جستجوی مقالات مرتبط با کلیدواژه « weed competition » در نشریات گروه « زراعت »

In order to evaluate the role of mulch of cover crop (barley) in two systems of, seedbed preparation in autumn and in spring, on weed biomass and qualitative and quantitative yield of sugar beet, a strip split plot experiment based on randomized complete block design with four replications was conducted in Karaj (2012-13 & 2013-14). The treatments consisted of five different seedbed preparation and barley mulch including sole cropping in autumn (b1), barley mulch applied in furrow in autumn-sowing (b2) and both in furrow and hill (b3), sole cropping in spring (b4), and barley mulch applied in furrow in spring-sown sugar beet cropping. Individual plots included 8 rows with a length and width of 25 and 4 m, respectively. Each row was divided into three parts comprising sole cropping at the beginning (hand weeding, w1), weed infested control at the middle (no weed control over the growing season, w2), and chemical control at the end (using selective herbicides). Green and cover crop biomass in autumn seedbed preparation were immediately dried by Paraquat herbicide application and were incorporated to the soil, but for spring seedbed treatments, selective herbicide was used. The results of combined analysis traits showed that the competition of natural weeds of the field significantly affected root yield, sugar yield and white sugar yield. The reduction of more than 50% of root yield (32.12 t/ha), sugar yield (4.75 t/ha) and white sugar yield (3.63 t/ha) in the infested weed control treatment compared to the weed free showed a high potential damage of weeds in sugar beet fields. In the seedbed system in autumn, which sugar beet seed was drilled directly in spring, the addition of barley to become mulch reduced root yield by 13% in the fall row method and 19% in the fall method compared to the control treatment preparation of seed bed in autumn without barley (with root yield 57.55 t / ha). Considering no significant difference between sole cropping in spring (spring control) with low tillage of sole cropping in autumn (autumn control) for quantitive and qualitative yield of sugar beet suggests that by preparing the seedbed in the autumn, it is possible for early drilling sugar beet and make optimal use of the potential of the area.

To investigate the effect of weed interference on the yield and yield components of rice an experiment was conducted in 2014 at Amol and Mahmoudabad cities in Mazandaran. The experiment was performed in a randomized complete block design with 12 treatments and three replications. Treatments to control weeds were of two types. The first treatment consistsed of controling weeds 10, 20, 30, 40, and 50 days after rice transplanting and then weeds interfered with plant during rest of growing season. A whole season weed control was used as check. The second type treatment at weed interference until 10, 20, 30, 40, and 50 days after rice transplanting and then weeds were controlled during rest of growing season. A whole season interference treatment was used as a weed infested check. The results of variance analysis showed a significant difference for grain yield in either weed free or weed infested treatments between two places. Weed control and interference (except panicle number and biological yield) significantly affected grain yield, grain numbers per panicle and 1000 grain weight. The highest grain yield (3010.83 kg.ha-1) belonged to weed control during whole growing season and lowest grain yield (2075 kg.ha-1) was obtained from weed infested check. Weed infested check resulted in lower grain yield (by 8.31%), panicle number (by 8.33%) and grains number per panicle (by 10.26%) as compared to the control. The critical period of weed control, based on the amount of 5 and 10 percent of yield losses, were fitted by Gompertz and Logestic regression to weed infested weed free treatments, respectively. The results showed that the critical period of weed control in Mahmoudabad region occurred during the days of 22 to 59 and 27 to 36 (from early to end of tillering) based on 10 and 5 percent of yield loss, respectively. The critical point was calculated to be 32 days after transplanting.Thecritical period for Amol region occurred during days of 15 to 54 and 20 to 37 (from early to end of tillering) based on 10 and 5 percent of yield loss, respectively. The critical point was calculated for day 25 after transplanting. In conclusion, the critical period of weed control seems to begin earlier in Amol than in Mahmoudabad and it also had a longer range.

In order to investigate the effect of different weed-free and weed-infested periods on the growth indices of black seed، a field experiment was conducted at the Agricultural Research Station of Ferdowsi University of Mashhad، during 2009-2010 growing season. The experiment was laid out in randomized complete block design with 12 treatments and 3 replications. Twelve experimental treatments consist of six initial weed-free periods in which plots were kept free of weeds for 0 (WF 0)، 14 (WF 14)، 28 (WF 28)، 42 (WF 42)، 56 (WF56)، 70 (WF 70) days after crop emergence (DAE)، and then weeds were allow to grow until harvesting، and six initial weed-infested periods in which weed allowed to grow for 0 (WI 0)، 14 (WI 14)، 28 (WI 28)، 42 (WI 42)، 56 (WI56)، 70 (WI 70) DAE، then plots kept free of weeds to harvesting. The results indicated that black seed height was strongly affected by different weed free and weed-infested periods. Interestingly، weed interference for entire growing season caused increase in black seed height by 39% compared with the treatment that was weed free throughout the growing season. Also، these periods had significant effects on leaf area index، green area index، dry matter accumulation، crop growth rate and relative growth rate. Mentioned traits increased with increasing duration of weed- free periods and were reduced by increasing length of weed- infested periods. However، these periods had no significant effects on net assimilation rate، specific leaf area and specific leaf weight.

A field experiment was conducted in research farm of Isfahan University of technology، Isfahan، Iran in 2011. Various weeding periods were investigated on growth and yield of potato under drip tape and furrow irrigation systems. A split plot arrangement was used in a randomized complete block design with three replications. Irrigation treatments were included in main plots and periods of weed control in sub plots. Weed treatments included two series of periods of weed free and weed interference at intervals of 20، 30، 40، 50 and 60 days after emergence. Two treatments of weed free and weed interference applied over the entire growing period were also considered as control treatments. The period of weed interference had significant effects on weed density. Overall، weed density was higher under drip compared to furrow irrigation. The highest weed density was observed at early stage of growing period under both irrigation systems. Howevere، during the later stages weed density was reduced، due to self-weeding but weed dry weight was increased. Results also showed that weed interference led to significant losses in plant height، latteral stems، stem number، and leaf dry matter and the yield of potato plants.

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.