新烟碱类和阿维菌素类药剂对蚯蚓的急性毒性效应

为评价农药对蚯蚓的生态风险提供基础数据,采用滤纸法和人工土壤法测定了新烟碱类和阿维菌素类药剂对蚯蚓的急性毒性效应。滤纸法测定结果表明,吡虫啉、啶虫脒、烯啶虫胺、氯噻啉和噻虫啉5种新烟碱类药剂对蚯蚓的LC50值范围为0.0089（0.0075～0.010）μg·cm^-2～0.44（0.34～0.56）μg·cm^-2（48h结果）,噻虫嗪对蚯蚓的LC50值在24h和48h均大于62.91μg·cm^-2;阿维菌素、依维菌素和甲氨基阿维菌素苯甲酸盐3种阿维菌素类药剂对蚯蚓的LC50值范围为4.52（3.71～5.50）μg·cm^-2～22.76（18.68～27.73）μg·cm^-2（48h结果）。人工土壤法测定结果表明,5种新烟碱类药剂（除噻虫嗪外）对蚯蚓的LC50值范围为1.54（1.43～1.71）mg·kg^-1～17.29（16.44～19.41）mg·kg^-1（14d结果）,噻虫嗪对蚯蚓的LC50值在第7d和14d均大于1200mg·kg^-1;3种阿维菌素类药剂对蚯蚓的LC50值范围为27.93（26.04～29.81）mg·kg^-1～175.33（162.82～188.91）mg·kg^-1（14d结果）。根据《化学农药环境安全评价试验准则》,吡虫啉、啶虫脒和烯啶虫胺对蚯蚓属于中毒级,其他的药剂对蚯蚓属于低毒级。     

三种森林土壤中莠去津对蚯蚓的毒性效应

通过研究三种不同森林土壤中蚯蚓对莠去津暴露的响应，为莠去津在林业上的科学使用和保护生态环境提供科学依据。采用室内实验的方法研究三种不同类型的森林土壤中莠去津对蚯蚓的影响，以40、80、160、320、480 mg/kg作为暴露浓度，暴露后于第0天，第7天，第14天，第21天，第28天，第35天分别测定土壤中蚯蚓鲜重和死亡率，于第0天和第35天测定土壤中蚯蚓体宽。结果表明，三种森林土壤中莠去津暴露浓度越高，暴露时间越长，对蚯蚓致死效应越强，对蚯蚓鲜重和体宽的抑制效应也越强，呈明显的时间-效应关系和剂量-效应关系。暴露浓度相同时，三种土壤中莠去津对蚯蚓死亡率、鲜重和体重的影响均表现为黄棕壤>雏形土>石灰土。莠去津对蚯蚓的毒性效应与土壤中有机质的含量之间具有明显负相关性，与全磷和有效磷的含量之间具有明显正相关性。研究结果揭示不同类型土壤中莠去津对蚯蚓的毒性作用具有明显差异，且与土壤的肥力具有显著相关性，其可为评估莠去津在农林业上使用的环境风险提供基础参考数据。     

蚯蚓对秸秆-污泥混合物的消解转化效果

为了探明蚯蚓对秸秆与污泥混合物的消解转化效果,在实验室条件下进行了模拟培养试验。试验共设不同配比混合物料6个处理,即水稻秸秆与城市生活污泥的质量比分别为0/100、10/90、20/80、30/70、40/60和50/50,各处理混合物料接种蚯蚓后在常温下培养。根据物料的消耗情况进行计量补充,并根据需要及时补充水分,始终维持培养料湿润。培养6星期后,去除未被消解的混合物料,分离并计测蚯蚓重量与蚓粪有机肥重量及养分含量,计算混合物料的消解量。结果表明,在本试验条件下,掺入10%-30%秸秆显著提高蚯蚓对混合物料的消解速率。掺入10%和20%秸秆的处理蚯蚓生物量的增长速率显著高于掺入50%秸秆的处理。掺入10%-50%秸秆均显著提高蚯蚓转化污泥-秸秆混合物料形成有机肥的速率。蚓粪有机肥的有机质含量随着掺入秸秆比例的增加而提高;全氮和全钾含量无显著影响;与单纯采用污泥相比,当掺入秸秆比例达40%和50%时,蚓粪全磷含量显著降低。     

土壤中亚致死剂量毒死蜱对蚯蚓抗氧化防御系统酶活性的影响

以赤子爱胜蚓(Eisenia fetida)为供试生物,研究了暴露于含有亚致死剂量毒死蜱的人工土壤中8周时间内蚯蚓超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、谷胱甘肽过氧化物酶(GSH-Px)活性的变化。结果表明,毒死蜱对蚯蚓SOD、CAT、GSH-Px酶活性具有显著抑制。蚯蚓抗氧化防御系统酶对毒死蜱毒性具有一定的指示作用。除蚯蚓的LC50、产卵率、卵孵化率等常用的蚯蚓生态毒理学指标外,蚯蚓的SOD、CAT、GSH-Px抗氧化酶活性与实验农药的毒性效应具有相关性,但各指标在对毒性的响应敏感性上存在差异,其中,SOD、GSH-Px最为敏感,而CAT最不敏感。因此,在生态毒性诊断时,应选择不同指标作为一套指标体系相互补充,以增强污染诊断的灵敏性及长期诊断。     

[C8mim]Br对蚯蚓抗氧化系统的亚慢性毒性效应

以OECD标准的基质染毒法测定了离子液体溴化1-辛基-3-甲基咪唑（[Csmim]Br）对蚯蚓（Eisenia foetida）的急性毒性效应和亚慢性毒性条件下蚯蚓体内CAT、SOD、GST的活性和GSH、MDA含量的变化,以期初步分析[Csmim]Br对蚯蚓抗氧化系统的作用及其毒性作用的可能机理。结果表明,[C8mim]Br对蚯蚓的7d—LD50和14d—LD50分别为206．8mg·kg-1和159．4mg·kg-1。亚慢性暴露42d后蚯蚓体内CAT的活性受到显著抑制;SOD的活性在低浓度（1～5mg·kg-1）受到抑制,高浓度（20～40mg·kg-1）被激活;在高浓度处理组（20—40mg·kg-1）GST的活性显著高于对照。10～40mg·k-1 浓度的[C8mim]Br处理组GSH的含量显著升高,各处理组MDA含量与对照相比没有差异。推测[C8mim]Br可能通过肠道吸收进入蚯蚓体内,并诱导了蚯蚓体内抗氧化系统的反馈效应。     

DEHP对土壤蚯蚓氧化胁迫及DNA损伤的研究

土壤环境中的酞酸酯污染日益严重,为了探讨和分析典型酞酸酯邻苯二甲酸二(2-乙基己基)酯(Di(2-ethylhexyl)phthalate,DEHP)对土壤动物的生态毒理效应,以赤子爱胜蚓为指示生物,暴露于DEHP浓度为CK、0.1、1、10、50 mg kg~(-1)人工土壤中,并于染毒后的7、14、21、28d取样测定。通过蚯蚓体内的超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、过氧化物(POD)、谷胱甘肽转移酶(GST)等指标反映DEHP对蚯蚓的氧化激活程度,通过活性氧自由基(ROS)的含量反映DEHP对蚯蚓的细胞毒性,通过丙二醛(MDA)含量和Olive尾矩反映DEHP对蚯蚓的遗传毒性,从多个角度评价DEHP对蚯蚓的生态毒理效应。结果表明:(1)在DEHP的刺激下,各浓度组蚯蚓的SOD、CAT、POD、GST活性均呈激活状态,表明DEHP对蚯蚓的抗氧化酶有诱导作用;(2)DEHP影响蚯蚓的ROS含量,各染毒处理组与对照组相比均升高且差异性明显,表现出明显的剂量—效应关系;(3)对比各染毒处理组之间的数据,DEHP对蚯蚓MDA含量的影响无明显规律;(4)DEHP可使蚯蚓GST呈激活状态,表明中高浓度的DEHP对蚯蚓GST具有诱导作用;(5)DEHP能够引起蚯蚓体腔细胞DNA的损伤,且随着浓度的增加,Olive尾矩值随之增加,说明DNA损伤程度与DEHP浓度之间具有剂量-效应关系。从实验结果可以看出,DEHP可以对蚯蚓机体和DNA造成一定程度的损伤,表现出较强的生态毒理效应。     

莫能菌素对蚯蚓的生态毒理效应

采用人工土壤法测定了不同浓度莫能菌素对蚯蚓的急性毒性和对蚯蚓生长、生存、繁殖以及超氧化物歧化酶（SOD）、谷胱甘肽-硫转移酶（GSH-S）、腺三磷酸酶（ATPase）、乙酰胆碱酯酶（T-CHE）活性的影响。结果表明,莫能菌素对蚯蚓14d的LC50为75.883mg·kg-1;当莫能菌素含量达到50mg·kg-1时显著影响蚯蚓的生存（P〈0.05）,死亡率达到20%;当莫能菌素含量达到25mg·kg-1时显著影响蚯蚓的生长（P〈0.05）;药物的染毒浓度与对蚯蚓生存和繁殖的抑制存在明显的剂量-效应关系。染毒21d后,低浓度的兽药莫能菌素就能显著影响蚯蚓体内SOD、GSH-S、ATPase、T-CHE的活性,药物浓度和酶活性间具有明显的剂量-效应关系。莫能菌素对土壤动物蚯蚓显示有毒性作用,对土壤环境具有潜在的生态风险。     

蚯蚓活动对城市生活污泥重金属的影响

采用塑料温棚内垄式堆积污泥培养蚯蚓方式,研究了蚯蚓处理对污泥重金属的影响。结果表明,污泥经蚯蚓处理后,理化性质发生了显著的变化,污泥的pH值、有机质、总氮和总磷都有不同程度的降低;蚯蚓能吸收富集污泥中的重金属,其中对重金属Cd有较强的富集能力;蚯蚓处理使污泥中重金属含量均出现不同程度的下降,重金属Cr、Zn、Pb、Cd、Cu、Ni分别减少27.98%、31.46%、32.81%、13.85%、23.86%和22.92%。利用盆栽试验,研究了污泥施用于土壤后生菜体内重金属积累的情况,结果表明,生菜体内重金属Zn、Cu、Pb和Ni的含量为污泥处理高于蚓粪处理;Cr和Cd则分别为差异不显著和略有降低。     

城市污泥的蚯蚓分解处理技术研究进展

城市污泥成分复杂,其中有机质、N、P、K含量丰富,Ca、Mg、Fe等矿物营养成分含量较高,此外还有许多重金属（Zn、Cu、Cd、Cr、Pb、Ni、Hg、As、Sn等）、有机有害成分以及病原菌。本文分析了国内外关于污泥处理处置的主要方法及其优缺点,重点讨论了一种新兴城市污泥处理技术,即城市污泥的蚯蚓分解处理技术（Vermicomposting）,利用蚯蚓处理城市污泥,不仅可以将污泥中的重金属富集于蚯蚓体内、去除病原菌、转移消化有机有害物,而且可将城市污泥转化为富含营养物质的有机肥,是一种无害化处理城市污泥的有效途径。最后,总结了目前城市污泥蚯蚓分解处理技术研究中存在的问题,并展望了其研究发展趋势。     

作物秸秆与城市污泥高温好氧堆肥产物对土壤氮矿化的影响

为揭示不同作物秸秆与污泥堆肥产物对土壤氮素矿化特征的影响,为科学施用城市污泥堆肥提供参考依据,通过室内培养试验研究了城市污泥与4种秸秆（小麦、水稻、玉米和油菜）高温好氧堆肥产物施入酸性紫色土、黄壤、石灰性紫色土后土壤氮矿化的差异。结果表明,4秸秆污泥堆肥均可显著提高3种土壤氮的潜在矿化势（N0）和矿化速度（k）,促进土壤氮的矿化,提高土壤NH4+-N、NO3--N质量分数,其中石灰性紫色土以油菜秸秆污泥堆肥和小麦秸秆污泥堆肥处理、黄壤以油菜秸秆污泥堆肥处理、酸性紫色土以小麦秸秆污泥堆肥处理提高幅度最大。作物秸秆与污泥堆肥施入土壤后,黄壤、酸性紫色土在培养60 d和30 d后趋于稳定,石灰性紫色土在培养60 d后仍有增高的趋势,但不同秸秆污泥堆肥对土壤氮矿化速度的影响无明显规律。结果说明秸秆污泥堆肥对土壤氮矿化的效应因土壤及秸秆类型的不同而异,根据研究结果提出了4种作物秸秆与城市污泥堆肥施用的建议。     

Lethal critical body residues as measures of Cd,Pb, and Zn bioavailability and toxicity in the earthworm<Emphasis Type="Italic">Eisenia fetida</Emphasis>

Background. Earthworm heavy metal concentrations (critical body residues, CBRs) may be the most relevant measures of heavy metal bioavailability in soils and may be linkable to toxic effects in order to better assess soil ecotoxicity. However, as earthworms possess physiological mechanisms to secrete and/or sequester absorbed metals as toxicologically inactive forms, total earthworm metal concentrations may not relate well with toxicity. Objective  The objectives of this research were to: i) develop LD₅₀s (total earthworm metal concentration associated with 50% mortality) for Cd, Pb, and Zn; ii) evaluate the LD₅₀ for Zn in a lethal Zn-smelter soil; iii) evaluate the lethal mixture toxicity of Cd, Pb, and Zn using earthworm metal concentrations and the toxic unit (TU) approach; and iv) evaluate total and fractionated earthworm concentrations as indicators of sublethal exposure. Methods  Earthworms (Eisenia fetida (Savigny)) were exposed to artificial soils spiked with Cd, Pb, Zn, and a Cd-Pb-Zn equitoxic mixture to estimate lethal CBRs and mixture toxicity. To evaluate the CBR developed for Zn, earthworms were also exposed to Zn-contaminated field soils receiving three different remediation treatments. Earthworm metal concentrations were measured using a procedure devised to isolate toxicologically active metal burdens via separation into cytosolic and pellet fractions. Results and Discussion  Lethal CBRs inducing 50% mortality (LD₅₀, 95% CI) were calculated to be 5.72 (3.54-7.31), 3.33 (2.97-3.69), and 8.19 (4.78-11.6) mmol/kg for Cd, Pb, and Zn, respectively. Zn concentrations of dead earthworms exposed to a lethal remediated Zn-smelter soil were 3-fold above the LD₅₀ for Zn and comparable to earthworm concentrations in lethal Zn-spiked artificial soils, despite a 14-fold difference in total soil Zn concentration between lethal field and artificial soils. An evaluation of the acute mixture toxicity of Cd, Pb, and Zn in artificial soils using the Toxic Unit (TU) approach revealed an LD₅₀ (95% CI) of 0.99 (0.57-1.41) TU, indicating additive toxicity. Conclusions  Total Cd, Pb, and Zn concentrations in earthworms were good indicators of lethal metal exposure, and enabled the calculation at LD₅₀s for lethality. The Zn-LD₅₀ developed in artificial soil was applicable to earthworms exposed to remediated Zn-smelter soil, despite a 14-fold difference in total soil Zn concentrations. Mixture toxicity evaluated using LD₅₀s from each single metal test indicated additive mixture toxicity among Cd, Pb, and Zn. Fractionation of earth worm tissues into cytosolic and pellet digests yielded mixed results for detecting differences in exposure at the sublethal level Recommendation and Outlook  CBRs are useful in describing acute Cd, Pb, and Zn toxicity in earthworms, but linking sublethal exposure to total and/or fractionated residues may be more difficult. More research on detoxification, regulation, and tissue and subcellular partitioning of heavy metals in earthworms and other invertebrates is needed to establish the link between body residue and sublethal exposure and toxicity. Keywords: Bioavailability; Cd; critical body residues; earthworms; metals; Pb; soil; Zn An erratum to this article is available at .     

Toxicity of metals to the earthworm Eisenia fetida

Summary Development of methods to measure the effect of man's residuals on soil ecosystems is desirable. Earthworms, as one of the largest and most easily obtained components of the soil biota, are suitable for evaluating perturbations to soil ecosystems.The impact of five metals (Cd, Cu, Ni, Pb, and Zn) on the survival of the earthworm Eisenia fetida (Savigny) was evaluated using the contact and artificial soil tests. There was no difference in toxicity between the different metal salts (acetate, chloride, nitrate, and sulfate) of each of the five metals using the contact test. In the contact test, the order of toxicity, from most toxic to least toxic, was Cu > Zn > Ni Cd > Pb. The nitrate salt of the five metals was tested using the artificial soil test and the order of toxicity, from most toxic to least toxic, was Cu Zn Ni > Cd > Pb. Stress on earthworm populations, as shown by weight loss, was shown to increase with increasing concentrations of metal salts.These studies indicate that: (a) earthworms can be a suitable biomonitoring tool to assist in measuring the effect of metals in wastes added to soils and (b) the contact and artificial soil tests can measure the biological impacts.Research Associate, Research Technician, and Research Support Specialist, respectivelyAt the time of this research, Dr. Loehr was a Professor of Agricultural Engineering and of Environmental Engineering, Cornell University. He currently is the H.M. Alharthy Centennial Chair Professor, Civil Engineering Department, University of Texas, Austin, Texas 78712     

The use of sewage sludge as soil amendment. The need for an ecotoxicological evaluation

Background, aim, and scope  Sewage sludge use in agriculture should be limited by the presence of metals and other persistent environmental pollutants. The present study aims to contribute for the definition of a test battery of ecotoxicological assays that allows a proper ecotoxicological characterization of sludges, providing information on their potential hazard and identified “safe” application levels. Materials and methods  Three sludges from distinct sources (urban, olive-processing, and electroplating industries) were tested using avoidance and reproduction tests with earthworms (Eisenia andrei) and springtails (Folsomia candida) and plant growth tests with turnips (Brassica rapa) and oats (Avena sativa). Different soil–sludge mixture concentrations mimicking recommended/realistic field dosages were tested. Results  Only the sludge from the electroplating industry induced an avoidance response from the earthworms (EC₅₀ = 0.4 t/ha) and collembolans (no observed effect concentration (NOEC) = 15 t/ha). This sludge was the only sludge responsible for any effect on the reproductive output of the earthworms (EC₅₀ = 7.74 t/ha). Regarding collembolans, none of the sludges tested caused any significant decrease in reproduction. In higher plant tests, the two industrial sludges were toxic, causing a decrease growth in both species. The EC₂₀ values determined for B. rapa were 20.3 and 24.2 t/ha and for A. sativa 14.7 and 16.2 t/ha for sludges from olive-processing and electroplating industries, respectively. Discussion  The metal loadings of the different test sludges could partially explain the results obtained. The toxicity of the test sludge from electroplating industry observed on the tested invertebrates and plants could be explained by the high amount of total chromium from which 22.3% was in the most toxic oxidation state—Cr(VI). However, the toxicity caused by the sludge from the olive-processing industry in the test plants could be attributed to the presence of other compounds (not measured in this study) since the metal content was not high enough to induce such an effect. The absence of toxicity showed by the urban test sludge was in agreement with its low levels of metals. Conclusions  The response of the different test organisms and end points varied according to the sludge type. The urban sludge was non-toxic whereas the sludge from the electroplating industry caused a toxic effect on almost all parameters measured (avoidance behavior of both test organisms, reproduction of earthworms, and growth of both plant species). Sludge from the olive-processing industry only caused a toxic effect on growth of both plant species. By analyzing the sensitivity of the different parameters for the most toxic sludge, it was found that avoidance and reproduction were more sensitive than plant growth, whereas plant seed germination was not sensitive at all. Recommendations and perspectives  The ecotoxicological evaluation of wastes can be used as an environmental safety control of sludge use in agriculture. A tiered approach could be adopted for this purpose, incorporating avoidance tests in the first tier (screening level) and reproduction and plant growth tests in a second tier. But more evidence aiming to define the most suitable ecotoxicological test battery for specific sludges with a different contamination profile is still needed.     

Influence of soil pH on the toxicity of aluminium for Eisenia andrei (Oligochaeta: Lumbricidae) in an artificial soil substrate

Toxicity of aluminium for the earthworm Eisenia andrei was studied in artificial soil at different pH levels. In a range-finding test, effects of three different aluminium salts on earthworm survival were determined. AlCl₃ appeared to be most toxic, with LC₅₀ values of 316, 359 and >1000 mg Al/kg dry soil at pH_KCl of 3.5, 4.4 and 6.7, respectively in the control soils. Effects of this salt interfered with a strong decrease of soil pH with increasing aluminium concentration. Al₂(SO₄)₃ was less toxic with LC₅₀ values of 457, >4000 and >4000 mg Al/kg dry soil at pH 3.24, 4.86 and 7.22, respectively. Al₂O₃ did not affect earthworm survival at concentrations of 5000 mg Al/kg and pH levels between 2.4 and 7.1.In the main test, earthworms were exposed for 6 weeks to soils treated with Al₂(SO₄)₃. As in the range-finding test, aluminium sulfate was most toxic at a pH of 3.4 with an LC₅₀ of 589 mg Al/kg dry soil. At this pH, growth and cocoon production of earthworms were significantly reduced at 320 mg Al/kg dry soil, while at 1000 mg Al/kg dry soil all earthworms died. Survival was not affected by 1000 mg Al/kg dry soil at pH 4.3 and 7.3. At pH 4.3, growth was significantly reduced at 1000 mg Al/kg dry soil and cocoon production at 320 and 1000 mg Al/kg dry soil. At pH 7.3, aluminium only affected cocoon production at the two highest exposure levels. At the highest two exposure levels at pH 7.3, growth was significantly increased, suggesting a trade-off between growth and reproduction. These effects of aluminium at the highest soil pH could not be explained from the concentration of extractable, monomeric (labile) aluminium in soil, which decreased with increasing soil pH.     

Interactive effects of biochar and the earthworm Pontoscolex corethrurus on plant productivity and soil enzyme activities

Purpose

There is a growing interest in the use of soil enzymes as early indicators of soil quality change under contrasting agricultural management practices. In recent years, there has been increasing interest in the use of biochar to improve soil properties and thus soil quality. In addition, earthworms can also be used to ameliorate soil properties. However, there is no literature available on how biochar and earthworms interact and affect soil enzymes. The general objective of the present study was to test the suitability of adding biochar and earthworms in two tropical soils with low fertility status in order to improve their characteristics and productivity.

Materials and methods

Biochars were prepared from four different materials [sewage sludge (B1), deinking sewage sludge (B2), Miscanthus (B3) and pine wood (B4)] on two tropical soils (an Acrisol and a Ferralsol) planted with proso millet (Panicum milliaceum L.). In addition, in order to investigate the interaction between earthworms and biochar, earthworm Pontoscolex corethrurus was added to half of the mesocosms, while excluded in the remaining half. The activities of invertase, β-glucosidase, β-glucosaminidase, urease, phosphomonoesterase and arylsulphatase were determined. The geometric mean of the assayed enzymes (GMea) was used as an integrative soil quality index.

Results and discussion

Overall, earthworms and especially biochar had a positive effect on soil quality. GMea showed B1, B2 and B3 performing better than B4; however, results were soil specific. Plant productivity increased under both biochar and earthworm addition. Fruit productivity and plant growth was enhanced by B1 and B2 but not by B3 or B4.

Conclusions

Enhancements of productivity and soil enzymatic activities are possible in the presence of earthworms and the combination of the practices earthworm and biochar addition can be suggested in low fertility tropical soils. However, scientists should proceed carefully in the selection of biochars as the results of this study show a high specificity in the biochar–soil interaction.     

Contrasted effect of biochar and earthworms on rice growth and resource allocation in different soils

Adding biochar to soils and maintaining high earthworm biomasses are potential ways to increase the fertility of tropical soils and the sustainability of crop production in the spirit of agroecology and ecological engineering. However, a thorough functional assessment of biochar effect on plant growth and resource allocations is so far missing. Moreover, earthworms and biochar increase mineral nutrient availability through an increase in mineralization and nutrient retention respectively and are likely to interact through various other mechanisms. They could thus increase plant growth synergistically. This hypothesis was tested for rice in a greenhouse experiment. Besides, the relative effects of biochar and earthworms were compared in three different soil treatments (a nutrient rich soil, a nutrient poor soil, a nutrient poor soil supplemented with fertilization). Biochar and earthworm effects on rice growth and resource allocation highly depended on soil type and were generally additive (no synergy). In the rich soil, there were both clear positive biochar and earthworm effects, while there were generally only positive earthworm effects in the poor soil, and neither earthworm nor biochar effect in the poor soil with fertilization. The analysis of earthworm and biochar effects on different plant traits and soil mineral nitrogen content, confirmed that they act through an increase in nutrient availability. However it also suggested that another mechanism, such as the release in the soil of molecules recognized as phytohormones by plants, is also involved in earthworm action. This mechanism could for example help explaining how earthworms increase rice resource allocation to roots and influence the allocation to grains.     

Effect of metal toxicity on the size of the soil microbial biomass

The amount of soil microbial biomass was measured by the chloroform fumigation technique on agricultural soils which had been previously treated with different bulky organic manures. Amounts of soil microbial biomass in soils receiving sewage sludge or sludge-containing composts were much smaller than in soils which received farmyard manure over the same period. This effect was attributed to the toxic metals present in the sludges and was readily detectable more than 20 years after the last sludge application.     

Inefficiency of mustard extraction technique for assessing size and structure of earthworm communities in UK pasture

An assessment of the efficiency of the mustard extraction method to quantify the total earthworm community structure on UK earthworms was carried out on a permanent pasture in Bedfordshire, UK. Earthworms were collected using mustard extraction and control treatments. Numbers and community structure of worms expelled from soils after surface applications of expellants were determined, and underlying soil from each replicate was hand-sorted to recover residual earthworms. The mustard-based treatment was the only method to expel earthworms to the surface, and 35.7% of the extant population emerged. The apparent earthworm community structures expelled indicated that mustard extraction was biased towards large, sexually mature anecic earthworms. This is likely due to the connectivity of burrows of these earthworms to the surface and hence a biased incursion of mustard solution down such channels. The mustard extraction technique is therefore inappropriate where accurate assessment of earthworm communities is required.     

Effects of earthworms on soil enzyme activity in an organic residue amended rice–wheat rotation agro-ecosystem

The effect of earthworms on soil hydrolases (protease, urease, invertase, and alkaline phosphatase) and dehydrogenase activities was investigated in maize residue amended rice–wheat rotation agro-ecosystem. Experimental plots in the rotation had five treatments, i.e. incorporation or mulching of maize residues with or without added earthworms and an untreated control. The application of maize residues to soil without earthworms significantly enhanced the five soil enzyme activities compared with the control treatment during rice and wheat cultivation. The presence of earthworms further significantly enhanced protease activity in the soils with both incorporated and mulched maize residues during two cultivation seasons, but only significantly increased alkaline phosphatase activity in the soil with incorporated maize residue during the rice cultivation season. Invertase activity was significantly enhanced by the presence of earthworms in the soil with maize residue incorporation during two cultivation seasons. There were no changes in dehydrogenase activity when earthworms were present. Additionally, the five enzyme activities in earthworm casts were significant higher than those in the surrounding soil, especially dehydrogenase and invertase activities. Whatever the treatment, the values obtained for the enzyme activities in both soil and casts, except for dehydrogenase activity in earthworm casts, were significantly higher under wheat than those in rice-cultivated soil. These results indicate that the presence of earthworms strongly affected soil enzyme activities, depending on the method of organic residue application, and the enhanced enzyme activities of earthworm casts probably contributed to the surrounding soil enzyme activities.