جستجوی مقالات مرتبط با کلیدواژه « رقابت علف هرز » در نشریات گروه « زراعت »

In order to evaluate changes in the vertical distribution of leaf area and dry matter of wheat different cultivars in different densities of wild mustard, a field experiment was conducted in Agricultural Research Station Gorgan depended on Agriculture Research Center of Golestan Province during 2010-2012. The experiment design consisted of four randomized complete blocks in a factorial arrangement. The design consisted of two factors, four wheat cultivars (Arta, Tajan, Mogan and Morvarid) and 5 levels of wild mustard densities (0, 4, 8, 16 and 32 plants.m-2). The results of combined analysis showed year effect wasn’t significant on light extinction coefficient, light use efficiency, vertical distribution of leaf area and dry matter, but cultivar×wild mustard density interaction effect was significant. In this research distinguished dry matter accumulation and too leaf area amount in all of evaluated layers in Morvarid cultivar was higher than other cultivars in competition and pure conditions. Also, wheat cultivars in competition conditions assigned higher of leaf area and dry matter to the upper layers of canopy that this event was more evident in Morvarid and Moghan. In this research, the means of light extinction coefficient in the maximum of wild mustard density in Morvarid, Moghan, Arta and Tajan was 0.23, 0.51, 0.63 and 0.65, respectively. The highest and lowest of light extinction coefficient observed in Tajan and Morvarid, respectively. Totally, the results of this experiment in two years showed Morvarid had the highest of seed yield for the reason that the most of vertical distribution of leaf area and light use efficiency and too, the lowest of light extinction coefficient in compared to other cultivars, and was the more of succeed in competition with wild mustard.

Growth response to sowing date and weed interference among lentil varieties was investigated in dryland situation of Khorramabad during 2005-2006 growing season. The experimental design was a randomized complete block in factorial arrangement with 4 replications. The experiment had 3 factors: weed interference at 2 levels (weed free, and weed infested throughout the total growing season), planting date at 3 levels (autumn, winter, and spring) and lentil varieties at 3 levels (Gachsaran, Flip 92-12L, and Lorestan landrace). Overall, weeding increased lentil yield by 46 percent. Based on sigmoid equations, maximum dry matter of lentil in autumn crop was 24.7 and 300.4% more than the potential of winter and spring crops, respectively. Maximum dry matter per plant for autumn lentil was 4 times more than that estimated for spring crop. Autumn and winter cultivations, respectively, with average yield of 1486 and 1161 kg/ha, had four and three times higher performance over the spring cultivation. Reproductive period (flowering to maturity) for the autumn planting was more than three times the cultivation of spring. Accordingly, shorter growth period resulted in less dry matter accumulation and declined grain yield.

To determine the critical period of weed control in safflower (Carthamus tinctorius), two field studies were conducted in 2002 at the Bajgah and Kooshkak Experimental Stations, College of Agriculture, Shiraz University. Each experiment consisted of two series of treatments. In the first series, weeds were kept in place until crop emergence, leaf formation, stem elongation, lateral stem emergence, head emergence, flowering and ripening, and were then removed and the crop kept weed-free for the rest of the season. In the second series, crops were kept weed-free until the above growth stages after which weeds were allowed to grow in the plots for the rest of the season. The beginning of the critical period was defined as the crop stage in which weed interference reduced crop yield by 10%. Similarly, the end of the critical period was defined as the crop stage in which the crop had to be weed free to prevent more than 10% yield loss. The Weibull and MMF models were used to determine the critical period. The critical period of weed control occurred between safflower early stem elongation and flowering stages (144-220 days after planting, DAP) at the Bajgah site and between early stem elongation andearly head emergence stages (135-184 DAP) at Kooshkak. The onset of interference seems to be less variable than its conclusion, indicating that early weed control is necessary to prevent yield loss. Also, with increase in as the weed interference period increased so yield components (number of heads per plant and number of seeds per head) decreased significantly.

To evaluate the genetic improvement in yield of wheat (Triticum aestivum) bred between 1956 and 1995, a field experiment was carried out in Arak, Iran, during the 2001-2002 growing season. Six wheat cultivars, from different years of release (Omid 1956, Bezostaya 1969, Azadi 1979, Ghods 1989, Alamot 1995 and Alvand 1995) were sown with and without competition from wild oat (Aven fatua). The results showed a trend to increasing yield at later release dates with a rate of 2.2 % yr-1 and 3.8% yr-1 under weed free and weedy conditions, respectively. The greater yield increase obtained in weedy conditions indicates an improvement in the potential competitive abilities of new cultivars. Harvest Index (HI) and biomass were highest in new cultivars. Increased HI could explain 74% of the gain in yield, whereas, the remaining 26% of yield improvement was attributed to increases in biomass. There were no differences betweencultivars in extinction coefficients (K) and Radiation Use Efficiency (RUE). However, RUE was reduced significantly in weedy conditions. RUE increased with the year of release by 0.77% yr-1 and 0.14% yr-1 under weed free and weedy conditions, respectively. Average RUE values of of 1.3 g MJ-1 (in terms of absorbed photosynthetically active radiation, APAR) and M. Beheshtian-Mesgaran et al. 33 0.83 g MJ-1 were estimated in weed free and weedy conditions, respectively. Leaf area index (LAI) was the only component that decreased as year of release increased.

In order to evaluate wild mustard competitive effect on winter wheat, an additive series experiment was conducted in 2000-2001 at Agricultural Research Station of Mashhad University.The experiment had 3 factor: wheat seed rate (175, 215 and 255 kg/ha), nitrogen rate (150 and 225 kg/ha), and a range of wild mustard densities. Hyperbolic functions was used to describe yield-weed density relationship. Increasing wild mustard density had a negative, asymptotic – type effect on wheat biomass and grain yield. By increasing wheat seed rate, in optimum nitrogen rate, maximum wheat biomas loss has reduced about 51 %. Maximum yield loss has increased from 42.1 % to 50.4 %, as nitrogen rate incrased from optimum to upper optimum rate of wheat. By increasing of wheat seed rate from 175 to 255 kg/ha, maximum tiller number reduction due to high densities of wild mustard, has decreased by 54 %. Reduction of fertile tiller number was mostly occurred at presence of high nitrogen level, thus, reduction of fertile tiller number compared to control in N1 was 18%, while in N2 has increased to 30%. Wild mustard competition has reduced wheat seed number per ear 30% in compare to weed free control. Results show that wheat 1000 seed weight was more affected by nitrogen rate than plant densities. Apparently, in competition with wheat, wild mustard was better able to utilize the added nitrogen and thus gained a competitive adventage over the wheat.