[Decomposition dynamics and driving factors of manure in reclaimed soils in coal mining area]. / ç ¤çŸ¿åŒºå¤åž¦åœŸå£¤ä¸­æœ‰æœºè‚¥çš„åˆ†è§£åŠ¨æ€åŠå ¶é©±åŠ¨å› ç´ .

Understanding the decomposition dynamics and driving factors of manure in the soil subjected to different reclaimed years could provide theoretical basis to rational utilization of manure and soil fertility improvement in coal mining area. Cattle manure and pig manure were mixed with soils subjected to different reclaimed years (one year, R1; 10 years, R10; and 30 years, R30) at the ratio of manure carbon to soil mass of 4 to 100, so as to examine manure decomposition characteristics using the nylon mesh bag (15 cm deep of soil buried) in the Shanxi coal mine reclamation area, with no manure addition as control (CK). Soil samples were collected at day 12, 23, 55, 218, 281, and 365 to measure the contents of soil manure residual, soil microbial biomass carbon (MBC), and dissolved organic carbon (DOC). The contributions of soil properties, manure properties, and hydrothermal condition to manure decomposition were quantified. The results showed that the decomposition rates of pig manure were significantly higher than cattle manure. The humification coefficient of pig manure (average 46.3%) was lower than that of cattle manure (average 71.7%). The humification coefficient of pig manure was significantly lower in the 30-year reclaimed soil (44.5%) compared to the 1-year and 10-year reclaimed soil (average 47.2%). There was no significant difference in the humification coefficient of cattle manure among the three reclaimed soils. The proportion and decomposition rate constant of labile carbon pool of pig manure and cattle manure were significantly different, with values of 52% and 26%, and 0.00085 and 0.00074 ℃-1, respectively. The positive effect of pig manure on MBC and DOC in reclaimed soil was significantly higher than that of cattle manure over 0-218 days, but no difference over 281-365 days. The magnitude of the enhancement of MBC and DOC in those three reclaimed soils after manure amendments showed a similar trend of R1 >R10 ≈ R30. Results of variance partitioning analysis showed that manure decomposition was mainly controlled by manure properties (17.9%) when considering soil properties, manure properties, and hydrothermal condition. In conclusion, the decomposition of pig manure but not cattle manure was regulated by reclamation year. Cattle manure, with higher humification coefficient than pig manure, was recommended for reclaimed mining area to improve soil fertility.

[Distribution and enrichment characteristics of organic carbon and total nitrogen in mollisols under long-term fertilization].

The characteristics and changes of soil organic carbon (SOC) and total nitrogen (TN) in different size particles of soil under different agricultural practices are the basis for better understanding soil carbon sequestration of mollisols. Based on a 31-year long-term field experiment located at the Heilongjiang Academy of Agricultural Sciences (Harbin) , soil samples under six treatments were separated by size-fractionation method to explore changes and distribution of SOC and TN in coarse sand, fine sand, silt and clay from the top layer (0-20 cm) and subsurface layer (20-40 cm). Results showed that long-term application of manure (M) increased the percentages of SOC and TN in coarse sand and clay size fractions. In the top layer, application of nitrogen, phosphorus and potassium fertilizers combined with manure (NPKM) increased the percentages of SOC and TN in coarse sand by 191.3% and 179.3% compared with the control (CK), whereas M application increased the percentages of SOC and TN in clay by 45% and 47% respectively. For subsurface layers, the increase rates of SOC and TN in corresponding parts were lower than that in top layer. In the surface and subsurface layers, the percentages of SOC storage in silt size fraction accounted for 42%-63% and 48%-54%, TN storage accounted for 34%-59% and 41%-47%, respectively. The enrichment factors of SOC and TN in coarse sand and clay fractions of surface layers increased significantly under the treatments with manure. The SOC and TN enrichment factors were highest in the NPKM, being 2.30 and 1.88, respectively, while that in the clay fraction changed little in the subsurface layer.

[Characteristics of soil pH and exchangeable acidity in red soil profile under different vegetation types].

The characteristics of soil pH and exchangeable acidity in soil profile under different vegetation types were studied in hilly red soil regions of southern Hunan Province, China. The soil samples from red soil profiles within 0-100 cm depth at fertilized plots and unfertilized plots were collected and analyzed to understand the profile distribution of soil pH and exchangeable acidity. The results showed that, pH in 0-60 cm soil from the fertilized plots decreased as the following sequence: citrus orchard > Arachis hypogaea field > tea garden. As for exchangeable acidity content, the sequence was A. hypogaea field ≤ citrus orchard < tea garden. After tea tree and A. hypogaea were planted for long time, acidification occurred in surface soil (0-40 cm), compared with the deep soil (60-100 cm), and soil pH decreased by 0.55 and 0.17 respectively, but such changes did not occur in citrus orchard. Soil pH in 0-40 cm soil from the natural recovery vegetation unfertilized plots decreased as the following sequence: Imperata cylindrica land > Castanea mollissima garden > Pinus elliottii forest ≥ Loropetalum chinensis forest. As for exchangeable acidity content, the sequence was L cylindrica land < C. mollissima garden < L. chinensis forest ≤ P. elliottii forest. Soil pH in surface soil (0-20 cm) from natural forest plots, secondary forest and Camellia oleifera forest were significantly lower than that from P. massoniana forest, decreased by 0.34 and 0.20 respectively. For exchangeable acidity content in 0-20 cm soil from natural forest plot, P. massoniana forest and secondary forest were significantly lower than C. oleifera forest. Compared with bare land, surface soil acidification in unfertilized plots except I. cylindrica land had been accelerated, and the natural secondary forest was the most serious among them, with surface soil pH decreasing by 0.52. However, the pH increased in deep soils from unfertilized plots except natural secondary forest, and I. cylindrica land was the most obvious among them, with soil pH increasing by 0.43. The effects of fertilization and vegetation type on pH and exchangeable acidity decreased with the increasing soil depth from all plots.

[Change characteristics of rice yield and soil organic matter and nitrogen contents under various long-term fertilization regimes].

A long-term (1982-2010) field experiment was conducted in the Red Soil Experiment Station of Chinese Academy of Agricultural Sciences in Qiyang County of Hunan Province, South-central China to investigate the dynamic changes of rice yield and soil organic matter (OM) and nitrogen contents under different fertilization treatments. The treatments included NPK, NPKM (M: manure), NPM, NKM, PKM, M, and CK. Fertilization increased the soil OM, total N, and alkaline-hydrolysable N contents and the rice yield. In treatment NPKM, the rice yield across the 28 years maintained at the highest level; while in treatment NPK, the yield showed a decreasing trend, being lower than that in other fertilization treatments. In the treatments applied with manure only or in combining with chemical fertilizers, the soil OM content increased rapidly in the first 16 years, and then fluctuated around a constant level (29.42-39.32 g x kg(-1)). In the treatments of chemical fertilization, the soil OM content only had a quicker increase in the first 8 years, and then fluctuated within a relatively stable range. Fertilization with manure increased the soil OM significantly, as compared to fertilization with chemical fertilizers only. The soil total N content in all fertilization treatments showed a rapid increase in the first 8 years, and the increment was the highest in treatment NPKM. The soil alkaline-hydrolysable N content in all fertilization treatments had a slower increase in the first 12 years, with an average annual increment of 0.66-2.25 mg x kg(-1) x a(-1). In 1994-1998, the soil alkaline-hydrolysable N content in fertilization treatments had a quicker increase, with an average annual increment of 6.45-32.45 mg x kg(-1) x a(-1); but after 1998, the soil alkaline-hydrolysable N content had a slight decrease. It was concluded that organic fertilization was the key measure to stably improve the physical and chemical properties and the productivity of red paddy soils by increasing their OM and nitrogen contents, and to sustain the rice production in red soil region in subtropical China.

[Response of black soil organic carbon, nitrogen and its availability to longterm fertilization].

Based on the long-term fertilization experiments, effects of various fertilization practices on the soil organic carbon (SOC) and total nitrogen (TN) in the surface (0-20 cm) and subsurface (20-40 cm) black soil in northeast China were studied. Results showed that, compared with the CK, long-term application of organic manure, especially the combination of mineral fertilizers and organic manure significantly increased the organic SOC and TN in the surface soil. Application of mineral fertilizers plus organic manure with conventional (NPM) and high application (N2P2M2) rate increased SOC significantly by 24. 6% and 25.1% , and TN by 29.5% and 32.8%, respectively. However, there was no significant difference among the treatments for SOC and TN at the subsurface. Compared with the CK (CKh), mineral fertilizer plus organic manure (NPM and N2P2M2) did not only increase the soil microbial biomass carbon (SMBC) and nitrogen (SMBN) , dissolved organic carbon (DOC) and nitrogen (DN), but also significantly increased the ratio of SMBC and DOC to SOC, SMBN and TN to TN. Application of the NPM and N2P2M2 increased the value of SMBC/SOC by 0.36 to 0.59 and SMBN/TN by 1.21 to 1.95 percentage points, respectively. The value of DOC/SOC and DN/TN ranged from 0.53% to 0.72% and 1.41% to 1.78%, respectively. This result indicated that SMBC, SMBN, DOC, DN and SMBC/ SOC, SMBN/TN, DOC/SOC, DN/TN were more sensitive than SOC and TN to long-term fertilization in the soil profile, and were better indicators for the impact of long-term fertilization soil fertility. The concluded that the application of manure especially manure plus mineral fertilizers can increase soil nutrients activity in the surface and subsurface black soil, acting as a helpful practice to improve soil fertility and the ability of nutrient supply, while it may cause potential environment pollution on carbon and nitrogen loss in the agroecosystem.

[Characteristics of soil phosphorous loss under different ecological planting patterns in hilly red soil regions of southern Hunan Province, China].

Taking a large standard runoff plot on a red soil slope in Qiyang County, southern Hunan Province as a case, this paper studied the surface soil phosphorus loss characteristics in the hilly red soil regions of southern Hunan under eight ecological planting patterns. The phosphorus loss from wasteland (T1) was most serious, followed by that from natural sloped cropping patterns (T2 and T3), while the phosphorus loss amount from terrace cropping patterns (T4-T8) was the least, only occupying 9.9%, 37%, 0.7%, 2.3%, and 1.9% of T1, respectively. The ecological planting patterns directly affected the forms of surface-lost soil phosphorus, with the particulate phosphorus (PP) as the main lost form. Under the condition of rainstorm (daily rainfall > 50 mm), rainfall had lesser effects on the phosphorus loss among different planting patterns. However, the phosphorus loss increased with increasing rain intensity. The surface soil phosphorus loss mainly occurred from June to September. Both the rainfall and the rain intensity were the factors directly affected the time distribution of surface soil phosphorus loss in hilly red soil regions of southern Hunan.

[Effects of soil properties on the stabilization process of cadmium in Cd alone and Cd-Pb contaminated soils].

In order to clarify the effects of soil properties on the stabilization process of the cadmium (Cd) added, 11 different soils were collected and incubated under a moisture content of 65%-70% at 25 degrees C. The changes of available Cd contents with incubation time (in 360 days) in Cd and Cd-Pb contaminated treatments were determined. The stabilization process was simulated using dynamic equations. The results showed that after 1.0 mg x kg(-1) Cd or 500 mg x kg(-1) Pb + 1.0 mg x kg(-1) Cd were added into the soil, the available Cd content decreased rapidly during the first 15 days, and then the decreasing rate slowed down, with an equilibrium content reached after 60 days' incubation. In Cd-Pb contaminated soils, the presence of Pb increased the content of available Cd. The stabilization process of Cd could be well described by the second-order equation and the first order exponential decay; meanwhile, dynamic parameters including equilibrium content and stabilization velocity were used to characterize the stabilization process of Cd. These two key dynamic parameters were significantly affected by soil properties. Correlation analysis and stepwise regression suggested that high pH and high cation exchange capacity (CEC) significantly retarded the availability of Cd. High pH had the paramount effect on the equilibrium content. The stabilization velocity of Cd was influenced by the soil texture. It took shorter time for Cd to get stabilized in sandy soil than in the clay.

[Effects of straw returning on the integrated soil fertility and crop yield in southern China].

Based on the data from 94 experiments of straw returning in Anhui, Jiangxi, Hunan, Hubei, Guangxi, Sichuan, and Chongqing, and by using mathematic modeling approach, this paper evaluated the effects of straw returning on the soil fertility and crop yield in southern China. Obvious regional differences were observed in the soil fertility index (SFI) and crop yield response. In study area, the croplands with the SFI of Grade III and Grade IV were predominant, occupying 69.1% and 21.3% of the total, respectively. Averagely, straw returning increased the SFI and crop yield by 6.8% and 4.4%, respectively, as compared with the control (no straw returning). The SFI was significantly linearly correlated with rice yield, and could well reflect the integrated soil fertility in study area. At present, straw returning with decomposing agent added is one of the most important measures to improve the integrated soil fertility in southern China, which should be widely popularized.

[Effects of long-term applying sulfur- and chloride-containing chemical fertilizers on weed growth in paddy field].

An investigation was made at a double-rice paddy field in the Qiyang Red Soil Field Experimental Station, Hunan Province, China to study the species and biomass of weeds growing in rice (Oryza sativa L.) growth season after 34-year application of sulfur (SO4(2-)) and chloride (Cl(-))-containing chemical fertilizers under the same application rates of nitrogen (N), phosphorus (P), and potassium (K). Long-term application of Cl(-)-containing chemical fertilizer resulted in the greatest species number of weeds and the highest biomass of floating weeds and wet weeds, compared with long-term application of SO4(2-) and Cl(-) +SO4(2-)-containing chemical fertilizers. In early rice growth season, the biomass of weeds after applying Cl(-)-containing chemical fertilizer was 51.4% and 17.6% higher than that after applying Cl(-) + SO4(2-) and SO4(2-)-containing chemical fertilizers, respectively; in late rice growth season, the increment was 144% and 242%, respectively. More floating weeds were observed after applying Cl(-) + SO4(2-) and SO4(2-)-containing chemical fertilizers, but few of them were found after applying Cl(-)-containing chemical fertilizer. The total dry mass of weeds and the dry mass of wet weeds were positively correlated with soil Cl(-) content (r = 0.764, P < 0.01 and r = 0.948, P < 0.01, respectively), but negatively correlated with soil SO4(2-)-S content (r = 0.849, P < 0.01 and r = 0.641, P < 0.05). Soil alkali-hydrolyzable N and available P, under the co-effects of soil SO4(2-)-S, Cl(-), and pH, had indirect effects on the total dry mass of weeds. By adopting various fertilization measures to maintain proper soil pH and alkali-hydrolyzable N and available P contents, increase soil SO42(-)-S content, and decrease soil Cl(-) content, it could be possible to effectively inhibit the growth of wet weeds and to decrease the total biomass of weeds in double-rice paddy field.

[Variations of soil fertility level in red soil region under long-term fertilization].

Based on the long-term (1982-2007) field experiment of "anthropogenic mellowing of raw soil" at the Qiyang red soil experimental station under Chinese Academy of Agricultural Sciences, and by using numerical theory, this paper studied the variations of the fertility level of granite red soil, quaternary red soil, and purple sandy shale soil under six fertilization patterns. The fertilization patterns included non-fertilization (CK), straw-returning without fertilizers (CKR), chemical fertilization (NPK), NPK plus straw-return (NPKR), rice straw application (M), and M plus straw-return (MR). The soil integrated fertility index (IFI) was significantly positively correlated with relative crop yield, and could better indicate soil fertility level. The IFI values of the three soils all were in the order of NPK, NPKR > M, MR > CK, CKR, with the highest value in treatment NPKR (0.77, 0.71, and 0.71 for granite red soil, quaternary red soil, and purple sandy shale soil, respectively). Comparing with that in the treatments of no straw-return, the IFI value in the treatments of straw return was increased by 6.72%-18.83%. A turning point of the IFI for all the three soils was observed at about 7 years of anthropogenic mellowing, and the annual increasing rate of the IFI was in the sequence of purple sandy shale soil (0.016 a(-1)) > quaternary red clay soil (0.011 a(-1)) > granite red soil (0.006 a(-1)). It was suggested that a combined application of organic and chemical fertilizers and/or straw return could be an effective and fast measure to enhance the soil fertility level in red soil region.

[Sustainability of crop yields in China under long-term fertilization and different ecological conditions].

By using sustainable yield index (SYI), this paper analyzed the sustainability of maize, rice, and wheat yields at 20 long-term fertilization experiment sites in China under different fertilization system and ecological conditions. The SYI value of test crops varied significantly with fertilization system, crop kind, effective accumulated temperature, and sunshine hour. Irrespective of fertilization, the SYI value of rice was generally higher than that of maize and wheat. Under long-term no fertilization, the SYI values of rice, wheat, and maize were lower, being 0.55, 0.44, and 0.43, respectively. Fertilization, especially a combined application of NPK and manure, promoted the sustainability of crop yields, with the SYI values of rice, wheat, and maize being 0.66, 0.58, and 0.57, respectively. Under the application of N and NK, the SYI values ranged in 0. 36-0. 47. SYI value > 0.55 represented the better sustainability of crop yields, while SYI < 0.45 represented a worse one. Longitude, altitude, and weather factors also affected the SYI values, especially that of maize. Under no fertilization, maize had the largest variation of SYI value, followed by wheat, and rice. Our results indicated that a combined application of chemical fertilizers with manure benefited high and stable yielding, being the optimal fertilization mode for maintaining the sustainability of grain yield.

[Content and evolution characteristics of organic carbon associated with particle-size fractions of grey desert soil under long-term fertilization].

Physical fractionation technique was used to analyze the content, distribution, and temporal evolution of organic carbon associated with particle-size fractions of grey desert soil under long-term (1990-2007) fertilization. Compared with no fertilization, a combined application of manure and chemical fertilizers increased the organic carbon associated with particle-size fractions significantly, with the highest increment (0.34 g x kg(-1) x a(-1)) in sand. Following also increased the organic carbon associated with clay and silt significantly. Straw return to cropland only maintained the organic carbon content in different particle-size fractions, while long-term application of chemical fertilizers was not beneficial to the organic carbon increase in particle-size fractions. Coarse silt and coarse clay had the highest distribution rates of organic carbon (27.9% and 27.1%, respectively), being the important fractions in sequestrating organic carbon. When manure was applied with chemical fertilizers, the organic carbon in sand was significantly increased by 119.4%, while that in fine silt and coarse clay was significantly decreased by 40.3% and 37.9%, respectively, which resulted in the increase in the ratio of particulate organic carbon content (W(POC)) to mineral-associated organic carbon content (W(MOC)), and improvd soil carbon property. Long-term application of manure combined with chemical fertilizers was the best mode to increase the organic carbon content in particle-size fractions and improve the fertility of grey desert soil.

[Effects of long-term fertilization on microbial biomass carbon and nitrogen and on carbon source utilization of microbes in a red soil].

In order to explore the effects of long-term fertilization on the microbiological characters of red soil, soil samples were collected from a 19-year long-term experimental field in Qiyang of Hunan, with their microbial biomass carbon (MBC) and nitrogen (MBN) and microbial utilization ratio of carbon sources analyzed. The results showed that after 19-year fertilization, the soil MBC and MBN under the application of organic manure and of organic manure plus inorganic fertilizers were 231 and 81 mg x kg(-1) soil, and 148 and 73 mg x kg(-1) soil, respectively, being significantly higher than those under non-fertilization, inorganic fertilization, and inorganic fertilization plus straw incorporation. The ratio of soil MBN to total N under the application of organic manure and of organic manure plus inorganic fertilizers was averagely 6.0%, significantly higher than that under non-fertilization and inorganic fertilization. Biolog-ECO analysis showed that the average well color development (AWCD) value was in the order of applying organic manure plus inorganic fertilizers = applying organic manure > non-fertilization > inorganic fertilization = inorganic fertilization plus straw incorporation. Under the application of organic manure or of organic manure plus inorganic fertilizers, the microbial utilization rate of carbon sources, including carbohydrates, carboxylic acids, amino acids, polymers, phenols, and amines increased; while under inorganic fertilization plus straw incorporation, the utilization rate of polymers was the highest, and that of carbohydrates was the lowest. Our results suggested that long-term application of organic manure could increase the red soil MBC, MBN, and microbial utilization rate of carbon sources, improve soil fertility, and maintain a better crop productivity.

[Phosphorus use efficiency of wheat on three typical farmland soils under long-term fertilization].

Field experiments were conducted on three typical farmland soils (loess soil, fluvo-aquic soil, and cinnamon fluvo-aquic soil) in Northern China to study the grain yield, phosphorus agronomic efficiency (PAE), and phosphorus use efficiency (PUE) of wheat under effects of long-term fertilizations. Seven treatments were installed, i.e., non-fertilization (CK), nitrogen fertilization (N), nitrogen-potassium fertilization (NK), nitrogen-phosphorus fertilization (NP), nitrogen-phosphorus-potassium fertilization (NPK), NPK plus straw returning (NPKS), and NPK plus manure application (NPKM). The averaged wheat grain yields under long-term P fertilizations (treatments NP, NPK, NPKS, and NPKM) ranged from 2914 kg x hm(-2) to 6219 kg x hm(-2), being 200%-400% higher than those under no P fertilizations (treatments CK, N, and NK), and no significant differences were observed between the P fertilizations. In the early years of the experiment, the PAE in treatment NPK on the loess soil, fluvo-aquic soil, and cinnamon fluvo-aquic soil was 17.0 kg x kg(-1), 20.3 kg x kg(-1), and 13.3 kg x kg(-1), and the PUE was 15.3%, 31.2%, and 23.8%, respectively. After 15-year fertilization, the PAE and PUE in treatment NPK increased annually by 3.9 kg x kg(-1) and 1.3% on loess soil, 2.5 kg x kg(-1) and 0.9% on fluvo-aquic soil, and 2.8 kg x kg(-1) and 1.0% on cinnamon fluvo-aquic soil, respectively. There were no significant differences in the PAE and PUE among the P treatments for the same soils. In Northern China, long-term P fertilization could increase the wheat grain yield and PUE significantly, and the mean annual increase of PAE and PUE in treatment NPKM was higher on loess soil than on fluvo-aquic soil and cinnamon fluvo-aquic soil.

[Effects of calcium on cadmium bioavailability in lateritic red soil and related mechanisms].

A pot experiment with Cd-polluted lateritic red soils was conducted to study the effects of applying different concentration (0, 40, 100, and 200 mg x kg(-1)) Ca on the rape biomass, its Cd uptake, and the Ca and Cd concentrations in soil solution. Comparing with no Ca application, applying Ca increased the rape dry mass, whether under high or low level Cd pollution. The increment of the dry mass in two cropping seasons was averagely 5.5% (low level Cd pollution) and 17.3% (high level Cd pollution). The Ca concentration both in soil solution and in rape plant increased markedly with increasing Ca application rate. At the Ca application rate 100 mg x kg(-1), the Cd concentration in soil solution increased by 74.5% (low Cd pollution) and 31.0% (high level Cd pollution), while that in rape plant decreased by 4.5% (low Cd pollution) and 13.1% (high level Cd pollution). There was a positive relationship between the Ca/Cd (mass ratio) in soil solution and the Cd concentration in rape plant under both low and high levels Cd pollution. The Ca/Cd (mass ratio) in soil solution affected the bioavailability of soil Cd, and further, affected the Cd up-take by rape.

[Changes in bio-availability of immobilized Cu and Zn bound to phosphate in contaminated soils with different nutrient addition].

Bio-availability of Cu and Zn fixed by phosphate in contaminated soils with application of nutrients were measured by pot experiment. It was simulated for the third national standardization of copper and zinc polluted soils by adding copper and zinc nitrate into red and paddy soils, respectively and together. Phosphate amendment was added to the soils to fix Cu and Zn, then added KCl and NH4Cl or K2SO4 and (NH4)2SO4 fertilizers following to plant Ryegrass, which was harvested after 40 d. Available Cu/Zn content in soils and biomass, Cu/Zn content in the shoot of Ryegrass were determined. Results showed that, compared with no nutrient application, adding KCl and NH4 Cl/K2SO4 and (NH4)2SO4 to polluted red and paddy soils increased the available Cu and Zn content in red soil significantly. The increasing order was KCl and NH4 Cl > K2SO4 and (NH4)2SO4. Especially in single Zn polluted red soil, the available Zn content increased by 133.4% in maximum. Although adding K2SO4 and (NH4)2SO4 could promote the growth of Ryegrass on red soil, and the largest increasing was up to 22.2%, it increased Cu and Zn content in the shoot of Ryegrass for 21.5%-112.6% remarkably. These nutrient effects on available Cu and Zn were not significantly in paddy soil. It was suggested that application of nitrogen and potassium fertilizers to soils could change the bioavailability of Cu/Zn. So it is necessary to take full account of the nutrient influence to the heavy metal stability which fixed by phosphate in contaminated soils when consider contaminated soils remediation by fertilization.

[Effects of different potassium fertilizers on the phytoavailability of Pb in soil and its mechanisms].

Effects of four kinds of potassium fertilizer (KH2PO4, K2SO4, KNO3 and KCl) in its conventional application rate as K, 0.11 g x kg(-1) on the Pb absorption by rape and speciation of Pb in paddy soil were examined by pot trial. Results showed that the Pb content in rape decreased with using KH2PO4 and K2SO4, and in the second season of pot trial for KH2PO4 treatment, Pb content in rape shoots under Pb1 (300 mg x kg(-1)) and Pb2 (500 mg x kg(-1)) level decreased by 35.6% and 45.4% respectively compared with control treatment. Applied KNO3 in soil also decreased Pb content in rape shoots to some extent, but KCl had adverse effect. At lower Pb level (300 mg x kg(-1)), KH2 PO4 and K2SO4 caused Pb in soil transformed from non-residual fractions to residual fraction substantially and for higher Pb level (500 mg x kg(-1)) only KH2PO4 application had similar effect. Under two contaminated Pb levels, exchangeable and carbonate fraction Pb in soil by using KCl were all enhanced, which indicated that KCl could promote the phytoavailability of Pb. As thus one of the most important mechanisms of potassium fertilizers influencing Pb phtoavailability was changing the speciation of Pb in soil.

[Aging characteristics of copper and zinc added to typical soils of China].

The aging processes of copper and zinc in single and combined metal-contaminated typical soils of China, red soil, paddy soil and cinnamon soil, were studied. The results showed that available copper and zinc (metals extracted by 0.01 mol x L(-1) CaCl2 ) decreased rapidly at initial stages, and then reduced slowly, where the turning point occurred at about 90 d. The difference in aging of copper and zinc was insignificant whether in single metal-contaminated soils or in combined metal-contaminated soils, suggested there were similar chemical behaviors between copper and zinc. The aging processes of copper and zinc in red soil, paddy soil and cinnamon soil fitted best a second-order equation (R2 = 0.9940-0.9999, p < 0.0001), whereas parabolic diffusion equation has less goodness of fit. It indicated that the transformation from availability to unavailability of metals, i.e. aging, was not completely controlled by diffusion, but controlled by the interactions from surface nucleation/precipitation, occlusion by organic matter, and diffusion, etc. The aging of copper and zinc in soils was significantly affected by pH. In soils with low pH such as red soil, the ratio of available metals was higher and the aging rate was slower [constant of rate, k2 4.36x10(-3)-7.05x10(-3) kg x (mg x d)(-1)]; whereas in soils with high pH, for example in cinnamon soil, the ratio of available metals was lower and the aging rate was faster [k2 1.095x10(-2)-1.377x10(-2) kg x (mg x d)(-1)]. That is, the aging rate of metals in soils increased obviously with increasing pH.

[Simulating and predicting of carbon cycling in typical wetland ecosystems].

A model was developed based on the theories of physiological ecology and turnover dynamics of organic carbon in wetland ecosystem. It aimed to illustrate the process and characteristics of carbon cycling and its potential changes under climate change scenarios in wetland ecosystems. The key environmental parameters to determine the effects of temperature, water-logging, and freeze-thaw were gained from the results of incubation experiments. Effects of CO2 fertilizing on the carbon sequestration and plant cover on organic carbon mineralization were also taken into account in this model. It was verified by the conventional observed meteorologic data in temperate and subtropical wetland ecosystems. Sensitivity analysis and prediction under climate change scenarios by this model were also discussed. There were significant correlations between the simulated and observed values of sediment respiration in temperate wetlands in Northeast China. It was estimated that the annual net carbon sequestration rate was about 104 g x m(-2) in permanently water-logged wetland ecosystems and 76 g x m(-2) in the seasonally water logged ones in temperate northeast China. The simulated value of the accumulated organic carbon density was within the changing range of the investigated data. The model was sensitive to the change of parameters of CO2 concentration and temperature. The potential changes in carbon cycling characteristics were also predicted under assumed climate change scenarios of A1B and A1FI. It indicated that the exchange of carbon between the atmosphere and the wetland ecosystem became more active under climate change scenario of warming and increased CO2 concentration assuming no changing of hydrological condition. The net primary production (NPP) and the organic carbon density in temperate wetland ecosystems would increase under the scenario of doubled CO2 concentration and less than 2.5 degrees C increment of temperature. In this case wetland ecosystem would act as a net carbon sink of the atmosphere. However, it had no advantage to the carbon sequestration and accumulation in wetland ecosystems under the more warming scenarios. Under these more warming scenarios, the amount of increased NPP resulted from CO2 fertilizing and warming could not compensate the carbon loss from the accelerated respiration caused by warming. The organic carbon accumulated in seasonally water-logged wetland even would decrease under the assumed scenarios.

[Effects and mechanism of amendments on remediation of Cd-Zn contaminated paddy soil].

Amendments are widely applied in agricultural soils to improve soil quality and crop yield. Effects of three amendments, lime, manure, and sepiolite on cadmium (Cd) and zinc (Zn) bioavailability in contaminated paddy soils were studied by pot experiment with cultivating rape. There were eight treatments, including lime, manure, and sepiolite separately applied and combined with others in contaminated soil. The biomass yield of rape was investigated after harvest. The amounts of absorbed Cd and Zn in harvested rape with application amendments were determined. Besides soil pH, different forms of Cd and Zn in the conducted soils were also measured. Results showed that the yield of rape increased after amendments application. The treatment of lime and manure co-application showed the highest increasing yield by more than 170% comparing with no amendments application in the eight treatments. The amount of absorbed Cd and Zn in rape decreased after the three amendments application. Lime application showed the best effect to decrease the heavy metal content in rape when amendments were separately applied. However, sepiolite could hardly decrease the content in rape after separately applied in contaminated soil. It was mainly due to the decrease of exchangeable Cd and Zn, which was available for rape, after lime application. Soil pH in these treatments increased in response. Accordingly, the carbonate combined and the Fe-Mn oxide fractions, which were unavailable in soil for rape, increased greatly. The uptake coefficient of Cd was higher than that of Zn. It indicated that Cd was more movable in soil and lime application could obviously decrease the uptake coefficient. The remediation efficiency was significantly improved in the treatment of co-application with lime and manure in Cd-Zn contaminated paddy soil. Compared with control (CK), it increased 13.5 times for Cd and 2.4 times for Zn, respectively.