实验室条件下威百亩及异硫氰酸甲酯在土壤中的降解特性

在实验室条件下,利用高效液相色谱研究了威百亩及其降解产物异硫氰酸甲酯在土壤中的降解特性及影响因素。结果表明:威百亩在土壤中的降解与土壤绝对含水量、环境温度和土壤有机质含量均密切相关。25 ℃下,威百亩在绝对含水量为0、20%、40%、60%的土壤中的半衰期分别为5.0、1.2、4.1和4.3 d,绝对含水量约为20%的土壤最有利于其降解。威百亩的降解速率还随温度的升高和土壤有机质含量的增加而加快。异硫氰酸甲酯的降解趋势与威百亩基本相同。研究结果可为威百亩的田间安全、合理施用提供参考。     

土壤环境条件对威百亩熏蒸防治黄瓜枯萎病的影响

为探究威百亩在不同土壤环境条件下的消毒效果,采用离体和活体方法研究施药量、覆膜熏蒸时间、土壤相对含水量及土壤温度对威百亩熏蒸防治黄瓜枯萎病的作用效果。结果表明,25℃条件下,威百亩12 mg(a.i.)/kg土壤熏蒸消毒,对尖孢镰刀菌Fusarium oxysporum的抑制率为78.82%,对黄瓜枯萎病的防治效果为87.03%,且对作物安全无药害;威百亩对尖孢镰刀菌的熏蒸抑制作用随着熏蒸时间的增加而增强,土壤熏蒸10 d后对尖孢镰刀菌的抑制率为95.21%;土壤相对含水量为30%和50%时,威百亩对黄瓜枯萎病的防治效果分别为72.32%和82.14%,含水量过高或过低均不利于药效的发挥,而且还会对作物产生药害反应。威百亩的熏蒸效果随着土壤温度的升高而增强,在25、30、35℃时对黄瓜枯萎病的防治效果分别为80.18%、98.20%和100.00%。表明威百亩结合日光消毒温度大于25℃、土壤相对含水量为30%或50%、熏蒸10~15 d可有效控制土壤中尖孢镰刀菌引起的黄瓜枯萎病。     

威百亩熏蒸对土壤反硝化作用及nirS型反硝化细菌群落结构的影响

为探究威百亩对土壤反硝化作用的影响及作用机制,采用理化分析和变性梯度凝胶电泳方法分析浓度20、100和500 mg/kg威百亩熏蒸对土壤反硝化作用及nirS型反硝化细菌群落结构的影响。结果显示,威百亩熏蒸处理0、14 d后,500 mg/kg浓度处理的土壤反硝化率为84.64%、90.52%,分别显著低于对照的86.72%和91.87%,100、20 mg/kg浓度处理的土壤反硝化率与对照均无显著差异;熏蒸处理28、56和84 d后,4个处理的土壤反硝化率均无显著差异。与对照相比,3个浓度威百亩熏蒸处理0、14、28、56和84 d后的土壤nirS型反硝化细菌群落的多样性指数和均匀度指数均差异不显著。除56 d外,20 mg/kg浓度熏蒸处理0、14、28和84 d的土壤细菌群落丰富度指数分别为8.77、14.77、9.77和8.75,均显著低于对照;100 mg/kg浓度熏蒸处理0、14和28 d后的土壤细菌群落丰富度指数分别为10.76、6.77和10.78,显著低于对照,而处理56、84 d后,土壤细菌群落丰富度指数与对照无显著差异。500 mg/kg浓度威百亩熏蒸处理后,土壤反硝化作用在熏蒸后0~14 d受到抑制,28 d后土壤反硝化作用自然恢复;土壤细菌群落丰富度指数无论熏蒸初期或后期与均对照差异不显著。威百亩对土壤反硝化强度的影响与nirS型硝化细菌群落结构变化无关,说明nirS型反硝化细菌在土壤反硝化作用中不起主要作用。     

威百亩熏蒸对土壤硝化作用及amoA型硝化细菌群落结构的影响

为探究威百亩对土壤硝化作用的影响及作用机制,通过理化分析和变性梯度凝胶电泳方法研究浓度为20、100和500 mg/kg威百亩熏蒸处理对土壤硝化作用及amoA型硝化细菌群落结构的影响。结果表明,威百亩熏蒸处理0、14、28 d后,3种浓度处理的土壤硝化率与对照差异不显著;处理56 d后,20、100和500 mg/kg浓度处理的土壤硝化率分别为81.15%、76.66%和94.08%,前两者与对照差异不显著,后者与对照差异显著;而处理84 d后,3种浓度处理的土壤硝化率与对照差异均不显著。与对照相比,3个浓度威百亩熏蒸处理不同时间后土壤amoA型硝化细菌群落的均匀度指数差异不显著。熏蒸处理14 d后,浓度20、100 mg/kg威百亩处理的土壤amoA型硝化细菌群落的香农多样性指数和丰富度指数分别为1.00、10.97和0.84、7.79,与对照的0.92和9.78均无显著差异;而浓度500 mg/kg威百亩处理的香农多样性指数和丰富度指数分别为0.59、5.77,显著低于对照。表明威百亩对土壤硝化强度的影响较amoA型硝化细菌群落延迟,说明土壤中硝化作用的强弱并非完全决定于土壤amoA型硝化细菌的作用。     

威百亩对西葫芦常见土传病原菌的毒力及田间防效

为明确威百亩对西葫芦常见土传病原菌的活性及田间防治效果,以1,3-二氯丙烯为对照药剂,采用改进的密封盘法比较了2种熏蒸剂对西葫芦菌核病菌等4种病原菌的毒力及对菌核萌发的影响,并于田间采用密闭熏蒸法比较了2种药剂对西葫芦茎基腐病的防治效果.室内结果显示:威百亩对西葫芦菌核病菌、茎基腐病菌、枯萎病菌及绵腐病菌的EC₅₀分别为0.060、0.945、1.380、2.953 mg/L,而1,3-二氯丙烯对这4种病原菌的EC₅₀为516.654、928.558、633.784、77.242 mg/L,威百亩0.228 mg/L可完全抑制菌核的萌发.田间药效试验表明:威百亩150、90、75、60 kg/hm²及1,3-二氯丙烯200 kg/hm²均能不同程度控制西葫芦茎基腐病的发生,防治效果分别为88.94%、87.58%、83.76%、80.60%和64.80%,且各试验剂量均对西葫芦安全并能在一定程度上起到增产作用,威百亩150 kg/hm²处理增产率最高,达34.82%.从防治效果及经济效益分析,在西葫芦田推荐使用威百亩防治土传病害.     

稀释倍数对虱螨脲乳液性能的影响规律及作用机制

农药制剂在使用过程中须按照不同的施药方式进行相应的稀释,而不同稀释倍数对药液性质有较大影响。本文以虱螨脲乳油为研究对象,探讨稀释倍数对乳液稳定性和润湿性能的影响规律及作用机制。结果表明:随着稀释倍数的增大,乳液粒径减小,粒径分布更均匀;同时,由于乳液粒径减小,液滴布朗运动加剧,沉降速率逐渐降低,离心稳定性逐渐增强;但是,助剂浓度的降低导致乳液表面张力逐渐增大,在疏水石蜡板上的接触角逐渐增大,润湿性能逐渐变差。该研究结果可为不同施药方式下农药的规范使用提供依据,对提高农药利用率具有重要的指导意义。     

3,4,5-三羟基苯甲酸甲酯防治番茄青枯病的物理作用方式及其对番茄根系次生代谢物质的影响

通过生物学方法测定3,4,5-三羟基苯甲酸甲酯(MG)防治番茄青枯病的物理作用方式,采用气相色谱-质谱联用方法分析该化合物对番茄根系组织次生代谢物质的影响。结果表明,3,4,5-三羟基苯甲酸甲酯对番茄青枯病有较好的预防作用,持效期较长,施药15d后接种青枯病菌,防效仍达52.12%;该化合物可快速扩散到番茄根系组织内,但其向植株顶部和基部的输导作用弱,对番茄青枯病的治疗效果差。番茄根系中共鉴定出36种次生代谢物质,与对照相比,3,4,5-三羟基苯甲酸甲酯处理对番茄根系次生代谢产物的组成和相对含量有明显影响,其中与抑菌活性相关的物质有香叶醇、豆甾醇、β-谷甾醇和木栓醇等4种,前3种物质在3,4,5-三羟基苯甲酸甲酯处理植株体内表现为含量显著升高,木栓醇则为苗期用3,4,5-三羟基苯甲酸甲酯处理后番茄根系新增的化合物。     

Surface water seal application to minimize volatilization loss of methyl isothiocyanate from soil columns

BACKGROUND: Metam‐sodium (MS, sodium methyldithiocarbamate) has been identified as a promising alternative chemical to replace methyl bromide (MeBr) in soil preplant fumigation. One degradation product of MS in soil is the volatile gas methyl isothiocyanate (MITC) which controls soilborne pests. Inconsistent results associated with MS usage indicate that there is a need to determine cultural practices that increase pest control efficacy. Sealing the soil surface with water after MS application may be a sound method to reduce volatilization loss of MITC from soils and increase the contact time necessary for MITC to control pests. The objective of this research was to develop a preliminary soil surface water application amount that would potentially inhibit the off‐gassing rate of MITC. RESULTS: Off‐gassing rate was consistently reduced with increasing water seal application. The application of a 2.5–3.8 cm water seal provided significantly lower (71–74% reduction in MITC volatilization) total fumigant loss compared with no water seal. The most favorable reduction in MITC off‐gassing was observed in the 2.5 cm water seal. CONCLUSION: This suggests that volatilization of MITC‐generating compounds can be highly suppressed using adequate surface irrigation following chemical application in this soil type (sandy clay loam), based on preliminary bench‐scale soil column studies. Copyright © 2010 Society of Chemical Industry     

Fumigant distribution in forest nursery soils under water seal and plastic film after application of dazomet, metam-sodium and chloropicrin

Adequate concentration, exposure time and distribution uniformity of activated fumigant gases are prerequisites for successful soil fumigation. Field experiments were conducted to evaluate gas phase distributions of methyl isothiocyanate (MITC) and chloropicrin (CP) in two forest-tree nurseries. Concentrations of MITC and CP in soil air were measured from replicated microplots that received dazomet, metam-sodium and CP. Half of the plots were covered with high-density polyethylene tarp immediately after fumigation; the other half were not covered but received daily sprinkler irrigation for 1 week to create and maintain a water seal. The magnitude of MITC concentrations was similar between nurseries for metam-sodium in both tarp and water seal treatments and for dazomet in the tarp treatment. Consistently greater MITC and CP concentrations were found in the upper 30 cm of soil in the tarped plots compared with the water-sealed plots. Despite potential environmental and economic benefits with the water seal method, tarp covers were more reliable for achieving and maintaining higher MITC and CP concentrations and less prone to variations due to irrigation/rain, soil bulk density and other environmental conditions.     

异硫氰酸甲酯对小麦网腥黑穗病菌杀灭效果研究

在20℃和60%温湿度条件下,分别测定了氧硫化碳、异硫氰酸甲酯(Methyl isothiocyanate,MITC)等7种新型熏蒸剂对小麦网腥黑穗病菌(Tilletia caries(DC.)Tul.,TCT)的熏蒸效果。结果表明,除MITC外,其他6种熏蒸剂均不能完全杀灭TCT病菌;MITC熏蒸120h可有效杀灭TCT病菌,其LD90、LD95、LD99、LD99.9963分别为15.438、17.046、20.530、32.414g/m3。但是,由于小麦对MITC的高吸附性导致熏蒸剂空间浓度过低,使得有载物熏蒸试验中投药50、100g/m3MITC均未能有效杀灭小麦中的TCT病菌。残留检测结果表明,散气16d后小麦中MITC残留量分别降至0.29、1.07mg/kg,残留较高。结论:MITC对TCT有很好的杀灭效果,但由于小麦对MITC的吸附性很强,需进一步研究熏蒸方式,方可实际应用。     

灌水量及可降解膜覆盖对滴灌玉米土壤呼吸及产量的影响

以小区试验,设置3个灌水水平(W1：4 625 m³·hm^-2,W2：5 625 m³hm^-2,W3：6 625 m³·hm^-2),2种可降解膜（M1：诱导期60 d,M2：诱导期：80 d）和普通塑料地膜（M3）,研究不同处理对滴灌玉米土壤呼吸速率及其影响因子、产量等指标的影响。结果表明：各处理土壤呼吸速率日变化呈单峰型曲线,在14∶00出现最高值;土壤呼吸速率自苗期至成熟期呈先升高后降低的变化趋势,抽雄期W2M3取得最大值7.89 μmol·m^-2·s^-1。土壤呼吸速率与土壤温度、气温均呈显著正相关关系,与土壤含水率无相关关系。土壤温度敏感系数（Q₁₀）变化范围1.584～2.034,玉米生育期内土壤呼吸总量变化范围是17.75～23.44 t·hm^-2,籽粒产量变化范围是11.60～12.81 t·hm^-2。W2M3的Q₁₀为2.034、土壤呼吸总量为23.44 t·hm^-2、产量为12.81 t·hm^-2、收益为6 815元·hm^-2,均达到最大值;但其iWUE为2.28 kg·m^-3、经济-环境效益为1.83 kg·kg^-1,均未达到最大值。iWUE在W1M2取得最大值为2.51 kg·m^-3,W2M2经济-环境效益最优为1.42 kg·kg^-1。通过综合分析土壤呼吸总量、籽粒产量、经济—环境效益值、收益、iWUE的关系模型,认为最优灌水量为5 625 m³·hm^-2,诱导期为80 d。     

不同灌水量对膜下滴灌冬马铃薯生长及水分利用效率的影响

通过田间试验,设置1350 m3·hm~(-2)、1650 m3·hm~(-2)、1950 m3·hm~(-2)、2250 m3·hm~(-2)4个灌水量和1个常规沟灌为对照,研究膜下滴灌对马铃薯的生长、产量和水分利用效率的影响。结果表明:膜下滴灌马铃薯生长发育快,株高、单株茎叶鲜重、单株结薯数、单株块茎鲜重高于常规沟灌,膜下滴灌较沟灌增产6 416.08 kg·hm~(-2),增产21.29%,水分利用率高79.5 kg·hm~(-2)·mm-1。膜下滴灌下不同灌水量马铃薯水分利用率随灌水量增加呈降低趋势,产量和耗水量随灌水量增加而增加,滴灌1950 m3·hm~(-2)的产量最高,为39 732.0 kg·hm~(-2),当灌水量增加到2250 m3·hm~(-2)时,产量较滴灌1950 m3·hm~(-2)处理的下降6 624.5 kg·hm~(-2),下降16.67%。从产量提高和节水方面考虑,在生育期间有效降雨量在70 mm左右时,灌水量在1650~1950 m3·hm~(-2)较为适宜。     

滴灌高频施肥条件下玉米适宜灌水量的试验研究

通过大田试验,在高频施肥条件下设置了低水(H1,0.56KcET0),中水(H2,0.8KcET0),高水(H3,1.04 KcET0)3个不同灌水量,研究风沙土滴灌灌水量对玉米生长、干物质积累和产量的影响.结果表明:H1处理土壤含水率长期低于60％的田间持水率,H2和H3处理土壤水分能长期保持在田间持水率的60％以上...     

Effect of soil physical factors on methyl iodide and methyl bromide

Production and importation of methyl bromide is scheduled to be banned by 2001. Methyl iodide was evaluated as a possible replacement soil fumigant. The effects of soil moisture, temperature, soil texture and fumigation time on the efficacy of methyl iodide for the control of two common weeds, Abutilon theophrasti and Lolium multiflorum, were characterized and compared with those of methyl bromide. The optimal soil moisture for methyl iodide to kill both weed species in sandy soils was 14% water content (w/w). Greater efficacy was obtained when the temperature during fumigation was above 20°C. Compared to methyl bromide, the efficacy of methyl iodide was more consistent in different soils. Time to 100% mortality of weeds was 24 h for methyl iodide fumigation and 36 h for methyl bromide when 200 μM of fumigant was used. On a molar basis methyl iodide was consistently more effective than methyl bromide across the range of environmental factors tested. In terms of application technology and spectrum of activity, methyl bromide can be directly replaced by methyl iodide. © 1998 SCI