Straw coverage alleviates seasonal variability of the topsoil microbial biomass and activity

Straw coverage on soil surface is a well-known practice for conserving soil and water. Seasonal variability of microbial biomass carbon (MBC) and basal respiration (BR) in surface soil (0–5 cm) was compared between conventional straw removal (SR) and straw coverage (SC) in a maize (Zea mays L.) field experiment, Northeast China. The straw coverage treatment significantly increased microbial energy, carbon and nutrient sources (soil C and N contents) and improved soil physical environment (moisture and porosity), and thus stimulated MBC and BR across the growth season of maize, as compared to the straw removal treatment. MBC and BR showed similar seasonal trends in soil temperature, with maximum values in summer. In both study years, the straw coverage treatment reduced seasonal variation of soil temperature, therefore it significantly moderated seasonal variability of MBC and BR. Our results demonstrate that straw coverage contributes to stabilizing soil microbial characteristics in season.     

Differential and successive effects of residue quality and soil mineral N on water-stable aggregation during crop residue decomposition

Residue quality has been shown to influence soil water-stable aggregation (WSA) during crop residue decomposition, but there is still little information about its interactive effect with soil mineral N availability. The aim of this study was to determine the effect of soil mineral N on WSA during the decomposition of two high-C/N crop residues (wheat straw with C/N = 125.6 and miscanthus straw with C/N = 311.3). The two crop residues were combined with three mineral N addition rates (0, 60, and 120 mg N kg⁻¹ dry soil). Respiration, soil mineral N content, and WSA (expressed as mean-weight diameter, MWD) were measured on several dates during a 56-d incubation. The effect of decomposing crop residues on WSA followed two phases. (i) Between 0 and 7 d, the increase in WSA was related to intrinsic residue quality with higher decomposability of the wheat straw resulting in higher WSA. (ii) Thereafter, and until the end of the experiment, mineral N addition rates had a predominant but negative influence on WSA. In this second phase, the average MWD of residue-treated soils was 0.92, 0.55, and 0.44 mm for the 0, 60 and 120 mg N kg⁻¹ dry soil addition rates, respectively. Mineral N addition which did result in higher crop residue decomposition did not lead to higher WSA. WSA during crop residue decomposition is therefore not simply positively related to the induced microbial activity, and changes in microbial community composition with differential effects on WSA must be involved. The impact of high-C/N crop residues inputs on WSA, initially assumed to be low, could actually be strong and long-lasting in situations with low soil mineral N content.     

南昌市市售蔬菜有机磷农药残留调查及其原因分析

对南昌市市售蔬菜有机磷农药残留超标情况进行了系统调查,发现 21. 1%的样品中有机磷农药残留超标。分析了导致蔬菜有机磷农药残留超标的原因。     

辛酰溴苯腈复合农药的应用及残留检测进展

辛酰溴苯腈及其复合农药对阔叶杂草和部分禾本科杂草灭除效果好。为了安全有效地使用该类型农药,研究人员通过气相色谱和高效液相色谱对该类型农药的残留进行检测,发现该类型农药降解快、残留量都未检出。但是也存在一些不足：一方面由于作物对农药产生的耐药性,使得复合农药的灭除效果面临新的挑战；另一方面,随着社会对食品安全和环境保护等问题的广泛关注,农药残留的限量要求日趋严格,检测技术的发展也越来越受到重视。本文对辛酰溴苯腈及其复合农药的应用及其检测方法进行了阐述与分析,在此基础上,对该类型农药在未来的使用及其残留检测趋势进行了探索提供参考。S     

钦州市蔬菜中有机磷农药毒死蜱残留分析

为了解钦州蔬菜中毒死蜱的残留情况,2011—2017年随机抽检2 968批次蔬菜样品,进行有机磷农药毒死蜱定性、定量残留监测。结果显示:样品中毒死蜱检出229批次,占总体的7.72%,超标41批次,占总体的1.38%。4个季度蔬菜中毒死蜱残留情况相似,但一、四季度毒死蜱超标率明显高于二、三季度。叶菜类蔬菜毒死蜱检出率和超标率均最高,分别为9.97%、2.19%;其次为豆类,其检出率和超标率分别为4.49%、0.56%。在县区基地、批发市场、农贸市场随机抽取的蔬菜样品中,其毒死蜱超标率相近,而超市随机抽取的蔬菜样品情况良好,100%合格。     

2016—2018年烟台苹果中杀菌剂残留及其膳食暴露风险分析

为了解烟台主产区苹果中杀菌剂残留状况,评估居民苹果来源杀菌剂膳食暴露风险,采用随机采样方法,2016—2018年每年10月于种植、贮存和流通环节共采集718份样本,进行18种杀菌剂检测。基于蒙特卡罗拟合计算危害指数,评估杀菌剂膳食暴露风险。结果表明,苹果中存在6种杀菌剂残留,检出率53.26%,3年检出率分别为38.43%、67.93%、38.43%,年度间差异显著(α=0.01);多菌灵最高40.39%,戊唑醇最低0.14%。6种杀菌剂残留量均值范围1.03~15.4 μg/kg,组间差异显著(α=0.05),戊唑醇、异菌脲、甲基硫菌灵、多菌灵各自最大残留量远小于最大残留限量(maximum residue limit,MRL),存在咪鲜胺和苯醚甲环唑超过MRL情况,超标率0.28%。6种杀菌剂共检出385频次,多菌灵最高290频次;同一样本存在多种杀菌剂残留,最多同一样本5种杀菌剂残留。各人群分组中,6种杀菌剂的日均膳食暴露量(estimated daily intake,EDI)各异,女性大于男性;未成年人组中,6种杀菌剂的EDI均值与年龄呈现负相关。除2~6岁组外,5种杀菌剂的膳食暴露风险商(hazard quotient,HQ)值远小于1;咪鲜胺HQ>1概率值各异,2~6岁风险概率值最大;多菌灵、苯醚甲环唑HQ>1仅存在全人群2~6岁组,其概率值分别为0.01%、0.02%。苹果来源杀菌剂的慢性膳食暴露风险危害概率值为0.30%~66%,女性大于男性,摄食者大于全人群,2~6岁、7~10岁组是高风险膳食暴露组。苹果中杀菌剂残留的总体质量状况处在可接受安全水平,咪鲜胺是苹果来源杀菌剂膳食暴露风险主要危害因子,尤其对于儿童、少年等低龄人群。     

β-激动剂克伦特罗在猪肝脏和肌肉组织中的残留

本文报道用高效液相色谱法检测β 肾上腺素能激动剂（克伦特罗Ｃｌｅｎｂｕｔｅｒｏｌ）在猪肝脏和背最长肌中的残留量。在肥育猪日粮中添加３ｍｇ／ｋｇ克伦特罗,试验期３０天,停药０、１、２、３、４天屠宰取肝脏和肌肉样。组织经匀浆浓缩提取,色谱条件为：ＣＬＣ ＯＤＳ色谱柱;以２０ｍｍｏｌ／ＬＫＨ２ＰＯ４＋３０μｍｏｌ／ＬＥＤＴＡ（ｐＨ３．９）乙腈＝８２１８（Ｖ／Ｖ）为流动相;紫外检测波长为２４３ｎｍ。结果表明,克伦特罗最低检测限为２ｎｇ／ｇ。停药当天（０天）肝脏和肌肉组织残留量分别为２０８．５ｎｇ／ｇ和１０．０ｎｇ／ｇ。停药后残留量迅速下降,肌肉在停药后第２天即检测不出,而肝脏要到第４天才检测不出。     

马杜霉素在鸡组织中残留检测方法的研究 Ⅱ 免疫亲合色谱—酶联免疫吸附法(IAC—ELISA)

本文首次报道ＩＡＣ—ＥＬＩＳＡ方法测定鸡组织中马杜霉素的残留。制备针对马杜霉素的特异性抗体ＩｇＧ和高容量ＩＡＣ柱（Ｉ柱动态柱容量为７ １６０ｎｇ·ｍｌ－ １ｇｅｌ,Ⅱ柱为３ ７５０ｎｇ·ｍｌ－ １ｇｅｌ） 。组织样品用甲醇提取,经ＩＡＣ柱分离纯化,ＥＬＩＳＡ检测,即ＩＡＣ—ＥＬＩＳＡ 方法。本试验揭示,以组织样本提取纯化稀释液为介质制备的标准曲线（Ｉ５０ 为３３３ ～３７１ｎｇ·ｍｌ－ １ ,斜率为１９５ ～２２０ ,检测极限为１０ ～２８ｎｇ·ｇ－ １） ,其Ｉ５０ 值和斜率与以ＰＢＳＴ－ １０ ％ 甲醇为介质的标准曲线相符,实际ＩＡＣ—ＥＬＩＳＡ检测时,各组织的标准曲线可用后者代替,使操作大为简化、实用。各组织添加马杜霉素３００ ～１２０ ．０μｇ·ｋｇ － １ 水平下,测得样本回收率为７６４ ％ ～１０９ ．０ ％ ,变异系数为３８ ％ ～１６ ．４ ％ 。结果证明了该方法的可靠性。本文建立的ＩＡＣ—ＥＬＩＳＡ法是目前国内外唯一报道的最简便、灵敏的马杜霉素残留检测方法。     

丁醚脲在甘蓝和花菜中的残留动态研究

[目的]研究丁醚脲在蔬菜中的残留检测方法和田间消解动态,为丁醚脲在蔬菜上的使用安全提供参考依据。[方法]结合Qu ECh ERS前处理技术和LC-MS/MS分析技术,开发建立丁醚脲在甘蓝和花菜中的检测方法,并采用田间试验方法研究丁醚脲在甘蓝和花菜中的残留消解动态规律。[结果]试验表明,在0.01~1.00 mg/kg添加水平范围内,甘蓝样品中的添加回收率在79.4%~86.8%,变异系数为4.6%~7.2%,花菜样品中的添加回收率在83.8%~88.5%,变异系数为5.1%~7.7%,检出限为2.5μg/kg。田间残留试验表明,丁醚脲在甘蓝和花菜中降解符合动力学曲线,丁醚脲在甘蓝和花菜中的消解半衰期分别为2.2和3.2 d。[结论]该试验方法进行甘蓝和花菜中丁醚脲残留测定,灵敏度高,重现性好,符合农药残留检测的要求。消解动态和最终残留试验结果结合我国和国外MRL值,建议推荐用量的丁醚脲在甘蓝和花菜中的安全间隔期为7 d,出口蔬菜中谨慎使用丁醚脲。     

Dynamics of residues from a novel nano-imidacloprid formulation in soyabean fields

Imidacloprid has been widely used to control vegetable pests in China. This research was conducted to establish a method for preparing a novel imidacloprid nano-formulation and develop a simple and efficient method for determination of residues of the novel imidacloprid formulation in soyabean fields. Imidacloprid micro-crystals were directly encapsulated with chitosan and sodium alginate through layer-by-layer self-assembly. The coated colloids and photocatalysts were characterized using confocal laser scanning microscopy and scanning electron microscopy. Residues of the novel imidacloprid were determined by HPLC equipped with a UV detector. The results showed that imidacloprid micro-crystals were obtained by association and had a mean length of 7 μm and a zeta potential of −37.5 mV. The pesticide loading and encapsulation efficiency were 56.2 ± 0.96% and 81.6 ± 0.96%, respectively. Degradation of the nano-imidacloprid and the suspension concentrate imidacloprid formulations in soil coincided with C = 0.227e^−0.152t and C = 0.544e^−0.177t with half lives of about 2.8 d and 6.2 d, respectively. Degradation of the two imidacloprid formulations in soyabean plants coincided with C = 6.644e^−0.475t and C = 8.585e^−0.573t with half lives of about 1.9 d and 4.5 d, respectively. Thus, in soil, the degradation rate of the nano formulation was faster than that of the suspension concentrate, but the degradation rates were vice versa in the plant. The final residue of the nano imidacloprid formulation after 35 days was below the limit of detection but in the soyabean plant, the final residue was 0.003 mg kg⁻¹, much lower than the USA Environment Protection Agency’s Maximum Residue Level. Therefore, a dosage of 900 ml hm⁻² is suggested for the nano-imidacloprid concentrate, which could be considered as safe to fields.