While organic waste amendments can initially improve soil physicochemical properties, including nutritional benefits to plants and increased microorganism activity, long-term application of excessive amounts of organic wastes can cause accumulation of heavy metals (HMs). Thus, the current study examined the accumulation of HMs in agricultural soil profiles following organic waste application.
Materials and methodsThree common organic sludge, including municipal sewage sludge (MSS), industrial sewage sludge (ISS), and leather sludge (LS), were applied annually to an agricultural soil under field conditions over 7 years (1994–2000) at a rate of 25 and 50 t ha?1 year?1. Subsequently, when organic sludge amendments were ceased, the experimental plots were cultivated without any treatments for another 12 years (2001–2012) and the changes in HM concentrations along the soil depth profile were monitored together with soil pH, dissolved organic carbon (DOC), and dehydrogenase activity (DHA).
Results and discussionSignificant increases in Cu, Pb, and Zn concentrations were observed down to a depth of 80 cm in soils treated with ISS and LS, where sludge application also increased the levels of Cd, Cr, Pb, and Zn and their movement down the soil profile. However, with the exception of Cu, no significant changes in HM concentrations were observed following treatment with MSS. At a depth of 80 cm, soils which had received 25 and 50 t ha?1 LS showed, respectively, 4 and 14 times higher Cr levels than the control soil.
ConclusionsOrganic sludge induced changes in soil pH and soil DOC concentration which were the key factors influencing HM movement and accumulation following organic sludge treatment.
相似文献Based on two consecutive years of field-scale trials, under different water managements, we illustrated the persistence of remediation effect of palygorskite on a Cd-polluted rice field.
Materials and methodsThe Cd uptake by a plant, pH and Cd chemical extractability, available P/K, and extractable Zn/Cu in paddy soils were used to evaluate the influence of palygorskite on Cd immobilization and soil fertility index.
Results and discussionIn contrast to the 1st year, at 0–1.5% palygorskite applied dose in soils, 0.025 M HCl–extractable Cd in continuous flooding reduced by 12.1–19.0%, and that in wetting irrigation increased by 10.9–18.9% in the 2nd year (p?<?0.05). The toxicity characteristic leaching procedure Cd reduction of 3.0–11.4% and increase of 8.9–12.0% were obtained under above-mentioned water managements (p?<?0.05). Compared with the 1st year, at different clay additional concentrations, grain Cd in continuous flooding reduced by 7.0–11.3%, and that in wetting irrigation increased by 6.5–10.8% in the 2nd year (p?<?0.05). Although trace elements in clay treated soils declined, they had no influence on the grain yield due to a minimum value higher than the critical value of 1.5 mg kg?1 for Zn and 2.0 mg kg?1 for Cu. The available P in continuous flooding took on a maximum increase of 8.2% in the 2nd year (p?<?0.05).
ConclusionsTwo consecutive years of field-scale in situ demonstration tests revealed that continuous flooding was a preferable water management regime for Cd immobilization using palygorskite in the rice field. There were no remarkable differences in extractable Zn/Cu between 2 years.
相似文献Decarboxylation of organic anions in crop straw is recognized as one of the mechanisms for increasing pH in acidified soils. However, the effectiveness of specific compounds in alleviating soil acidification from nitrification has not been well determined. This study examined three organic anions commonly found in crop straws and their effect on soil acidity and N transformation processes following urea application to a red soil (Ferralic Cambisol).
Materials and methodsA 35-day incubation experiment was conducted using soil after receiving 26 years of two different nutrient treatments: (1) chemical nitrogen, phosphorus, and potassium fertilization (NPK, pH 4.30) and (2) NPK plus swine manure (NPKM, pH 5.88). Treatments included three rates (0.25, 0.5, and 1.0 g C kg?1) of calcium citrate, 0.5 g C kg?1 calcium oxalate, 0.5 g C kg?1 calcium malate, urea-only (control) soil, and a non-treated soil as a reference. Soil acidity, mineral N species, decarboxylation, and their correlations were determined.
Results and discussionAll three organic anions significantly increased pH in both soils and the effectiveness was positively correlated with application rate. The change in total exchangeable soil acidity was dominated by aluminum concentration in the NPK soil, but by proton concentration in the NPKM soil. At ≥?0.5 g C kg?1, the anions decreased soil exchangeable acidity by 25–68% in NPK soil and by 63–88% in NPKM soil as compared with control. Oxalate was the most effective in increasing soil pH by 0.70 and 1.31 units and reducing exchangeable acidity by 3.79 and 0.33 cmol(+) kg?1 in NPK and NPKM soils, respectively, and also resulted in the highest CO2 production rate. Addition of organic anions led to a lower nitrification rate in NPKM soil relative to the NPK soil.
ConclusionsThese results imply that crop straws rich in organic anions, especially oxalate, would have a higher potential to alleviate soil acidification.
相似文献The aim of this meta-analysis was to investigate the interactive effects of environmental and managerial factors on soil pH and crop yield related to liming across different cropping systems on a global scale.
Materials and methodsThis study examined the effects of liming rate, lime application method, and liming material type on various soil chemical properties and crop yield based on data collected from 175 published studies worldwide since 1980.
Results and discussionThe most important variables that drive changes in soil pH and crop yield were liming rate and crop species, respectively. Soil conditions, such as initial soil organic matter and soil pH, were more important for increasing soil pH in field-based experiments, while lime material type and application method were more important for improving crop yield. To effectively neutralize soil acidity, the optimum liming duration, rate, and material type were?<?3 years, 3–6 Mg ha?1, and Ca (OH)2, respectively. Averaged across different crop species, the application of CaO, CaCO3, Ca (OH)2, and CaMg (CO3)2 increased yield by 13.2, 34.3, 29.2, and 66.5%, respectively.
ConclusionsThis meta-analysis will help design liming management strategies to ameliorate soil acidity and thus improve crop yield in agroecosystems.
相似文献In the rice-wheat rotation area, Cd contamination affects food safety of rice and wheat. However, there have been conflicting results and different conclusions on the difference in Cd accumulation capacity of rice and wheat, and the factors that led to the difference were not clear.
Materials and methodsA field survey study was conducted by collecting 60 soil and grain samples in pairs during rice and wheat harvest in 30 long-term rice-wheat rotation areas with clean and mild Cd contamination in Jiangsu Province, China. The soil physicochemical properties, total Cd, soil available Cd, and grain Cd were determined, and the factors affecting Cd accumulation in rice and wheat were analyzed.
Results and discussionThe soil pH during wheat season (22 sampling points) was slightly higher than that during rice season; thus, soil available Cd in wheat was generally lower (with an average three times lower) than that in rice soil. The mean Cd content in rice grain was only half of that in wheat grain, and the Cd concentration in rice and bioconcentration factor of rice at 26 sampling points (86.7% of total samples) were lower than those of wheat, indicating that Cd accumulation capacity of wheat was stronger than that of rice. Pearson correlation coefficient and multivariate linear regression models revealed that the main factors affecting the difference of Cd accumulation in rice and wheat were soil pH and available Cd content in soil.
ConclusionsThe Cd accumulation capacity of wheat was higher than that of rice, especially in neutral and alkaline soil, and the Cd contents in rice and wheat grain depended on the soil pH and available Cd content. The food security risk of wheat was more noteworthy than rice in rice-wheat rotation area.
相似文献Being carbon-rich and porous, biochar has the potential to improve soil physical properties, so does conventional farming practice. Here, a field trial was conducted to investigate the combined effects of biochar use and farming practice on the physical properties of a salt-affected compact soil for wheat–maize rotation in the Yellow River Delta region.
Materials and methodsSalix fragilis L. was used as feedstock to produce biochar in the field via aerobic carbonization at an average temperature of 502 °C, terminated by a water mist spray, for use as a soil amendment at 0, 1, 2, and 4 g kg?1 doses (CK, T1, T2, and T3, respectively). Farming practices included rotary tillage/straw returning for wheat sowing, spring irrigation, no-tillage seeding of maize, and autumn irrigation. Both cutting ring and composite samples of the soil were collected at four stages of wheat–maize rotation (22, 238, 321, and 382 d after the benchmark date of land preparation for wheat sowing) for the determination of soil properties by established methods.
Results and discussionRotary tillage/straw returning reduced soil bulk density (BD) from 1.48 to 1.27 g cm?3 (CK) and 1.14 g cm?3 (T3) and increased saturated hydraulic conductivity (Ks) from 0.05?×?10?5 to 0.75?× 10?5 cm s?1 (CK) and 1.25?× 10?5 cm s?1 (T3). This tillage effect on BD and Ks gradually disappeared due to the disturbance from the subsequent farming practice. Biochar use lessened the disturbance. At maize harvest, BD was 1.47 (CK) vs. 1.34 g cm?3 (T3), and Ks was 0.06?×?10?5 (CK) vs. 0.28?×?10?5 cm s?1(T3); in comparison with CK, T3 increased Na+ leaching by 65%, Cl? leaching by 98%, organic carbon content by 40.3%, and water-stable aggregates (0.25–2 mm) by 38%, indicating an improvement in soil properties.
ConclusionsBiochar use and rotary tillage improved soil physical properties (BD, Ks) and favored soil aeration, water filtration, and salt leaching, which further helped the accumulation of soil organic carbon, the formation of water-stable aggregates, and the amelioration of salt-affected compact soil.
相似文献Natural organic acids, such as humic acid (HA), play crucial roles in biogeochemistry of anions and cations in soil due to their numerous functional groups on their surfaces. Selenium (Se) and cadmium (Cd) could bind strongly to HA; nevertheless, it is still unclear as to the effects of HA on Se and Cd uptake in rice which will be focused on in this paper.
Materials and methodsPot experiments were carried out at Huazhong Agricultural University, Wuhan City, Hubei Province, China. Agricultural soils were treated with different concentrations of HA (0, 4, and 8 g kg?1 soil) and Se (SeIV or SeVI) (0 and 2 mg kg?1 soil) as well as with base fertilizer 3 days prior to planting. For Cd treatment, experimental soils were treated with Cd (0 and 2 mg kg?1 soil) 1 month before sowing. For element determination, root (after DCB extraction) and shoot samples were digested with a mixed solution of HNO3-HClO4, and the Se and Cd in digest solution were measured by HG-AFS and ICP-MS, respectively. Fe, Se, and Cd in iron plaque were extracted by DCB extraction and measured by AAS, HG-AFS, and ICP-MS, respectively.
Results and discussionHA reduced Se (or Cd)-induced growth stimulation and Se and Cd uptake in rice seedlings, whereas iron plaque formation varied little with different treatments. HA inhibited SeIV (or SeVI) uptake in rice seedlings by reducing Se translocations from soil to iron plaque (or by increasing Se adsorption capacity of iron plaque and decreasing Se transport from iron plaque to root). HA reduced Cd uptake in rice seedlings by reducing Cd transport from soil to iron plaque and from iron plaque to root. Compared with single addition of SeIV or SeVI or HA, adding HA combined with SeIV or SeVI could further reduce Cd uptake in rice seedlings, whereas Se contents of aerial tissues did not change obviously.
ConclusionsHA inhibited the accumulation of Se (SeIV or SeVI) and Cd in rice seedlings; nevertheless, the mechanism was different. Compared with adding Se (or HA) alone, application of Se mixed with HA might be a more effective way to produce Se-enriched and Cd-deficient crop in Cd-contaminated soil.
相似文献This study examined the usefulness of 15N natural abundance (δ15N) with in situ core incubation to quantify the predominant N transformation processes in a natural suburban forest of subtropical Australia, which was subjected to prescribed burning.
Materials and methodsIn situ core incubation for 3 days with 20 ml water, or 160.79 ml of 60 mg L?1 NO3?-N surface application, and in situ core with 160.79 ml water but without incubation were set up in Toohey forest for sampling three times as before (once) and after (twice) a prescribed burning. The δ15N of NH4+-N and NO3?-N in the top 5 cm soil before and after the incubation, and δ15N of NO3?-N in the 5–10 cm soil before incubation were compared with each other to examine the soil N mineralisation, nitrification, denitrification, and nitrate leaching processes.
Results and discussionThe significant decrease in δ15N of NH4+-N after incubation under 20 ml water treatment was ascribed to soil N mineralisation, and the significant decrease in δ15N of NH4+-N and significant increase in δ15N of NO3?-N after incubation with elevated water and nitrate inputs were associated with N mineralisation and nitrification, respectively, 2 months after the burning. The 160.79 ml water treatment also triggered nitrification in the baseline soil cores in both samplings after the burning. Water was crucial to stimulate soil N mineralisation and nitrification, but excessive water depleted labile N pools and reduced N mineralisation and nitrification. Burning effects were hard to separate from the seasonal impacts on soil N cycling processes.
ConclusionsThe δ15N in soil mineral N pools was sensitive to indicate soil N mineralisation and nitrification processes. Soil water and labile N were determining factors for N transformations in the soil. It is suggested that δ15N combined with soil inorganic N concentrations and net N transformation rates could be used to identify primary N transformation processes. More frequent samplings would be needed to differentiate burning impacts from the seasonal impacts on soil N cycling processes.
相似文献Phosphorus (P)-containing passivators have a stabilizing effect on cadmium (Cd)-contaminated agricultural soils to be safely used, offering good potential for risk control of Cd-contaminated agricultural soils to be strictly controlled. In this study, an incubation experiment was conducted to evaluate the risk control effects of using hydroxyapatite (HAP) and monocalcium phosphate (MCP) on Cd-contaminated agricultural soils to be strictly controlled.
Materials and methodsSamples of topsoil were collected (0–20 cm) from agricultural land near a lead–zinc mine in Southwestern China containing 32.07 mg kg?1 Cd with a pH of 7.28. The amounts of passivators added were equal to approximately 3% of the soil by weight. The soil Cd content, physicochemical properties, enzyme activity, and microbial community were analyzed.
ResultsThe results showed that the application of HAP and MCP decreased the activity and mobility of Cd in soils to be strictly controlled. HAP was more effective in decreasing the exchangeable Cd (CdEx) than MCP (rate of decrease was 48.1% for HAP and 24.4% for MCP). According to the results of the geometric mean (GMean) and the integrated total enzyme activity (TEI) index, the total soil enzyme activity of the HAP treatment was higher than that of CK and MCP treatment. HAP and MCP significantly decreased the Chao and Shannon bacterial community indices and the Shannon index of the soil fungal community. HAP increased Actinobacteria abundance, which is beneficial to soil fertility enhancement and plant growth, and MCP increased Rhizobiales abundance, which promotes soil P cycling and plant growth. Primary driving factors for the changes in bacterial and fungal community composition in the stabilized soils were CEC and CdEx for bacteria and Cd bound to carbonates (CdCar) and residual Cd (CdRes) for fungi.
ConclusionsHAP is more suitable for risk control of Cd-contaminated agricultural soils to be strictly controlled than MCP from the perspective of soil Cd activity and mobility, soil enzyme activity, and diversity and composition of the soil microbial community.
相似文献This study focused on the effects and mechanisms of biochar amendment to Cd-contaminated soil on the uptake and translocation of Cd by rice under flooding conditions.
Materials and methodsPot and batch experiments were conducted using Cd-contaminated soil collected from a field near an ore mining area and a cultivar of Oryza sativa ssp. indica. Biochar derived from rice straw under anaerobic conditions at 500 °C for 2 h was mixed with the soil at the rate of 0, 2.5, and 5%.
Results and discussionThe application of 5% biochar reduced CaCl2-extractable soil Cd by 34% but increased Cd concentration in brown rice by 451%. Biochar amendment decreased water-soluble Fe2+ in soils and formation of Fe plaques on roots and weakened the Fe2+-Cd2+ competition at adsorption sites on the root surface. Biochar increased water-soluble Cd in the soil and consequently Cd uptake by rice roots by releasing water-soluble Cl?. Biochar application also reduced the proportion of cell wall-bound Cd in the root, which caused easier Cd translocation from the cortex to the stele in the root and up to the shoot.
ConclusionsRice straw biochar (with high concentration of water-soluble Cl?) reduced CaCl2-extractable soil Cd but increased Cd concentration in rice under flooding condition.
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