Assessment method for allelopathic effect from leaf litter leachates

In order to elucidate the allelopathic effect of leaf litter leachates under laboratory conditions, a modified 'sandwich method', which places leaves between two layers of agar, was used. Fifty mg of leaves was used per 10 cm² cell. Agar concentrations at 0.5–1.0% were the best for gel support in determining radicle and hypocotyl elongation of lettuce. The optimum incubation time for bioassay was three days after imbibition onset. Among 20 typical tree species in Asia, Cymbopogon citratus and Derris scandens showed the strongest inhibitory activity determined by the sandwich method, followed by Piper betle, Tamarindus indica, and Gliricidia sepium. This bioassay seems to be a reliable method for screening allelopathic activity from leaf litter leachates.     

Current options in integrated management of plant-parasitic nematodes

Efficient management of plant-parasitic nematodes requires the carefully integrated combination of several methods. Although each individual method of management has a limited use, together, they help in reducing the nematode populations in agricultural soils or in plants. A public desire for methods of managing plant pests in ways that do not pollute or otherwise degrade the environment has increased concomitantly with progress in research. Integrated pest management (IPM) provides a working methodology for pest management in sustainable agriculutural systems. In this paper, current methods for the management of plant-parasitic nematodes are discussed within the guidelines of IPM. The emphasis is on the methods by which decisions are made to manage nematode problems with the most effective and widely used management strategies. The advantages and difficulties associated with nematicidal chemicals (i.e. cost, reinfestation of soil after harvest, contamination of ground water and residues in fruits and vegetables), biological control (by predatory or parasitic fungi and nematodes) and management with cultural methods (including the use of uncontaminated plants or seeds, crop rotation, modification of sowing and/or harvesting times, trap crops and resistant varieties etc.) are considered     

Response of winter wheat (Triticum aestivum L.) and weeds to tank mixtures of 2,4-D plus MCPA with clodinafop propargyl

Field and greenhouse experiments were conducted in 2004 and 2005 to study weed control and the response of winter wheat to tank mixtures of 2,4-D plus MCPA with clodinafop propargyl. The field experiments were conducted at Yazd and Oroumieh, Iran, with factorial combinations of 2,4-D plus MCPA at 0, 975, and 1300 g ai ha⁻¹ and with clodinafop propargyl at 0, 64, 80, 96, and 112 g ai ha⁻¹ in four replications. The greenhouse experiments further evaluated the effect of these tank mixtures on weed control, where each herbicide mixture was considered as one treatment and the experiment was established in a randomized complete block design with four replications. In the field experiments, the herbicides were applied at wheat tillering, while in the greenhouse experiments they were applied at the beginning of the tillering stage and at the four-leaf stage of the grass and broadleaf weeds, respectively. The results indicated antagonistic effects between 2,4-D plus MCPA and clodinafop propargyl. The best tank mixture with regard to weed control efficacy was 2,4-D plus MCPA at 975 g ai ha⁻¹ with clodinafop propargyl at 96 g ai ha⁻¹. The wheat grain yield was also increased by the tank mixture of clodinafop propargyl with 2,4-D plus MCPA. Generally, to inhibit clodinafop propargyl efficacy reduction due to tank-mixing with 2,4-D plus MCPA, it is recommended that the application dose of 64 g ai ha⁻¹ should be increased to 96 g ai ha⁻¹.     

Increased foliar activity of clodinafop‐propargyl and/or tribenuron‐methyl by surfactants and their synergistic action on wild oat (Avena ludoviciana) and wild mustard (Sinapis arvensis)

Surfactants can improve postemergence herbicide efficacy and reduce the amount of herbicide required to obtain weed control. The effect of surfactants on the efficacy of herbicides is complicated and depends on the interaction among the plant, surfactant, and herbicide. The effects of surfactants on the efficacy of clodinafop‐propargyl and/or tribenuron‐methyl on wild oat (Avena ludoviciana) and wild mustard (Sinapis arvensis) under greenhouse conditions were investigated. In addition, the surface tension of aqueous solutions of the surfactants and surfactants + herbicides was determined. Significantly lower surface tension values were obtained with the aqueous solutions of citofrigate (Citogate plus Frigate) alone and with the herbicides used in this study. The citofrigate surfactant lead to the greatest enhancement of clodinafop‐propargyl and/or tribenuron‐methyl efficacy and the effect was species‐dependent. The efficacy of clodinafop‐propargyl and/or tribenuron‐methyl in the presence of surfactants in controlling wild oat was higher than for wild mustard. The foliar activity of the tested herbicides rose with increasing surfactant concentrations. The tank mixture of clodinafop‐propargyl and tribenuron‐methyl showed a synergistic effect in controlling wild oat and wild mustard. The synergistic effect in controlling wild mustard was greater than for wild oat.     

Factors affecting the seed germination and seedling emergence of redflower ragleaf (Crassocephalum crepidioides)

Redflower ragleaf (Crassocephalum crepidioides) is a weed, as well as a minor vegetable, in tropical and subtropical regions of the world. The influence of environmental factors and seed conditions on the germination and emergence of redflower ragleaf have been evaluated in order to help understand its distribution and to develop effective management strategies. The seeds germinated at a constant temperature in the range of 10–30°C and reached a maximum at 15–20°C. The highest germination rate was recorded at an alternating temperature of 20/15°C (day/night). The seeds germinated over a wide pH range (2–12), with the highest germination rate at between 4 and 10. Germination under saturated and flooded conditions was also high. The germination of seeds from opened (mature) capitula was significantly higher than from partially opened or unopened capitula. The germination of seeds without a pappus was significantly higher than for seeds with a pappus. The germination rate of 1 year old seeds decreased drastically when compared to that of freshly harvested seeds. The seedling emergence rate was ～63% for those seeds placed on the soil surface, but no seedling emerged from a depth of ≥1 cm. These results indicate that redflower ragleaf seeds can germinate in various environmental conditions, but that the percentage that germinates will be different in different environments. Regeneration could be effectively prevented by at least a 1 cm soil covering or by destroying the plant before the capitula open. In contrast, freshly harvested seeds from opened capitula should be sown on the soil surface when redflower ragleaf is to be cultivated as a vegetable.     

Competitive effects of redroot pigweed (Amaranthus retroflexus) on the growth indices and yield of corn

The mutual effects of redroot pigweed ( Amaranthus retroflexus ) on corn ( Zea mays ) were evaluated in an experiment conducted in 2005 at the Iranian Plant Protection Research Institute at Qazvin, considering the different densities of redroot pigweed against four different corn densities. Redroot pigweed, at 0, 35, 50, 65, and 80 plants m⁻¹ row⁻¹, was arranged factorially with corn at four, five, six, and seven plants m⁻¹ row⁻¹ in a randomized complete block design. Crop–weed competition resulted in a reduction in the total dry matter, Leaf Area Index, and crop growth rate of corn. Furthermore, an increasing weed density ≤65 plants m⁻¹ row⁻¹ reduced the corn grain yield and biological yield. Overall, six corn plants m⁻¹ row⁻¹ was suggested as the optimum density of this crop in competition with redroot pigweed.     

Effects of the relative time of emergence and the density of common lambsquarters (Chenopodium album) on corn (Zea mays) yield

Common lambsquarters (Chenopodium album) is one of the world's worst weeds. In order to study the competitive potential of single‐cross 704 corn (Zea mays) in competition with common lambsquarters at different relative times of emergence and density levels of the weed, an experiment was conducted in 2006 at the farm of the Faculty of Agriculture, Ferdowsi University of Mashhad, Mashhad, Iran. This experiment was designed as a split plot based on a randomized complete block design with three replications. The emergence time of the weed was considered at three levels (7 days and 14 days earlier than corn and simultaneously with corn) as the main plot, while the density of the weed was considered at six levels (0, 4, 8, 12, 16, and 20 plants per m²) as the subplot. The results showed a decrease in the grain yield and biomass of corn, as the emergence time of corn was delayed in comparison with the weed in a way that the maximum reduction was observed at the earlier emergence of the weed, compared to corn, and also at a high density of the weed. As the weed emerged earlier than corn, the rate of yield loss resulting from the first flush of weeds was not that high. However, with every few days that the weed emerged earlier than corn, the rate of yield loss became higher as the density of the weed increased to its maximum. The maximum reduction in the yield components was observed at 14 days earlier emergence of the weed, compared to corn, and at high densities, as the corn plants were overshadowed by the weed canopy and no ear was produced.     

伊朗西部地区碱性土壤中共离子对Zn吸附的影响

Zinc(Zn) is essential to plant growth and relatively mobile in soils.This study was conducted to assess the effect of common ions(Ca 2+,K +,Na +,NH + 4,Cl,NO 3,and H 2 PO 4) on sorption of Zn in surface samples of ten calcareous soils from western Iran using 10 mmol L 1 KCl,KNO 3,KH 2 PO 4,Ca(NO 3) 2,NaNO 3,and NH 4 NO 3 solutions as background electrolytes.The results indicated that both NH + 4,K +,and Ca 2+ equally decreased Zn sorption as compared to Na +.Zinc sorption was decreased by H 2 PO 4 as compared to NO 3 and Cl.The Langmuir and Freundlich equations fitted closely to the sorption data of all ions.The Langmuir maximum,bonding energy constant,and Freundlich distribution coefficient for Zn sorption differed among the various ionic background electrolytes.Langmuir sorption parameters showed that the presence of H 2 PO 4 decreased the maximum Zn adsorbed,but increased the bonding energy.Although K + and NH + 4 equally influenced maximum Zn adsorbed,they differed in their effect on the distribution coefficient of Zn in soils.Values of saturation index calculated using Visual MINTEQ indicated that at the low Zn concentration,Zn solubility was controlled by sorption reactions and at the high Zn concentration,it was mainly controlled by sorption and mineral precipitation reactions,such as precipitation of Zn 3(PO 4) 2.4H 2 O,Zn 5(OH) 6(CO 3) 2,and ZnCO 3.For most ionic background electrolytes,soil pH,CaCO 3,and cation exchange capacity(CEC) were significantly correlated with sorption parameters.     

Agronomic practises for weed control in turmeric (Curcuma longa L.)

Weeds are the main problem with turmeric (Curcuma longa L.) cultivation where herbicides are not allowed. This is because herbicides cause water contamination, air pollution, soil microorganism hazards, health hazards, and food risks. Considering turmeric's medicinal value and the environmental problems caused by herbicides, various agronomic practises have been evaluated for non‐chemical weed control in turmeric. One additional weeding is required before turmeric emergence and weed infestation is much higher when turmeric is planted in February and March, as compared to April, May or June planting. A similarly higher yield of turmeric is achieved when it is planted in February, March, and April, compared to late plantings. Weed emergence and interference are not affected by planting depth, seed size, planting pattern, planting space, ridge spacing, and the row number of turmeric until 60 days after planting. This is because turmeric cannot develop a canopy structure until then. Thereafter, weed infestation reduces similarly and significantly when turmeric is planted at depths of 8, 12, and 16 cm, compared to shallower depths. The yield of turmeric at these depths is statistically the same, but the yield for the 16 cm depth is difficult to harvest and it tends to decrease. Turmeric grown from seed rhizomes (daughter rhizomes) weighing 30–40 g reduces weed infestation significantly and obtains a significantly higher yield compared to smaller seeds. The mother rhizome also can suppress weed infestation and increase the yield markedly. Around 9% weed control and 11% higher yield are achieved by planting turmeric in a triangular pattern compared to a quadrate pattern. The lowest weed infestation is found in turmeric grown in a 20 or 30 cm triangular pattern and the highest yield is obtained with the 30 cm triangular pattern. Turmeric gown on two‐row ridges spaced 75 cm apart shows excellent weed control efficiency and obtains the highest yield. This review concludes that turmeric seed rhizomes of 30–40 g and/or the mother rhizome could be planted in a 30 cm triangular pattern at the depth of 8–12 cm on two‐row ridges spaced 75–100 cm apart during March to April in order to reduce weed interference and obtain a higher yield. Mulching also suppresses weed growth and improves the yield. The above agronomic practises could not control weeds completely; biological weed management practises could be integrated in turmeric fields using rabbits, goats, sheep, ducks, cover crops or intercrops.