Field experiments were carried out to compare the effect of herbicide application rate on the distribution and persistence of atrazine (ATR), terbuthylazine (TBA), and their dealkylated degradation ...products in two conventionally cultivated cornfield soils: a silt loam soil and a silty clay loam soil, both typical for the crop-producing area of continental Croatia. Herbicides were applied pre-emergence at the registered (R) (1.0–1.5kgha−1), double-registered (2R), and triple-registered (3R) rates. Topsoil (0–30cm) and subsoil (30–60cm) samples were collected periodically during a crop rotation cycle of 17months. Soil microcosm experiments were performed under controlled conditions to investigate the influence of the herbicide application rate on their biodegradation in herbicide-treated cornfield topsoils. The herbicide half-lives (DT50) calculated by using monophasic and biphasic first-order kinetics models were compared. The herbicide sorption intensity in the studied soils was evaluated in terms of the Freundlich sorption isotherm. Under field conditions, TBA was retained within the first 60cm of both agricultural soils at least twice as long as ATR. While ATR residues persisted in soil only until corn harvest (5months), the residues of TBA and its N-deethylated degradation product were still measurable at the end of the crop rotation cycle (17months). The persistence of both herbicides was higher in soil with higher herbicide sorption intensity. ATR and TBA application rates higher than registered generally did not significantly influence the herbicide biodegradation rates or dissipation from the topsoil layers. The enhanced application rate slightly decreased the TBA persistence only in soil exhibiting a rather slow biodegradation. A temperature-leaching potential index for ATR and TBA applied at R rate showed the same leachability class for both herbicides. The leachability class of TBA could be higher than that of ATR in soil with moderate TBA persistence (DT50=30–100days). From an environmental perspective, TBA could pose a similar risk for groundwaters as ATR.
•Atrazine persisted in crop-cultivated soils until corn harvest (5months).•Terbuthylazine persisted in the same soils three times as long as atrazine.•Deethylterbuthylazine was detectable in soils equally long as terbuthylazine.•Higher herbicide application rates may slightly promote their biodegradation in soil.•Longer TBA persistence in soil need not imply lower leaching.
Rhizobia are an important component of sustainable agricultural production. In symbiosis with legumes, they provide adequate amounts of nitrogen for their growth and leave nitrogen in the soil for ...crops that follow in the rotation. One of the major threats to symbiotic nitrogen fixation are herbicides. The effect of herbicides on symbiotic nitrogen fixation can be positive or negative. The positive effect is manifested in the stimulation of growth and development of rhizobia. When symbiosis is negatively affected, the efficiency of nitrogen fixation is reduced, resulting in lower legume growth and yield. Herbicides can contact rhizobia immediately after application or, in the case of persistent herbicides, later in the growing season. Herbicides may affect the rhizobia, the host plant, or the establishment and development of the symbiosis. This paper reviews previous research on the effects of herbicides on rhizobia.
The phytotoxic effects of mesotrione residues on sugar beet (
Beta vulgaris
L.) were determined in two agricultural soils (humofluvisol and hipogley) in order to show the relevance of soil ...characterization in crop rotation practice. Soils were treated with mesotrione at seven rates that simulated the levels of mesotrione in soil considering its field half-life. The visual injury and reduction in fresh weight and total carotenoid content were determined during the three-week cultivation in plastic pots under controlled conditions. The Freundlich isotherm model was used to reach the adsorption parameters of mesotrione in both soils. Humofluvisol showed at least twice as less adsorption affinity for mesotrione as hipogley. The effective dose (ED
50
) of mesotrione for 50% reduction in sugar beet fresh weight content was 5.9 g a i ha
−1
in hipogley and 4.4 g a i ha
−1
in humofluvisol. The ED
50
for 50% reduction in total carotenoid content was 4.7 g a i ha
−1
in hipogley and 2.1 g a i ha
−1
in humofluvisol. The crop rotation has to be performed considering the soil characteristics due to its effect on the bioavailable amount of mesotrione residues in soil resulting in different levels of crop injury in two soils at the same rate.
At the global level, the invasion of alien organisms is considered the second largest threat to biodiversity. The assumption is that the high allelopathic potential is one of the features that helps ...invasive plant species to spread to new areas. Allelopathic potential of 8 invasive plant species (donor species) and their impact on test-species was determined in the study. Donor species were velvetleaf (Abutilon theophrasti Med.), ragweed (Ambrosia elatior L.), jimsonweed (Datura stramonium L.), common cocklebur (Xanthium strumarium L.), tree of heaven (Ailanthus altissima (Mill.) Swingle), indigo bush (Amorpha fruticosa L.), Japanese knotweed (Reynoutria japonica Houtt.) and giant goldenrod (Solidago gigantea Aiton). Three cultivated plant species from 3 different plant families were used as test-species. Test-species were: oat (Avena sativa L.), oilseed rape (Brassica napus subsp. oleifera) and sunflower (Helianthus annuus L.). Water extracts made of whole plants of donor species were applied to the seeds of the test-species. High allelopathic potential was proven for all species included in experiment. Allelopathic effects were exclusively negative. Impact on germination for all species was much lower in relation to the impact on the radicle and shoot length of the test-species. Perennial donor species had a stronger allelopathic potential than annual donor species. Tree of heaven was the species with the strongest allelopathic potential. Its extracts inhibited germination, radicle and shoot length of oilseed rape by 19%, 94.88% and 98.91% respectively.
Sunflower is the most important oil crop in the Republic of Croatia. In the last two decades, it has been grown on average on 33,506 ha with a average grain yield of 2.66 t/ha. Weeds represent one of ...the most important causes of biotic stress, and their action is reflected in the competition for nutrients, water, light and space. The weed flora in sunflower crops in Croatia is extremely diverse, and we will most often meet: Polygonum persicaria L., Polygonum lapathifolium L., Ambrosia artemisiifolia L., Chenopodium polyspermum L., Amaranthus retroflexus L., Solanum nigrum L. emend Miller, Abutilon theophrasti Medik, Datura stramonium L., Xanthium strumarium L., Convolvulus arvensis L., Cirsium arvense (L.) Scop., Echinochloa crus-galli (L.) Pb., Setaria glauca (L.) Pb., Setaria viridis (L.) Pb., Digitaria sanguinalis (L.) Scop., Panicum spp. and Sorghum halepense (L.) Pers. For many years, weed control was based on the intensive use of chemical preparations, which were most often used after sowing and before emergence, in double or triple combinations. In addition to a number of advantages of using chemicals in sunflower production, the problem of broadleaf weeds was not satisfactorily solved until the advent of Clearfield, Clearfield plus and Express sun technology, i.e. hybrids tolerant to herbicides from the group of imidazolinone (imazamox) and sulfonyl-urea (tribenuron-methyl) at the beginning of this century. Integrated plant protection, including integrated weed management, with its holistic approach and greater application of direct and indirect non-chemical measures, is only environmental quality solution for controlling weeds in sunflowers.
Variations in soil pH have been shown to affect mesotrione adsorption, which in turn, may have an impact on crop susceptibility. Therefore, a greenhouse experiment was conducted to evaluate the ...effect of simulated mesotrione residues on pea crop grown in the typical agricultural soil (gleysol) of north-western Croatia. The soil pH was manipulated to obtain neutral (pH 7.0) and acidic (pH 5.0) values. Simulated mesotrione residues were 1.1, 2.3, 4.5, 9.0, 18, 36 and 72 g a.i. ha−1. Crop visual injuries as well as reductions in chlorophyll fluorescence and aboveground dry biomass were higher at pH 7.0 than at pH 5.0. With increasing mesotrione residues, the reductions in chlorophyll fluorescence ranged from 38.8% to 89.7% at pH 5.0 and from 63.7% to 99.3% at pH 7.0. Compared to chlorophyll fluorescence, the reductions in dry biomass were smaller and ranged from 49.2% to 96.8% at pH 7.0 and from 32.0% to 82.6% at pH 5.0 for the mesotrione residues from 1.1 to 72 g a.i. ha−1. These results indicate that soil pH is an important factor determining the susceptibility of pea crop to simulated mesotrione residues.
Huds. is an important pinoxaden-resistant grass weed in many countries of Europe. Recently, the low efficacy of pinoxaden was reported in winter cereals in Croatia, but a preliminary dose-response ...trial showed no herbicide resistance for the investigated weed population. Therefore, a two-year experiment was conducted under greenhouse conditions to determine the efficacy of various pinoxaden doses (20, 40 and 80 g a.i. ha
) on weed visual injuries and biomass reduction after herbicide application at different growth stages. As expected, the maximum weed biomass reduction (97.3%) was achieved by applying the highest dose (80 g a.i. ha
) at the earliest growth stage (ZCK 12-14). A pinoxaden dose of 20 g a.i. ha
resulted in satisfactory weed biomass reduction (88.9%) only when applied at ZCK 12-14. The recommended dose (40 g a.i. ha
) also provided sufficient weed control up to the growth stage ZCK 21-25. Slightly delayed (ZCK 31-32) application of the recommended dose brought about a low weed biomass reduction (60.1%). Double than the recommended dose also failed to provide satisfactory weed control at the advanced weed growth stages (ZCK 31-32 and ZCK 37-39). Thus, reported low efficacy of pinoxaden is most likely because of delayed herbicide application when
is overgrown.
Rainfall accompanied with winds favour lodging of Italian ryegrass (Lolium multiflorum Lam.). Thus, the main objective was to determine the changes in seed yield and quality resulting from lodging of ...Italian ryegrass crop grown under various nitrogen (N) fertilization rates. Nitrogen fertilization consistently increased lodging score and seed moisture content at harvest. The onset of considerable lodging (>50%) was observed before crop heading at the highest N fertilization, while delayed lodging occurred at lower N fertilization rates. Seed yield decreased at the highest N rate. In spite of increased lodging score, the 1000-seed weight tended to increase with higher N fertilization rates, which was not found for seed germination.
Ever since terbuthylazine (TBA) replaced atrazine in herbicide crop treatment, its much greater persistence has raised considerable environmental concern. The aim of our field experiment was to ...establish the dissipation dynamics of TBA and its degradation product desethylterbuthylazine (DET) in soil over five months of maize growth. We applied TBA as part of pre-emergent treatment in the regular and double-the-regular amounts. Soil samples were collected periodically at the following depths: 0-10 cm, 10-20 cm, 20-30 cm, and 30-50 cm. For TBA and DET soil residue analysis we used microwave-assisted extraction with methanol, followed by HPLC-UV/DAD. Regardless of the application rate, more than 80 % of the applied TBA dissipated from the first 50 cm of soil in the two months after herbicide application and 120 mm of rainfall. Three months later (at maize harvest), less than 4 % of total TBA remained in the soil, mostly in the top 20 cm rich with organic carbon on which TBA is likelier to adsorb. The loss of TBA from soil coincided with the rise in DET, especially the top soil layers, during the periods of low rainfall and highest soil temperatures. This points to biodegradation as the main route of TBA dissipation in humic soils. The applied amount had no significant effect on TBA dissipation in the top (humic) layers, but in the layers with less than 1 % of organic carbon, it was higher when the doublethe- regular dose was applied.
Cilj istraživanja bio je primjenom digitalnog mikroskopa utvrditi utjecaj i dinamiku učinka različitih koncentracija herbicida pendimetalina na rast bakterije Bradyrhizobium japonicum. Istraživane ...koncentracije pendimetalina iznosile su 0,00; 0,165; 0,33; 0,66; 1,32 i 2,64%. Koncentracija 0,66% odgovara količini pendimetalina koja se uobičajeno primjenjuje u praksi (registrirana dozacija). Utjecaj pendimetalina na rast bakterija utvrđivan je mjerenjem širine zone inhibicije oko filter-diskova tretiranih istraživanim koncentracijama pendimetalina 5, 7, 10 i 12 dana nakon nacjepljivanja (DNN) bakterija na hranjivu podlogu. Najmanji inhibitorni učinak utvrđen je kod prvog mjerenja (5 DNN), kad se prosječna širina zone inhibicije kretala od 0,18 mm kod najniže (0,165%) do 0,97 mm kod najviše (2,64%) istraživane koncentracije. Pri svakom sljedećem mjerenju utvrđena je progresija inhibitornog učinka pendimetalina na rast bakterija. Najveći inhibitorni učinak utvrđen je kod posljednjeg mjerenja (12 DNN) kad je širina zone inhibicije kod koncentracije pendimetalina od 0,165% iznosila 0,61 mm. Povećanjem koncentracije znatno se povećavala, te je kod koncentracije od 2,64% iznosila 2,46 mm. Rezultati istraživanja ukazuju na negativan učinak herbicida pendimetalina na rast bakterija B. japonicum čak i kod koncentracija manjih od preporučene koja se primjenjuje u praksi.
The objective of this study was to determine the effect of different concentrations of herbicide pendimethalin on the growth of nitrogen-fixing bacteria Bradyrhizobium japonicum using a digital microscope. Pendimethalin was applied at concentrations of 0.00; 0.165; 0.33; 0.66; 1.32 and 2.64%, where the concentration of 0.66% presents the amount of herbicide which is usually applied in the field (recommended dose). The influence of pendimethalin on the growth of B. japonicum was determined by measuring the width of the inhibition zone around the discs 5, 7, 10 and 12 days after inoculation (DAI) of bacteria on a nutrient medium. The lowest inhibitory effect of pendimethalin for all concentrations determined was 5 DAI, when the average width of inhibition zone was between 0.18 mm for the lowest (0.165%) to 0.97 mm for the highest (2.64%) concentration. The progression of the inhibitory effect of pendimethalin occurred with every following assessment. The highest inhibitory effect determined was 12 DAI, when the width of the inhibiton zone at a concentration of 0.165% was 0.61 mm. The width of the inhibition zone significantly increased with increasing the pendimethalin concentrations and at a concentration of 2.64% it was 2.46 mm. The results of this study indicate the negative effect of herbicide pendimethalin on bacteria B. japonicum, even at concentrations lower than recommended concentrations that are applied in the field.
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