Spatial distribution and characterization of long-term aged 14C-labeled atrazine residues in soil

The long-term behavior of the herbicide atrazine and its metabolites in the environment is of continued interest in terms of risk assessment and soil quality monitoring. Aqueous desorption, detection, and quantification of atrazine and its metabolites from an agriculturally used soil were performed 22 years after the last atrazine application. A lysimeter soil containing long-term aged atrazine for >20 years was subdivided into 10 and 5 cm layers (at the lysimeter bottom: soil 0-50 and 50-55 cm; fine gravel 55-60 cm depth, implemented for drainage purposes) to identify the qualitative and quantitative differences of aged (14)C-labeled atrazine residues depending on the soil profile and chemico-physical conditions of the individual soil layers. Deionized water was used for nonexhaustive cold water shaking extraction of the soil. With increasing soil depth, the amount of previously applied (14)C activity decreased significantly from 8.8% to 0.7% at 55-60 cm depth whereas the percentage of desorbed (14)C residues in each soil layer increased from 2% to 6% of the total (14)C activity in the sample. The only metabolite detectable by means of LC-MS/MS was 2-hydroxyatrazine while most of the residual (14)C activity was bound to the soil and was not desorbed. The amount of desorbed 2-hydroxyatrazine decreased with increasing soil depth from 21% to 10% of the total desorbed (14)C residue fraction. The amount of (14)C residues in the soil layers correlated well with the carbon content in the soil and in the aqueous soil extracts ( p value = 0.99 and 0.97, respectively), which may provide evidence of the binding behavior of the aged atrazine residues on soil carbon. The lowest coarse layer (55-60 cm) showed increased residual (14)C activity leading to the assumption that most (14)C residues were leached from the soil column over time.     

Effect of long-term liquid pig manure application on atrazine mineralization in a soil cultivated with maize

Soil samples were collected in plots from a field experiment in maize monoculture receiving 0, 60 and 120 m³ ha^-1 liquid pig manure (LPM) for 19 years. Soils were sampled from the 0- to 20-cm layer in August and October 1997 and in June, July and September 1998. Subsurface samples were also evaluated in September 1998. Laboratory soil radiorespirometry was used to evaluate atrazine mineralization using [U-ring-¹⁴C]-atrazine mixed with commercially available product. The effect of atrazine dose (50, 100 and 500 mg atrazine kg^-1 soil) was evaluated on soils sampled in August 1997. For the other sampling dates, the soils were spiked with 50 mg atrazine kg^-1 soil. No LPM dose effect on atrazine mineralization was obtained in the different experiments. Increasing atrazine dose to 500 mg kg^-1 decreased significantly the mineralization rate (R_i) and the maximum of atrazine mineralized (MAX), while the time needed to mineralize 50% of MAX (DT-50%) was not significantly affected. Sampling time had a significant effect on atrazine mineralization. Atrazine mineralization in the soils sampled in June 1998 showed lower R_i and MAX than in the soils sampled at the other dates. Atrazine mineralization in subsurface soils (20–60 cm) was very variable and quite high in some samples. This may be due to atrazine pre-exposure in subsoils resulting from atrazine deep movement by preferential flow.     

Modelling long-term in situ soil profile evolution: application to the genesis of soil profiles containing stone layers

Models of soil genesis are potentially of great importance in assessing the effects of global change on ecosystems, and may also contribute to our understanding of soil genetic processes. Many quantitative models have so far focused on individual soil genetic processes and are difficult to extrapolate to the landscape scale. A few attempts have been made to model soil evolution as a whole from a pedologic perspective. This study develops a quantitative model of soil formation at the profile scale, taking into account major soil‐forming processes. These include physical and chemical weathering of primary minerals, strain processes, and bioturbation. The model allows the quantification of the evolution of the particle size, mineral composition and bulk density of the soil. The model is applied with varying values of input parameters, and is compared with actual soil genetic processes. Running the model results in the formation of stone‐layered soil profiles. Stone‐line formation by means of bioturbation, as already described in the literature, seems to be adequately simulated. Planned improvements of the model include implementation of other major soil genetic processes such as leaching, organic matter influence, etc. This model will then have to be implemented spatially considering particularly redistribution processes, to reproduce soil formation at the landscape scale.     

Biodegradation of aged residues of atrazine and alachlor in a mix-load site soil

A selected microbial consortium (SMC) capable of degrading two specific herbicides, alachlor (2-chloro-2′,6′-diethyl-N-[methoxymethyl]-acetanilide; AL) and atrazine (2-chloro-4-ethylamino-6-isopropylamino-S-triazine; AT) was isolated from a pesticide-contaminated mix-load site soil. Evaluation of bioaugmentation as a feasible bioremediation strategy for this mix-load site soil (Site 5A) was initiated in standard laboratory biometer flasks utilizing the isolated SMC. The biometer flasks were monitored for CO₂ evolution and pesticide degradation. The total amount of CO₂ evolved from the treated biometer flasks was significantly different from the control flasks. The rate of CO₂ evolution was 2.6 times faster in the treated soil (0.0123 mM CO₂ d⁻¹ vs. 0.0048 mM CO₂ d⁻¹). The total net CO₂ produced in the treated biometer flasks was 0.9481 mM, representing mineralization of approximately 10% of the AT and AL initially present. Forty-eight percent of AT and 70% of AL was degraded in the inoculated biometer flasks. The first-order rate constants were 0.0064 d⁻¹ and 0.1331 d⁻¹ for AT and AL, respectively. The calculated half-life of AT was 108 d while a 50% decrease in AL occurred by Day 5. In just 2 d, 20% of the AT was degraded while only 10% of the AL disappeared. The initial fast degradation rate of AT was followed by a much slower, more gradual degradation rate period that lasted about 35 d. Alternatively, the rate of AL degradation increased after the second day resulting in 60% of the AL being transformed by the end of the first week. Alachlor degradation appeared to be dependent upon AT degradation especially during the first several days of the incubation period. Complete disappearance of the herbicides over the study time was not achieved.     

土壤调理剂PAM的农用研究和应用

90年代 ,新型PAM产品 (具有很高分子量的阴离子型PAM )和改进的应用技术 (低用量配合灌溉水 )使得PAM在农业上的使用成本大大减少 ,而农用效益大大提高 ,土壤调理剂PAM的农用重新受到重视。目前美国西部已将PAM的农用作为一项农田水土保持新技术而得到越来越广泛的应用。土壤调理剂PAM曾于 80年代后期介绍到我国 ,但是由于成本高等其它问题而未能在农业上推开 ,目前新型PAM的农用研究也在我国引起重视。国外大量研究和国内有关研究表明 ,PAM的农用效益体现在水土保持、灌溉效率、农业生产、环境、经济等方面。土壤调理剂PAM用于农田水土保持、防止水土流失前景看好     

土壤剖面不同土层硝态氮植物利用及运移规律研究

采用外源标记15NO-3--N微注射技术的田间微区试验,研究了我国北方灌溉农作体系中,由于氮肥的高量投入导致作物收获后土壤剖面大量残留NO-3--N对后作的氮素供应潜力及其去向。结果表明,在本试验水氮管理条件下,菠菜（Spinacia oleracea L.）对土壤剖面15、45、75 cm位置标记氮的利用率分别为28.2%、22.3%、16.3%; 冬小麦（Triticum aestivum L.）小偃54对相应位置标记氮的利用率分别为21.8%、17.4%、11.5%,而京411为21.8%、11.6%、7.4%。菠菜对土壤不同层次残留氮的利用率显著大于小麦,小偃54显著高于京411。菠菜的根长密度低于小麦,土壤剖面多数层次两个小麦品种的根长密度差异不显著,小麦的根长密度与相应土层标记硝态氮的利用率呈显著的正相关关系; 根干重在土壤剖面多数层次呈现小偃54＞京411＞菠菜的趋势。生长季结束标记氮发生了向下移动,3个标记处理分别在土壤剖面60—80、60—80、80—100 cm出现积累峰; 但菠菜15 cm位置收获后整个剖面的%Ndff值均很低,标记氮在剖面中几乎没有积累峰; 不同标记位置的残留氮均发生向上运移,上移距离分别为15、45、35 cm,残留氮标记的层次越深,其在土壤中再分布能力愈弱,残留越集中。     

Changes in the atrazine extractable residues in no-tilled Mollisols

The effect of application dose and soil organic matter (SOM) stratification on changes in atrazine (6-chloro-N²-ethyl-N⁴-isopropyl-1,3,5-triazine-2,4-diamine) extractable residues (ER) were investigated. Two soils [Entic Haplustoll (EH) and Typic Hapludoll (TH)] with contrasting SOM content and form and without previous atrazine exposure were selected. Sampling was carried out at two depths: 0–2 and 2–5 cm. Atrazine ER were measured at 0, 3, 7, 14, 28, and 56 days in laboratory incubation. Atrazine concentration recovered 1 h after of its application (C_t0) was used as an index of the soil capacity to reduce the atrazine extractable fraction. SOM stratification was studied by means of physical fractionation. In both soils, the higher OC concentration was found in the 200–2000 μm fraction (OC_{f 200–2000}). Soils differed in terms of the OC_f 50–200/OC_{f 200–2000} ratio. This ratio increased with depth in EH soil: 0.23 (0–2 cm) and 2.00 (2–5 cm). In TH soil, the ratio was 0.80 (0–2 cm) and 0.50 (2–5 cm). The t_1/2 values ranged from 9 to 19 days, depending on soil type and atrazine application dose. The upper layer C_t0 and k were higher for higher atrazine doses. Implementation of a split application dose of atrazine may be an effective alternative to extend its half-life in soil solution, as well as involving a lower potential risk of soil accumulation or vertical movement in the soil profile towards deep soil layers and groundwater.     

Regional characterization of the long-term change in soil organic carbon under intensive agriculture

Abstract. To study the change in soil organic carbon (SOC) since it was recorded during the Belgian National Soil Survey some 40 years ago, we recently revisited 939 locations still under use as arable land. The study area comprised almost the entire province of West Flanders (about 3000 km²) characterized by profound changes in its arable land management. Taking the increased ploughing depth (by 9.8 cm on average) into account, a significant (P= 0.001) increase of the SOC content by 0.2% on average was found. Expressed as an amount, the SOC in the topsoil rose by 9.3 t/ha on average, representing an increase of 25%. This is comparable with the conversion of arable land into grassland for 2 to 3 decades. Geostatistical tools were used to map the SOC at the two times of observation. These showed that most of the spatial variation occurred within about 4 km. Since the community level is the smallest spatial resolution on which agricultural statistics are gathered officially, a detailed modelling of the change in SOC was impossible. However, by selecting communities with extreme changes in SOC, we found indications that the major source of increase in SOC was due to the large increase in pig breeding.     

波涌灌间歇入渗饱和-非饱和土壤水分运动数值模拟及试验

考虑到地下水浅埋对上层包气带水分分布造成一定影响,该研究结合波涌灌技术,对地下水浅埋下间歇入渗的土壤水分分布特征和运动规律进行了分析,建立了基于饱和-非饱和土壤条件下一维间歇入渗水分运动模型,根据试验实测资料采用Hydrus-1D软件反推土壤水分运动参数,并对入渗过程进行了模拟。在此基础上,确定了饱和导水率的估算模型。结果表明:所建参数估算模型较好地反映了饱和导水率与间歇周期数、循环率以及周期时间之间的相关关系,所建水分运动模型模拟值与实测值比较,累计入渗量、土壤含水率以及湿润体运移距离总体相关系数高于0.96,均方差在0.5以内,吻合度较高,能够较好地描述了地下水影响条件下波涌灌间歇入渗饱和-非饱和土壤水分运动特征。该研究为波涌灌技术进一步发展奠定了科学基础。     

地下渗灌土壤水分运动数值模拟

为了寻找一种准确实用的土壤水分运动模拟方法用于指导田间渗灌,该文对一种橡塑渗灌管田间渗灌过程进行监测,并采用Green-Ampt积水入渗模型和一维水平吸渗模型Philip解法分别对渗灌过程中土壤水分在垂直和水平方向的运动进行模拟,通过与田间实测值对比,检验模型的适用性。结果表明,应用Green-Ampt积水入渗模型模拟田间渗灌过程垂直方向土壤水分运动具有较好的准确性,一维水平吸渗模型Philip解法在水平方向的模拟则存在一定偏差。     

红壤长期施肥养分的下移特征

本研究了长期施肥（７年和１７年）在红壤和红壤性水稻 养分在土壤剖面中的下移。结果表明施入氮肥使水解氮在整个剖面中比对照处理均有增加，氮素下移可达１００ｃｍ，而磷中估耕层有显加，交换性钾的下移虽较磷素为深，但主要集中在４０ｃｍ土层中，有机肥中磷的活动性较为肥为大，下移浓度可达４０ｃｍ以上。     

农用聚磷酸铵在土壤中的有效性研究进展及在农业上的应用

近年来,农用聚磷酸铵作为一种新型肥料逐渐进入我国化肥领域,常用作高浓度液体复合肥料的基础磷肥。聚磷酸铵pH值近中性,结晶温度低,具有螯合性、缓释性,有着很大发展空间。本文综述了聚磷酸铵在土壤中有效性(溶解性与移动性)的影响因素,重点分析水解速率、土壤矿物、土壤质地与水分对聚磷酸铵在土壤中的有效性,并分析聚磷酸铵在农业上的应用与发展前景。     

设施蔬菜连作障碍原因综合分析与防治措施

  目的  为了探索种养模式下,不同品种蚯蚓对连作土壤微生态及西瓜长势的影响,阐释蚯蚓防控西瓜连作障碍机制。  方法  基于连作6 a的西瓜设施大棚,以连作障碍成因为切入点,设置不投放蚯蚓（CK）、投放0.6 kg m⁻²赤子爱胜蚓（T1）、投放0.6 kg m⁻²威廉环毛蚓（T2）3个处理,监测不同时期土壤微生态、西瓜长势的变化动态,并分析它们之间的相关性。  结果  与CK相比,西瓜移栽前,T1、T2增加了土壤总养分（23.92% ~ 31.90%）、有效养分（10.67% ~ 13.70%）的含量;西瓜种植季,T1、T2显著降低土壤的pH（2.03% ~ 8.25%）、总酚酸（23.98% ~ 60.80%）、容重（3.79% ~ 5.39%）、西瓜枯萎病病原菌的数量（22.93% ~ 59.18%）,显著提高了细菌数量、土壤细菌/真菌比值,显著降低了西瓜枯萎病的发病率（10.00%以上）,促进了主蔓生长（增加了71.43%以上）。而与T1相比,T2能更好的改善土壤微生态环境,降低连作障碍的发生。  结论  蚯蚓能显著改善土壤微生态,促进西瓜生长,从而缓解连作障碍,而且土壤微生态、西瓜长势均与土壤微生物密切相关。     

Solvent extraction characterization of bioavailability of atrazine residues in soils

Characterization of pesticide bioavailability, particularly in aged soils, is of continued interest because this information is necessary for environmental risk assessment. The objective of this study was to correlate atrazine residue bioavailability in aged soils, as determined by solvent extraction methods, to atrazine mineralization by an atrazine-degrading bacterium. Webster clay loam and Zimmerman fine sand soils were treated with UL-ring-labeled [14C]atrazine and incubated for up to 8 weeks. At the end of each incubation period, soils were either not extracted, extracted with 0.01 M CaCl2, or extracted with 0.01 M CaCl2/aqueous methanol. Soils were then inoculated with the bacterium Pseudomonas sp. strain ADP, which is capable of rapidly mineralizing the atrazine ring. This allowed for the evaluation of the bioavailability of aged atrazine residues without the contribution of atrazine desorption from soil. Results of these studies indicated that the amounts of atrazine residues in aged soils extracted by 0.01 M CaCl2 and aqueous methanol were correlated to amounts of atrazine mineralized by Pseudomonas sp. strain ADP. Consequently, 0.01 M CaCl2/methanol extractable atrazine in aged soils may be used to estimate bioavailable residues, and this technique may be useful to determine the bioavailability of other compounds in soils, especially other triazine herbicides.     

Initial formation of soil organic matter from grass residues in a long-term experiment

Summary The formation of soil organic matter from grass residues was studied using samples of a long-term experiment (34 years) on humus and soil formation at Rostock, Germany (Hu 3), by elemental analyses (C and N) and pyrolysis-field ionization mass spectrometry of grass residues, humus-free loamy marl, mixtures of this loamy marl with grass roots, and whole soil samples from the 2nd, 7th, 13th, 19th, 25th, 29th, and 34th year of the experiment. The pyrolysis-field ionization mass spectra of the two grass species Phleum pratense and Lolium multiflorum were similar insofar as signals characteristic of lignin dimers and phytosterols dominated at higher masses and for mono-and polysaccharides at lower masses. The most prominent differences between overand underground plant constituents were indicated by higher relative abundances of lignin dimers in the stems and leaves and of sugars and suberin-derived phytosterols in the roots. In the investigation of the influence of mineral to organic matter ratios, comparatively weak effects of the inorganic matrix were obtained: firstly, in the lower mass range (m/z<250), secondly, for organic matter concentrations between 1.0% and 2.0%, and thirdly, for certain classes of compounds such as phenols, alkanes/alkenes, N heterocycles and mono-and polysaccharides. The qualitative differences in the molecular composition of soil organic matter were clearly attributed to its rapid increase during the first 7 years of the experiment and largely originated from a relative enrichment of lignin dimers. Then, in the period of steady-state soil organic matter levels, dynamic changes were indicated by slight enrichments of mono-and polysaccharides, alkanes/alkenes, fatty acids, N heterocycles, and fluctuating data for phenols/lignin monomers, lignin dimers, and the sum of N compounds. Alkylaromatics showed a steep increase between the 13th and 19th years and remained then on a high level.     

Measurement and simulation of anion diffusion in natural soil aggregates and clods

The diffusion of indigenous nitrate from small (<5 mm) aggregates of a clay-loam soil, and added bromide from larger (30–70 mm) clods of a sandy clay, were studied under saturated conditions. The time (t_0.5) taken for half the diffusional solute loss to occur from the small aggregates was well related to the square of the aggregate radius (a²). The impedance factor (f_i) of 0.54 calculated from the t_0.5 v. a² relationship gave satisfactory results in simulations of the measured M_t/M∞. v. time curves. t_0.5 was also well related to a² for the clods, but the f_t values calculated from it were not only very large (>0.9) but also decreased with increasing clod size, possibly because of anion exclusion effects. The model simulated bromide diffusion from chalk cubes of mixed sizes better when computations were made for each size than when a single volume-averaged size was taken.     

Modifications to atrazine degradation pathways in a loamy soil after addition of organic amendments

The effects of two organic amendments, a municipal solid waste compost and a composted straw, on [U-ring- ]atrazine degradation pathways in a loamy soil (Grignon, Yvelines, France) were studied during laboratory incubations under controlled conditions. Three month conditionings were conducted under sterile or non-sterile conditions, with soil plus atrazine, organic amendment plus atrazine, or soil plus organic amendment. Then either an organic amendment or soil or atrazine was added, respectively, to these three treatments and incubated for an additional 3 months under non-sterile conditions. Both organic amendments modified the behaviour of atrazine in soil but via different processes. The addition of municipal compost increased atrazine sorption and decreased its availability for degradation by soil microorganisms. The effect of the composted straw was mainly related to its high enzymatic activity, which appeared to be responsible for the production of large amounts of hydroxyatrazine. This hydroxylation favoured the opening of the triazine ring and its subsequent mineralization in the soil. At the end of the incubations, less atrazine was mineralized in the presence of the two types of organic amendment, which both increased the formation of non-extractable residues of atrazine. The addition of municipal compost preserved larger amounts of extractable atrazine, while the addition of composted straw enhanced hydroxyatrazine production. In all cases, the greatest effects were found when atrazine was directly in contact with the organic amendment during conditioning.     

土壤微生物生态学在农业中的应用研究综述

土壤微生物生态学是陆地生态系统研究中最重要的组成部分,是土壤学、微生物学和生态学相互渗透、相互结合的一门新兴学科。本文从研究方法、农业施肥、农业种植制度、生态防治及应用展望等方面对土壤微生物生态学的应用研究现状作了综述,加强土壤微生物生态学在农作物生长和调控应用等领域的研究具有巨大的潜在应用前景和重要意义。     

Bioavailability of organoclay formulations of atrazine in soil

Pesticide formulations based on organoclays have been proposed to prolong the efficacy and reduce the environmental impact of pesticides in soil. This research addressed the question of whether atrazine in organoclay-based formulations is irreversibly sorbed or is bioavailable for bacterial degradation in soil. Different cations of l-carnitine (CAR), tyramine (TYRAM), hexadimethrine (HEXADIM), phenyltrimethylammonium (PTMA), hexadecyltrimethylammonium (HDTMA), and Fe(III) were incorporated into Na-rich Wyoming montmorillonite (SWy-2) and Ca-rich Arizona montmorillonite (SAz-1) at 100% of the cation exchange capacity (CEC) of the clays as a strategy to enhance the affinity of the clay minerals for atrazine. A Buse loam soil from Becker, MN, was treated with three organoclay-based formulations of 14C-atrazine or free herbicide and incubated for 2 weeks. To determine the bioavailability of 14C-atrazine, the soil was inoculated with Pseudomonas sp. strain ADP, which rapidly mineralizes atrazine. At day 0, and after a 2 week incubation, mineralization and the amount of 14C-atrazine residues distributed between the aqueous-extractable, methanol-extractable, and bound fractions in the soil were determined to characterize the availability of nonaged and aged atrazine residues. By the end of the 2 week incubation, the microorganisms had mineralized >80% of the initial readily available (water-extractable) and >70% of the less readily available (methanol-extractable) 14C-atrazine in the soil. Bound residues increased from <4% at day 0 to ～17% after the 2 week incubation for both the formulated and free forms of atrazine. The results of these incubation experiments show that the bioavailabilities of atrazine were similar in the case of the organoclay formulations and as free atrazine. This indicated that whereas more atrazine was sorbed and less likely to be transported in soil, when formulated as organoclay complexes, it was ultimately accessible to degrading bacteria, so that the herbicide is likely to be naturally attenuated by soil microorganisms.