strongly with plant uptake measures. The use of 1M HCl is therefore recommended for first-level screening of soil contaminated with heavy metals, followed by 0.1M HCl as the second best choice if only one extractant is to be used. Regardless of the soils and the extractants used, the relative extractability was higher for Pb compared with Cd and Zn. Sequential extraction showed that Cd was associated mostly with the 1M NH_4Cl extractable fraction, while Pb and Zn were associated with the 0.005M DTPA, 0.1M EDTA, 0.1M HCl and 1M HCl fractions in most cases. The fractions of metals extracted varied widely using the sequential extraction procedure compared to single extractions for all soil types.

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Salinity severely constrains the expansion of cultivated areas and diminishes the productivity of rice lands in major irrigated paddy fields in the inland dry zone and coastal areas of Sri Lanka. The Angithathmkulam yaya is situated in the dry zone of Sri Lanka and is strongly affected by high salinity in paddy fields. As a result, rice cultivation is extremely difficult. Various technologies namely, preparation of drainage canals, deep plowing, land leveling, application of organic manure and maintenance of water level were implemented in paddy fields to reduce salinity, and salt tolerant rice varieties (Bg 5-110, Bg 11-139, Bg 4-91, At 354) as well as salt-sensitive variety (Bg 352) were examined to study their performance. In situ electrical conductivity was determined throughout the growing season, and Ca, Mg and Na contents in the soil were determined at planting and harvesting. It was revealed that paddy fields in Angiththamkulam yaya are mainly affected by salinity due to Na, Mg and Ca salts. Na, Ca and Mg contents of >800, >700 and >400mg kg^<-1>, respectively, were much higher than that required for normal growth of rice. Management practices reduced the Na and Mg contents resulting in a grain yield of 3t ha^<-1> from Bg 352, the salt-sensitive variety. The salt-tolerant rice variety Bg 11-139 recorded the highest yield of 7.0t ha^<-1> followed by Bg 5-110 and Bg 4-91, which produced yields of 6.4 and 6.1t ha^<-1>, respectively. These results suggest that adopting suitable management practices along with salt-tolerant rice varieties can potentially improve the productivity of saline paddy fields.

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We investigated the effects of nitrogen fertilizer, pH, and electrical conductivity (EC) on cadmium (Cd) solubility in soil solution. Water extracts of soils with added urea as a nitrogen source (soil(+)N), as well as soils with no additional N source (soil(-)N), were obtained at various times over the course of a 60 day incubation period. The EC (W-EC), pH (W-pH), and concentrations of NO_3^- (W-NO_3^-), SO_4^<2-> (W-SO_4^<2->), Cl^- (W-Cl^-), and Cd (W-Cd) of the water extracts were analyzed. W-Cd and W-NO_3^- in soil(+)N rapidly increased between day 0 and day 7 and then slowly increased until the end of the incubation. Simultaneously, the pH decreased rapidly during the first 7 days and then decreased slowly. For soil(-)N, W-EC increased slowly and W-pH decreased slowly, and the rates of change were stable over the entire incubation period. Similar trends were observed for W-NO_3^-. These results indicate that the changes in EC and pH could be attributed to the nitrification of urea and soil organic matter, which in turn increased the W-Cd (i.e., increased Cd desorption from the soil). In addition, we carried out multiple linear regression analysis (n=30) of W-Cd, W-pH, and W-EC. This analysis indicated that the partial regression coefficients for W-pH and W-EC on W-Cd were -0.561 and 0.774, respectively, and that W-pH and W-EC together were sufficient to explain the solubility of Cd in the soil (R^2=0.851).

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Escalating intensity of rice cultivation has increased the burden on to the land in Indonesia through massive additions of chemical fertilizers and pesticides. To examine the long-term effects of intensive rice cultivation on the heavy metal content in sawah soil, a comparative study was conducted in Java, Indonesia. The term sawah refers to leveled and bounded rice fields with inlets and outlets for irrigation and drainage. Soil samples collected in 1970 and new samples from the same sites or close to the original sites were analyzed and compared. For the 40 sites studied, the topsoil layer had increased mean levels of several extractable heavy metals. Lead (Pb) increased from 6.02 to 8.67ppm (65.5%), boron (B) from 5.92 to 7.01ppm (18.5%), cadmium (Cd) from 1.00 to 1.41ppm (42.1%), cobalt (Co) from 1.82 to 2.24ppm (28.6%), copper (Cu) from 7.51 to 8.57ppm (18.0%), manganese (Mn) from 122.10 to 133.24ppm (9.8%) and zinc (Zn) from 5.64 to 7.58ppm (39.5%). The change in the average content of these heavy metals throughout the soil profile was smaller than that in the topsoil layer. Iron (Fe) was the only parameter that decreased over the study period. In the topsoil layer, Fe decline from 175.54 to 149.05ppm (14.0%), while throughout the soil profile it decreased from 158.89 to 96.44ppm (9.9%). The changes in extractable heavy metal content are strongly related to chemical fertilizer application and the increase in cultivation intensity. The initial content for all heavy metals examined was higher at seedfarm sites than at non-seedfarm site, because rice was planted at a higher cultivation index and chemical fertilizers were applied according to government recommendations at seedfarm sites. At non-seedfarm sites, on the other hand, rice and upland crops were planted in various rotation patterns with regular use of manure and low doses of chemical fertilizers. In 2003, both sites had equal cultivation indexes; thus, the changes in cultivation intensity at non-seedfarms were greater than at seedfarms over the study period. This resulted in a similar percentage change in the heavy metal content in this soil. Over the study period, the Pb content at seedfarms and non-seedfarms changed by 50.6% and 80.7%, respectively, while changes at seedfarm and non-seedfarm sites for other heavy metals were 20.1% and 17.3% for B; 43.4% and 42.7% for Cd; 27.0% and 22.9% for Co; 17.3% and 18.0% for Cu; -13.8% and 14.0% for Fe; 11.3% and 9.1% for Mn and 27.2% and 47.0% for Zn, respectively. The application of manure might be the main contributor to the large gap between the changes in Pb and Zn content at seedfarm and non-seedfarm sites.

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Trace element contamination of the soils at shooting ranges has become a major environmental concern in the Republic of Korea. This study was carried out to find out the distribution, fraction and species of Cd, Cu, Pb and Zn in soils from two artillery ranges, AA and BB, in Gyeonggi Province in Korea to ascertain the level of heavy metal contamination at these sites. Eight soil samples from each shooting range were selected based on the 0.1N HCl extractable portion of Cd (for AA) and Cu (for BB). Levels of Cd, Cu, Pb and Zn in the soil samples were analyzed for total as well as 0.1N HCl extractable contents. The Cd content of the soils from the range AA, determined by sequential fractionation was distributed in the order of sulfide/residue>carbonate>organically bound>exchangeable&cong;adsorbed&cong;water soluble, whereas from the range BB, the distribution was carbonate>sulfide/residue>adsorbed>organically bound>water soluble&cong;exchangeable. Chemical speciation analysis of the soil samples showed that trace elements were distributed as various species depending upon soil pH.

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In the Sahel region of West Africa, wind erosion can affect the soil organic carbon (SOC) level through the transport of soil organic matter (SOM). Coarse organic matter (COM) is the preferentially blown fraction of SOM, which was defined in this study as free organic debris >200μm in diameter. Considering the lack of a reliable method for determining the amount of COM transported by wind, an Aeolian Materials Sampler (AMS) was designed to be used with a Big Spring Number Eight (BSNE) sampler. The performance of the AMS in determining the amount of COM transported was verified by a wind tunnel experiment and a field experiment. The wind tunnel experiment showed that the AMS accurately estimated the COM mass flux at the height of 0-0.05m using wind data and some simple equation. The field experiment showed that the COM loss from the cultivated field calculated using the conventional method (employing only the BSNE sampler) for estimating the amount of soil particles transported was not consistent with the actual value (Q value=1.25±0.23 on April 13; if Q is close to 1, it indicates that the estimated COM loss agreed with the actual value). The estimated COM loss using a combination of the AMS and BSNE samplers (new method) agreed with the actual value (Q value=1.12±0.21 on April 13). These data support the conclusion that the AMS can be used to determine the amount of COM transported during wind erosion events in the Sahel.

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To understand and estimate soil organic carbon (SOC) sequestration and depletion potentials in humid (monsoon) Asia, it is necessary that factors controlling the SOC pools with different turnover rates be determined. Eighty-nine surface soil samples were collected in Thailand, Indonesia and Japan from cropland and forest ecosystems. The SOC was fractionated to two pools: potentially mineralizable organic carbon (PMC) and recalcitrant organic carbon (ROC). The PMC for the soils was determined by fitting models to the cumulative curves of CO_2 released during incubation of the fresh soils under constant temperature and moisture conditions. The ROC was determined by subtracting PMC from total carbon (TC). The soil and meteorological properties were divided into five factors using principal component analysis: "light fraction (LF)", "amorphous", "clay", "humid and warm" and "carbon to nitrogen ratio (C:N)". Using multiple regression analysis and a stepwise method, equations were determined that could be used to estimate PMC and ROC using the five identified factors as follows: [numerical formula] PMC was well estimated by the LF and clay factors. This suggests that both the clay-associated organic matter as well as the LF are partially labile in nature. Major factors controlling ROC were LF organic matter, amorphous materials and clay content, suggesting the importance of parent materials in estimating the amount of recalcitrant organic matter in humid Asia.

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