Mapping field spatial distribution patterns of isoproturon-mineralizing activity over a three-year winter wheat/rape seed/barley rotation

The temporal and spatial variability of the activity of soil microorganisms able to mineralize the herbicide isoproturon (IPU) pesticide was investigated over a three-year long crop rotation between 2008 and 2010. Isoproturon mineralization was higher in 2008, when winter wheat was treated with this herbicide, than in 2009 and 2010, when rape seed and barley were treated with different herbicides. Under laboratory conditions, we showed that isoproturon mineralization was not promoted by sulfonylurea herbicide applied on barley crop in 2010. IPU mineralization was shown to be highly variable at the field scale in years 2009 and 2010. Principal component analyses and analyses of similarities revealed that soil pH and equivalent humidity, and to a lesser extent soil organic matter content and cation exchange capacity (CEC) were the main drivers of isoproturon-mineralizing activity variance. Using a rather simple model that yields the rate of isoproturon mineralization as a function of soil pH and equivalent humidity, we explained up to 85% of the variance observed. Mapping field-scale distribution of isoproturon mineralization over the three-year survey indicated higher variability in 2009 and in 2010 as compared to 2008, suggesting that isoproturon treatment applied to winter wheat promoted isoproturon mineralization activity and reduced its spatial variability. Field-scale distribution of isoproturon mineralization showed important similarity to the distribution of soil pH, equivalent humidity and to a lesser extent to soil organic matter and cation exchange capacity (CEC) thereby confirming our model.     

Functional soil organic matter fraction in response to short-term tillage management under the double-cropping rice paddy field in southern of China

Environmental Science and Pollution Research - Soil organic matter (SOM) and its fraction play an important role in maintaining and improving soil fertility of paddy field. However, there is still...     

Dissipation of epoxiconazole in the paddy field under subtropical conditions of Taiwan

The environmental fate and distribution of fungicide epoxiconazole were studied by a rice paddy field model ecosystem. One week before the head-sprouting stage, rice plant was treated separately once with OPUS (tradename of epoxiconazole) 12% SC 2.1 kg ha(-1) and 1.4 kg ha(-1), respectively. Soil, water and rice plant were sampled seven days intervals nine times after application. The bioconcentration factor of epoxiconazole on mosquito fish in the ecosystem was also determined, based on the amounts of epoxiconazole content both in fish and water. This was initiated one day after the fungicide treatment, and continued for four days. In addition, the residue of epoxiconazole in rice grains was analyzed after harvest. After harvest, both planted water spinach (Ipomoea aquatica Forsk) and edible amaranth (Amaranthus mangostanüs L.) were analyzed. The results showed that epoxiconazole degraded in the local environment under the experimental conditions described. The degradation equations were in accordance with the first order kinetics. The DT50 of soil, field water and rice plant were 20-69 days, 11-20 days and 14-39 days, respectively. The bioconcentration factors of epoxiconazole on mosquito fish were 12.9 and 10.6 from 2.1 kg ha(-1) and 1.4 kg ha(-1) treatment, respectively. Residues of epoxiconazole in both rice and harvest vegetables were non-detectable. This indicates that epoxiconazole applied to rice at the recommended rates and application frequencies will not accumulate on rice grain and successive cropping vegetables.     

Movement and degradation of aldicarb residues in the saturated zone under citrus groves on the Florida ridge

A 1.7-ha section of citrus grove near Lake Hamilton was the site of a three-year field study designed to monitor the movement and degradation of the nematicide and insecticide aldicarb in the central ridge area of Florida. Soil cores were used to monitor the fate of aldicarb residues in the unsaturated zone and over 2,000 groundwater samples were collected from 174 monitoring wells to measure horizontal and vertical transport of aldicarb residues in the saturated zone. A simple saturated zone model was used to estimate the degradation rate of aldicarb residues and extrapolate findings to other ridge areas.The results of the study suggest that in the saturated zone aldicarb residues degrade at a rate corresponding to a half-life of approximately eight months. The predominantly horizontal movement of groundwater at this site limits aldicarb residues to the upper three to five meters of the saturated zone. Field data from this site together with unsaturated and saturated zone simulations suggest that in this area of Florida current restrictions on aldicarb used near potable wells are adequate to protect drinking water supplies.     

根施钙镁磷肥与叶喷硅/硒联合调控水稻镉吸收

南方水稻镉（Cd）污染是我国当前面临的主要环境问题之一。以中稻丰两优1号为材料,采用大田小区实验,研究了根区施加钙镁磷肥（P1：1 800 kg·hm-2、P2：3 000 kg·hm-2）、叶面喷施硅/硒（LS：2.0 mmol·L-1 Na2SiO3、LX：25 μmol·L-1 Na2SeO3、LSX：1.0 mmol·L-1 Na2SiO3+12.5 μmol·L-1 Na2SeO3）以及根区与叶面联合处理（P1LS、P1LX、P1LSX、P2LS、P2LX、P2LSX）下水稻对Cd的吸收。结果表明：1）根施钙镁磷肥显著降低了土壤有效态Cd含量（p1、P2较对照分别降低16.1%和29.5%;单独的根施钙镁磷肥或叶喷硅/硒处理后,稻米Cd含量较对照均显著降低（p1 40.8%、P2 57.2%、LS 42.3%、LX 35.0%、LSX 39.2%;根施钙镁磷肥与叶喷硅/硒联合调控对降低稻米Cd含量表现出显著的协同效应（p值显著性）,其中P1LS、P1LX和P1LSX较单独的P1分别降低了61.2%、59.5%和68.2%,P2LS、P2LX和P2LSX较单独的P2分别降低了75.0%、54.2%和75.7%。2）Cd从秸秆向籽粒转运系数（SS）大于从根向秸秆转运系数（RS）,根区与叶面联合处理明显降低RS和SS,并有显著的协同效应（p1与Si/Se联合,RS和SS平均降低了7.4%和22.0%,P2与Si/Se联合,RS和SS平均降低了16.0%和19.6%。3）从食品安全来说,单独的根施钙镁磷肥或叶喷硅/硒,大米Cd含量多数超标（国标0.2 mg·kg-1）,而根区与叶面联合处理几乎都能实现Cd含量不超标,其中降幅最大的为P2LS 和P2LSX,稻米Cd含量不到0.09 mg·kg-1。因此,根施钙镁磷肥与叶喷硅/硒联合处理可显著降低水稻Cd吸收、保障稻米质量安全。     

SCR脱硝系统烟道内流场优化

为了改善选择性催化还原法(SCR)催化剂上游烟气的流场、温度场和浓度场分布,基于CFD仿真分析技术,建立了整个脱硝系统三维模型,并通过优化导流板及整流格栅,使得速度标准偏差、浓度标准偏差、温度偏差、速度偏转角以及压降等性能指标都满足设计要求,在满足脱硝效率和氨逃逸率前提下,大大降低了烟气对催化剂层的冲刷,保证催化剂的使用寿命。最后,为了合理布置吹灰器,对优化结构下粉尘颗粒在烟道内的运动情况进行了仿真分析研究,为设计提供了依据。     

The nitrate leached below maize root zone is available for deep-rooted wheat in winter wheat-summer maize rotation in the North China Plain

In winter wheat (Triticum aestivum L.)-summer maize (Zea mays L.) rotation system in the North China Plain, maize roots do not extend beyond 1.2 m in the vertical soil profile, but wheat roots can reach up to 2.0 m. Increases in soil nitrate content at maize harvest and significant reductions after winter wheat harvest were observed in the 1.4-2.0 m depth under field conditions. The recovery of 15N isotope (calcium nitrate) from various (1.0, 1.2, 1.4, 1.6, 1.8 and 2.0 m) soil depths showed that deep-rooting winter wheat could use soil nitrate up to the 2.0 m depth. This accounted partially, for the reduced nitrate in the 1.4-2.0 m depth of the soil after harvest of wheat in the rotation system.     

Interaction between water flow and spatial distribution of microbial growth in a two-dimensional flow field in saturated porous media

Bacterial growth and its interaction with water flow was investigated in a two-dimensional flow field in a saturated porous medium. A flow cell (56 x 44 x 1 cm) was filled with glass beads and operated under a continuous flow of a mineral medium containing nitrate as electron acceptor. A glucose solution was injected through an injection port, simulating a point source contamination. Visible light transmission was used to observe the distribution of the growing biomass and water flow during the experiment. At the end of the experiment (on day 31), porous medium samples were destructively collected and analyzed for abundance of total and active bacterial cells, bacterial cell volume and concentration of polysaccharides and proteins. Microbial growth was observed in two stripes along the length of the flow cell, starting at the glucose injection port, where highest biomass concentrations were obtained. The spatial distribution of biomass indicated that microbial activity was limited by transverse mixing between glucose and nitrate media, as only in the mixing zone between the media high biological activities were achieved. The ability of the biomass to change the flow pattern in the flow cell was observed, indicating that the biomass was locally reducing the hydraulic conductivity of the porous medium. This bioclogging effect became evident when the injection of the glucose solution was turned off and water flow still bypassed the area around the glucose injection port, preserving the flow pattern as it was during the injection of the glucose solution. As flow bypass was possible in this system, the average hydraulic properties of the flow cell were not affected by the produced biomass. Even in the vicinity of the injection port, the total volume of the bacterial cells remained below 0.01% of the pore space and was unlikely to be responsible for the bioclogging. However, the bacteria produced large amounts of extracellular polymeric substances (EPS), which likely caused the observed bioclogging effects.     

Adsorption and desorption variability of four herbicides used in paddy rice production

This investigation was performed to determine the effect of physicochemical soil properties on penoxsulam, molinate, bentazon, and MCPA adsorption-desorption processes. Four soils from Melozal (35° 43' S; 71° 41' W), Parral (36° 08' S; 71° 52' W), San Carlos (36° 24' S; 71° 57' W), and Panimavida (35° 44' S; 71° 24' W) were utilized. Herbicide adsorption reached equilibrium after 4 h in all soils. The Freundlich L-type isotherm described the adsorption process, which showed a high affinity between herbicides and sorption sites mainly because of hydrophobic and H-bonds interaction. Penoxsulam showed the highest adsorption coefficients (4.23 ± 0.72 to 10.69 ± 1.58 mL g?1) and were related to soil pH. Molinate showed K(d) values between 1.72 ± 0.01 and 2.3 ± 0.01 mL g?1 and were related to soil pH and organic matter, specifically to the amount of humic substances. Bentazon had a high relationship with pH and humic substances and its K(d) values were the lowest, ranging from 0.11 ± 0.01 to 0.42 ± 0.01 mL g?1. MCPA K(d) ranged from 0.14 ± 0.02 to 2.72 ± 0.01 mL g?1, however its adsorption was related to humic acids and clay content. According to these results, the soil factors that could explain the sorption process of the studied herbicides under paddy rice soil conditions, were principally humic substances and soil pH. Considering the sorption variability observed in this study and the potential risk for groundwater contamination, it is necessary to develop weed rice management strategies that limit use of herbicides that exhibit low soil adsorption in areas with predisposing conditions to soil leaching.     

Adsorption and desorption variability of four herbicides used in paddy rice production

This investigation was performed to determine the effect of physicochemical soil properties on penoxsulam, molinate, bentazon, and MCPA adsorption–desorption processes. Four soils from Melozal (35° 43′ S; 71° 41′ W), Parral (36° 08′ S; 71° 52′ W), San Carlos (36° 24′ S; 71° 57′ W), and Panimavida (35° 44′ S; 71° 24′ W) were utilized. Herbicide adsorption reached equilibrium after 4 h in all soils. The Freundlich L-type isotherm described the adsorption process, which showed a high affinity between herbicides and sorption sites mainly because of hydrophobic and H-bonds interaction. Penoxsulam showed the highest adsorption coefficients (4.23 ± 0.72 to 10.69 ± 1.58 mL g^?1) and were related to soil pH. Molinate showed K_d values between 1.72 ± 0.01 and 2.3 ± 0.01 mL g^?1and were related to soil pH and organic matter, specifically to the amount of humic substances. Bentazon had a high relationship with pH and humic substances and its K_d values were the lowest, ranging from 0.11 ± 0.01 to 0.42 ± 0.01 mL g^?1. MCPA K_d ranged from 0.14 ± 0.02 to 2.72 ± 0.01 mL g^?1, however its adsorption was related to humic acids and clay content. According to these results, the soil factors that could explain the sorption process of the studied herbicides under paddy rice soil conditions, were principally humic substances and soil pH. Considering the sorption variability observed in this study and the potential risk for groundwater contamination, it is necessary to develop weed rice management strategies that limit use of herbicides that exhibit low soil adsorption in areas with predisposing conditions to soil leaching.     

Long-term effects of fertilization on the forms and availability of soil phosphorus in rice paddy

The changes in total P accumulation and P compounds with time in the plough layer in a paddy soil in southern Korea were investigated in relation to the continuous application of chemical fertilizers (NPK), straw based compost (Compost), combination these two (NPK+Compost) for 31 years. Continuous fertilization increased the total and inorganic P contents in plough layers. In NPK, inorganic P fraction did not change with time, but organic P content increased significantly. Long-term application of chemical fertilizer together with compost accelerated the decrease in the organic P fraction, presumably due to promoting microbial activity in the plow layer, and then increased significantly inorganic P fraction. Compost application decreased the residual P and Fe-P fractions and then increased inorganic P fraction, in spite of continuous compost application. Increase in total, inorganic and extractable P with time may be closely related to the increase in the availability of accumulated P for rice growth.     

碳源强化下的硫自养/异养反硝化协同作用

为强化硫自养反硝化过程,通过向连续稳定运行的硫自养反硝化反应器内投加少量碳源以进行强化,乙酸钠投加量分别为5.99、11.98、23.96 mg·L⁻¹。分析投加前后反应器内硝氮、COD、硫酸根和耗碱量的变化;研究了碳源强化下硫自养反硝化运行效能及反应机理。结果表明,投加少量碳源可增强自养反硝化过程硝氮的去除效果;在3种碳源投加量条件下,COD的利用率均大于85%,但硫酸盐生成量并未减少;在5.99 mg·L⁻¹碳源投加量下,系统实际耗碱量大于以硫酸根和COD计的理论耗碱量,而在11.98 mg·L⁻¹和23.96 mg·L⁻¹投加量下,实际耗碱量均介于2种理论值之间。在投加少量碳源后,自养反硝化脱氮效果明显提高,异养反硝化趋势随着碳源投加量的增加而增加。     

Environmental fate of rice paddy pesticides in a model ecosystem.

The distribution and metabolic fate of several rice paddy pesticides were evaluated in a modified model ecosystem. Among the three BHC isomers, beta-isomer was the most stable and bioconcentrated in all of the organisms. Alpha- and gamma-isomers were moderately persistent and degraded to some extent during the 33 day period. Disulfoton was relatively persistent due to the transformation to its oxidation products. Pyridaphenthion was fairly biodegradable. N-Phenyl maleic hydrazide derived from the hydrolysis of pyridaphenthion was not detected in the organisms though it was found in the aquarium water after 33 days. Cartap and edifenphos were considerably biodegradable, and the ratio of the conversion to water soluble metabolites was very high. There was a distinct difference in the persistence of Kitazin P and edifenphos in the aquarium water. It appeared that the hydrolysis rate of the pesticides affected their fate in the organisms. PCP appeared to be moderately biodegradable. CNP was considerably stable and stored in the organisms though the concentration in the aquarium water was relatively low. The persistence and distribution of the pesticides in the model ecosystem were dependent on their chemical structures. In spite of the limitation derived from short experimental period, the model ecosystem may be applicable for predicting the environmental fate of pesticides.     

Effects of steel slag amendments on accumulation of cadmium and arsenic by rice (Oryza sativa) in a historically contaminated paddy field

Environmental Science and Pollution Research - Paddy soil contamination by cadmium (Cd) and arsenic (As) is a great concern. Field experiments were conducted to study the effects of steel slag (SS,...     

Biological control of broad-leaved dock infestation in wheat using plant antagonistic bacteria under field conditions

Conventional weed management systems have produced many harmful effects on weed ecology, human health and environment. Biological control of invasive weeds may be helpful to minimize these harmful effects and economic losses incurred to crops by weeds. In our earlier studies, plant antagonistic bacteria were obtained after screening a large number of rhizobacteria for production of phytotoxic substances and effects on wheat and its associated weeds under laboratory conditions. In this study, five efficient strains inhibitory to broad-leaved dock and non-inhibitory to wheat were selected and applied to broad-leaved dock co-seeded with wheat both in pot trial and chronically infested field trial. Effects of plant antagonistic bacteria on the weed and infested wheat were studied at tillering, booting and harvesting stage of wheat. The applied strains significantly inhibited the germination and growth of the weed to variable extent. Similarly, variable recovery in losses of grain and straw yield of infested wheat from 11.6 to 68 and 13 to 72.6% was obtained in pot trial while from 17.3 to 62.9 and 22.4 to 71.3% was obtained in field trial, respectively. Effects of plant antagonistic bacteria were also evident from the improvement in physiology and nutrient contents of infested wheat. This study suggests the use of these plant antagonistic bacteria to biologically control infestation of broad-leaved dock in wheat under field conditions.

     

Loss of carbofuran from rice paddy water: Chemical and physical factors

Abstract

The loss of carbofuran was studied from rice paddy water treated with a granular formulation of the insecticide, and from ponds filled with drainage from the paddy. The average half‐life (t_1/2) for carbofuran loss was 57 hr. Controlled experiments indicated that pH was the predominating factor governing carbofuran loss from water in the environment studied. The loss due to hydrolysis was over 700 times more rapid at pH 10 (t_1/2 = 1.2 hr.) than at pH 7 (t_1/2 = 864 hr.) in buffered deionized water. The average pH of the rice paddy was 8, but diurnal fluctuations of 7 to 9.5 are common in similar environments. Impurities in the water, sunlight, and temperature influence the rate of carbofuran loss but not nearly so much as pH. There was no evidence for significant loss due to evaporation or oxidation. The results have important implications for the duration of the insecticide's activity and the effect on fish within or downstream from treated paddies.     

抗侵蚀型生态沟渠构建及其稻田应用效果

根据沟渠水力学和工程力学特征,通过引进三维植物网护坡技术,构建了一种抗侵蚀型稻田生态沟渠,横断面0.9 m2,沟壁和沟底水生植物覆盖度分别为62.8%和35.3%,沟壁抗坡面侵蚀强度较土质沟渠可提高2倍以上,在优化污染物拦截去除功能的同时,大大延长了其使用寿命。稻田应用实验表明,径流排水停留时间超过48 h后,SS、TN和TP去除率分别达59.5%、57.8%和45.3%,配置比例按照1 hm2水稻田配300 m该型生态沟渠实施,则超过80%以上的稻田径流排水能够得到有效处理。该型生态沟渠工程造价约245元/m,接近传统混凝土排水渠单价,经近2年的运行观测,沟渠系统结构稳定,净化植物长势良好。     

丙溴磷在稻田环境中的残留动态研究

确立了气相色谱法测定丙溴磷残留量的检测方法.采用该方法,丙溴磷在土壤、植株、糙米、稻壳和田水中的平均添加回收率为87.2％～103.6％,变异系数为3.20％～11.50％,最低检测质量浓度:田水为0.005 mg/kg;土壤、植株、糙米和稻壳为0.050 mg/kg.残留动态研究表明,丙溴磷在田水、植株和土壤中的半衰...     

Evaluation of soil characteristics potentially affecting arsenic concentration in paddy rice (Oryza sativa L.)

Paddy rice may contribute considerably to the human intake of As. The knowledge of soil characteristics affecting the As content of the rice plant enables the development of agricultural measures for controlling As uptake.During field surveys in 2004 and 2006, plant samples from 68 fields (Italy, Po-area) revealed markedly differing As concentration in polished rice. The soil factors total As_{(aqua regia)}, pH, grain size fractions, total C, plant available P_(CAL), poorly crystalline Fe_(oxal.) and plant available Si_(Na-acetate) content that potentially affect As content of rice were determined.A multiple linear regression analysis showed a significant positive influence of the total As_{(aqua regia)} and plant available P_(CAL) content and a negative influence of the poorly crystalline Fe_(oxal.) content of the soil on the As content in polished rice and rice straw.Si concentration in rice straw varied widely and was negatively related to As content in straw and polished rice.     

Concentration of global fallout 99Tc in rice paddy soils collected in Japan

Analysis of global fallout 99Tc in environmental samples should provide useful information for predicting the nuclide behaviour under natural conditions which is important from the viewpoint of radioecology. Concentrations of 99Tc in rice paddy soils collected in Japan have been studied. After chemical separation, 99Tc in the final solution was measured by ICP-MS. The activity ratio of 99Tc/137Cs was used to understand the 99Tc behaviour in the environment because the fission yields of 99Tc and 137Cs from 235U or 239Pu are almost the same. The theoretical activity ratio from fission which is calculated now is about 3.0 x 10(-4). Our results showed that the range of activity ratios of 99Tc/137Cs in the soil samples was (2.0-5.2) x 10(-3); these ratios were one order of magnitude higher than the theoretical one. 99Tc has been accumulating in rice paddy soil like 137Cs has, although their mechanisms might differ. One of the reasons for the high ratio in the surface soil might be the ratios in the atmospheric samples, which have increased from the order of 10(-3) to 10(-2) (García-León et al., 1993).