A lysimeter experiment to investigate the effect of surface sealing on hydrology and pesticide loss from the reconstructed profile of a clay soil. 1. Hydrological characteristics

Abstract. A laboratory experiment was designed to assess the impact of surface seal development on the hydrological response of a clay soil. The influence of surface sealing on vertical macropore flow and lateral throughflow was of particular interest. The extent and development of the surface seal in repacked lysimeters was designed to match that recorded over two growing seasons at a clay field site in Essex, and was not extensive enough to reduce significantly the infiltration capacity of the soil. Consequently, the hydrological response of the lysimeters was similar under sealed and unsealed conditions, with a more rapid wetting response under sealed conditions being attributed to the higher soil moisture content required to create the surface seal. Macropore flow was initiated at the A/B soil boundary of the lysimeters, in response to the development of a saturated layer. The rate of macropore and throughflow in the soil was dictated by rainfall intensity at the soil surface as this controlled the depth of water in the perched water table. Simulation of the tensiometer response in the lysimeters demonstrated that it was possible to attribute the rapid movement of water through the A horizon to water displacement processes alone, without recourse to preferential flow processes.     

Zum Einfluß organischer Bodenbedeckung auf den lateralen Transport von Isoproturon auf der Bodenoberfläche

On the Effect of Organic Surface Cover on Lateral Transport of Isoproturon on Soil Surface The losses of the herbicide isoproturon with the surface runoff and the sediment loss have been measured by means of rainfall simulations on microplots (0.5 × 1 m²) with different mulch materials and increasing soil cover percentages (wheat straw vs. rape leafs). Soil cover by straw showed no significant effect on the runoff discharge, but the total loss of isoproturon increased between 22 and 37%. Soil cover by rape leafs diminished the runoff by between 13 and 61%, the reduction of isoproturon loss was in the same range. It was shown, that the different influences of different mulch materials on runoff and soil loss can lead to different pesticide losses. Therefore, the only giving of “mulch” without specification does not describe such experiments sufficiently.     

Harsh summer conditions caused structural and specific functional changes of microbial communities in an arable soil

The mineralization of the herbicide 3-(4-isopropylphenyl)-1,1-dimethylurea (isoproturon) was reduced after the dry and hot summer 2003 in a soil profile placed in a field lysimeter. A different isoproturon mineralization pattern remained in soil material taken at two different soil depths (0–5 cm and 15–20 cm), although soil material was re-equilibrated at adequate climatic conditions. Special soil microcosms were designed to determine if the changes in this special soil function 'isoproturon mineralization' were related to the climatic scenario of summer 2003. These microcosms were filled with lysimeter soil from the 15–20 cm depth and the temperature and dryness of summer 2003 were simulated. Afterwards, soil samples were taken from the microcosms and re-equilibrated under controlled conditions for 4 weeks. Subsequently, isoproturon mineralization was investigated. The soil microbial community reduced drastically its original capability of isoproturon mineralization in the course of the model experiments.
Analysis of 16S-rRNA by denaturing gel gradient electrophoresis (DGGE) revealed substantial differences in the band patterns of the bacterial communities from both depths of the field lysimeter soil and from the soil incubated in microcosms. The different soil microbial biomass determined by microcalorimetry reinforced these results. In conclusion, the factors higher temperature and smaller soil moisture content generated important and enduring changes in the microbial community structure and therefore in specific soil functions of the community, as shown here by the function of isoproturon degradation. Results are discussed in connection with environmental conditions and conservation tillage.     

Interrill soil erosion as affected by tillage and residue cover

No-till cropping systems are effective in reducing soil erosion. The objective of this study was to determine whether high infiltration rates and low runoff and soil loss under long-term, no-till conditions in loessial regions of the Midwest US result from both the well-structured, porous condition of the soil and the protective cover of crop residue or primarily from residue cover. Soil loss, runoff, and infiltration were measured using a rainfall simulator on interrill erosion plots with and without residue cover on a conventional and two no-till systems in central Illinois. For both conventional till and no-till conditions, removing surface residue significantly decreased infiltration rates and increased soil loss. Tilling the no-till surface while maintaining an equal surface cover as with the no-till system slightly increased interrill erosion. Removing residue on a no-till system, however, increased soil loss significantly. A no-till soil condition without adequate residue cover will seal, crust, and erode with extremely high soil losses following surface drying.     

Investigation into the effect of tillage on solute movement to drains through a heavy clay soil

Abstract. Eight lysimeters, each with a surface area of 0.5 m² and a length of 60 cm, were taken over mole drains from a Denchworth soil and divided into two groups with either a standard agricultural tilth or a finer, deeper topsoil tilth. They were variously instrumented to measure soil moisture content at three depths and losses of nitrate, a bromide tracer and radiolabelled isoproturon, all of which were followed over a year. Leaching of isoproturon was initiated by artificial irrigation either 1 or 39 days after application. The finer tilth seemed to increase the water-holding capacity of the topsoil, and this resulted in slower wetting of the subsoil, decreased flow volumes from the first events of the season and a delay of approximately four weeks in the time to the maximum concentration of the bromide tracer in leachate. The finer topsoil tilth also decreased maximum concentrations of isoproturon from 29 to 15 μg l⁻¹ following irrigation 1 day after treatment and from 43 to 9 μg l⁻¹ following irrigation 39 days after treatment. Total losses of isoproturon were three times larger with the standard agricultural tilth. Differences were attributed to a decrease in bypass flow through the topsoil with the finer tilth, particularly during events early in the season. There was a small decrease in total losses of nitrate in leachate from the finer tilth compared to that from the standard tilth.     

Tillage and application effects on herbicide leaching and runoff

Herbicides are key products in sustaining agricultural production and, to minimize agro-environmental concerns regarding their use, continued assessment of their behavior under different management practices is required. Leaching and runoff losses of four herbicides applied preplant-incorporated (PPI) were evaluated in two tillage systems over a 3-year period (1989–1991). Scant leaching during the droughty 1991 growing season limited treatment evaluations to 2 years. Herbicides were applied at recommended rates (1.7 and 2.2 kg active ingredient (a.i.) ha⁻¹) to conventional tillage (CT) and mulch tillage (MT) corn (Zea mays L.) fields on Hagerstown silty clay loam (fine, mixed, mesic Typic Hapludalf). Tillage treatments were defined as moldboard plow-disk-harrow (CT) and single-disking (MT). During this study, CT followed 5 years of corn production in a comparable CT system on this site and, similarly, MT followed a 5-year no-tillage (NT) system. Herbicides were applied preemergence (PRE) to CT and NT in the 5-year study and preplant-incorporated (PPI) in this study. Herbicide mobility in subsurface drainage was evaluated from herbicide mass transported to pan lysimeters installed 1.2 m deep. Surface drainage losses of these chemicals were determined from residues in runoff collected with automated sampling and recording equipment.

Leachate volumes were greater from MT than CT in 1989 and 1990 and exceeded all seasonal losses during the previous 5 years under NT management. Comparisons of total seasonal leachate discharged to pan lysimeters within and among studies and herbicide mass leached showed that timing of leachate-inducing precipitation relative to herbicide application was the key factor in regulating herbicide translocation. Herbicide mass transported through the root zone averaged from less than 0.1% to 0.9% of applied rates in CT and from 1.4% to 5.1% in MT.

Leachate-availability of herbicide residues and extent of herbicide longevity in this soil under MT conditions were similar to previous findings under NT management. Despite these behavioral similarities for herbicides among tillages, herbicide mass discharged per unit of percolate was most often lower for MT compared with NT, particularly in early growing seasons of comparable precipitation. Thus, the PPI treatment in MT appeared to reduce leaching of these chemicals compared with PRE application in NT.

Runoff losses of PPI herbicides ranged from 0.35% to 0.77% of applied rates in CT and from 0.13% to 0.28% in MT. Losses of PRE-applied herbicides from NT averaged less than 0.1% of applied rates; maximum yearly losses ranged from 0.06% to 0.18%. Thus, the character of the disked, minimally tilled surface provided a level of impedance to runoff that was greater than achieved with the tilled surface on this 3 to 5% slope, but less than previously obtained with an untilled, mulch-covered surface.     

Aspects of the adsorption and degradation of isoproturon in a heavy clay soil

Abstract. Degradation of isoproturon in a heavy clay soil followed first-order reaction kinetics with half-lives at 15 °C of 27 and 208 days in the topsoil and subsoil, respectively. Adsorption when shaken with 3 mm sieved samples of the soil fitted the empirical Freundlich relationship with k values of 3.25 in the topsoil and 1.06 in the subsoil. Adsorption in a static system with different sized aggregates of soil did not reach equilibrium, even after 24 hours contact, and the rate of adsorption was slower with larger aggregates. Following an adsorption period of 24 hours, desorption equilibrium was reached more rapidly with larger (6–10 mm) than with smaller (<3 mm) aggregates. Adsorption isotherms measured in a static system with a soil:water ratio typical of field conditions in winter also indicated less adsorption than that measured in shaken, laboratory systems with low soil:water ratios. The rate of change in water extractable residues of the herbicide was more rapid than that of total extract-able residues following application of isoproturon to the heavy clay soil in the field. The implications of the results for isoproturon leaching under field conditions are discussed.     

定植孔密封方式对土壤水热盐及番茄苗存活率的影响

为了提高河套灌区盐碱地番茄移栽成活率,以番茄定植孔采用土封孔为对照,监测了沙封孔、不封孔株间和根际的土壤水分、土壤盐分、土壤温度及番茄幼苗的生长状况。结果表明,不同处理株间土壤水分、土壤盐分、土壤温度无显著差异。沙封孔、不封孔与土封孔相比,根际0～10cm土层土壤水分降低了11.73%和14.80%,≥10～20cm土层降低了9.60%和13.64%;根际5cm土层最高温度降低了1.2和3.6℃,日均温降低了1.6和2.2℃;根际0～10cm土层土壤盐分降低了19.11%和24.84%,≥10～20cm土层降低了11.48%和19.67%。沙封孔、不封孔番茄幼苗移栽成活率较土封孔提高了20.57%和19.40%。河套灌区盐碱地地膜覆盖栽培番茄,定植时采用沙封孔或不封孔,可降低根际土壤水分及土壤温度,阻碍盐分表聚于根际土壤,提高了番茄幼苗的移栽成活率,该研究为河套灌区盐碱地种植番茄提供指导。     

Effects of rainfall intensity and slope gradient on the dynamics of interrill erosion during soil surface sealing

Soil erosion during rainfall is strongly affected by runoff and slope steepness. Runoff production is drastically increased when a seal is formed at the soil surface during rainfall. Therefore, a complex interaction exists between soil erosion and surface sealing. In this study, the dynamics of interrill erosion during seal formation is studied under different simulated rainfall and slope conditions. A sandy soil was exposed to 70 mm of rainfall at two intensities, 24 mm h^− 1 and 60 mm h^− 1, and five slope gradients, from 5% to 25%. Infiltration, runoff and soil loss rates were monitored during rainfall. Final infiltration rates increased with slope gradient at both rainfall intensities, this effect being stronger for the higher intensity. Cumulative runoff at the end of the rainfall event was lower as slopes were steeper, while an opposite trend was obtained for soil loss. For the 5% and the 9% slopes, the sediment concentration in runoff reached quickly a stable value during the whole rainfall event, while it reached a peak value before declining for the higher slopes. The peak value and its timing were rainfall intensity dependent. Soil erodibility during seal formation was evaluated using two empirical multiplication-of-factors type models. It seems that slope and rainfall erosivity are accounted for only partly in these models. For mild slope gradients below 9%, the value of K_i estimated by means of the two expressions becomes practically constant shortly after runoff apparition. Consequently, the estimates resulting from this type of expressions remain valuable from the practical point of view.     

Interaction between humus form and herbicide toxicity to Collembola (Hexapoda)

Laboratory experiments were conducted using intact collembolan communities, exposed to Madit D^®, a phenylurea herbicide (active ingredient isoproturon). Effects were investigated using two distinct humus types, an acid Dysmoder and a neutral Eumull. Within two weeks, no effect of the herbicide was displayed by the Eumull population, while the Dysmoder population was stimulated. When animals were able to escape from the herbicide through a perforated wall separating two compartments filled with natural soil, the behavior of collembolan communities exhibited interactive (non-additive) effects of humus type and herbicide application. The combination of an acid soil (supposedly providing greater tolerance to organic pollutants) with a neutral soil, increased biodiversity of Collembola, but caused the disappearance of some acido-sensitive species, pointing to complex relationships between pesticides, soils and soil organisms. Parallel experiments with single species demonstrated that at the recommended dose Madit D^® may cause avoidance effects, but no toxicity.     

A laboratory investigation of the release of a conservative tracer and herbicide from topsoil aggregates under varying rainfall intensities

Abstract. This paper describes the results of laboratory-based research which investigated the losses of the herbicide, isoproturon, and a non-adsorbing solute, bromide, from topsoil aggregates under high (7 mm h⁻¹ and low 2.7 mm h⁻¹) intensity simulated rainfall. The structures of the micro- and macro-aggregates from a clay soil of the Denchworth Series (from Wytham, Oxfordshire, UK) were observed using a scanning electron microscope, and the slaking of the topsoil aggregates was also investigated in order to provide a context for interpreting the experimental results. The topsoil at Wytham was found to have a bimodal structure with small microaggregates of 0.71 to 1 mm diameter clustered together to form larger macroaggregates of up to several centimetres diameter. Selected aggregates were air dried and then repacked in Buchner funnels to several centimetres depth in order to remove variability in the experimental results due to the effects of surface microrelief. Under saturated surface conditions high intensity simulated rainfall was less efficient at removing both non-adsorbing and adsorbing solutes from the repacked topsoil aggregates than low intensity rainfall. The observed decrease in the concentration of isoproturon and bromide in the leachate with time could be explained by a transport non-equilibrium effect.     

土壤溶质迁移至地表径流过程的室内模拟试验

关于土壤溶质迁移到地表径流,现有研究大多是概念性的认识,对迁移过程中各个部分的定量研究却很少。该文为了量化研究土壤溶质迁移流失过程及其作用机理,通过设计2种水文条件即土壤水分饱和和土壤渗流条件,其中土壤渗流条件设置了2种水头（5 cm,10 cm）,采用人工模拟5组不同地表径流流速,分别研究土壤溶质迁移到地表径流过程中4种途径：土壤侵蚀、伯努利效应、扩散和对流。试验结果表明了伯努利效应导致土壤溶质迁移量增加;特别是在土壤水分饱和条件下,当地表径流流速从55 mL/s升到 200 mL/s时,伯努利效应引起的土壤溶质流失通量占总流失通量的比例从14%升到53%,在土壤水分饱和条件下,混合层深度小于5 mm;但是在土壤渗流条件下,混合层深度随着水头的高低和径流流速的大小而变化。土壤溶质迁移过程同地表径流流速和地下水位高低有着重要关系。     

Mineralization of hydroxylated isoproturon metabolites produced by fungi

When exposed to the herbicide isoproturon, some soil fungi in pure culture metabolize the substance to hydroxylated metabolites. Hydroxylated metabolites of isoproturon have also been detected in soil studies. In an agricultural soil not previously exposed to isoproturon we found that the hydroxylated isoproturon metabolite N-(4-(2-hydroxy-1-methylethyl)phenyl)-N′,N′-dimethylurea mineralized faster than both isoproturon and its N-demethylated metabolite N-(4-isopropylphenyl)-N′-methylurea (MDIPU), thus indicating that mineralization of isoproturon is stimulated by fungal hydroxylation in this soil. In soils previously treated with isoproturon, in contrast, isoproturon and both its hydroxylated and demethylated metabolites mineralized at almost the same rate with up to 52% of the ¹⁴C-ring-carbon being degraded to ¹⁴CO₂ within 63 days. Thus hydroxylated metabolites of isoproturon do not seem to be more persistent than isoproturon, and hence may degrade before they can leach from topsoil and contaminate the aquatic environment. While an isoproturon-mineralizing bacterium Sphingomonas sp. SRS2 and a MDIPU-mineralizing mixed bacterial culture were able to deplete the medium of hydroxylated metabolites, little or no mineralization took place. This indicates that other bacteria must be present in the soil that are able to benefit from isoproturon being made available to mineralization by fungal hydroxylation.     

Effects of solid olive-mill waste addition to soil on sorption, degradation and leaching of the herbicide simazine

Abstract. A laboratory study was conducted to investigate the effects of adding an intermediary byproduct of olive oil extraction ( alperujo or solid olive-mill waste, SOMW) on the sorption, degradation and leaching of the herbicide simazine in a sandy loam soil. The effect of SOMW addition on soil porosity was also assessed. The soil was amended in the laboratory with SOMW at two different rates (5% and 10% w/w). Simazine sorption isotherms showed a great increase in herbicide sorption after SOMW addition to soil; sorption increased with the amount of SOMW added. Incubation studies showed extended persistence by reduced biodegradation of simazine in the soil amended with SOMW compared with the unamended soil. Although the addition of SOMW to soil increased the total porosity, breakthrough curves of simazine in handpacked soil columns showed that SOMW addition retarded the vertical movement of the herbicide through the soil and reduced the total amount of herbicide leached. It appeared that the longer residence time of simazine in the amended soil columns (>20 days) compared with that in the unamended soil column (<20 days) allowed enhanced degradation and/or irreversible sorption under column leaching conditions. The results revealed important changes in herbicide behaviour upon SOMW addition, confirming the need to assess these changes in order to optimize the combined use of organic wastes and soil-applied pesticides.     

A comparison of water flux measurements: passive wick‐samplers versus drainage lysimeters

Quantification of soil water flow is a prerequisite to accurate prediction of solute transfer within the unsaturated zone. The monitoring of these fluxes is challenging because the results are required to answer both scientific and practical questions regarding protection of groundwater, sustainable management of agricultural, forestry, mining or set‐aside industrial areas, reducing leachate loss from landfills or explaining the fate of environmentally harmful substances. Both indirect and direct methods exist for estimating water‐flux rates and have been used with varying success. In Europe, the use of direct lysimetry methods for measuring water and solute fluxes in soils has increased in recent years. This technique ensures reliable drainage data, but requires relatively large investment and maintenance expenses. Other research groups, especially in the USA, have developed alternative techniques. In this paper we compare the functioning of a passive‐wick sampler, especially the deep‐drainage meter type (DDM), with two different types of drainage lysimeters (weighing and non‐weighing) under field conditions in Germany for the measurement period from May 2004 until April 2009. The study showed that under sandy soil conditions no significant differences occurred between the measurements from DDM and both drainage lysimeter types. Only in periods with increased precipitation was there a tendency of drainage over‐estimation by the DDM in comparison with the lysimeters tested. For longer periods, no significant differences in the amount of drainage or the pattern of drainage formation were found between weighing and non‐weighing gravitation lysimeters. The practical use of DDMs is restricted because the groundwater level must be >2 m from the soil surface. Suggestions are made for the technical improvement of the DDM as well as the testing of the device with more cohesive soils.     

开发建设中扰动地面新增水土流失研究

针对神府东胜煤田开采过程中所引发的严重新增水土流失问题,采用野外放水冲刷的试验研究方法,对神府东胜煤田扰动地面新增水土流失机理和流失量进行了初步研究。结果表明:在相同放水冲刷流量和坡度下,原始地面的平均土壤入渗率较扰动地面的增加30%;两种不同类型下垫面的径流量均随时间的增加而增加,冲刷的前6min,径流量均较小,且原始地面>扰动地面,在6min以后,径流量迅速增大,且原始地面<扰动地面,扰动地面的平均径流量较原始地面增加14%;原始地面的侵蚀产沙在整个放水冲刷过程中没有显著变化,基本维持在一个常数水平;扰动地面在放水冲刷0—15min的侵蚀产沙量较高,此后侵蚀产沙随冲刷历时的延长而下降并最终趋于稳定;扰动地面的平均含沙量较原始地面增加96%,平均产沙量增加89%;新增土壤流失量随放水流量和坡度的增大而增大,10°时,新增土壤流失量最大;同一坡度条件下,放水流量越小,土壤流失量增加的百分比就越大,反之则越小。     

生育期对红壤旱坡花生地氮素径流流失的影响

探明作物不同生育期的氮素流失特征,以期为红壤旱坡地氮素流失预测与有效防控提供理论依据。采用土壤水分渗漏试验装置,对自然降雨条件下赣北第四纪红壤旱坡花生地不同生育期的地表径流、渗漏水及其各形态氮素输出过程进行连续观测。结果表明:(1)红壤旱坡花生地产流主要发生在降雨量最为集中的开花下针期。渗漏水是各生育期主要的径流形式,占总径流量的64%。(2)各生育期,氮素流失的主要途径为渗漏水,主要形式为可溶性氮,占总氮(TN)流失量的54%～99%。除饱果成熟期外,各生育期渗漏水中氮素流失的主要成分为硝态氮,占TN的38%～50%。(3)地表径流和渗漏水氮素浓度总体表现为幼苗期和开花下针期较大,饱果成熟期最小,而氮素流失量则表现为开花下针期最大。因此,幼苗期和降雨量最为集中的开花下针期为防治红壤旱坡花生地氮素流失的关键时期,控制硝态氮等氮素淋溶损失是减少红壤旱坡花生地氮素流失的关键途径。     

Lysimeter study of water and salt dynamics in a saline metallurgical waste

In Germany, mounds of solid wastes (mainly rock salt, NaCl) from potash mining produce large amounts of briny runoff which are frequently conveyed into surface waters. This study was conducted to evaluate a saline, fine‐grained aluminum recycling by‐product as soil substitute in a surface barrier over potash mining waste mounds. Four free‐drainage lysimeters were monitored for three years under field conditions. Two lysimeters were filled with a by‐product from aluminum recycling, and the other two with a mixture of this by‐product and a coal combustion waste. Precipitation, evaporation, discharge, as well as pressure head in three depths were measured continuously. Electrical conductivity in the discharge and in suction cup solutions from four depths was used to monitor desalinization. It was found that mean annual discharge from the pure metallurgical waste and from the mixture was 39% and 24% of rainfall. Materials were sufficiently leached to support growth of ryegrass (Lolium perenne, L.) after 444 (pure metallurgical waste) and 281 mm (mix) of seepage, or 28 months of lysimeter operation. We conclude that the mix seems the better material for an engineered mine‐waste surface barrier.     

Multi-Year Measurements of Field-Scale Metolachlor Volatilization

Volatilization is a critical pathway for herbicide loss from agricultural fields, and subsequently deposited downwind from the edge of the field. To better understand the volatilization process, field-scale turbulent volatilization fluxes of metolachlor (2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl) acetamide) were quantified for 13 consecutive years using a combination of herbicide concentration profiles and eddy diffusivities derived from turbulent fluxes of heat and water vapor. Site location, type of herbicides, and agricultural management practices remained unchanged during this study in order to evaluate the effect of soil moisture on metolachlor volatilization. Twenty gravimetric surface soil moisture samples (0–5 cm) were collected immediately after herbicide application and then at 0430 hours each morning to determine the impact of surface moisture on herbicide volatilization. Five days after application, cumulative herbicide volatilization ranged from 5 to 63% of that applied for metolachlor. Metolachlor volatilization remained an important loss process more than 5 days after application when the soil surface was moist. Conversely, if the soil surface was dry, negligible volatilization occurred beyond 5 days. Furthermore, the total amount of metolachlor volatilized into the atmosphere increased exponentially with surface soil water content during application (r ²?=?0.78). Metolachlor volatility was found to be governed largely by surface soil moisture.