Factors controlling degradation of pesticides in soil

Rates of pesticide degradation in soil exhibit a high degree of variability, the sources of which are usually unclear. Combining data from incubations performed using a range of soil properties and environmental conditions has resulted in greater understanding of factors controlling such degradation. The herbicides clomazone, flumetsulam, atrazine, and cloransulam-methyl, as well as the former insecticide naphthalene offer examples of degradation kinetics controlled by coupling competing processes which may in turn be regulated separately by environmental conditions and soil properties. The processes of degradation and volatilization appear to compete for clomazone in solution; sorbed clomazone is degraded only after the solution phase is depleted. Similarly, volatilization of naphthalene is enhanced when degradation has been inhibited by high nutrient levels. Degradation of the herbicide flumetsulam has been shown to be regulated by sorption, even though the compound has a relatively low affinity for the soil. The fate pathway for cloransulam-methyl shifts from mineralization to formation of metabolities, bound residues and physically occluded material as temperature increases. Atrazine degradation in soil may be controlled in part by the presence of inorganic nitrogen, as the herbicide appears to be used as a nitrogen source by micro-organisms. New insight gained from measurement of multiple fate processes is demonstrated by these examples.     

Uptake of pesticides from water and soil by earthworms

The uptake of pesticides by earthworms from aqueous solutions was examined and shown to be a reversible physical process. Measurements of distributions of pesticides between aqueous solutions and worm solids showed that adsorption coefficients were related to octanol-water distribution coefficients, as are soil-water distributions. From these relationships it was calculated that concentration factors of stable chemicals in earthworms from soil should be similar, except for polar substances which penetrate poorly, and be determined mainly by the soil organic matter content. Examination of uptake from soils indicated that the calculated concentration factors are unlikely to be achieved because of slow diffusion of chemicals in soils and because of metabolism in the soil or the worm.     

不同药剂埋施对花卉害虫综合防效比较试验

花卉害虫种类繁多，如蚜虫、叶跳虫、多种鳞翅目害虫等。这些害虫往往在花圃混合发生，一直是花卉生产上的难题。在夏秋季节，采用喷药防治，往往因早晚洒水保苗，很难达到应有的防效。为了寻求一种简便经济有效的防治手段，笔者于2000年8月进行了埋药防治试验，现将结果报告如下。     

Factors affecting residues of pesticides in tea

This paper presents a discussion on residue behaviour of 17 pesticides on tea, on the basis of the research conducted during the last 20 years. Sunlight photolysis and growth dilution were the most important factors affecting pesticide persistence in the growing tea plant, while vapour pressure played an important role in loss of pesticide residues during tea processing. The percentage of pesticide extracted during the tea infusion process was highly related to water solubility. It is suggested that in studies on pesticide residue behaviour on tea, all the four factors should be considered integrally.     

玉米施水播种增加灌水下渗的松土方法和试验

研究了下插式土壤松耕方法,分析了其工作原理、理想的刀具结构和合适的松土距离为50～70 mm,并用这种方法松土后进行了施水试验。结果表明：灌水入渗深度比未耕地或旋耕地对应值平均增加20 mm以上,且土壤湿润区整体下移约13 mm,灌水水平方向和垂直方向入渗深度的比值由1.3降低到0.8,而且,土壤紧实度和含水率均满足玉米施水播种的需要。这种方法有效增加了玉米施水播种灌溉水的下渗深度,减少了水分蒸发。     

农户对水土保持技术的支付意愿及影响因素分析——基于社会关系网络视角

基于对黄土高原区农户的微观调查数据,运用两阶段二元Probit模型,探析农户水土保持技术支付意愿与支付方式影响因素,重点考察社会关系网络对农户水土保持技术支付意愿的影响。结果表明:64.32%的农户愿意支付,且平均支付意愿为94.16元/亩,其中,81.68%的农户选择以投钱为主,18.32%的农户选择以投劳为主。社会关系网络对农户支付意愿的影响存在差异,与同质性关系相比,异质性关系对农户支付意愿的影响更为显著。家庭收入、政府投资、合作社参与情况、农户认知特征、户主文化程度等对农户支付意愿有不同影响;户主年龄、户主文化程度、家庭规模、耕地面积、非农就业比率、政府投资、自然灾害严重程度等是影响农户支付方式的主要因素。     

农药污染土壤的植物修复研究

植物可以吸收、转移元素和化合物,可以积累、代谢和稳定污染物,具修复被污染土壤等作用值得关注。本文综述了植物修复被农药污染土壤的机理和研究现状,列举了修复各种有机污染物的典型植物,及对此方法存在的问题和发展前景作了相应的讨论。     

Mode of entry of oxime carbamates into insects

The outcome of our earlier work suggested that the transport of contact insecticides into insects does not involve the haemolymph, but that the chemical probably reaches the internal organs by migrating in and/or over integumental tissue. This applies to various insects having quite different integumental organisation, and to various groups of insecticides differing widely in physical and chemical characteristics. The present work has shown that carbamates (1-alkylthioacetaldoxime carbamates) with high water solubility are no exception. The permeability of the body wall of the housefly for the methyl homologue (methomyl) which is the most water-soluble of the series, although relatively high, is not high enough to account for the toxicity of the compound if it followed the haemolymph route. Methomyl when injected with water instead of an organic solvent was also found to be less toxic than the equivalent amount topically applied. Lateral migration in the integument could be demonstrated with all the carbamates tested and dissimilarities in rates were apparent. Methomyl migrated the most rapidly and the cyanomethylene homologue the most slowly. Differences in mobility may be partly responsible for inequality in toxic effect, but it is thought that metabolic detoxication is of over-riding importance.     

Photocatalytic degradation of pesticides and bio-molecules in water

Two approaches are suggested for the acceleration of the photocatalytic oxidation of organic contaminants of water: acceleration by oxidants and photo-enhancement by dyes. These processes were examined with several substances: two widely applied herbicides, bromacil (a uracil) and metribuzin (a triazine), and three proteins, studied as models of biocontaminated waters. The effects of oxygen and hydrogen peroxide indicated two different reaction patterns of photo-oxidation of the herbicides. With metribuzin, oxygen had a pronounced effect on the rate of photo-oxidation, while the influence of hydrogen peroxide was quite moderate; with bromacil, oxygen had a limited effect on the rate of photo-oxidation, which however was considerably enhanced by hydrogen peroxide. Acceleration of the photo-catalytic oxidation of colourless refractory contaminants by photo-excited dye was observed. Both UV and visible light were required for the enhanced decomposition. The mechanism of the reaction seems to involve a combination of oxidation by hydroxyl radicals, via the hole-electron semiconductor route, with subsequent oxidation of photo-intermediates by singlet oxygen formed by dye sensitization. The TiO2-photocatalyzed oxidation of proteins (albumin, ovalbumin and gamma-globulin) showed the susceptibility of proteins to photocleavage and of the amino acids to photocatalytic degradation. Tyrosine was the most sensitive, while the degradation of the aliphatic amino acids Gly and Asp was slow.     

Applicability of five models to simulate water infiltration into soil with added biochar

As a soil amendment, biochar can reduce soil bulk density, increase soil porosity, and alter soil aggregates and thus affect the infiltration. Researchers have proposed and revised several theoretical models to describe the process of soil infiltration. Although these models have been successfully used to evaluate the soil infiltration in different scenarios in agricultural fields, little effort has been devoted to assess their performances in arid and semi-arid soils after the addition of biochar. A laboratory experiment was performed to study the infiltration characteristics of two typical Loess Plateau soils at three particle sizes(2–1, 1–0.25, and 0.25 mm) and five biochar application amounts(0, 10, 50, 100, and 150 g/kg). The performance of five models(i.e., the Philip model, Kostiakov model, Mezencev model, USDA-NRCS model, and Horton model) in simulating the infiltration process was then evaluated based on the adjusted coefficient of determination and a reduced Chi-Square test. Results indicated that the Horton model best simulated the water-infiltration process in an aeolian sandy soil with added biochar. However, the Mezencev model best simulated the infiltration process in a loamy clay soil(Eum-Orthic Anthrosol). The three-parameter model, i.e., Mezencev and Horton models can better describe the relationship between cumulative infiltration and infiltration time. In conclusion, biochar reduced the soil infiltration capacity of the aeolian sandy soil and increased that of the Eum-Orthic Anthrosol.     

The effect of three different pesticides on soil protozoan activity

Three pesticides, dimethoate, pirimicarb and fenpropimorph, had a negative impact on the colonization of a sterilized soil by a natural population of soil protozoa. Fenpropimorph has an effect at the lowest concentration applied; 25 mg litre^?1. Dimethoate reduced the soil respiration significantly for about 10 days after application. In single species cultures of soil protozoa in liquid media, a flagellate Cercomonas sp., was a better test organism than a ciliate, Colpoda sp., or an amoeba, Acanthamoeba sp., with respect to interpretation of dose-response curves and ease of observation.     

Integrating water use systems and soil and water conservation measures into a hydrological model of an Iranian Wadi system

Water resources are precious in arid and semi-arid areas such as the Wadis of Iran. To sustainably manage these limited water resources, the residents of the Iranian Wadis have been traditionally using several water use systems (WUSs) which affect natural hydrological processes. In this study, WUSs and soil and water conservation measures (SWCMs) were integrated in a hydrological model of the Halilrood Basin in Iran. The Soil and Water Assessment Tool (SWAT) model was used to simulate the hydrological processes between 1993 and 2009 at daily time scale. To assess the importance of WUSs and SWCMs, we compared a model setup without WUSs and SWCMs (Default model) with a model setup with WUSs and SWCMs (WUS-SWCM model). When compared to the observed daily stream flow, the number of acceptable calibration runs as defined by the performance thresholds (Nash-Sutcliffe efficiency (NSE)≥0.68, -25%≤percent bias (PBIAS)≤25% and ratio of standard deviation (RSR)≤0.56) is 177 for the Default model and 1945 for the WUS-SWCM model. Also, the average Kling-Gupta ef?ciency (KGE) of acceptable calibration runs for the WUS-SWCM model is higher in both calibration and validation periods. When WUSs and SWCMs are implemented, surface runoff (between 30% and 99%) and water yield (between 0 and 18%) decreased in all sub-basins. Moreover, SWCMs lead to a higher contribution of groundwater flow to the channel and compensate for the extracted water by WUSs from the shallow aquifer. In summary, implementing WUSs and SWCMs in the SWAT model enhances model plausibility significantly.     

水土保持植物——芨芨草对土壤养分影响的研究

以自然植被下土壤为对照，通过对芨芨草地土壤全氮，全磷、全钾、速效磷、钾、土壤有机质及阳离子交换量的测定，了解芨芨草对土壤养分的影响，结果表明，芨芨草对土壤有机质及全量养分影响不大，但能明显提高土壤速效养分的含量，并能提高土壤阳离子代换量及降低土壤pH值。     

Movement of pesticides to surface waters from a heavy clay soil

A field experiment at Cockle Park, Northumberland on a clay loam soil (Dunkeswick series) cropped with winter wheat investigated the effects of drainage and season of application on pesticide movement. Isoproturon, mecoprop, fonofos and trifluralin were applied in two consecutive seasons at normal agricultural rates to three hydrologically isolated plots each of 0.25 ha. Two of the plots were mole-drained and the third was an undrained control. Surfacelayer flow and drainflow from each plot were monitored at 10-min intervals. Samples of flow were analysed for pesticides to evaluate transport of applied chemicals from the site. Despite widely differing properties (K_oc 20–8000 ml g^?1, t_1/2 10–60 days), all four pesticides were found in surface-layer flow and mole drainflow from the site. Maximum concentrations of pesticides in flow ranged from 0.1 to 121 μg litre^?1 (aqueous phase) and < 0.2 to 48 μg litre^?1 (particulate phase). Over two contrasting seasons, total losses of pesticides in flow followed total amounts of flow and were approximately four and five times larger, respectively, in 1990/91 than in 1989/90. The maximum loss occurred from the undrained plot and was 2.8 g isoproturon (0.45% of that applied). Total losses of autumn-applied pesticides from an undrained plot were up to four times greater than losses from a mole-drained plot. Mole drainage decreased movement of pesticides from this slowly permeable soil by reducing the amount of surfacelayer flow. Maximum concentrations of mecoprop and isoproturon in drainflow were 10–20 times larger following spring application than after application in autumn. Bypass flow down soil cracks was an important process by which pesticide was lost from the site, with transport to the drainage system via mole channels (55 cm depth) after less than 0.5 and 6.7 mm net drainage in the two winters.     

三种拟除虫菊酯类农药在砂土和壤土中的淋溶行为

采用土柱淋溶法和气相色谱法研究了3种拟除虫菊酯类农药三氟氯氰菊酯、联苯菊酯和高效氯氰菊酯在热带地区主要土壤类型砂土和壤土中的淋溶特性。结果表明:3种拟除虫菊酯类农药在砂土和壤土中主要残留于第1段土壤 (0～5 cm) 中,且驻留量随土壤深度增大而减少。三氟氯氰菊酯、高效氯氰菊酯和联苯菊酯在砂土中的R_i值分别为52.86%、94.73%和83.19%,在壤土中的R_i值分别为54.70%、77.28%和55.33%,均大于50%。根据农药在土壤中的淋溶性等级划分标准,3种药剂均属于难淋溶农药,不易对地下水造成污染。本研究结果可为热带地区土壤和地下水中农药污染修复提供参考。     

Contribution of non-agricultural pesticides to pesticide load in surface water

Two small creeks, tributaries of the River Ruhr near Schwerte, Federal Republic of Germany, were investigated to reveal the regional agricultural and non-agricultural sources of pesticide inputs and the main pathways to surface water. In addition, the receiving water was monitored for pesticides. The watersheds are situated at the northern margin of the Rhenian Schiefergebirge, a highland landscape in North-Rhine-Westphalia. Solid carboniferous shale is covered by a shallow layer of quaternary unconsolidated rock (porous aquifer thickness <5 m). Occurrence of herbicides such as chlortoluron, isoproturon and terbuthylazine in surface water could be due to their broad agricultural application in regional dominant crops, such as barley, wheat and maize. Occurrence of diuron and glyphosate results from their use in residential settlements and industrial areas as well as from weed control on railway tracks. Atrazine concentrations up to 0.8 microg litre(-1) indicated recent use of this herbicide, which has been banned since 1991, and was also the result of non-agricultural applications. Pathways for pesticide input to the receiving waters were related to both surface run-off and underground passage. Two-thirds of the observed diuron load in the surface water resulted from an input by run-off. This was expected as a result of total herbicide application targets to sealed surfaces infringing current regulations and recommendations. Diuron load varied between 0.6 and 1.2% of the estimated amount applied annually in the investigated catchments. Non-agricultural pesticide use contributed more than two-thirds of the whole observed pesticide load in the tributaries and at least one-third in the River Ruhr.     

Factors influencing infection of eucalypts by Cylindrocladium pteridis

The pattern of Cylindrocladium pteridis adhesion, germination and penetration in eucalypt leaves was assessed using scanning electron microscopy. The effects of inoculum concentration, leaf wetness period, plant age and branch position of cylindrocladium leaf blight and defoliation severity were assessed in greenhouse studies using two Eucalyptus grandis × E. urophylla hybrid clones. Penetration occurred through stomata, and there was no difference in the number of penetrations between young and old leaves. Percentage leaf area with lesions and defoliation increased with the increase in inoculum concentration (1 × 10² to 10⁵ conidia mL⁻¹), duration of leaf wetness period (6 to 48 h) and plant age (60 to 180 days). Branch position in plants also significantly affected the percentage leaf area with lesions and defoliation, the latter variable being significantly higher at the stem base. The highest values of lesion area were also observed on leaves at the stem base in both clones. The Pearson correlation between defoliation and leaf area with lesions was significant in all experiments ( r  > 0·9) indicating a high association between these two variables.     

压实新土体水分动态研究

新土体是资源化利用矿化垃圾和采矿、采石场弃渣石配置而成的工矿企业污染场地植被修复生长基质.为了提高新土体的持水能力,解除弃渣场、尾矿库等困难立地条件下土壤水分对植物存活、生长的制约,本试验对新土体进行不同程度的机械压实,对10 ～ 100cm的土壤含水量进行为期2年的观测,在不同的时间尺度上分析土壤水分动态变化特征.研究结果表明:1)压实显著提高新土体含水量和持水能力.2)由于持水能力增加,重度压实区月平均含水量峰值滞后于月降水量峰值,对照及轻度压实区月平均含水量峰值与月降水量峰值时间一致.3)轻度压实区不同深度的土壤月平均含水量与降水量具有非线性相关关系,重度压实区下层含水量与降水量相关性不显著.4)雨季新土体含水量由雨前含水量和降雨量决定,决定系数为0.657 ～0.861.随着压实度增加,雨前含水量和降雨量的影响增加.5)随着土壤深度增加,土壤含水量的波动幅度下降,60 ～ 100cm土层在观测期间仅接受过1次降雨补给.     

土壤温、湿度对两种微胶囊杀虫剂毒力的影响

以华北大黑鳃金龟幼虫为生测对象,在常规毒力测定的基础上研究土壤温、湿度对35%辛硫磷和30%毒死蜱微囊悬浮剂毒力的影响。结果显示:35%辛硫磷微囊悬浮剂对华北大黑鳃金龟幼虫的毒力高于30%毒死蜱微囊悬浮剂,约是其毒力的3～9倍;在试验湿度和温度范围内,35%辛硫磷和30%毒死蜱微囊悬浮剂对供试幼虫的杀虫效果随着温度的升高而逐渐增强;在相同温度条件下,2种微囊制剂在含水量为10%的土壤中杀虫效果高于含水量20%的土壤。     

保护性耕作下黑土水热动态研究

通过连续监测东北典型黑土耕作长期定位试验下的土壤含水量和温度,研究了保护性耕作措施下农田黑土水热动态规律。结果表明:免耕秸秆覆盖(NTS)可显著提高0~50 cm土层水分含量,其中免耕在0~20 cm土层平均土壤体积含水量最高值分别比少耕(RT)和传统(CT)高3%~10%,尤其是可提高作物播种期表层土壤含水量。0~10 cm土层深度范围内RT土壤温度均高于NTS和CT,其中5 cm土层土壤温度日平均最高值较NTS和CT分别高3.04℃和5.27℃。三种耕作措施下的水热动态表明,少耕是我国东北旱作黑土区最佳的保护性耕作措施。