生态农业的传统与创新发展——以生态农业“稻田养鱼”模式为例

以保护“稻鱼共生系统”这样的农业文化遗产,探讨如何继承和挖掘、发扬传统农业文化中的生态文化内涵,促进当代生态农业的发展。     

四川省农业文化遗产保护现状及对策探析

从联合国粮农组织2002年提倡农业文化遗产的保护以来,农业遗产、全球重要农业文化遗产、中国重要农业文化遗产等一些新的概念也如雨后春笋般地涌现出来。2005年浙江省的青田稻鱼共生系统首次入围全球重要农业文化遗产名录。随后我国对农业文化遗产的挖掘、保护和研究也与日俱增。四川省作为一个农业大省,具有丰富的农业文化遗产资源,对其农业文化遗产的挖掘与保护可以丰富我国的农业文化遗产。通过对四川省农业文化遗产发展的现状、存在的问题进行分析,提出了完善农业文化遗产保护政策、培育农业文化遗产传承人、适度发展旅游业、做强特色农产品品牌建设等建议。     

中国GIAHS保护试点: 价值、问题与对策*

中国农业文明历史悠久,留存了丰富的农业文化遗产。它们不仅体现了中国的传统哲学思想,同时也对全球可持续农业产生积极影响,并成为现代生态农业发展的基础。2002年,联合国粮农组织(FAO)发起了全球重要农业文化遗产(GIAHS)保护项目,旨在对全球重要的、受到威胁的传统农业文化与技术遗产进行保护。目前我国已有4个GIAHS保护试点,即浙江青田稻鱼共生系统、云南哈尼稻作梯田系统、江西万年稻作文化系统和贵州从江县侗乡稻鱼鸭系统,2个候选试点,即云南普洱古茶园和茶文化及内蒙古敖汉旱作农业系统。本文基于FAO对GIAHS项目价值标准的解释,系统梳理了这6个试点的概况、价值、面临的威胁以及保护建议等,以期为我国农业文化遗产的保护提供指导依据。GIAHS的价值主要包括生态价值、经济价值、社会和文化价值、科研与示范价值等。目前农业文化遗产面临的主要威胁包括比较效益降低、适龄劳动力大量外流、现代观念的冲击和多重价值认识不足等。文章还提出了对GIAHS试点保护的建议,主要为引入动态保护途径,增加农民收入;加强宣传力度,建立科学的保护理念;完善制度建设,形成可持续的保护机制;调动农民的积极性,建立多方尤其是社区参与机制以及建立农业文化品牌,形成动态的保护机制等。     

卷首语

正对于中国的农业文化遗产保护事业, 2005年注定是一个值得记住的年份。2005年5月,在原农业部国际合作司的支持下,中国科学院地理科学与资源研究所、联合国大学以及浙江省、青田县有关部门经过两年多的努力,成功将浙江青田稻鱼共生系统推荐为联合国粮农组织(FAO)拟申请的全球环境基金(GEF)项目——全球重要农业文化遗产(GIAHS)动态保护与适应性管理的项目试点。6月5日,时任浙江省委书记就此专门作出批示;6月9—11日,在杭州和青田分别召开了项目启动会和授牌仪式。自此,以系统性、活态性为主要特征的农业文化遗产保护工作正式起步。     

稻田养鱼与常规稻田耕作模式的综合效益比较研究——以浙江省青田县为例

农业是整个国民经济发展的基础,不可否认现代化大规模农业生产在保障粮食数量安全方面贡献巨大,但在一些适合小规模耕作的山区,经典的传统农业模式比常规农业耕作方式更具优势。本文基于生态价值观,以浙江省青田县稻鱼共生系统和常规稻作系统为例,针对农户和国家两个不同层次主体,综合计算了上述两种农业生产模式的效益。结果表明,就直接经济收入而言,稻鱼共生系统的净收入比常规稻作系统高2184元·hm-2,投入多1453元·hm-2,其投入产出比和投资利润率较低;但若考虑社会-经济-生态综合效益,稻鱼共生系统的生态系统服务价值比常规稻作系统高7447元·hm-2,平均每公顷的综合价值高9631元,同时其投入产出比和投资利润率优于常规稻作系统。基于效益分析,稻鱼共生系统的补偿标准下限为6532元·hm-2,上限为16045元·hm-2,政府可以通过对农户的补贴实现直接经济价值和社会综合效益的双赢。     

传统稻鱼系统生产力提升对稻田水体环境的影响

如何在提升传统农业系统生产力的同时又不破坏其内涵、还对环境不产生负面影响,是一个受到研究者持续性关注的挑战性课题。本研究以具有1 200年历史的全球重要农业文化遗产稻鱼系统为例,研究稻鱼系统鱼的放养密度对生产力和环境的影响,探讨能够显著提升稻鱼系统生产力且又不破坏其传统性(产品优质、环境友好)的途径。研究表明,传统稻鱼系统(RF)(田鱼目标产量375 kg.hm 2)与水稻单作系统(RM)水体的化学需氧量(COD)、总氮(TN)、总磷(TP)及铵态氮(NH4+-N)含量均没有显著性差异。随着田鱼养殖密度提高(鱼产量由750 kg.hm 2提高到3 000 kg.hm 2)和饲料投入的相应增加,稻鱼系统的生产力和经济产出大幅度提高(稻鱼系统的净经济收入增加25.2%~101.4%),但稻鱼系统(RF)水体的COD值及TN、TP和NH4+-N含量均呈现增加的趋势,尤其是当鱼目标产量增至3 000 kg.hm 2时,水体TP含量和COD值显著提高,面源污染风险增加。分析还表明,鱼放养目标产量为2 250 kg.hm 2时,稻鱼系统经济效益最佳,此时净经济收入比传统稻鱼系统增加55.9%,并且不会对水体环境质量产生负面影响。     

稻-鱼系统的发展与未来思考

耕地和淡水是保证全球食物可持续供应所必不可少的资源,如何有效利用有限的水土资源、在保障食物供给的同时降低农业生产过程对资源环境的负面影响,是当今世界农业面临的重大挑战。稻-鱼系统(本文的"鱼"是水产生物的统称)是通过有效利用水土资源同时产出稻谷和水产品的重要农业方式,对保障区域食物供给和保护当地资源和环境有重要作用。近几十年来全球稻鱼-系统迅速发展,至目前全球六大洲的稻作区共28个国家都有了稻-鱼系统的分布;在中国稻-鱼系统也正由原来传统、规模小、养殖单一的模式逐渐发展为规模化、专业化、机械化和养殖多样化的模式。大量研究表明,稻-鱼系统可实现水稻产量稳定和获得水产品,稻-鱼系统同时具有化肥农药减量和农业面源污染降低等效应;稻-鱼系统也有助于解决水产单一养殖而产生的面源污染。虽然全球1.63亿hm2稻田面积90%以上具有发展稻-鱼系统的潜力,但目前稻-鱼系统的比例仍很低,我国稻-鱼系统面积也仅占稻田面积的4.48%。因此,保障稳产高效可持续的稻-鱼系统发展,需要对不同稻作区发展稻-鱼系统的生态经济可行性和适应性进行评估,同时必须建立新的技术体系(田间设施、种养结合技术、农业机械等),并适当扩大规模和创建品牌以增加农民收益。     

重要农业文化遗产价值体系构建及评估(I):价值体系构建与评价方法研究

重要农业文化遗产是一类典型的资源可持续利用保护地,其水土管理方式、知识体系、文化内涵等对于协调社区生计与生态保护具有积极作用。这类传统生计区域往往与自然保护地毗邻或在其范围内,对其蕴含的价值进行识别与保护,不仅是提升农业文化遗产管理的诉求,也能够支持自然保护地体系优化与功能区划管理。本研究对重要农业文化遗产价值进行系统识别,基于农业文化遗产的广义概念与全球重要农业文化遗产的狭义概念,借鉴多类型自然保护地与世界遗产、生态系统服务功能、自然资源资产等价值体系,从农业文化遗产的复合性、活态性与战略性特点出发,把握其核心价值,构建重要农业文化遗产的价值体系。在充分吸收生态系统服务价值评估、自然资源资产价值核算、自然文化遗产价值评估、品牌价值评估等定量或定性评价方法的基础上,提出一套完整的重要农业文化遗产货币价值评价方法。以系统科学和可持续发展理论为基础,重要农业文化遗产价值主要包括存在价值和潜在价值,其中存在价值以载体价值和服务价值为核心,服务价值则可细分为产品价值、生态价值、社会价值等9类,25个具体指标。研究进一步提出存在价值的评价方法与潜在指标可能测算路径。构建的重要农业文化遗产价值体系以及所提出的评价方法,可为以价值保护为基础进行农业文化遗产管理提供理论依据,为管理决策者在区域保护与发展协调决策中提供科学基础。     

重要农业文化遗产价值体系构建及评估(Ⅰ):价值体系构建与评价方法研究

重要农业文化遗产是一类典型的资源可持续利用保护地,其水土管理方式、知识体系、文化内涵等对于协调社区生计与生态保护具有积极作用。这类传统生计区域往往与自然保护地毗邻或在其范围内,对其蕴含的价值进行识别与保护,不仅是提升农业文化遗产管理的诉求,也能够支持自然保护地体系优化与功能区划管理。本研究对重要农业文化遗产价值进行系统识别,基于农业文化遗产的广义概念与全球重要农业文化遗产的狭义概念,借鉴多类型自然保护地与世界遗产、生态系统服务功能、自然资源资产等价值体系,从农业文化遗产的复合性、活态性与战略性特点出发,把握其核心价值,构建重要农业文化遗产的价值体系。在充分吸收生态系统服务价值评估、自然资源资产价值核算、自然文化遗产价值评估、品牌价值评估等定量或定性评价方法的基础上,提出一套完整的重要农业文化遗产货币价值评价方法。以系统科学和可持续发展理论为基础,重要农业文化遗产价值主要包括存在价值和潜在价值,其中存在价值以载体价值和服务价值为核心,服务价值则可细分为产品价值、生态价值、社会价值等9类,25个具体指标。研究进一步提出存在价值的评价方法与潜在指标可能测算路径。构建的重要农业文化遗产价值体系以及所提出的评价方法,可为以价值保护为基础进行农业文化遗产管理提供理论依据,为管理决策者在区域保护与发展协调决策中提供科学基础。     

稻渔共生系统研究取得重要进展

正稻田浅水环境为水产动物(鱼、虾、蟹等)提供了良好的栖息环境,为稻鱼共生生态系统的形成提供了条件。稻鱼共生系统中水稻和"鱼"(这里的"鱼"是稻田中各类水产动物的统称)"生活"在同一空间里,如何根据水稻和鱼的特点调控其生长和发育,并发挥水稻和鱼正相互作用的效应,是提高稻鱼共生系统生产力和资源利用效率、降低外部投入、提高抵御自然灾害能力的关键。浙江大学生命科学学院稻渔共生系统研究团队,在国家十三五重点研发项目(2016YFD0300905)、国家自然科学基金项目(31270485, 31500349, 31661143001, 31770481)、     

低氮和干旱胁迫对富士和秦冠生长及氮素利用的影响

【目的】以富士（Fuji）、 秦冠（Qinguan）嫁接在平邑甜茶（Malus hupehensis Rehd.）上的当年生盆栽苗为试验材料,采用砂培方法,研究了缺氮胁迫和干旱对富士和秦冠生长情况、 光合参数、 植株各部位氮磷钾含量及氮素利用效率的影响,分析比较了低氮干旱条件下富士和秦冠生长及氮素利用的差异,以期为果树生产高效肥水利用提供理论指导。【方法】试验共设四个处理: 正常氮正常水（ZZ）、 低氮正常水（DZ）、 正常氮干旱（ZG）、 低氮干旱（DG）。氮素和水分均设置两个水平,分别为正常氮（6 mmol/L NO-3-N）、 低氮（0.3 mmol/LNO-3-N）、 正常供水（保持盆中砂子相对含水量为饱和含水量的80%~85%）、 干旱处理（保持盆中砂子相对含水量为饱和含水量的60%~65%）。【结果】富士和秦冠的生物量（茎和叶）、 株高茎粗等生长指标以及光合速率、 气孔导度、 蒸腾速率均为正常氮正常水（ZZ）＞低氮正常水（DZ）＞正常氮干旱（ZG）＞低氮干旱（DG）,并且相对应处理下秦冠的以上指标均高于富士;正常供水下,缺氮处理使富士、 秦冠的根冠比比正常氮处理均有所增加,富士提高了2.05%,秦冠提高了22.40%。富士和秦冠的氮、 磷、 钾含量均表现出正常氮正常水（ZZ）＞低氮正常水（DZ）＞正常氮干旱（ZG）＞低氮干旱（DG）; 氮、 钾元素含量在植株各部位的分布顺序依次是叶＞根＞茎,磷元素则是根＞叶＞茎;光合氮素利用效率（PNUE）和氮素利用效率表现为秦冠处理之间差异极显著,富士处理之间差异不显著;秦冠的PNUE和NUE明显高于富士,在低氮正常水（DZ）处理下,秦冠氮肥利用率比富士高42.07%,在低氮干旱（DG）处理下高64.14%;低氮胁迫下富士和秦冠的NUE显著提高,并且秦冠提高的幅度高于富士。【结论】施用氮肥能够显著提高富士与秦冠的干物质量,同等水肥条件下,秦冠生长优于富士;水分亏缺会减少叶片对氮的吸收,干旱条件下适度增施氮肥,可提高果树的抗旱能力;低氮干旱胁迫下秦冠的生长指标、 光合指标及氮素利用效率指标均优于富士,表现出较强的抗低氮干旱胁迫的能力。     

Pasture Vegetation Elemental Analysis by Laser-Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy (LIBS) is a new technique for the analysis of plant material. This study investigates the application of LIBS to pasture-based plant samples. The LIBS measurements were obtained from pelletized pasture samples (100 samples) that had been also analyzed by inductively coupled plasma–optical emission spectroscopy (ICP-OES) following microwave digestion for calibration and comparison purposes. Comparisons for elements sodium (Na), potassium (K), magnesium (Mg), calcium (Ca), manganese (Mn), iron (Fe), copper (Cu), zinc (Zn), boron (B), phosphorus (P), and sulfur (S) showed that LIBS could be used for almost all the standard profile total elements with concentrations down to low mg/kg levels (observed error of Na: 0.024 percent, K: 0.18 percent, Mg: 0.016 percent, Ca: 0.073 percent, P: 0.017 percent, Mn: 31 mg/kg, Fe: 150 mg/kg, Zn: 6.6 mg/kg, and B: 1.1 mg/kg). Elemental analysis at less than mg/kg levels was not possible using LIBS. The elements S and Cu were particularly difficult to analyze with reliability using LIBS at the concentration levels found in the plant samples. Replacing microwave digestion and subsequent ICP analysis with a direct analysis of dried plant samples using LIBS has the potential to improve the productivity and reduce the cost of testing.     

Faculty positions:Center for Agricultural Resources Research,Chinese Academy of Sciences

正The Center for Agricultural Resources Research(CARR),the Institute of Genetics and Developmental Biology(IGDB),Chinese Academy of Sciences,invites applicants for several research group leader positions.CARR is one of the research organizations in Chinese Academy of Sciences(CAS).We seek nominations and applications from individuals who have expertise and a record of accomplishment in research areas related to ecology,agro-hydrology,     

Macroinvertebrates in North American tallgrass prairie soils: effects of fire, mowing, and fertilization on density and biomass

The responses of tallgrass prairie plant communities and ecosystem processes to fire and grazing are well characterized. However, responses of invertebrate consumer groups, and particularly soil-dwelling organisms, to these disturbances are not well known. At Konza Prairie Biological Station, we sampled soil macroinvertebrates in 1994 and 1999 as part of a long-term experiment designed to examine the effects and interactions of annual fire, mowing, and fertilization (N and P) on prairie soil communities and processes. For nearly all taxa, in both years, responses were characterized by significant treatment interactions, but some general patterns were evident. Introduced European earthworms (Aporrectodea spp. and Octolasion spp.) were most abundant in plots where fire was excluded, and the proportion of the total earthworm community consisting of introduced earthworms was greater in unburned, unmowed, and fertilized plots. Nymphs of two Cicada genera were collected (Cicadetta spp. and Tibicen spp.). Cicadetta nymphs were more abundant in burned plots, but mowing reduced their abundance. Tibicen nymphs were collected almost exclusively from unburned plots. Treatment effects on herbivorous beetle larvae (Scarabaeidae, Elateridae, and Curculionidae) were variable, but nutrient additions (N or P) usually resulted in greater densities, whereas mowing usually resulted in lower densities. Our results suggest that departures from historical disturbance regimes (i.e. frequent fire and grazing) may render soils more susceptible to increased numbers of European earthworms, and that interactions between fire, aboveground biomass removal, and vegetation responses affect the structure and composition of invertebrate communities in tallgrass prairie soils.     

Variation in quality parameters between and within 14 Nordic tree fruit and berry species

Abstract

A 3-year study was carried out to investigate quality parameters in 14 tree fruit and berry species grown in southern Norway. The species were blueberry, apple, aronia, sour cherry, sweet cherry, red raspberry, strawberry, blackcurrant, gooseberry, red currant and elderberry, harvested along with wild bilberry, cloudberry and lingonberry. Significant differences between species were identified for all quality parameters. The coefficient of variation between species was lowest for pH (12.5%), dry matter (18.9%) and soluble solids (25.3%), followed by titratable acids (59.3%), total phenolics (83.8%), antioxidant capacity FRAP (85.7%) and antiradical power by the DPPH-assay (97.8%), total monomeric anthocyanins (132%) and ascorbic acid (137%). Average coefficient of variation within species were lower and ranged from 4 (pH) to 62% (ascorbic acid). Only the FRAP values were significantly affected by harvesting year with lower levels in 2004 than in 2005 and 2006. There were significant interactions between species and harvesting year for dry matter, soluble solids, pH, ascorbic acid and FRAP. The results indicate generic ranges in composition within species independent upon growing location and climate, and the composition of the tree fruits and berries is not likely to deviate from these ranges. It is concluded that desirable composition of tree fruits and berries and their products should primarily be achieved by selection among species rather than searching fors broadened variation within individual species.     

Potassium Fixation and Release Characteristics in Rhizosphere and Nonrhizosphere Soils for a Rapeseed–Rice Cropping Sequence

Potassium (K) fixation and release in soil are important factors in the long-term sustainability of a cropping system. Changes in K concentration and characteristics of K fixation and release in rhizosphere and nonrhizosphere soils in the rapeseed (Brassica napus L.)–rice (Oryza sativa L.) rotation were investigated using a rhizobox system. The concentrations of different forms of K in both rhizosphere and nonrhizosphere soils decreased with plants compared to without plants, regardless of K fertilizer application. Potassium uptake by crops mainly came from the rhizosphere soil. In the treatment without K fertilizer (–K), the main form of K supplied by the soil to the crops was 1.0 mol L^?1 nitric acid (HNO₃) nonextractable K, followed by nonexchangeable K, and then exchangeable K. In the treatment with K fertilizer (+K), the main K forms supplied by the soil to the crops were exchangeable K and nonexchangeable K. The amount and rate of K fixation after one cycle of the rapeseed–rice rotation was greater in rhizosphere soil than in nonrhizosphere soil. The amount and rate of K fixation of soil in the +K treatment were significantly less than in the –K treatment. The cumulative amounts of K released with 1.0 mol L^?1 ammonium acetate (NH₄OAc) and 1.0 mol L^?1 HNO₃ extraction increased with the increasing numbers of extractions, but the K-releasing power of soil by successive extraction decreased gradually and finally became almost constant. The release of K was less in rhizosphere soil than in nonrhizosphere soil. The release of K in the +K treatment was similar to that in the –K treatment in rhizosphere soil, but the K release in nonrhizosphere soil was greater with the +K than the –K treatment. Overall, the information obtained in this study will be helpful in formulating more precise K fertilizer recommendations for certain soils.     

Biodiversity and ecogeography of wild Lactuca spp. in some European countries

Staff members of the Department of Botany of Palacký University in Olomouc and Gene Bank Department – Workplace Olomouc, Research Institute of Crop Production in Prague, Czech Republic, conducted an expedition in seven European countries (Austria, Czech Republic, France, Germany, Italy, the Netherlands, Switzerland) in August/September 1999 to collect wild Lactuca spp. germplasm and study its geographic distribution, ecology and biodiversity. During the mission, more than 600 locations were visited resulting in the collection of 602 seed samples (accessions) of wild Lactuca species and 13 seed samples of related genera (Chondrilla and Mycelis). Lactuca serriola f. serriola, L. serriola f. integrifolia, L. saligna and L. viminea subsp. chondrilliflora were prevalent in southern Europe (Italy, France), however, only L. serriola was common in central and western Europe (Austria, Czech Republic, Germany, Netherlands, Switzerland). The greatest diversity of Lactuca species was found in France, where also the most seed samples (165) were collected. The most characteristic habitats with a high density of Lactuca spp. populations were observed along roads and highways, grassy ditches, ruderal communities, and dust-heaps. Natural infections by powdery mildew (Erysiphe cichoracearum) and downy mildew (Bremia lactucae) on some wild Lactuca spp. were observed. Recent observations concerning the geographic distribution, population structure, habitats, and natural occurrence of diseases of Lactuca spp. are discussed. This assemblage of genetic resources of Lactuca spp. can serve as the basis of future studies of species diversification, spatial population structure, plant microevolution, domestication processes, and genetic variability of host-parasite interactions.     

Increase in auxiliary photoprotective photosynthetic pigments in wheat seedlings induced by Azospirillum brasilense

Inoculation of wheat seedlings with the plant growth-promoting bacterium Azospirillum brasilense Cd was immobilized in alginate microbeads and, without applying any stress, significantly increased the quantity of several photosynthetic pigments, such as chlorophyll a, chlorophyll b, and the auxiliary photoprotective pigments violaxanthin, zeaxanthin, antheroxanthin, lutein, neoxanthin, and β-carotene. This resulted in greener plants with no apparent visible stress. After monitoring the quantity of photosynthetic pigments for 4 weeks, we observed that inoculated plants had higher quantities of pigments in shoot and stem. The greatest difference in the quantity of all pigments between inoculated and noninoculated plants occurred in the first week of growth. Regardless of treatment, the quantity of pigments in stems was three to four times less than the quantity of these pigments in shoots. Application of Azospirillum, either as liquid inoculant or as alginate microbeads, did not alter the positive effect of the bacteria on pigment production or the positive response of the plants towards A. brasilense Cd inoculation.     

In-situ enrichment and analysis of atrazine-degrading microbial communities using atrazine-containing porous beads

We examined the community composition of microbes that colonized atrazine-containing beads buried in agricultural soils that differed in atrazine treatment history. Bacterial abundance was 5-40-fold greater in atrazine-fortified beads. In beads containing 20 mg atrazine kg⁻¹ buried in soil with a history of atrazine application (conditioned soil), the abundance of Actinobacteria increased approximately 80-fold whereas in control soil, Actinobacteria were enriched only 10-fold and the gamma-Proteobacteria and Planctomycetes increased by 60- and 25-fold, respectively. The gamma-Proteobacteria were enriched by 120- and 230-fold in beads containing 200 mg atrazine kg⁻¹ in conditioned and control soil, respectively. The results demonstrate that BioSep^® beads are a suitable matrix for recruiting a diverse subset of the bacterial community involved in atrazine degradation.     

Properties of anaerobically digested and composted municipal solid waste assessed by linking soil mesofauna dynamics and nitrogen modelling

We have studied the effect of anaerobically digested (ADMSW) and composted municipal solid waste (CMSW) on mineralization and foodweb dynamics to verify the hypothesis that ADMSW would immobilize N right after addition to soil in contrast to addition with CMSW. Another hypothesis was that the mesofauna (enchytraeids and microarthropods) would stimulate N release from the decomposer community. We measured excretion of -N and urea-N from the mesofauna and hypothesized that enchytraeids would release urea. ADMSW and CMSW were amended to pots with sandy loam and barley. The pots were divided into treatments with or without mesofauna. Mesofauna, plant N and biomass, soil N and ergosterol (fungal biomass) were measured over a 113-day period of four equidistant samplings. Soil respiration, N mineralization and N release by the mesofauna were modelled from concurrent studies. ADMSW- and CMSW-treated soils initially (<20 days) immobilized N. The amendments did not increase plant growth substantially, and this was probably due to N-limitation in the early stages of plant growth. Enchytraeid abundance was about three times higher in ADMSW- than CMSW-treated soils, indicating that ADMSW contained more labile compounds, bacteria, and microfauna. The mesofauna did not affect N-content, but the cumulated -N excreted by the mesofauna was estimated to be substantial and about one-fifth of total plant N in ADMSW. An explanation for this discrepancy might be that in the absence of the mesofauna, other members of the detrivore and microbivore community performed the mesofauna’s function. Neither enchytraeids nor microarthropods excreted urea.