مجله پژوهش علف های هرز
سال هفتم شماره 1 (بهار و تابستان 1394)

Due to the reduction of non-renewable resources, increased global demands for providing energy, seems essential in the present circumstances. Beyond the pyrolysis process, biomass has this ability to become bio-energy (biochar) as a renewable resource. Biochar is known as a mean for carbon sequestration, reducing greenhouse gas emissions, uses as a renewable energy and also for improving soil structure and fertility. Fewer studies have been conducted on its quality benefits in agronomy. The amount of chemicals which are applied in agriculture and the risks of ground water resources contamination are the important issues in all aspects of life levels. Herbicides are commonly used in agriculture and they have this ability to penetrate and leak into the deeper layer of the soil and then groundwater resources, hence, they can cause irreparable hazards on the on quality of living organisms. Previous Studies showed that use of biochar on the soils could increase sorption and reduce the leaching of herbicides. Therefore, the effects of various biochar on uptake and leaching of herbicides can be illustrated as an appropriate way to reduce contamination by these chemicals.

A field experiment was carried out in 2014 at Agricultural Research Station, Ferdowsi University of Mashhad to evaluate the use of herbicides in cumin weed control. The experimental design was a randomized block with 17 treatment and 3 replicates. Treatments included full season hand weeding, full season of weed competition with cumin, 2 times hand weeding in 25 and 45 days after cumin planting respectively and the application of trifluralin, metribuzine, oxiflurfen, pendimetalin, eradican, oxadiazon and haloxyfop-R-methyl herbicides at their recommended dose and their reduced dose application plus hand weeding at 45 days after cumin planting. Results showed that applied treatments affected cumin yield and weed control significantly (P≤0.01). Based on the results, the highest cumin seed yield (338 Kg h-1) was recorded in full season hand weeding treatment, that had not significant difference (P≤0.05) with applying of oxyfluorfen herbicide at recommended dose reduced dose (312 kg ha-1) and its reduced dose plus hand weeding at 45 days after cumin planting (321 kg ha-1) applying of pendimethalin herbicide (0.5 kg a.i. ha-1) plus hand weeding 45 days after cumin planting (310 kg ha-1). According to the results, application of oxyfluorfen herbicide at recommended dose and reduced dose plus weeding 45 days after cumin planting and the application of pendimethaline (0.5 kg a.i. ha-1) plus hand weeding 45 days after cumin planting have selective properties in cumin chemical weed control.

An experiment was carried out in 2014 at the Research Farm of Bu-Ali Sina University, Hamedan, to evaluate light absorption and use efficiency of soybean in competition with redroot pigweed. The experimental design was a randomized complete block with three replications. Treatments were pigweed density at five levels: 0, 2, 4, 6 and 8 plant.m-2. The result showed that leaf area index, total dry matter accumulation, light absorption and radiation use efficiency of soybean were decreased. The highest (5.66) and the lowest (4.38) leaf area index of soybean were related to weed free condition and 8 plant per.m-2 of redroot pigweed density, respectively. The light absorption of soybean followed by leaf area index and decreased about 60% in 8 plant.m-2 of redroot pigweed density compare to weed free condition. The highest (425.02 g m-2) and lowest (249.15 g m-2) total dry matter accumulation of soybean were observed in weed free condition and 8 plant.m-2 of redroot pigweed density, respectively. In addition, the highest (0.44 g MJ-1) and the lowest (0.28 g MJ-1) radiation use efficiency of soybean were related to weed free condition and 8 plant.m-2 of redroot pigweed density, respectively. The soybean radiation use efficiency redacted about 60% in 8 plant.m-2 of redroot pigweed density compare to weed free condition.

A two-year field experiment was conducted in 2007 and 2008 to determine the relationship between competitive indices of maize, Xanthium strumarium and Amaranthus retrolexus. Five doses of herbicide nicosulfuron as the main factor, and a combination of 16 densities comprised four densities of A. retroflexus × four densities of X. strumarium as sub plots were arranged in a one-replicate split factorial. Four indices were considered for maize which is influenced by competition: grain yield, biomass, leaf area, and plant height. Biomass was determined as the direct factor that controlled grain yield, and the biomass was directly depended on maize leaf area. The plant height had the most important role in the maize leaf area. Field observations confirmed the efficacy of plant height in evaluating the plant competition. Increase in X. strumarium biomass indicated direct effect on maize grain yield. The X. strumarium biomass was controlled by its leaf area and the number of lateral shoots. However, the plant density as an external factor had significant effect on crop-weeds competition, herbicide dose was determined the most important determinant that caused major change in the X. strumarium height and leaf area. Among the A. retroflexus indices, its leaf area was the most effective, which was directly controlled by its biomass. Deep understanding of the system behavior, relations and interactions with herbicide is a great help in managing the weed damage.

Broomrape is a parasitic weed that reduces the yield of many plants. In this study, in the liquid culture conditions in the laboratory, broomrape seed germination and connection to the roots of some crop plants were evaluated. In the greenhouse, effect of these plants under intercropping and rotation with tomatoes was also evaluated on broomrape germination. In the laboratory cotton (Gossypium hirsutum), sunflower (Helianthus annuus), soybean (Glycine max), hairy vetch (Vicia villosa), mung bean (Vigna radiate) and alfalfa (Medicago sativa) and in the greenhouse in addition to aforesaid crop plants, wheat (Triticum aestivum), barley (Hordeum vulgare) and rye (Secale cereale) was also used. Tomato (Lycopersicum esculentum) was used as a control. In the laboratory, the broomrape seed germination rate by all plants that were tested was 10 to 70 percent. In tomato, cotton and sunflower, the rate of connection was more than germination rate. Alfalfa, soybean, mung bean and hairy vetch acted as a trap or catch crop, but alfalfa did not show any connection, and in soybeans, mung bean and hairy vetch broomrape germination rate was much more than connection rate. Greenhouse results showed that cotton and sunflower in intercropping reduced broomrape stem number, but in rotation increased the tubercles number of tomato roots. Soybean, mung bean and hairy vetch relative to other plants, in intercropping stimulated broomrape stem and tubercle production on tomato roots and alfalfa in rotation increased the number of tubercle. It seems broomrape germination response to different plants vary depending on environmental conditions. In both intercropping and rotation systems, all of the plants reduced the dry weight of broomrape. The decline in intercropping was between 25 and 95 percent and in the rotation was between 31 to 57 percent. Grass species in intercropping system had a significant impact on reducing the number and dry weight of broomrape plants, but on the other hand led to a high reduction in dry weight of tomato root and shoot. However, grass species in rotation, reduced the dry weight of broomrape, but it did not show a decreasing effect on tomato dry weight. According to the results, it seems that the use of plants as traps or catch crop to reduce germination broomrape can be included in the system of integrated management of broomrape control.

A laboratory experiment was conducted to quantify the rate of germination response to temperature, seed position in spikelet and with or without glume, lemma and palea. The experimental design was a completely randomized design with factorial arrangement of treatments with four replications. Experimental treatments were seed position (lower and upper seeds), temperatures (5, 10, 15, 20, 25 and 30 ◦C) and with and without lemma and palea. The results in laboratory showed that lemma and palea and seed position had significant effect on germination. The results indicated that lower seeds without lemma and palea germinated at lower To and Tc than upper seeds without glumes and large seeds with glumes. The base temperature (Tb), optimum (To) and ceiling (Tc) for lower seed without glumes, were 1.5, 21 and 40°C for lower seed with glumes were 1, 30.01 and 44.82 ◦C and for upper seed without glumes were 2.01, 25.25 and 37.6 °C respectively. Upper seed with glumes germination zero or less than 15 percent. Lower seeds without glumes germinate wider than the other. There was a highly significant positive correlation between temperature and rate of germination and percentage of germination in wild oat seeds (Lower Seeds without glumes, upper seeds without glumes and large seeds with glumes) using Dent like model. Seed position and glumes have an effect on dormancy and germination.