Leaching of pesticides and a bromide tracer through lysimeters from five contrasting soils

In each of two seasons, undisturbed lysimeters 0.8 m in diameter and 1.05 m in length taken from five soil types were cropped with winter wheat. They received autumn applications of the pesticides isoproturon and linuron as well as a bromide tracer and spring applications of dimethoate and MCPA. Leachate was collected at regular intervals and concentrations of the various solutes determined. Rainfall from December to March was 290 and 191 mm in the first and second seasons, respectively. Both springs were exceptionally dry with less than 50% of the mean April‐to‐June rainfall of 138 mm. Total flow from the lysimeters ranged from 335 to 477 mm (and from 0.78 to 3.95 pore volumes) over the two seasons. Leaching to drainage of bromide highlighted soils where preferential flow was influential with total losses ranging from 24% of applied for a strongly structured, alluvial clay loam to 79% for an unstructured sand. Leaching to drainage of isoproturon (K_oc ≈ 100 ml g⁻¹) was observed from all but a peat soil with losses greater (0.31–1.01% of applied) from the clay loam and a deep medium loam, where patterns of leaching clearly indicated preferential flow mechanisms, than from the sand and a light loam over gravel (0.04–0.18% of applied) where a broad breakthrough curve indicated that matrix flow was more important. Linuron (K_oc ≈ 500 ml g⁻¹) was detected in occasional samples of leachate from the clay loam, the light loam over gravel and the medium loam during the first season only (maximum loss 0.12% of applied). The sandy soil, often considered most vulnerable to leaching, gave the smallest total losses of pesticide of the four mineral soils, whilst significant preferential flow in the deep, medium loam was believed to result from a compacted topsoil. Neither of the spring‐applied pesticides was detected in the leachate, as flow following application was very small and relatively slow. © 2000 Society of Chemical Industry     

Influence of different field sites on pesticide movement into subsurface drains

Pesticide movement to subsurface drains was monitored in two typical crop production areas in Germany. Field trials were conducted on two subsurfacedrained soils, a silt loam and a poorly structured sandy soil, under different climatic conditions. Over a period of one year, the drainflow was measured and the drain water was analysed for all applied herbicides. Different leaching behaviour was observed at the two field sites. Following autumn application of pendimethalin and isoproturon to the Soester Börde soil, maximum concentrations of about 62 μg litre^?1 for isoproturon and 0.7 μg litre^?1 for pendimethalin were observed in drainflow from this silt loam. The early occurrence of both herbicides in the drain water only two days after application is consistent with fast flow through macropores. In contrast, on the subsurfacedrained sandy soil in Brandenburg, isoproturon did not reach the drains until two months after autumn application and was found at maximum concentrations of only 1.4 μg litre^?1; pendimethalin was not detected in the drain water. Pesticide movement after spring application seemed to be of minor importance. At both locations, spring application led to low concentrations of pesticides in the drainflow (pendimethalin < 0.01 μ litre^?1; metolachlor ? 0.05 μ litre^?1; chloridazon ? 0.15 μ litre^?1; metamitron ? 0.02 μg litre^?1; terbuthylazine ? 1.4 μ litre^?1).     

Lysimeter study to investigate the effect of rainfall patterns on leaching of isoproturon

The influence of five rainfall treatments on water and solute leaching through two contrasting soil types was investigated. Undisturbed lysimeters (diameter 0.25 m, length 0.5 m) from a sandy loam (Wick series) and a moderately structured clay loam (Hodnet series) received autumn applications of the radio-labelled pesticide isoproturon and bromide tracer. Target rainfall plus irrigation from the end of November 1997 to May 1998 ranged from drier to wetter than average (235 to 414 mm); monthly rainfall was varied according to a pre-selected pattern or kept constant (triplicate lysimeters per regime). Leachate was collected at intervals and concentrations of the solutes were determined. Total flow (0.27-0.94 pore volumes) and losses of bromide (3-80% of applied) increased with increasing inputs of water and were larger from the Wick sandy loam than from the Hodnet clay loam soil. Matrix flow appeared to be the main mechanism for transport of isoproturon through the Wick soil whereas there was a greater influence of preferential flow for the Hodnet lysimeters. The total leached load of isoproturon from the Wick lysimeters was 0.02-0.26% of that applied. There was no clear variation in transport processes between the rainfall treatments investigated for this soil and there was an approximately linear relationship (r2 = 0.81) between leached load and total flow. Losses of isoproturon from the Hodnet soil were 0.03-0.39% of applied and there was evidence of enhanced preferential flow in the driest and wettest treatments. Leaching of isoproturon was best described by an exponential relationship between load and total flow (r2 = 0.62). A 45% increase in flow between the two wettest treatments gave a 100% increase in leaching of isoproturon from the Wick soil. For the Hodnet lysimeters, a 35% increase in flow between the same treatments increased herbicide loss by 325%.     

Influence of Soil Moisture on Long-Term Sorption of Diuron and Isoproturon by Soil

Long-term sorption of diuron and isoproturon by a clay loam soil was investigated for nine weeks at two herbicide doses (0·6 or 3 mg kg⁻¹) and two soil moisture contents (35 or 62% w/w, i.e. 3·16 or 1 kPa) by measuring changes in herbicide concentrations in the soil solution sampled by means of glass microfibre filters in presence of sodium azide (200 mg litre⁻¹) which inhibited biodegradation for more than four weeks. After the first day equilibration period, where adsorption mainly occurred (>70% adsorbed), herbicide concentrations in the soil solution decreased (about 50% for diuron; up to 38% for isoproturon) for two weeks but equilibration required about one month. Small amounts of herbicides were sorbed during this process (<10% of the initial (24-h) adsorption). These were similar for both herbicides, although diuron was initially more adsorbed. Values of the partition coefficients of herbicides between soil and soil solution were increased (75–125% for diuron; 29–67% for isoproturon). High soil moisture enhanced sorption speed for both herbicides and increased final sorption only for diuron. Sodium azide inhibited long-term sorption of the more stable diuron and this effect was reversed by low temperature only at the low soil moisture. Sodium azide action might be complex (competition, effect on soil micro-organisms) and was not elucidated.     

Movement of pendimethalin,ioxynil and soil particles to field drainage tiles

Knowledge of the movement of herbicides and soil particles to sub-surface tile drainage may help to predict chemical leaching to surface waters and deeper groundwater systems. The movement of pendimethalin (2 years), ioxynil (1 year) and soil particles (3 years) to two tile drains was investigated on a sandy loam soil under natural weather conditions. Herbicide and particle concentrations in the drain water showed a very dynamic pattern. The largest herbicide concentrations were detected during the first tile drain flow events after application. Very little herbicide was lost with drain water later than 2 months after application. The turbidity, reflecting concentrations of soil particles, correlated positively and strongly with the pendimethalin concentration and negatively with the rate of drain water discharge, whereas it was uncorrelated with the ioxynil concentration. Peak turbidity values occurred during or shortly after rainfall events, either in break of frost situations, or on unfrozen soil coinciding with the occurrence of peak moisture contents in the topsoil well (3-7%) above field capacity. On average, 0.0013% of the applied pendimethalin and 0.0015% of the applied ioxynil were lost with drain water. The results suggest that preferential flow promotes the movement of all three substances to the tile drains but indicate somewhat different transport mechanisms for the two herbicides.     

Evaluation of uncalibrated preferential flow models against data for isoproturon movement to drains through a heavy clay soil

The uncalibrated predictive ability of four preferential flow models (CRACK‐NP, MACRO/MACRO_DB, PLM, SWAT) has been evaluated against point rates of drainflow and associated concentrations of isoproturon from a highly structured and heterogeneous clay soil in the south of England. Data were available for four plots for a number of storm events in each of three successive growing seasons. The mechanistic models CRACK‐NP and MACRO generally gave reasonable estimates of drainflow over the three seasons, but under‐estimated concentrations of isoproturon over a prolonged period in the first season and over‐estimated them in the two remaining seasons. CRACK‐NP simulated maximum concentrations of isoproturon over the first two events of each of the three seasons of 156, 527 and 24.4 µg litre^?1, respectively, and matched the observed data (465, 65.1 and 0.65 µg litre^?1) slightly better than MACRO (69.1, 566 and 58.5 µg litre^?1). Automatic selection of parameters from soils information within MACRO_DB reduced the emphasis on preferential flow relative to the stand‐alone version of MACRO. This gave a poor simulation of isoproturon breakthrough and simulated maximum concentrations were 0, 50.1 and 35.1 µg litre^?1, respectively. The capacity model PLM gave the best overall simulation of total drainflow for the first two events in each season, but over‐estimated concentrations of isoproturon (967, 808 and 51.3 µg litre^?1). The simple model SWAT represented total drainflow reasonably well and gave the best simulation of maximum isoproturon concentrations (140, 80.2 and 8.2 µg litre^?1). There was no clear advantage here in using the mechanistic models rather than the simpler models. None of the models tested was able to simulate consistently the data set, and uncalibrated modelling cannot be recommended for such artificially drained heavy clay soils. © 2001 Society of Chemical Industry     

Movement of pesticides to surface waters from a heavy clay soil

A field experiment at Cockle Park, Northumberland on a clay loam soil (Dunkeswick series) cropped with winter wheat investigated the effects of drainage and season of application on pesticide movement. Isoproturon, mecoprop, fonofos and trifluralin were applied in two consecutive seasons at normal agricultural rates to three hydrologically isolated plots each of 0.25 ha. Two of the plots were mole-drained and the third was an undrained control. Surfacelayer flow and drainflow from each plot were monitored at 10-min intervals. Samples of flow were analysed for pesticides to evaluate transport of applied chemicals from the site. Despite widely differing properties (K_oc 20–8000 ml g^?1, t_1/2 10–60 days), all four pesticides were found in surface-layer flow and mole drainflow from the site. Maximum concentrations of pesticides in flow ranged from 0.1 to 121 μg litre^?1 (aqueous phase) and < 0.2 to 48 μg litre^?1 (particulate phase). Over two contrasting seasons, total losses of pesticides in flow followed total amounts of flow and were approximately four and five times larger, respectively, in 1990/91 than in 1989/90. The maximum loss occurred from the undrained plot and was 2.8 g isoproturon (0.45% of that applied). Total losses of autumn-applied pesticides from an undrained plot were up to four times greater than losses from a mole-drained plot. Mole drainage decreased movement of pesticides from this slowly permeable soil by reducing the amount of surfacelayer flow. Maximum concentrations of mecoprop and isoproturon in drainflow were 10–20 times larger following spring application than after application in autumn. Bypass flow down soil cracks was an important process by which pesticide was lost from the site, with transport to the drainage system via mole channels (55 cm depth) after less than 0.5 and 6.7 mm net drainage in the two winters.     

Differentiating between physical and chemical constraints on pesticide and water movement into and out of soil aggregates

A laboratory experiment comparing the movement of ³H₂O and [¹⁴C]isoproturon into and release from soil aggregates is described. Small aggregates (2.0–2.4 mm) were prepared from a clay topsoil and maintained at three different initial moisture conditions. A small volume of the radioisotope solution was introduced prior to bathing the aggregates in a 2 mM CaCl₂ solution to represent new rainwater. Whilst the ³H₂O was imbibed by the air-dry aggregates, the pesticide did not follow the water but remained on the surface of the aggregates. This may be related to its sorptive properties and an excess of sorption sites on the sorbent with respect to the sorbate. Increasing the length of exposure of the moist aggregates to [¹⁴C]isoproturon reduced the initial release of the compound into the bathing solution, probably due to diffusion (retarded by sorption) into the aggregates. The diffusion model described by Crank and a non-equilibrium desorption model were used to analyse the ³H₂O and [¹⁴C]isoproturon release curves. This showed that the release of ³H₂O from the dry aggregates was controlled by diffusion. The release of isoproturon was probably controlled by non-equilibrium sorption/desorption from air-dry aggregates and by a combination of non-equilibrium sorption/desorption and diffusion from wet aggregates. © 1999 Society of Chemical Industry     

Spatial variability in the degradation rates of isoproturon and chlorotoluron in a clay soil

Thirty separate soil samples were taken from different locations at the Brimstone farm experimental site, Oxfordshire, UK. Incubations of isoproturon under standard conditions (15 °C; ?33 kPa soil water potential) indicated considerable variation in degradation rate in the soil, with the time to 50% loss (DT₅₀) varying from 6 to 30 days. These differences were confirmed in a second comparative experiment in which degradation rates were assessed in 11 samples of the same soil in two separate laboratories using an identical protocol. There was a significant negative linear relationship (r²= 0.746) between the DT₅₀ values and soil pH in this group of soils. In a third experiment, degradation rates of the related compound chlorotoluron were compared with those of isoproturon in 12 separate soil samples, six of which had been stored for several months, and six of which were freshly collected from the field. Degradation of both herbicides occurred more slowly in the stored samples than in the fresh samples but, in all of them, chlorotoluron degraded more slowly than isoproturon, and there was a highly significant linear relationship (r²=0.916) between the respective DT₅₀ values.     

Persistence and leaching of the herbicides acetochlor and terbuthylazine in an allophanic soil: comparisons of field results with PRZM‐3 predictions

Rates of degradation and adsorption of acetochlor [2‐chloro‐N‐ethoxymethyl‐6′‐ethylaceto‐o‐ toluidide] and terbuthylazine [N ²‐tert‐butyl‐6‐chloro‐N⁴‐ethyl‐1,3,5‐triazine‐2,4‐diamine] in a Horotiu sandy loam soil (Typic Orthic Allophanic) were determined under controlled temperature and soil moisture regimes. These were then combined with site‐specific soil properties and climatic conditions in the Pesticide Root Zone Model (PRZM‐3) to predict dissipation and leaching of the herbicides in the field. PRZM‐3 significantly under‐estimated dissipation of both herbicides in the field using parameters derived from the laboratory incubation studies. When these parameters were derived from the field trials, PRZM‐3 adequately predicted dissipation of both herbicides using a two‐rate dissipation sub‐model but under‐predicted the dissipation when a simpler single‐rate sub‐model was used. Earlier‐than‐expected appearance of both herbicides in sub‐soil layers were postulated to result from the non‐equilibrium adsorption/transport of the herbicides and preferential flow, which cannot be simulated by PRZM‐3. © 2000 Society of Chemical Industry     

Influence of soil moisture on short-term adsorption of diuron and isoproturon by soil

The adsorption of diuron and isoproturon by a clay loam soil at 35% (3-16 kPa) and 62% (1 kPa) soil moisture content was studied by means of glass microfibre filters capable of sampling soil solution for herbicide analysis. Adsorption was rapid, with 40–80% of the final (24 h) sorption being achieved within 2 min. These equilibria were achieved more rapidly for diuron, which was also the more highly adsorbed. Adsorption of both herbicides was favoured by low soil moisture initially, but was enhanced by higher soil moistures at sorption times greater than 30 min. However, increasing the soil moisture from 31% (10 kPa) to 62% (1 kPa) had little effect on the final soil sorption capacity. Regarding the water status in the soil, it is thought that adsorption took place in small pores (<3 μm). Herbicides diffused rapidly into small pores and adsorption by wet soil was delayed for a short period of time (about 30 min).     

Effects of soil redistribution by tillage on subsequent transport of pesticide to subsurface drains

BACKGROUND

Tillage operations will change the distribution in soil for any pesticide residues still present from earlier applications. This redistributive effect of tillage has been neglected in the study of pesticide leaching behavior. This study reviews the literature to characterize this redistributive effect for different tillage operations and uses a pesticide leaching model to investigate the impact of redistribution on pesticide transport to subsurface drains which is a significant input route to surface water bodies.

RESULTS

Inversion ploughing moves the majority of any residues of pesticide present at or near the soil surface into the bottom two-thirds of the plough layer, whereas non-inversion ploughing has only a limited redistributive effect. Incorporating this redistributive effect into model simulations resulted in large changes (typically 5–10-fold difference) in both the maximum concentration and total mass of pesticide transported to drains over the winter following cultivation. More intense cultivation decreased subsequent leaching for relatively mobile compounds (Koc ≤1000 mL g⁻¹), but increased it for strongly sorbed pesticides (Koc ≥2000 mL g⁻¹).

CONCLUSION

The redistributive effect of soil tillage on pesticide residues can have a large effect on subsequent transport to subsurface drains. This effect has been neglected in the literature. Field research is required to validate the model simulations presented here, and consideration should be given as to whether the effect needs to be included within risk assessment procedures. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

Mobility and persistence of four herbicides in soil of a South Australian vineyard

The use of persistent herbicides has increased the potential for contamination of soil, soil water and groundwater. The mobility, dissipation and fate of four herbicides, norflurazon, oxadiazon, oxyfluorfen and trifluralin, used in South Australian viticulture, have been studied in a typical sand‐over‐clay vineyard soil. Following herbicide application at field rates to plots up‐slope of miniature lysimeters, surface soil and soil water were sampled regularly over the period of annual rainfall. The concentration of each herbicide in the soil cores, surface soil and soil water was determined by GLC‐NPD following solid‐phase concentration procedures where necessary. Oxadiazon dissipated more quickly than the other three herbicides in the soil. Norflurazon was the most mobile of these herbicides in this soil. However all four herbicides were found in the soil water within the first year, though only norflurazon was found in the soil water in the subsequent year. Norflurazon moved laterally to a greater extent than the other herbicides. © 2000 Society of Chemical Industry     

Desorption of diuron and isoproturon from undispersed clay loam soil

Studies were conducted to investigate the desorption of diuron and isoproturon adsorbed on undispersed clay loam soil, and the influence of residence time in soil on desorption. The soil was treated at 0·6 or 3 mg kg^-1, at 70% moisture content and in the presence of sodium azide to prevent degradation. Measurement of herbicide concentrations in soil solution sampled by means of glass microfibre filters showed that adsorption mainly occurred for one day but long-term sorption proceeded for >two weeks. After a one-day or three-week residence time, soil solution was partly replaced (28%). Measurement of concentrations in solution showed rapid desorption, with equilibria being achieved within 1 h (diuron) or a few hours (isoproturon). After 16 successive desorptions done at 30-min or 12-h intervals, equilibration times tended to be longer. For the short residence time, desorption and long-term sorption could occur simultaneously and equilibration might be faster. Residence time had no significant effect on desorption kinetics nor on the small hysteresis observed for diuron. The aging effect, involving long-term sorption only, decreased the proportion of diuron removed from the soil by successive desorptions but, for isoproturon, desorption frequency and desorption kinetics were more important. © 1997 SCI     

Anwendung von Isoproturon, allein und in Kombination mitanderen Wirkstoffen, im Nachauflauf–Winter (NA–W) und Nachauflauf–Frühjahr (NA–F) zu Winterweizen und Wintergerste

Use of isoproturon, alone and in combination with other compounds, post–emergence in winter and spring, on winter wheat and winter barley. II. Side effects on dehydrogenase activity, nitrogen transformation and straw decomposition in the soil The effect of isoproturon, alone and combined with dinoseb acetate and bifenox, on dehydrogenase activity, nitrogen transformations and straw decomposition following post–emergence application in winter and spring to winter wheat and winter barley was studied over two years at two sites. Isoproturon caused limited transient stimulation and inhibition of dehydrogenase activity, maximum 40%, and nitrogen turnover, 70–90%. Dinoseb acetate reduced general metabolic activity by up to 30%. Ammonium and nitrite concentrations were at times more than 100% higher than control values. In the laboratory, with temperature, soil moisture and sampling times similar25 to those in the field, isoproturon caused reductions in dehydrogenase activity in only a few cases but dinoseb acetate reduced the activity by up to 50%. The herbicide effects were clearer in a sandy than in a clay soil. The effect of time of application on the response of soil microbial activity to herbicides was evident only in the field.     

生物炭施用对冬麦田土壤水热环境及土壤呼吸的影响

探究施用生物炭对冬麦田土壤水热因子及土壤呼吸的影响,对生物炭在麦田应用及农田固碳减排有重要的实践意义。2018年10月至2021年6月在关中灌区连续3 a进行了麦田生物炭施用试验,试验设置生物炭施用量水平分别为：0 t·hm^-2·a^-1（C0）、10 t·hm^-2·a^-1（C10）、20 t·hm^-2·a^-1（C20）,通过测定小麦生长季的土壤温度、土壤水分、土壤呼吸速率及产量,明确不同施炭量对冬小麦田土壤水热因子及土壤呼吸的影响。各处理生育期内土壤呼吸速率及全生育期CO₂排放量存在显著性差异（P<0.05）,均表现为C0>C20>C10。生物炭施入增加了生育期内的平均土壤温度,同时显著提高了0～20 cm土壤含水量（P<0.05）,并减弱了土壤水分在生育期内的变化幅度。C10、C20处理3 a平均土壤含水量较C0分别增加了17.0%、29.0%。5 cm及10 cm土壤温度能分别解释土壤呼吸变化的54.7%～...     

Leaching potential and decomposition of fluroxypyr in Swedish soils under field conditions

The mobility and decomposition of the herbicide fluroxypyr (4-amino-3,5-dichloro-6-fluoro-2-pyridyloxyacetic acid) was studied under field conditions in a sandy soil and a clay soil. Leachate was collected in lysimeters with undisturbed soil (sand) and in tile-drained plots (clay). Soil samples to a depth of one metre were also collected in both soils to characterize the temporal depth distribution of fluroxypyr in the profiles. The herbicide was applied as the I-methylheptyl ester of fluroxypyr at two rates, 187.5 and 375.0 g a.e. ha^?1, representing the normal and double the dose of the compound used for spring cereals. Some lysimeters received supplementary watering. Only two leachate samples (one from each soil) had concentrations of fluroxypyr above the detection limit (1 μg litre^?1), i.e. 2 and 5 μg litre^?1. Both samples were collected within two months after application, when less than 2 mm of drainage had been collected. The methylheptyl ester of fluroxypyr was not found in any of the samples. Fluroxypyr levels above the detection limit in soil (5 μg kg^?1 dry soil), were never found below the topsoil (0.2 m) in the clay profile, while, in the sandy profile, levels just above the detection limit were found occasionally in deeper soil layers. Concentrations were reduced to undetectable or very low levels within three months after spraying.     

基于MTVDI与DDI二元回归模型对毛乌素沙地腹部土壤表层水分的研究

采用温度植被干旱指数法(MTVDI)与荒漠化指数法(DDI),利用2016年4月、9月的Landsat数据对毛乌素沙地腹部的土壤水分进行反演,并与实测的土壤水分进行对比检验,将所反演的土壤含水量图划分为4个等级,基于此分析了2个时期毛乌素沙地腹部的旱情土壤水分分布变化。结果显示：(1)4月份MTVDI指数与0~10 cm、10~20 cm、20~30 cm土层土壤含水量的R²值分别为0.656、0.646、0.637,整体高于9月份R²值0.457、0.436、0.431,MTVDI能够较好地反映毛乌素沙地腹部土壤表层水分,且精度较高;(2)荒漠化指数DDI与MTVDI结合建立二元线性回归模型监测区域土层0~10 cm深度含水量,平均相对误差为10.95 %;(3)4月份,研究区0~10 cm表层土壤含水量5%~10%区域占总面积的53.72%以上,达到了6 256 km²,含水量偏低,需要加强当地水资源管理。     

Influence of soil moisture on isoproturon activity against Alopecurus myosuroides

Alopecurus myosuroides Huds. (blackgrass) in sandy loam soil in pots was treated at the three-leaf stage with formulated isoproturon. Damage to plants resulted mainly from herbicide entry via the soil. When the soil moisture levels were maintained close to 50, 100 and 150% of field capacity (FC) throughout the experiment damage increased with the amount of water in the soil. After spraying plants raised at field capacity, change to 150 or 50% FC resulted in more and less damage respectively. Water applied to the soil surface compared with sub-irrigation caused more damage. A delay of up to 21 days between spraying plants in soil at field capacity and surface watering did not reduce damage provided the time interval between the onset of surface watering and assessment remained constant. A delay of 7 days between spraying isoproturon onto plants in dry soil (50% FC) and increasing the moisture to field capacity by surface watering decreased the damage to A. myosuroides. These results are discussed with reference to the soil moisture distribution in soil columns and rainfall patterns under field conditions.     

Effects of herbicide-fertiliser interactions on nitrogen and phosphorus transformations and herbicide persistence in soil

The effects of seven herbicides, alone or combined with a commercial compound fertiliser, on nitrogen and phosphorus transformations in soil, were investigated in the laboratory. No significant effect was observed without the fertiliser. When the fertiliser (N:P:K ratio 20:14:14) was applied (2 gkg^?1 of soil), asulam markedly reduced nitrification, while increasing the mineralisation of nitrogen; chloridazon, glyphosate, isoproturon and paraquat all prevented the reduction in available phosphate that occurred in the control soil in the first 2 weeks. The rates of degradation of dalapon and isoproturon were greatly reduced in fertilised soil. The importance of these results is discussed in the context of the requirements of registration authorities.