Comparative proteome profiles of Polygonatum cyrtonema Hua rhizomes (Rhizoma Ploygonati) in response to different levels of cadmium stress.

BACKGROUND: The Polygonatum cyrtonema Hua rhizomes (also known as Rhizoma Polygonati, RP) are consumed for their health benefits. The main source of the RP is wild P. cyrtonema populations in the Hunan province of China. However, the soil Cadmium (Cd) content in Huanan is increasing, thus increasing the risks of Cd accumulation in RP which may end up in the human food chain. To understand the mechanism of Cd accumulation and resistance in P. cyrtonema, we subjected P. cyrtonema plants to four levels of Cd stress [(D2) 1, (D3) 2, (D4) 4, and (D5) 8 mg/kg)] compared to (D1) 0.5 mg/kg. RESULTS: The increase in soil Cd content up to 4 mg/kg resulted in a significant increase in tissue (root hair, rhizome, stem, and leaf) Cd content. The increase in Cd concentration variably affected the antioxidant enzyme activities. We could identify 14,171 and 12,115 protein groups and peptides, respectively. There were 193, 227, 260, and 163 differentially expressed proteins (DEPs) in D2, D3, D4, and D5, respectively, compared to D1. The number of downregulated DEPs increased with an increase in Cd content up to 4 mg/kg. These downregulated proteins belonged to sugar biosynthesis, amino acid biosynthesis-related pathways, and secondary metabolism-related pathways. Our results indicate that Cd stress increases ROS generation, against which, different ROS scavenging proteins are upregulated in P. cyrtonema. Moreover, Cd stress affected the expression of lipid transport and assembly, glycolysis/gluconeogenesis, sugar biosynthesis, and ATP generation. CONCLUSION: These results suggest that an increase in soil Cd content may end up in Huangjing. Cadmium stress initiates expression changes in multiple pathways related to energy metabolism, sugar biosynthesis, and secondary metabolite biosynthesis. The proteins involved in these pathways are potential candidates for manipulation and development of Cd stress-tolerant genotypes.

Influence of landform, soil properties, soil Cd pollution and rainfall on the spatial variation of Cd in rice: Contribution and pathway models based on big data.

Landform, soil properties, soil cadmium (Cd) pollution and rainfall are the important factors affecting the spatial variation of rice Cd. In this study, we conducted big data mining and model analysis of 150,000 rice-soil sampling sites to examine the effects by the above four factors on the spatial variation of rice Cd in Hunan Province, China. Specifically, the variable coefficient of rice Cd in space was significantly correlated with the partition scale according to the logistic fitting. The improved random forest results suggested that elevation (DEM) and pH were the two most important factors affecting the spatial variation of rice Cd, followed by relief, soil Cd content and rainfall. Typically, variance partitioning analysis (VPA) revealed that both the soil property and the interactive effects between the soil property and Cd pollution were the principal contributors to the rice-Cd variation, with the respective contributing rates of 30.5 % and 29.0 %. Meanwhile, the partial least square-structural equation modelling (PLS-SEM) elucidated 4 main paths of specific indirect effects on rice-Cd variation. They were landform → physicochemical property → soil acidity → rice-Cd variation, landform → soil acidity → rice-Cd variation, physicochemical property → soil acidity → rice-Cd variation, and soil texture → soil acidity → rice-Cd variation. This work can provide a general guidance for scientific zoning, accurate prediction and prevention of Cd pollution in paddy fields.

[Effects of Equal Amounts Silicon Fertilizer Application on Soil Bioavailability of Cadmium and Cadmium Uptake by Rice].

Cadmium (Cd) contamination of paddy fields is a global concern, as it can cause the accumulation of Cd in food. To explore the effects of equal application of silicon fertilizers on the bioavailability of cadmium and soil Cd uptake at different growth stages of rice, a field experiment was conducted with five silicon fertilizers under the same silicon dose (225 kg·hm-2). The results revealed that the Cd contents in roots, stems, and leaves increased with the extension of the rice growth stage. The application of silicon fertilizers reduced the Cd contents in roots, stems, and leaves in brown rice by 14.9%, 28.2%, and 12.2%, respectively. Compared with that in the control, the Cd content of brown rice in the SiCaMgFe and SiW treatments was decreased by 21.1% (P<0.05) and 21.2% (P<0.05), respectively. Similarly, Cd content in iron plaque (DCB-Cd) increased with the extension of the rice growth period, which accounted for 15.8%-42.8% of the total Cd content in roots, and the DCB-Cd content was different in each stage of rice. The content of exchangeable Cd (Exc-Cd) in soil at the mature stage of rice decreased by 36.4%, and the other fractions increased by 12.5%-48.2%. The results showed significant negative correlations between the Cd contents and Si in roots, DCB-Cd and soil available Cd and available Si, Exc-Cd and Car-Cd, and soil available Cd and pH value. Cd content in roots was positively correlated with DCB-Cd. With the equal dose of silicon fertilizer, the treatments of SiCaMgFe and SiW could effectively reduce the Cd content in rice. The application of silicon fertilizer promoted the transfer of Exc-Cd to Carb-Cd by increasing the soil pH value and the soil available Si content, meanwhile reducing the soil available Cd, Exc-Cd contents, the adsorption of Cd by the iron film on the root surface, and the adsorption capacity of iron plaque and root, thereby reducing the absorption of Cd by rice.

[Primary Factors Affecting Soil Bioavailable Cadmium and Asenic by Different Properties of Silicon Fertilizer].

To clarify the primary factors affecting soil bioavailable cadmium (Cd) and arsenic (As) by silicon fertilizer, we chose different properties of silicon fertilizer, including three types of alkaline silicon fertilizer[Na2SiO3, CaSiO3, and ASSF (pH 9-11)] and one weak acid neutral soluble silicon fertilizer (NSSF, pH 5-6), to carry out a pot experiment by adding different amounts of Si fertilizer (25-800 mg·kg-1, calculated as Si). After 21 days of flooding, soil basic physical and chemical properties, along with diffusive gradients in thin film Cd and As (DGT-Cd and DGT-As) were investigated. The results showed that the application of Si fertilizer with different properties had different significant effects on the basic physical and chemical properties of soil. Specifically, the three types of alkaline silicon fertilizer significantly increased the soil pH (P<0.05), among which Na2SiO3 exhibited the strongest ability; however, the application of NSSF remarkably reduced soil pH (P<0.05), and per unit (mg) Si application of NSSF could reduce soil pH by 0.0017 units. Furthermore, with each fertilizer application rate that reached 400 mg·kg-1 (calculated as Si), the changes in soil pH and Eh tended to be gentle. The ability of the four types of silicon fertilizer to improve soil available silicon ranked as NSSF>Na2SiO3>ASSF>CaSiO3. Additionally, the application of the three types of alkaline silicon fertilizer apparently decreased soil DGT-Cd while increasing soil DGT-As (P<0.05). When the addition rate of CaSiO3 was up to 100 mg·kg-1(calculated as Si), soil DGT-Cd concentration could be significantly decreased by approximately 50.89% without causing a significant increase in soil DGT-As concentration. Conversely, when the NSSF application rate was up to 400 mg·kg-1 (calculated as Si), the soil DGT-As basically reached its steady-state, and the DGT-As reduction rate reached 85.87%. Strikingly, the correlation analysis of the influencing factors of soil DGT-Cd and DGT-As showed that soil pH was the main factor affecting soil bioavailable Cd and As (DGT-Cd and DGT-As), and the effect of soil available Si and P on soil Cd and As bioavailability was negligible. Consequently, soil DGT-Cd and soil DGT-As could reach a minimum when soil pH was adjusted to 6.5-7.0 or 5-5.5 by alkaline silicon fertilizer or NSSF, respectively. It is undoubtedly of great significance, to clarify the primary factors that influence soil bioavailable Cd and As to ensure food security production.

[Impacts of Uptake and Accumulation of Cd on Double Rice-Paddy Soil by Silicon Fertilizer Continuous Application].

The impacts of silicon (Si) fertilizers on cadmium (Cd) bioavailability in soil and Cd accumulation in paddy-rice plants were investigated in a field positioning test. The results indicated that the continuous application of 180 kg·hm-2 Si fertilizers improved soil bioavailable Si in paddy-rice fields by 108.1%-275.0% and improved pH values by 1.15-1.33 in soil. The difference in the contents of DTPA-Cd in soil by 12.3% and 15.9% was significant in early and late rice, respectively. The continuous application of silicon promoted the transformation of soil cadmium to a stable form and reduced the contents of exchangeable Cd and carbonate binding state Cd in the soil by 2.6%-5.1% and 8.6%-24.9%. The contents of ferric manganese oxide binding state Cd were increased significantly; meanwhile, the contents of organic binding state Cd and residue state Cd in soil were improved by 2.3%-12.8% and 2.3%-6.0%, respectively. The contents of Cd in the root, shoot, and rice were reduced by 38.4%, 49.7%, and 50.9% in early season rice and by 30.6%, 34.4%, and 39.2% in late season rice, respectively. The absorption factors and translocation factors were reduced significantly by 25.5%-49.6% and 13.5%-52.6%, and the average bioaccumulation factors were decreased by 6.0% and 8.0% in early and late season rice. The powder Si fertilizer had the best results overall. In conclusion, Si fertilizer could reduce the absorption and accumulation in rice; however, the continuous Cd reduction effect of continuous application Si fertilizer was not obvious.

Combined amendment improves soil health and Brown rice quality in paddy soils moderately and highly Co-contaminated with Cd and As.

In situ remediation technology applied aims to not only decrease cadmium (Cd) and arsenic (As) uptake by rice but also improve soil health and rice quality in contaminated paddy soils. Here the effects of a combined amendment, consisting of limestone, iron powder, silicon fertilizer, and calcium-magnesium-phosphate fertilizer, with three application rates (0, 450, and 900 g m-2) on soil health, rice root system, and brown rice quality were compared in moderately versus highly Cd and As co-contaminated paddy fields. After the amendment application, soil pH, cation exchange capacity, four kinds of soil enzyme activities increased (sucrase, urease, acid phosphatase, and catalase), and concentrations of leached Cd/As decreased, as measured by the DTPA (diethylene triamine pentaacetic acid) and TCLP (toxicity characteristic leaching procedure). Changes in the above soil indicators promoted soil health. In both fields, the dithionite-citrate-bicarbonate (DCB)-Fe and DCB-Mn concentration in iron plaque increased and root length became longer. Changes in the above root system indicators reduced the root system's absorption of Cd and As but increased that of nutrients. Under 900 g m-2 treatment, the Cd concentration in brown rice of two sites decreased by 55.8% and 28.9%, likewise inorganic As (iAs) decreased by 50.0% and 21.1%, whereas essential amino acids increased by 20.4% and 20.0%, respectively. Furthermore, the Cd and iAs concentrations in brown rice were <0.2 mg kg-1 (maximum contaminant level of Cd and iAs in the Chinese National Food Safety Standards GB2762-2017 for brown rice) under the 900 g m-2 in the moderately contaminated field. These results suggest the combined amendment can improve soil health and brown rice quality in the moderately and highly Cd- and As-co-contaminated paddy soils, offering potential eco-friendly and efficient remediation material for applications in such polluted paddy soils.

Influence of soil properties on cadmium accumulation in vegetables: Thresholds, prediction and pathway models based on big data.

Soil properties, such as soil pH, soil organic matter (SOM), cation exchange capacity (CEC), are the most important factors affecting cadmium (Cd) accumulation in vegetables. In this study, we conducted big data mining of 31,342 soil and vegetable samples to examine the influence of soil properties (soil pH, SOM, CEC, Zn and Mn content) on the accumulation of Cd in root, solanaceous, and leafy vegetables in Hunan Province, China. Specifically, the Cd accumulation capability was in the following order: leafy vegetables > root vegetables > solanaceous vegetables. The soil property thresholds for safety production in vegetables were determined by establishing nonlinear models between Cd bioaccumulation factor (BCF) and the individual soil property, and were 6.5 (pH), 30.0 g/kg (SOM), 13.0 cmol/kg (CEC), 100-140 mg/kg (Zn), and 300-400 mg/kg (Mn). When soil property values were higher than the thresholds, Cd accumulation in vegetables tended to be stable. Prediction models showed that pH and soil Zn were the leading factors influencing Cd accumulation in root vegetables, explaining 87% of the variance; pH, SOM, soil Zn and Mn explained 68% of the variance in solanaceous vegetables; pH and SOM were the main contributors in leafy vegetables, explaining 65% of the variance. Further, variance partitioning analysis (VPA) revealed that the interaction effect of the corresponding key soil properties contributed mostly to BCF. Meanwhile, partial least squares (PLS) path modeling was employed to analyze the path and the interactive effects of soil properties on Cd BCF. pH and SOM were found to be the biggest two players affecting BCF in PLS-models, and the most substantial interactive influence paths of soil properties on BCF were different among the three types of vegetables.

Input and output of cadmium (Cd) for paddy soil in central south China: fluxes, mass balance, and model predictions.

It is important to provide a more comprehensive understanding of cadmium (Cd) input and output in different contamination zones. In this study, we choose 15 sampling areas in three types of contamination zones (industrial and mining, suburb, and rural) to systematically study the inventory of soil Cd input and output in Changzhutan (CZT) urban agglomerations, Hunan Province, China. The results showed that the value of total Cd input in industrial and mining (34.58 g/ha/year) was respectively about 2 and 3 times of that in suburb and in rural. Meanwhile, the total output flux in industrial and mining also presented highest value (38.67 g/ha/year) among the zones. As for the contributions, atmospheric deposition was responsible for 85-89% of the total input fluxes, which was significantly higher than those of irrigation water and fertilizer. Crop harvesting, especially straw removal, was the dominant output pathway, contributing 66-78%. Moreover, Cd annual balance illustrated that the net input fluxes under straw removal scenario were negative in all zones, and it was opposite under straw returning scenario. Further, the changes of soil Cd concentrations under straw returning and straw removal scenario were compared by a dynamic mathematical model. The modeling results presented that the soil Cd content continued to increase under straw returning in 100 years, while it was declining under straw removal scenario. This prediction indicated straw removal was an important remediation for Cd-polluted paddy soil, especially in Hunan. Nevertheless, more treatment measures need to conduct to reach the safety limits in paddy soil.

[Temporal and Spatial Variation Patterns of Picophytoplankton and Their Correlations with Environmental Factors During the Wet Season in East Lake Dongting].

Picophytoplankton (<3 µm), comprising picocyanobacteria (PCY) and photosynthetic picoeukaryotes (PPEs), are considerably important in the material circulation and energy flow of aquatic ecosystems. To explore the temporal and spatial variation patterns of picophytoplankton and their correlations with environmental factors in lotic Yangtze-connected lakes, field in-situ investigations were performed on a monthly basis during the wet season (May to August) in 2019 in East Lake Dongting, a Yangtze-connected lake. The results indicated that both the Chla biomass and abundances of picophytoplankton exhibited significant spatial and temporal variability (P<0.05). The picophytoplankton Chla biomass showed an average concentration of 8.52 µg·L-1 and accounted for 41.6% to total phytoplankton on an average. From May to August, Chla biomass of picophytoplankton kept increasing with increasing temperature, especially in the north and south of the lake, and it was the lowest in the east of the lake. PCY dominated picophytoplankton abundance in East Lake Dongting and was 3.4 times the abundance of PPEs on an average. Similar spatial and temporal variation patterns were observed between PCY and PPEs. The abundances of PCY and PPEs both increased first and then decreased during the wet season. Spatially, picophytoplankton showed a trend to migrate from the northern lake to the southern lake from May to July, and the abundance significantly declined in August and peaked mainly in the north of the lake. The analysis results showed that picophytoplankton in East Lake Dongting exhibited significant spatial and temporal variability during the wet season; the water level and N：P ratio were determined to be the most important factors explaining the variation of the abundance proportion of PCY and PPEs.

[Effects of silicon fertilizer on nitrogen and phosphorus contents in the rice-surface water-soil of paddy field]. / ç¡ è‚¥å¯¹æ°´ç¨»-田面水-土壤氮磷含量的影响.

Examining the effects of silicon fertilizer on the yield of double-cropping rice and the leaching loss of soil nitrogen (N) and phosphorus (P) could provide a basis for the optimization of formula fertilizer and the comprehensive control technique of agricultural surface source pollution in typical double cropping paddy field. A field experiment was conducted to investigate the effects of silicon fertilizer of 0, 750, 1500, 2250 and 3000 kg·hm-2(T0, T1, T2, T3, T4) on yield and N and P absorption of double-cropping rice, dynamics of N and P in the field surface water, soil available silicon, organic matter, alkali nitrogen and available phosphorus under the fixed nitrogen and phosphorus fertilizers. The results showed that compared with control (T0), the silicon fertilizer increased the yield of early and late rice by 2.2%-30.4% and 3.9%-9.2%, respectively, enhanced rice N accumulation increased by 2.4%-47.3%, rice P accumulation by 2.2%-41.3%, straw N accumulation by 0.4%-28.3%, and straw P accumulation by 5.1%-31.0%. On the first day after fertilization, the total nitrogen (TN) content in the surface water was decreased by 3.4%-28.8% in silicon treatments compared with T0, the ammonium nitrogen (NH4+-N), total phosphorus (TP) and total soluble phosphorus (TDP) was decreased by 10.4%-25.6%, 25.5%-29.2%, 30.8%-38.0%, respectively. 45 days later, TP and TDP contents in the field surface water were significantly higher than T0. The silicon fertilizer treatment was beneficial to increase soil silicon level, contents of organic matter and alkali nitrogen of the double cropping rice, among which the T1 treatment performed the best. Soil available phosphorus showed a decreasing trend with the increasing silicon fertilizer.

[Effect of different organic fertilizers on bioavailability of soil Cd and Zn].

The active effect of soil Cd and Zn and their interaction was studied in typical paddy field in south China by monitoring the contents of Cd and Zn in soil and rice in rice fields applied with pig manure, chicken manure or rice straw for 4 years continuously. The results showed that applying pig manure, chicken manure or rice straw had no significant impact on the soil total Cd content, soil available Cd content and soil Cd activity, but tended to increase the soil total Cd content and increased the soil total Zn content, soil available Zn content and Zn activity significantly. Applications of pig manure, chicken manure and rice straw all reduced the Cd content of brown rice, in order of pig manure > chicken manure > rice straw. The Cd contents of brown rice, stem and leaf in the treatment applied with pig manure were lower than in the control by 37.5%, 44.0% and 36.4%, respectively; the Cd contents of brown rice, stem and leaf in the treatment applied with chicken manure were lower than in the control by 22.5%, 33.8%, and 22.7%, respectively; the Cd content of brown rice in the treatment applied with rice straw was lower than in the control by 7.5% but its contents in stem and leaf increased by 8.2% and 22.7% , respectively. The reduction in the brown rice Cd content was mainly due to the reduction of Cd enrichment from soil to brown rice after application of pig or chicken manure, but mainly due to the reduction of Cd transportation from stem to brown rice after straw application. Applications of pig manure, chicken manure and rice straw increased Zn contents in rice stem by 53.4%, 53.4% and 13.9%, respectively, but all had no significant effect on brown rice and leaf' s Zn contents. Zn and Cd had the significant antagonistic effects in the soil and rice stem. The increase of Zn content in soil and rice stem inhibited the adsorption and accumulation of Cd in the brown rice, stem and leaf significantly, and with the increase of the proportion of Zn/Cd, the competitive absorption between Cd and Zn by rice was the main control factor affecting the Cd absorption by rice than their competitive adsorption by soil.

[Effects of phosphorous fertilizers on phytoavailability of cadmium in its contaminated soil and related mechanisms].

To explore an effective measure to ensure the safety of rice quality in cadmium (Cd)-contaminated farmland, a pot culture experiment was conducted to study the effects of of low Cd content (Cd < 0.2 mg x kg(-1)) phosphorous fertilizers with an application rate of 0.10 or 0.20 g P2O5 x kg(-1) on the phytoavailability of Cd in its contaminated p add y soil, with the related mechanisms discussed. Compared with no phosphorous fertilization, applying 0.10 P2O5 x kg(-1) of calcium magnesium phosphate (CMP) and monopotassium phosphate (MKP) increased soil pH and decreased soil available Cd content significantly, and CMP and calcium superphosphate (CSP) decreased the Cd accumulation in rice significantly. When the application rate was up to 0.20 g P2O5 x kg(-1), calcium hydrogen phosphate (CHP) increased the soil pH and decreased the soil available Cd content significantly, and CMP, MKP, and CHP decreased the DTPA-extractable soil Cd content by 11.8%, 9.8%, and 11.8%, and the NH4 OAc-extractable soil Cd content by 9.5%, 7.1%, and 7.1%, respectively. All test phosphorous fertilizers could significantly decrease the stem and leaf Cd contents, with a decrement of 24.9%-50.8%, and except CHP, the others could significantly decrease the Cd content of brown rice. With the application CMP and CSP, the Cd content of brown rice was close to the National Hygienic Standard for Grains (GB 2715-2005). Among the test phosphorous fertilizers, those can increase soil pH (CMP, MKP, and CHP) could significantly decrease the availability of soil Cd significantly, and those containing calcium (CMP and CSP) were more effective in decreasing the Cd accumulation in rice. The efficiency of the phosphorous fertilizers was mainly determined by their chemical properties. Alkaline calcium-containing phosphorous fertilizers were more effective in decreasing the Cd absorption and accumulation in rice plant in Cd-contaminated farmland.

[Effects and mechanism of alkaline wastes application and zinc fertilizer addition on Cd bioavailability in contaminated soil].

The effects of paper mill sludge, red mud and zinc fertilizer addition on remediation of acid cadmium contaminated paddy soil were studied in a pot experiment, and their beneficial effects were verified in a field experiment, by using lime as comparison. The pot experiment results showed that a single application (2 g x kg(-1)) of lime, paper mill sludge or red mud increased soil pH significantly. Compared with no applying alkaline substances, the soil exchangeable Ca content was increased by 33.1%-76.0% at 7 days after applying alkaline substances and 31.0%-78.3% at 30 days after rice transplanting, respectively. The soil available Cd content was significantly decreased by 38.4%-45.0% at 7 days after the three alkaline substances applications, and was decreased by 37.4%-52.9% and 33.2%-38.7% at 30 days and 60 days after rice transplanting, respectively. The Cd content in rice root and brown rice was decreased by 24.0%-48.5% and 26.3%-44.7%, respectively. With equal applications of lime, paper mill sludge and red mud, the effects on increase of soil pH and decrease in Cd accumulation by rice was lime > red mud > paper mill sludge. Compared with a single application (2 g x kg(-1)) of paper mill sludge or red mud, Cd accumulation decreased significantly following the application of zinc fertilizer (0.2 g x kg(-1)) field experimental results were similar to the pot experiment that Cd accumulation apparently declined in the first and second crops (late rice and autumn rape) following the application of paper mill sludge, red mud and addition of zinc fertilizer. The Cd content in brown rice and rape seeds was decreased by 27.1-65.1% and 16.4%-41.6%, respectively, compared with no alkaline substances application. The Cd content in brown rice reached the National Hygienic Standard for Grains (GB 2715-2005). Therefore, combined application of paper mill sludge or red mud with zinc fertilizer was a feasible method to remediate acid cadmium contaminated paddy soil. Rice quality was guaranteed by determination of rational amount of alkaline wastes and a proportion of zinc fertilizer which was in accord with soil Cd contamination level and chemical properties, etc.

[Carbon sequestration effects of rice straw return in double season paddy field in Southern China].

In a long-term site-specific experiment with rice straw return (RSR) and in a short-term experiment with different RSR modes, this paper studied the effects of RSR on the soil organic carbon (SOC) sequestration, methane emission, and net carbon sink in a double season paddy field. RSR increased the SOC content, and the annual increasing rate of soil carbon sink in plow layer (0-15 cm) under long-term RSR was 0.07 t C x hm(-2) x a(-1). With the increasing amount of RSR, the apparent SOC transformation rate decreased. RSR promoted the methane emission from the paddy field significantly, and the methane emission flux in treatment RSR plus NPK during early- and late rice growth seasons increased by 75.0% and 251.5% (P < 0.01), respectively, compared with that in treatment NPK. The methane emission increased with the increasing amount of RSR. Under the similar tillage mode and rice yield, the rice straw returned had the similar apparent methane transformation rate. Considering the soil carbon sequestration and the net carbon sink after methane emission in the paddy field comprehensively, treatment RSR plus NPK had significant negative effect on the carbon sink which was basically approached to the bio-fixation of carbon by rice and increased by 158.3%, as compared with treatment NPK. Among different RSR modes, rice straw mulching plus no tillage decreased soil methane emission significantly, with the net carbon sink decreased by 50.9% as compared with the treatment high stubble plus tillage, and benefited the high and stable yielding of rice.

[Effects of controlled release nitrogen fertilizer on surface water N dynamics and its runoff loss in double cropping paddy fields in Dongtinghu Lake area].

By using leakage pond to simulate the double cropping paddy fields in Dongtinghu Lake area, this paper studied the effects of urea (CF) and controlled release nitrogen fertilizer (CRNF) on the dynamics of surface water pH, electrical conductivity (EC), total nitrogen (TN), ammonia nitrogen (NH4(+)-N) and nitrate nitrogen (NO3(-)-N) and the runoff loss of TN in alluvial sandy loamy paddy soil and purple calcareous clayed paddy soil, the two main paddy soils in this area. The results showed that after applying urea, the surface water TN and NH4(+)-N concentrations reached the peak at the 1st and 3rd day, respectively, and decreased rapidly then. Surface water NO3(-)-N concentration was very low, though it showed a little raise at the 3rd to 7th day after applying urea in purple calcareous clayed paddy soil. In early rice field, surface water pH rose gradually within 15 days after applying urea, while in late rice field, it did within 3 days. EC kept consistent with the dynamics of NH4(+)-N. CRNF, especially 70% N CRNF, gave rise to distinctly lower surface water pH, EC, and TN and NH4(+)-N concentrations within 15 days after application, but NO3- concentration rose slightly at late growth stages, compared with urea application. The monitoring of TN runoff loss indicated that during double cropping rice growth season, the loss amount of TN under urea application was 7.70 kg x hm(-2), accounting for 2.57% of applied urea-N. The two runoff events occurred within 20 days after urea application contributed significantly to the TN runoff loss. CRNF application resulted in a significantly lower TN concentration in runoff water from the 1st runoff event occurred within 10 days of its application, and thereafter, the total TN runoff loss for CRNF and 70% N CRNF application was decreased by 24.5% and 27.2%, respectively, compared with urea application.