Potential of barnyard grass to remediate arsenic‐contaminated soil

The present study investigated the arsenic (As) remediation potential of barnyard grass (Echinochloa crus‐galli L. Beauv. var. formosensis Ohwi), with a special focus on the behavior of As in the soil in comparison with rice (Oryza sativa L. cv. Nipponbare). For both plants, very little growth inhibition was observed in the As‐contaminated soil. The amount of As in the soil was reduced by the plant's uptake and the level of As in the soil water from the rice‐growing pots was remarkably lower than that in the plant‐free soil water. In the soil with the barnyard grass, the amount of As in the soil water was higher than that in the plant‐free soil water, but the amount of As in the soil and the amount of As that was adsorbed on the soil solid were reduced by the plant's uptake. At the highest As level in the soil (100 mg kg^?1), 249.60 and 101.26 µg As pot^?1 were taken up by the rice shoot and barnyard grass shoot, respectively, and total amounts of 1468.65 and 1060.57 µg As pot^?1 were taken up by the barnyard grass and rice seedlings, respectively. At the same As level in the soil, the As concentrations were 14.99 and 37.76 µg g^?1 in the shoot of barnyard grass and rice, respectively, and 486.61 and 339.32 µg g^?1 in the root of barnyard grass and rice, respectively. Barnyard grass took up more As than rice, but the As concentration in the shoot of barnyard grass was lower than that in the shoot of rice. A considerable amount of As was taken up by both barnyard grass and rice, suggesting that the plant species have the potential to remediate As‐contaminated soil.     

Effect of soil placement and shoot uptake of prometryne and terbutryne on peas

The effect of placing terbutryne in different soil layers with reference to different depths of sowing of peas was studied by measuring plant top growth. Increasing the depth of sowing resulted in greater plant injury by the same layer of herbicide-treated soil. Exposing the upper part of the emerging epicotyl (nearest the soil surface) to soil treated with terbutryne was more injurious than exposing the lower part of the epicotyl (nearest the seed). Uptake of ¹⁴C-labelled prometryne and terbutryne by pea seedlings during emergence and early growth was measured according to different soil-zone treatments. The absorbed amount of each herbicide decreased in the order: root system, lower epicotyl, upper epicotyl. Translocation of the herbicides to the foliage was higher from the upper than from the lower part of the epicotyl. Shoot and root uptake and translocation of prometryne were higher than of terbutryne.     

Weed seedling herbivory by field cricket Teleogryllus emma (Orthoptera: Gryllidae) in relation to the depth of seedling emergence

This study aimed to determine whether seedling herbivory by the field cricket, Teleogryllus emma (Ohmachi et Matsuura), promoted the mortality of Italian ryegrass (Lolium multiflorum Lam.), a non‐native grass weed in Japan, whether the impact of seedling herbivory differed depending on the depth of seedling emergence and the influence of cricket density on seedling mortality. First, the seedlings at emergence depths of 0, 1 and 2 cm were exposed to the cricket for 2 days in plastic cups and the amount of seedling mortality by herbivory was calculated. The level of mortality of 60 seedlings that emerged from seeds on the soil surface was 92.4%, significantly higher than that of the seedlings that emerged from seeds at depths of 1 cm (10.8%) and 2 cm (9.6%). Second, the seedlings at the emergence depths of 0 and 1 cm were exposed to the crickets at four different densities (zero, one, two and three individuals per 5700 cm²) for 5 days in plastic containers and the amount of seedling mortality by herbivory was calculated. The level of mortality by herbivory of the seedlings that emerged from 100 seeds on the soil surface was higher (33.3–61.3%) than that of the seedlings that emerged from seeds at a depth of 1 cm (4.7–13.1%) in the containers with one‐to‐three crickets. The level of seedling mortality tended to increase with an increasing cricket density. These results suggest that seedling herbivory by crickets is an important factor in weed mortality, particularly in no‐till fields and in field margins, where the seeds are more prevalent near the soil surface.     

Oregano green manure for weed suppression in sustainable cotton and corn fields

A 2 year field experiment was conducted in northern Greece to study the biomass effects of four oregano (Origanum vulgare) biotypes, used as incorporated green manure, on the emergence and growth of barnyard grass (Echinochloa crus‐galli), bristly foxtail (Setaria verticillata), common purslane (Portulaca oleracea), cotton (Gossypium hirsutum), and corn (Zea mays). The oregano biotypes were selected on the basis of their high phenolic content. The phytotoxic potential of the oregano biotype extracts also was determined in the laboratory by using a perlite‐based bioassay with cotton, corn, and barnyard grass. The bioassays indicated that the germination, root elongation, and fresh weight of cotton, corn, and barnyard grass were reduced by the oregano biotype extracts. In the field, the emergence of common purslane, barnyard grass, and bristly foxtail was reduced by 0–55%, 38–52%, and 43–86%, respectively, in the oregano green manure treatments, as compared with the oregano green manure‐free treatments (the controls). At harvest, the cotton lint and corn grain yields in the oregano green manure treatments were 24–88% and 5–16%, respectively, greater than those in the corresponding green manure‐free, weedy treatments. These results indicated that when the biomass of the oregano biotypes with a high phenolic content were incorporated into the soil as green manure, they could be used to suppress barnyard grass, bristly foxtail, and common purslane in cotton and corn and consequently to minimize herbicide usage.     

The origins of selectivity and performance of a new pre-emergence bleaching herbicide,WL 110547. Part II: Plant and environmental factors influencing biological activity

Pre-emergence applications of the novel tetrazole herbicide WL 110547 control a number of economically important grass and broad-leaved weed species in small grain cereals. To assess the influence of plant and environmental factors on the biological performance of WL 110547, a series of tests were carried out under controlled conditions and, where appropriate, comparisons were made with field observations. When presented with the maximum opportunity for compound uptake in the absence of soil, differences in the degree of susceptibility to WL 110547 were observed amongst both monocotyledonous and dicotyledonous species, although the latter group generally showed higher levels of phytotoxicity. This species susceptibility to WL 110547 was unaffected by temperature. Increasing the sowing depth in soil decreased the level of effect of WL 110547 on a number of monocotyledonous species, although small-seeded species (e.g. blackgrass, annual meadow grass), emerging from deep in the soil profile, subsequently developed levels of phytotoxicity comparable to, or even greater than, shallow-planted seedlings. This was attributed to less vigorous seedlings, emerging from depth, that were unable to regenerate new tissue and grow away from a treated soil layer. Reduced growth rates of wild oat, blackgrass and speedwell, induced by low temperatures, also increased the phytotoxicity of WL 110547. Furthermore, applications of WL 110547 during seedling emergence maximised herbicide effect, as did seedling emergence through moist rather than dry soil. The results are discussed in relation to the mobility of the herbicide in soil, the mode of action of WL 110547, its availability to the plant and the duration of contact between emerging shoot and treated soil layer.     

7‐(4,6‐Dimethoxypyrimidinyl)oxy‐ and ‐thiophthalides as novel herbicides: Part 1. CGA 279 233: a new grass‐killer for rice

A series of novel types of 7‐(4,6‐dimethoxypyrimidin‐2‐yl)oxy ‐ and ‐thio‐3‐methyl‐1 (3H)‐isobenzofuranones were discovered at Dr R Maag AG. From the thio‐isobenzofuranyl series, CGA 279 233—BSI‐proposed common name pyriftalid—was chosen for further development as a grass herbicide for use in rice. General synthetic approaches to these new phthalic acid‐derived compounds are given, with emphasis on the synthesis of pyriftalid and its physico‐chemical behaviour. © 2001 Society of Chemical Industry     

Factors affecting the performance and crop phytotoxicity of a new rice herbicide,cinmethylin. I. Effects of water depth and soil type on the distribution and uptake of cinmethylin by transplanted and direct-seeded rice

Following successful glasshouse evaluation, first-year field trials showed that cinmethylin could give excellent control of barnyard grass (Echinochloa crus-galli) in rice paddies. However, for the successful development of a herbicide in rice, a thorough understanding of its distribution over time between water, soil and plants as affected by water depth and soil type is necessary. An application of an emulsifiable concentrate formulation to laboratory paddies containing transplanted rice showed that more of the cinmethylin became associated with and moved into the soil of shallow paddies than in the more usual deep paddies. After the first day this resulted in slightly higher concentrations of cinmethylin being accumulated by the apical meristem, the site of action of cinmethylin, in shallow-paddy plants and explains the higher phytotoxicities observed in this situation. Rapid removal of cinmethylin by the soil from the paddy water could reduce that available for absorption by the apical meristem of barnyard grass, just below the water surface, and might result in poorer control of this weed. Deeper paddies are therefore recommended for the use of cinmethylin in transplanted rice. An experiment involving direct-seeded rice confirmed that a decrease in paddy water depth and higher organic-matter soils increased the association of cinmethylin with the paddy soil. Thus paddy-water concentrations and availabilities of cinmethylin to various parts of plants were influenced by water depth and soil type. In contrast to transplanted rice, the apical meristem of direct-seeded rice is submerged in the paddy water and the stem concentrations of cinmethylin were then generally correlated with the paddy-water concentrations. They were highest from the shallow, sandy paddies and lowest from the deep, silt clay loam paddies. These relative concentrations correlate with observed relative phytotoxicities of direct-seeded rice, activities against barnyard grass and the narrower selectivity margins between the weeds and the direct-seeded crop. The cinmethylin concentrations in the apical meristems of the transplanted rice were always lower than those from the direct-seeded rice and give an illustration of a classical case of depth protection' of a crop from an applied herbicide.     

Development and evaluation of a model for predicting Lolium rigidum emergence in winter cereal crops in the Mediterranean area

Lolium rigidum is an extremely competitive and prevalent grass weed in cereal fields of Mediterranean areas. The proper timing of control measures is a prerequisite to maximising herbicide efficacy, in terms of both improved control and reduced herbicide inputs. The development of models to predict emergence flushes will contribute to this goal. Pooled cumulative emergence data obtained during three seasons from a cereal field were used to develop a Gompertz model. This explained relative seedling emergence from crop sowing onwards as a function of: (i) standard soil thermal time accumulation (TT) with a base temperature of 1.8°C and (ii) soil thermal time accumulation corrected for soil moisture (cTT). For the latter, no thermal time accumulation was computed for days in which the soil water balance within the upper 10‐cm soil layer indicated no water available for plants, because evapotranspiration was greater than rainfall plus the stored water remaining from the previous day. The model was validated with six datasets from four different sites and seasons. Compared with TT, the model based on cTT showed better performance in predicting L. rigidum emergence, particularly in predicting the end of emergence. Complemented with in‐field observations to minimise deviations, the model may be used as a predictive tool to better control this weed in dryland cereal fields of Mediterranean climate areas.     

Phytotoxic activity of pethoxamid in soil under different moisture conditions

The phytotoxic activity of soil-applied pethoxamid [2-chloro- N -(2-ethoxyethyl)- N -(2-methyl-1-phenyl-1-propanyl) acetamide], (TKC-94), on the plant growth of rice ( Oryza sativa cv. Kiyohatamochi ) seedlings as an assay plant in soil was investigated under different soil moisture conditions. The phytotoxic activity of pethoxamid mixed with soil on the shoot and root growth of rice seedlings was uppermost under the highest soil moisture condition and it decreased with declining soil moisture content, while the inhibition was greater on the root growth than the shoot growth. The amount of pethoxamid adsorbed on soil solid and the concentration of pethoxamid in soil water from soil applied with this herbicide were not influenced by the soil moisture content. In addition, the phytotoxic activity on the growth of rice seedlings in sea sand culture applied with the soil water from the herbicide-applied soil was not influenced by the soil moisture content. In the sea sand culture, the phytotoxic activity of pethoxamid was significantly reduced in negative water potential as the concentration of polyethylene glycol-6000 added to the water increased. It is suggested that the phytotoxic activity of pethoxamid in the soil primarily depends on the concentration in soil water, but the phytotoxic activity was affected by soil moisture through the effect on absorption of this herbicide by rice seedlings.     

Modelling the effect of weed-seed distribution in the soil profile on seedling emergence

Experiments to monitor weed seedling emergence from various soil depths were begun in 1989. Recently shed seeds were buried in either narrow bands at a range of depths in the soil or mixed evenly between the soil surface and each of these depths. Total emergence of Stellaria media (L.) Vill., Matricaria spp., Veronica persica Poiret, Veronica arvensis L. and Polygonum aviculare L., declined with increasing depth of burial. A similar pattern was observed for Chenopodium album L. with the exception of emergence from the surface layer. The reduction in emergence with increasing soil depth was greater for seeds in the narrow-banded treatments than for those in broad layers. A model was developed using the data from the narrow-banded treatments to predict emergence from distributions over broad layers. Predictions from the model closely agree with the data from the present broad-layer treatments and those from a similar experiment made in the 1960s. By including the effects of depth of seed burial on seedling emergence, this model could be combined with models that determine the effects of cultivation on seed distribution, and therefore improve precision of predictions of seedling emergence from the seedbank.     

Effects of glycerol ethers on monocotyledon nucleic acid and protein biosynthesis

The growth of the root systems of 2-day-old wheat seedlings was more sensitive to the experimental herbicide WL 29226 than was the growth of the shoots. Inhibition of root growth was observed after 12 hr of exposure to the herbicide. The nuclear activity in these root systems, as estimated by RNA and DNA synthesis, was significantly inhibited before this time, ～30% after 4 hr increasing to ～55% after 8 hr. Nuclear activity was inhibited by ～80% after 24 hr and showed little increase in inhibition with any further increase in exposure to the herbicide. Protein synthesis was initially less inhibited, ～6% after 4 hr, rapidly increasing to ～40% after 8 hr. DNA polymerase activity was monitored as an indication of the nucleic acid biosynthetic capacity of herbicide-treated maize and barnyard grass chromatin. In both plants, the herbicide induced an inherent modification of this activity. In maize this was reflected by an inhibition of activity and in barnyard grass by a stimulation. The effect on barnyard grass chromatin is likely to be more complex than in maize because of the presence of a chromatin-bound DNase in the chromatin from control plants. There is no evidence for such an enzyme in the chromatin from either maize or glycerol ether-treated barnyard grass. The apparent stimulation of DNA polymerase activity may in some way be associated with the loss of this nuclease activity. In order to obtain an inhibition of chromatin DNA polymerase, the plants must be pretreated with the herbicide prior to chromatin extraction. The failure of the herbicide to induce an inhibition in vitro on isolated chromatin does not support a direct interaction between the herbicide and chromatin. The results suggest that, following herbicide application to the plant, chromatin integrity has been altered.     

土层深度对三种麦田禾本科杂草出苗及生长的影响

为明确小麦田禾本科杂草在不同土层深度的出苗及生长情况,选取雀麦Bromus japonicas、节节麦Aegilops tauschii和野燕麦Avena fatua三种小麦田常见禾本科杂草,采用盆栽法系统研究不同土层深度对杂草出苗及生长的影响。结果表明,小麦田禾本科杂草雀麦、节节麦和野燕麦出苗和生长与不同土层深度密切相关,在浅土层中均有较好的出苗率,且后期生长也正常。从出苗时间来看,雀麦和野燕麦集中出苗时间在播种后5～11 d,节节麦略晚于这2种杂草;从最适出苗土层深度来看,雀麦最适出苗土层深度为0.5～3.5 cm,出苗率在76.0%～87.0%之间,节节麦的最适出苗深度为0.5～8.0 cm,出苗率在66.7%～79.3%之间,而野燕麦的最适土层深度为0.5～18.0 cm,出苗率达84.2%～94.4%;从出苗后生长影响来看,0～20 cm土层对野燕麦后期生长没有显著影响,土层深度大于10.0 cm对节节麦生长有显著抑制作用,大于6.0 cm即对雀麦有显著影响。研究表明通过深翻土地可以对雀麦和节节麦达到一定的控制作用,但对野燕麦控制效果相对略差。     

Alachlor placement in the soil as related to phytotoxicity to maize (Zea mays L.) seedlings*

Growth chamber studies were conducted to investigate the effects of alachor (2-choloro-2′,6′-diethyl-N- (methoxymethyl) acetanilide) on emerging seedlings of maize (Zea mays L.) planted 2.5 and 8.0 cm deep in a Plano silt loam soil. Alachlor was localized in the shoot zone, in the root zone, and in the shoot and root zones. Four days after emergence, seedlings were harvested and total shoot and root lengths used as measures of herbicidal effectiveness. The herbicide applied at a rate of 2.5 kg/ha caused a severe reduction in seedling height when placed in the shoot zone of seeds planted at the shallow depth. This injury was prevented when seeds were planted at the deeper level. When alachlor was placed in the root zone, there was no inhibition of shoot growth. When both shoot and root zones were exposed to the herbicide, severe growth inhibition again occurred. Roots were less sensitive to alachlor. A simple technique involving use of sand and activated charcoal barriers to effectively separate the shoot and root zones is described.     

Rate of bentazone transformation in four layers of a humic sandy soil profile with fluctuating water table

The rate of transformation of a pesticide as a function of the depth in the soil is needed as an input into computations on the risk of residues leaching to groundwater. The herbicide bentazone was incubated at 15 °C in soil materials derived from four layers at depths of up to 2.5 m in a humic sandy soil profile with a fluctuating water table (0.8 to 1.4 m), while simulating the redox conditions existing in the field. Gamma‐irradiation experiments indicated that bentazone is mainly transformed by microbial activity in the soil. The rate constant for transformation was highest in the humic sandy top layer; it decreased with depth in the sandy vadose subsoil. However, material from the top of the phreatic aquifer had a higher rate constant than that from the layers just above. The presence of fossil organic material in the fluviatile water‐saturated sediment probably stimulated microbial activity and bentazone transformation. The changes in the transformation rate constant with depth showed the same trend as those in some soil factors, viz organic carbon content, water‐extractable phosphorus and microbial density as measured by fluorescence counts. However, the (low) concentration of dissolved organic carbon (DOC) in the top of the aquifer did not fit the trend. The rate constant for bentazone transformation in the layers was higher at lower initial contents of the herbicide. © 2001 Society of Chemical Industry     

Effect of soil placement on the activity of herbicides on Cyperus rotundus L. *

The effect of herbicide placemem in the soil on control of Cyperus rotundus L. was studied in the greenhouse with EPTC, alaehlor, norfiurazon, perlluidone, napropamide, trifluralin, and naptalam, EPTC was the mosl active herbicide, increasing the number of sprouts per tuber but inhibitmg bud development at an early stage of growth. The effect was greatest when EPTC was incorporated with the soil around the tubers. The effects of alaehlor were similar, but higher doses were required. Another active herbicide, norfiurazon, was taken up by the roots but its effect was to produce small, chlorotic leaves, Perfluidone was mosl effective when incorporated into the soil around the tubers or when placed in a layer 1 cm above them. Very little effect of napropamide trifluralin and naptalam was observed. In studies of growth and deveiopmenl with different planting depths, C. rotumtus produced basal bulbs, roots and most of its early reproductive parts in a layer of soil 1–3 cm from the surface, irrespective of the depth at which the tubers were planted. Shoots etncrged from 35 im deep but not from 50 cm.     

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     

Biological activity of dinitramine in soils

In pot studies with dinitramine the susceptibility of French bean (Pltaseolus vulgaris L.) seedlings to the herbicide was influenced by the depth of sowing the seed and the dose and depth of incorporation of the herbicide. Maximum phytotoxicity occurred when the seeds of French bean were sown into a zone in which dinitramine had been incorporated. Where the seeds were separated from the herbicidetreated zone by a layer of untreated soil, the susceptibility of the French bean seedlings increased with increasing depth of sowing. The greater the distance between the point of contact with the herbicide and the soil surface the greater was the injury. Dinitramine is active in the vapour phase, and volatilization and bioactivity were directly related to concentration and inversely related to depth of incorporation and of placement in the soil.     

Technique for measuring the relative movement of herbicides in soil under leaching conditions

A technique for determining the relative leaching of herbicdes in soil is described. This consists of coating a glass plate with a uniformly thin layer of soil, applying the herbicde as a streak to the bottom of the plate and then cluting it with water. This is analogous to thin-layer chromatography. After clution, the position of the herbicide is determined by a bioassay with browntop grass (Agrostis tenuis). This provides a speedy and economical method which is particularly useful as a screen for experimental herbicides.     

Burial depth and cultivation influence emergence and persistence of Phalaris paradoxa seed in an Australian sub-tropical environment

Emergence and persistence characteristics of Phalaris paradoxa seeds in no- and minimum-till situations and at different burial depths were studied in a sub-tropical environment. Three experiments were carried out using naturally shed seeds. In the first experiment, seedlings emerged from May through to September each year, although the majority of seedlings emerged in July. In the second experiment with greater seed density, cultivation in March of each year stimulated seedling emergence, altered the periodicity of emergence and accelerated the decline of seeds in the seedbank compared with plots that received no cultivation. The majority of seedlings in the cultivated plots emerged in May whereas the majority of seedlings in the undisturbed plots emerged in July. Emergence accounted for only 4–19% of the seedbank in both experiments over 2 years. Seed persistence was short in both field experiments, with less than 1% remaining 2 years after seed shed. In the third experiment, burial depth and soil disturbance significantly influenced seedling emergence and persistence of seed. Seedlings emerged most from seed mixed in the top 10 cm when subjected to annual soil disturbance, and from seed buried at 2.5 and 5.0 cm depths in undisturbed soil. Emergence was least from seed on the soil surface, and buried at 10 and 15 cm depths in undisturbed soil. Seeds persisted longest when shed onto the soil surface and persisted least when the soil was tilled. These results suggest that strategic cultivation may be a useful management tool, as it will alter the periodicity of emergence allowing use of more effective control options and will deplete the soil seedbank more rapidly.