Biotic and abiotic processes of nitrogen immobilization in the soil-residue interface

The interface between decaying plant residues and soil is a hotspot for microbial immobilization of soil inorganic N. Recent studies on forest and grassland soils have demonstrated that rapid abiotic immobilization of inorganic N is also induced by the presence of plant residues. We, therefore, examined (1) how N immobilization varies with distance from the soil-residue interface and (2) whether abiotic immobilization occurs in agricultural soils. Spatiotemporal changes of N immobilization in the soil-residue interface were evaluated using a box that enabled soil to be sampled in 2 mm increments from a 4 mm-thick residue compartment (RC). The RC was filled with paddy soil containing ground plant residue (rice bran, rice straw or beech leaves) uniformly at a rate of 50 g dry matter kg⁻¹. Soil in the surrounding compartments contained no residue. After aerobic incubation for 5, 15 and 30 days at 25 °C, soils in each compartment were analyzed. After 5 days, significant depletion of inorganic N occurred throughout a volume of soil extending at least 10 mm from the RC in all residue treatments, suggesting extensive diffusion of inorganic N towards the RC. The depletion within 10 mm of the RC amounted to 5.0, 4.3 and 3.4 mg for rice bran, rice straw and beech leaf treatment, respectively. On the other hand, microbial N had increased significantly in the RC of the rice bran and rice straw treatments (11 mg and 5.5 mg, respectively) and insignificantly in the RC of the beech leaf treatment (0.06 mg). This increase amounted to 221% (rice bran), 129% (rice straw) and 1.7% (beech leaves) of the decrease in inorganic N within 10 mm of each RC. Thereafter the rate of N mineralization exceeded that of immobilization, and inorganic N levels had recovered almost to their original level by 15 days (rice bran) and 30 days (rice straw and beech leaves). These results suggested the predominance of biotic immobilization in soil near rice bran and rice straw and of abiotic immobilization in soil near beech leaves. No significant increase in both microbial and soluble organic N in the vicinity of beech leaves after incubation for 5 days further suggested that the abiotic process was responsible for the transformation of inorganic N into the insoluble organic N.     

高效液相色谱—串联质谱法测定羊肉中6种磺胺类药物残留

建立了高效液相色谱—串联质谱法(LC/MS/MS)测定羊肉中残留的6种磺胺类药物:磺胺喹噁啉(sulfaquinoxaline,SQX)、磺胺嘧啶(sulfadiazine,SDZ)、磺胺二甲氧嘧啶(sulfadimethoxine,SDM)、磺胺间甲氧嘧啶(sulfamonomethoxin,SMM)、磺胺对甲氧嘧啶(sulfameter,SMT)、磺胺甲噁唑(sulfamethoxazole,SMZ)。样品经乙腈匀浆提取,正己烷脱脂后旋转蒸发至近干,氮气吹干,流动相溶解并定容,再用正己烷净化后上机检测,在多反应监测模式下检测,外标法定量。结果表明,6种磺胺质量浓度在10～500μg/L内线性关系良好,相关系数R2为0.998 1～0.999 8,回收率为78%～105%,定量限为10μg/kg。     

Cropping systems and crop residue management in the Trans-Gangetic Plains: Issues and challenges for conservation agriculture from village surveys

Conservation agriculture practices are being advocated to help sustain crop productivity gains and secure environmental sustainability in the Trans-Gangetic Plains, India’s Green Revolution heartland. The paper illustrates the use of village surveys as a quasi-quantitative system analysis tool to derive implications for agricultural research and development. Drawing from village surveys in 170 communities, the paper assesses current crop residue management practices in Punjab and Haryana’s rice-wheat, basmati-wheat and non-rice-wheat cropping systems. The prevalence of wheat as the winter crop implies an intensive collection, trading and use of wheat straw as basal feed for dairy livestock; which contrasts with the diverse crop residue management of the monsoon crops. The increased use of combine harvesters has spurred the rapid advent of mechanical wheat straw reapers whereas the bulk of combine harvested rice straw is burned in situ. Present crop residue management practices are largely incompatible with year-round mulch retention despite significant biomass production. The research and development community faces the challenge of evening out straw use and management over seasons to ensure at least partial residue retention if its calls for conservation agriculture in this important sub-region are to succeed. The paper also reiterates the worrying decline of groundwater tables associated with the rice-wheat system.     

毒死蜱在林下土壤中的残留动态

利用气相色谱法检测了应用毒死蜱喷雾防治松突圆蚧后,林下土壤中药后当天及1,3,7,14,28 d的残留量,结果表明,该药在林下土壤中1个月内的残留量较高,降解速度慢,28 d时最高降解率为89.24%,平均半衰期为11.48 d。     

溴苯腈在土壤及水中残留分析方法的研究

本文研究建立了溴苯腈在土壤及水中的残留测定方法。研究了溴苯腈在土壤及水中残留分析的不同检测法、提取净化法,比较了不同提取溶剂和提取次数对水中溴苯腈残留的提取效果及索氏提取法、振荡提取法和超声-微波协同萃取法对土壤中溴苯腈残留的提取效果。结果表明,溴苯腈在土壤及水中的残留测定适合采用高效液相色谱法;确立了溴苯腈在水中的残留测定方法为正己烷作萃取溶剂,液-液分配萃取2次,用高效液相色谱测定。当溴苯腈在水中的添加浓度为0.10～1.00mg·L-1时,标准添加回收率为98.7%～111.1%、变异系数为0.80%～7.85%;溴苯腈在土壤中残留分析的3种提取方法均能达到农药残留分析的要求,通过比较不同提取时间和溶剂用量的提取效果,最终确定了溴苯腈在土壤中的残留分析方法为用丙酮∶水∶冰乙酸=80∶18∶2(V∶V∶V)经振荡提取或超声-微波协同萃取,再经液-液分配净化,最后用高效液相色谱测定。当溴苯腈在土壤中的添加浓度为0.05～5.00mg·kg-1时,振荡提取法相应的标准添加回收率为90.9%～102.0%、变异系数为0.08%～18.44%,超声-微波协同萃取法相应的标准添加回收率为95.6%～109.4%、变异系数为0.18%～16.01%,均符合农药残留分析的要求。     

秸秆还田与实地氮肥管理对水稻产量及品质的影响

以扬粳9538为材料,通过秸秆还田与氮素管理与秸秆不还田(对照)比较试验,研究了水稻产量及品质的表现。结果表明:秸秆还田与实地氮肥管理(SSNM)可以在减少氮肥施用量,秸秆全量还田的同时,增加水稻的产量,降低单位面积穗数,提高每穗粒数、结实率。秸秆还田与实地氮肥管理降低稻米的垩白米率、垩白度和直链淀粉含量,改善稻米的外观品质和营养品质,淀粉谱的最高粘度和崩解值增加,消减值减低,稻米食味品质得到改善,该技术同时减少穗分化前干物质积累,增加抽穗期光合速率、根系活力与ATP酶活性,促进同化物向籽粒的运转,减少茎杆中非结构性碳水化合物的残留。对秸秆还田与不同氮素管理在产量、品质上的差异进行了讨论。     

酶联免疫吸附分析法测定黄瓜中的甲基对硫磷

采用自制多克隆抗体,考察了不同离子强度和不同甲醇含量对竞争反应的影响,并对反应体系进行了优化,最终建立了黄瓜中甲基对硫磷的残留检测ELISA方法。实验表明,甲基对硫磷对抗体竞争性结合的I50为0.13mg/L,方法检出限I20为6.7μg/L。除倍硫磷与杀螟硫磷表现了一定的交叉反应外,其它结构相类似的有机磷农药均无交叉反应。黄瓜样品经简单前与处理后分别采用ELISA和GC测定,用ELISA方法测得黄瓜中甲基对硫磷的添加回收率为83.10%￣93.46%,C.V为6.61%￣10.36%,最低检出限为0.003mg/kg,与GC测定数据基本相符,符合农药残留分析的要求。     

土壤中乙羧氟草醚残留分析方法及降解动态研究

利用气相色谱仪建立了土壤中乙羧氟草醚残留量的分析检测方法,并在实验室条件下研究了其在河南潮土、吉林黑土、江西红壤中的降解动态,为其环境和生态安全性评价提供重要的科学依据。结果表明:①土壤中的乙羧氟草醚残留物用丙酮-乙酸乙酯(1∶2,V/V)混合液提取,经弗罗里硅土SPE柱净化,浓缩后用气相色谱仪(带63Ni-ECD)进行检测;当添加浓度为0.01、0.05、0.5mg.kg-1时,添加回收率为86.9%～98.3%,标准偏差为1.50%～9.99%,最低检出量为1×10-12g,最低检出浓度为0.01mg.kg-1。②乙羧氟草醚在3种不同类型的土壤中降解速率大小依次为河南潮土>吉林黑土>江西红壤,降解速率常数分别为9.92×10-2、6.42×10-2和2.89×10-2,降解半衰期分别为7.0、10.8和24.0h,符合一级动力学方程。土壤pH值对乙羧氟草醚的降解有显著影响,乙羧氟草醚在碱性土壤中降解较快,在酸性土壤中降解较慢。根据国内农药在土壤中的残留性划分标准,乙羧氟草醚为易降解农药。     

喹乙醇在鲤鱼体内的积累与残留

分别用8个不同喹乙醇剂量(0、50、100、200、400、800、1600、3200mg／kg)的饵料和6个不同喹乙醇剂量(0、200、400、800、1600、3200mg／kg)的饵料对鲤鱼Crprinus carpio L进行2批饲养试验，采用高效液相色谱法(HPLC)，测定并分析了不同剂量和摄食时间(实验1)、不同剂量和停药时间(实验2)鲤鱼组织中药物的积累和残留。结果表明，各种组织中喹乙醇的蓄积量随时间的延长和给药量的增加而逐渐增加。不同组织对会喹醇的蓄积能力不同。其中以肝脏为最大，肌肉为最小。组织喹乙醇的消除速度，以肌肉的为最慢。肾脏为最快。在所有给药组中，喹乙醇在组织中的残留水平可在停药6d后降低到检测限以下，说明其消除速度较快。     

哒螨灵的残留分析方法研究进展

哒螨灵是一种广谱性杀螨剂，多用于柑桔树、苹果树上防治红蜘蛛，本文综合阐述了目前国内外关于哒螨灵的残留检测技术的研究进展，包括在哒螨灵残留分析中运用的固相萃取（SPE）、凝胶渗透色谱（GPC）等前处理方法，以及气相色谱（GC）、高效液相色谱（HPLC）、气质联用（GC—MS）、液质联用（LC—MS）等检测方法的应用进展。