نشریه بوم شناسی علف های هرز
سال یکم شماره 2 (زمستان 1389)

In order to investigate the effects of summer cover crops, their residues as well as mechanical and chemical methods on weed density and biomass in citrus orchards, an experiment was conducted based on randomized complete block (RCB) design with 7 treatments and 3 replications in Rudan, Bandar_Abas, Iran. The treatments includes soybean (Glycine max L.), alfalfa (Medicago rigidula L.), and berseem clover (Trifolium alexandrinum L.), cultivation, barley straw mulch, glyphosate herbicide and weedy check. cover crops were planted on 3rd February, 2009. Barley straw mulch was used simultaneously. During the experiment, cultivation was retreated monthly. Herbicide was applied on 19th April, 2009 as cutting the cover crops. The results showed that soybean and alfalfa cover crops produced the highest and the lowest weed biomass, respectively. Barley straw mulch and berseem clover cover crop were the best controls of decreasing weed density, while alfalfa cover crop resulted in the least efficacy. In short, soybean cover crop and tillage were the most efficacious and alfalfa cover crop was the most inefficacious treatment for weed management in citrus orchard.

Drought and salinity stresses, as the most common constraints, have crucial role in describing crop production worldwide. The resistance of bindweed towards different potentials of drought and salinity levels in germination and early seedling growth is studied. The experiment was conducted on a complete randomized block design in 4 replications and 5 different drought levels of PEG (0, -3, -6, 9 and -12 bar) and 4 concentration of NaCl (0, 8, 16 and 24 dS/m) were treated. The experiment was done by using a completely randomized design with four replications. The results of data analysis showed that there were significant differences between treatments. About root length, shoot length, seedling length, seedling fresh weight and seed vigor traits normal condition was significantly higher than other treatment. Orthogonal comparisons in this experiment showed that, salinity and drought stress had different effects on germination and early seedling growth of bindweed. According to the fitted ternary parameter logistic model for drought and salinity conditions, it was determined that the NaCl and PEG concentration levels required for 50% reduction of germination was 23 dS/m and -16 bar respectively.

In order to study the effects of aqueous extracts and shoot powder of rye (Secale Cereal L.) on germination indices and seedling growth of three canola cultivars, two factorial experiments in a completely randomized design with three replications were conducted at a laboratory and a green house in 2009. In the first experiment, the factors included three cultivars of canola (Okapy, Zarfam and Modena) and five levels of aqueous extracts (control, 25,50,75 and 100%) obtained from shoot of rye. The second experiment factors included three cultivars of canola mentioned above and five levels of shoot powder (control, 0.5, 0.75,1 and 1.25% of soil pots). The results of both experiments showed that cultivar, aqueous extracts and shoot powder had significant effects on all variables. The highest percentage, germination rate, hypocotyls and epicotyls length and seed vigor were obtained at control treatment (distilled water) and all indices were increased by increasing aqueous extracts concentration. Moreover, the highest number of leaf, leaf area, root and shoot length and fresh and drought weight of seedling were obtained in control treatment (soil with no shoot powder). All traits were decreased by increasing shoot powder percentage in soil pots. Modena cultivar had the highest and Zarfam had the lowest resistance to allelopathic effects of aqueous extracts and shoot powder of rye.

To study the light competition between potato with lambsquarter and redroot pigweed, an additive experiment was conducted in the spring of 2004 in split-split plot based on a randomized complete block design with 4 replications in Firouzkooh. The treatments included 2 weed species in main plots (Amaranthus retroflexus and Chenopodium album), weed density in sub plots of 2, 4 and 8 per meter of row and the relative time of weed emergence in sub plots of 8 and 4 days prior to potato planting with potato emergence at the same time. The simulation of light competition was done by INTERCOM model in potato and weed canopy. The results showed the leaf area indices in redroot pigweed were 56.1, 64.1 and 69.9 after canopy closure in 2, 4 and 8 concentrations over potato canopy, respectively. These amounts for lambsquarter were 48.5, 59.7 and 65.4 percent, respectively. They were 50.5, 58.5 and 62.3 for lambsquarter with different density while they were 55.5, 58.9 and 62.3 for redroot pigweed. By increasing weed density and leaf area, light absorption decreased in potato. The same condition was seen in the time of emergence so that by quickening in weed emergence, the percentage of potato light absorption decreased. Also, the percentage of weed light absorption is over potato canopy. In weed growing period during 8 and 4 days before or simultaneous with potato, light absorption for lambsquarter is beyond potato canopy with 52.9, 53.2 and 50.9 and they are 63, 56.3 and 52.9 for pigweed. By increasing density and quickening in weed growth as well as decreasing in light absorption by potato canopy, potato function fell down significantly.

Velvet leaf (Abutilon theophrasti L.) is one of the most important weeds in sesame (Sesamum indicum L.) fields in Golestan province. The effects of nitrogen on vegetative components of sesame in interference with velvet leaf were investigated in Golestan province, Ramiyan. The experimental treatments were arranged in a split plot based on a complete randomized block design with four replications in 2009. Two nitrogen amounts of 50 and 100 kg N/ha and two sesame row spacing of 40 and 60 cm were arranged in main plots with equal density of 16.6 bushes per square meter. Four velvet leaf densities of 0, 4, 8 and 12 plants per square meter were arranged as sub plots. Nitrogen increase in different weed densities had significant negative effects on sesame leaf area index and shoot dry weight. Also, weed density increase led to final plant height decrease, main stem diameter, aerial organs dry weight, the number of sub branches as well as sesame yield in nitrogen regimes. The average of sesame seed yield was 644 and 800 kg/ha in 50 and 100 kg N/ha and 895, 740, 653 and 601 kg/ha in 0, 4, 8 and 12 velvet leaf plant per square meter, respectively.

A greenhouse study was conducted in Agriculture department of Shiraz university in 2009 to examine the allelopathic interactions of wheat (Triticum aestivum L.), corn (Zea mays L.) and canola (Brassica napus L.) extract on seedling growth of wild oat(Avena fatua L.), wild barely (Hordeum spontaneum Koch.) and pigweed (Amaranthus retroflexu L.). The experiment was done in a completely randomized design with 3 factorial replications. The treatments included water extract of wheat, corn and canola as individual, binary and ternary mixtures at 50% and 100% which were made and their effects on the growth factors of weeds was investigated. The results showed the binary mixture of wheat and corn extracts with 50% and the same mixture at 100% concentrations have the inhibitoriest effects on dry weight and final height of pigweed. The individual wheat extract at 50% concentration had the inhibitoriest effect on wild oat dry weight. The binary mixture of wheat and canola extract at 50%concentration decreased wild oat leaf area. The binary mixture of corn and canola extraction at 50% concentration and the individual corn extract at 100% concentration decreased wild barely dry weight. The individual canola extract at 100% concentration has the most inhibiting effect on final height of pigweed. The ternary mixture of wheat, canola and corn at 50% concentration decreased the wild barely leaf area. The results showed the extract at 100% concentration compared with 50% had the inhibitoriest effect. Also, binary and ternary mixtures of extracts had inhibitory effects compared to individually extract.

In order to evaluate redroot pigweed (Amaranthus retroflexus L.) growth and development at interference with sunflower (Helianthus annus L.) oil producing cultivars, a factorial experiment was conducted during 2005-2006 with three sunflower cultivars (Azarghol, Hysun and Allstar) and three redroot pigweed densities (8.3, 25 and 41.7 plants m-2) at 3 relative times of weed emergence (with sunflower, 15 and 30 days after sunflower emergence) using additive design. The results indicated that each one-day delay in weed emergence, the number of its leaves in three sunflower cultivar treatments reduced 2.7, 3.2% and 3.1%, respectively. By enhancement of weed density and earlier emergence time, weed cover increased in all 3 cultivars, especially in Allstar. Emerging 41.7 weeds/m2 with sunflower, increased weed leaf area index up to 45%, 62% and 70% compared with control, in three sunflower cultivars, respectively. With increasing of weed density from 8.3 to 25 plants/m2, weed leaf area per plant reduced from 1170, 1630 and 1910 cm2 to 410, 571 and 690 cm2 in three sunflower cultivars, respectively. In short, the results showed that the growth traits of redroot pigweed were influenced not only by the emergence time and density, but also by the cultivar traits in sunflower as well. It is suggested that redroot pigweed controlling in sunflower should be considered as soon as possible, especially in short height cultivars with less LAI such as Allstar.