Background and objectives: rice (Oryza sativa) is a major cereal crop and staple food for more than half of the world's population. About 90% of the world's rice is produced and consumed in Asia. Iran is one of the arid and semi-arid regions and due to the lack of water in many parts of the country, the area under rice cultivation decreases. Direct rice cultivation is a good way to save water. The most important challenge in this cultivation system is weed control. The traditional methods of weed control in rice include hand-weeding by hoe or hand pulling, but this is becoming less common because of labour scarcity at critical time of weeding and increasing labour costs. Herbicides play a key role in weed control and are used extensively today. Therefore, this experiment was conducted to evaluate the effectiveness of different weed management practices for Direct seeded rice at varying row spacing.Materials and methods: This study was conducted to investigate the effect of planting distance on rows and herbicides on weed suppression and Direct rice cultivation performance in the research farm of Sari Agricultural Sciences and Natural Resources University as a factorial experiment in a randomized complete block design with three replications in 2019. Distance between plants at two levels of 3 and 5 cm and chemical management of weeds in five levels of weed-free (control), weed-infested (control), application of trifamone + ethoxysulfuron herbicide 30% (council active) at the rate of 150 g ha-1 in stage of 2 up to 6 leaves of weeds, application of bisopiribac sodium herbicide OF10% (nomini) at the rate of 250 ml ha-1 in stage of 2 to 6 leaves of weeds and application of a mixture of two herbicides halofop butyl OD 20% with 2.5 liters ha-1 with basagran (bentazone) were 3 liters ha-1 in the 2 to 6 leaves stage of the weeds.Results: Results showed that although planting row spacing had no effect on the desired traits; however, weed management had a significant effect on the studied traits. Visual evaluation of weed damage in two evaluation stages (15 and 30 days after spraying) showed that among the chemical control treatments, trifamone + ethoxysulfuron herbicide was superior to other herbicides with 75 and 83.33% weed control, respectively. The lowest weeds biomass was observed in 6 weeks after spraying (20.50 g m-2) and 10 weeks after spraying (20.83 g m-2) in trifamone + ethoxysulfuron herbicide treatment, which was not significantly different with weed free (control). The highest height of rice plants (103.17 and 98.41 cm) was observed in the complete weed control and trifamone + ethoxy-sulfurone herbicide treatments, respectively. It is worth mentioning that the maximum biological yield of rice (6244.4 and 5808.4 kg ha-1) and grain yield (2391.218 and 2290.27 kg ha-1, respectively) was observed in weed-free (control) and application of triafamone + ethoxysulfuron herbicide. According to the results of this experiment, the use of trifamone + ethoxysulfuron herbicide at the rate of 150 g ha-1 is recommended for proper control of weeds in Direct rice cultivation.Conclusion: The highest and lowest height, number of tillers and spike length were observed in weed-free control treatment and weed-infected control treatment. Among the herbicides used in this experiment, in the treatment of triafamone + ethoxysulfuron with better weed control, In plant height, tiller number, spike length and number of seeds per spike were superior to other herbicides. According to the results of the experiment, the application of the herbicide triafamone + ethoxysulfuron, while better control of weeds, can increase grain yield.

In order to evaluate the competitive ability of rice genotypes against weeds in Direct seeding system and determination the traits that may confer such attributes, field experiment was conducted at rice Research Institute of Iran in Rasht during 2016-17 cropping season. The experiment was laid out in a split plot based on randomized complete block design with three replications. The treatments included two levels of weed management (weedy (under natural weed flora) and weed-free) as the main plots and ten rice genotypes (Hashemi, Abjiboji, Tazeh Hasani, Gilaneh, Shiroodi, Saleh, RI18430-1, RI18430-60, RI18430-72, RI18430-77) as subplots. The results showed genotypic differences in competitive ability against weeds. Under weed-free conditions, grain yield varied from 3293. 5 in Saleh to 6796. 1 kg. ha-1 in Shiroodi. Under weedy conditions, grain yield was also registered from 260. 6 in breeding line RI18430-72 to 1291. 2 kg. ha-1 in Hashemi. The highest and lowest amounts of weed biomass at flowering were also observed in Abjiboji and shiroodi, respectively. Average yield loss due to weed competition ranged from 73. 55 to 94. 1% in different rice genotypes. The results also indicated a positive significant correlation between competitive ability and grain yield, so Hashemi, Shiroodi and the breeding line RI18430-60 having the highest competitive ability against weeds and also grain yield (the basis for Direct selection under weedy condition) can be applied in integrated weed management programs to reduce herbicide use. The study revealed that early growth (vigor), leaf area index, crop biomass and height had significant positive correlation with competitive ability and hence, can be used as useful inDirect selection criteria of genotypes with high competitive ability.

The effect of seeding dates were evaluated on growth and yield of rice under Direct seeding in a split plot experiment based on RCBD during growing season of 2007. Four seeding dates were April 30 and May 10, 20 and 30 using three cultivars (Hashemi, Tarom and Elpaso) with four replications. Seeding dates and cultivars were assigned to main and sub plots, respectively. The results showed that date of seeding did not have any significant effect on the number of panicle per m2 while the effect of date of seeding on seed yield, number of non-bearing tillers per m2, length of panicle, number of full and empty fruits per square meter and plant height were significant.Second date of seeding produced 5029 Kg per hectares with plant height of 111 cm, Elpaso produced 5378 Kg per hectare, the highest seed yield, Hashemi with height equal to 117 cm had the highest plant height. Date of seeding by cultivar interaction for number of non-bearing tillers, number of panicles per m2, length of panicles, number of full and empty seeds were significant. Elpaso, on second seeding date, produced highest full seed per m2 (19270), number of panicle per m2 (322), and highest yield (6854 Kg per hectare).

The diversity of weed communities and their differences in response to herbicides have made mixed herbicides application inevitable. In this research, the efficacy of transplanted rice herbicides in controlling weeds in rice Direct seeded rice was investigated. Comparison of the efficiency of premixed herbicide pretilachlor + pyribenzoxim (solito, EC 32%, 480 g ai ha-1) in a pot experiment with the common herbicides bispyribac-sodium (two formulations SC40%, SC10%), pyribenzoxim and bentazone + MCPA showed that the premixed herbicide provided similar control of barnyardgrass and bulrush as did common herbicides. Field experiment treatments included bentazone + MCPA + pendimethalin, bentazone + MCPA + thiobencarb, bispyribac-sodium + pendimethalin, bispyribac-sodium + thiobencarb, pretilachlor + bensulfuron-methyl and doses of 0, 50, 100, 150 and 200% of pretilachlor + pyribenzoxim mixed with thiobencarb. The results showed that pretilachlor + pyribenzoxim did not show any phytotoxicity symptoms on rice up to twice the recommended dose. Application of the recommended dose of pretilachlor + pyribenzoxim + thiobencarb provided 90% and 70% control of barnyardgrass (Echinochloa crus-galli) and bulrush (Bolboschoenus planiculmis) respectively. The lowest and highest yield of paddy was 517 and 5495 kg/ha, respectively, which was recorded in the weedy and bispyribac-sodium + thiobencarb treatments. The yield of paddy at the recommended and twice the recommended dose of pretilachlor + pyribenzoxim was statistically the same 4761 and 4827 kg/ha, respectively. Overall, the results of this research indicated that the application of pretilachlor + pyribenzoxim (480 g ai ha-1) after soil-applied thiobencarb (2750 g ai ha-1) provided very good control on the important weeds of rice in Direct cultivation on wet bed and can be introduced as a suitable alternative to common herbicides.

Energy efficiency is one of the most important factors for sustainable agriculture. This study explored the energy consumption and global warming potential for puddled transplanted (PTR), un-puddled transplanted, and Direct-seeded rice (Oryza sativa L. ) (DSR) production systems under sprinkler, flood, and drip irrigation systems in Gorgan City fields, Golestan Province, Iran. According to the results, the average energy input and output for different irrigation systems in puddled transplanted treatment was higher than the other treatments, while the highest input and output energy was related to drip irrigation system (36366 and 249971 MJ. h-1). The highest energy consumption in different irrigation and cultivation systems was related to water and nitrogen fertilizer. The results also showed that energy use efficiency for different systems ranged from 5. 05 to 7. 35 kg. MJ-1. Energy use efficiency for pressurized irrigation systems was higher in puddled transplanted treatment and for flood irrigation systems was higher in un-puddled transplanted treatment. Also, the energy productivities of different treatments were between 0. 1 to 0. 24 kg. MJ-1, while the mean energy efficiencies of PTR and un-puddled transplanted treatments did not differ significantly and were more than DSR treatment. The specific energy and net energy for different treatments ranged from 4. 29 to 10. 2 MJkg-1 and 112784 to 213825 MJ. ha-1, respectively. The puddled transplanted treatment had the highest GWP for all irrigation systems. The largest share of GWP in rice cultivation was related to the use of nitrogen fertilizers, fuels, and machinery. The results of mean comparison of GWP per unit area, weight, input energy, and output energy showed that modern pressurized irrigation systems with un-puddled transplanted cultivation method (due to less input and a yield similar to PTR) can be a suitable method for rice cultivation to reduce energy consumption and global warming potential.

This field experiment was carried out at Agricultural Research Farm of Institute of Agricultural Sciences, Banaras Hindu University, Varanasi, during the Kharif season of 2016 and 2017. The experiment was established in a split-plot design with three replicates and comprised of total 15 treatment combinations involving three crop establishment methods as: (i) conventional till-Direct seeded rice, (ii) the conventional till-wet Direct-seeded rice, and (iii) and zero till-Direct seeded rice in the main plot and five Zn application treatments (i) control (No Zn application), (ii) 3 kg Zn ha-1 (basal application), (iii) 3 kg Zn ha-1 (foliar application), (iv) 6 kg Zn ha-1 (basal application), and (v) 6 kg Zn ha-1 (foliar application) in the subplot. The crop establishment methods significantly (p=0.05) influenced weeds density and dry weight at 20, 40, 60, and 80 days after sowing. Among crop establishment methods, the conventional till-wet Direct-seeded observed the lowest density and dry weight of grassy, sedge, and broad-leaf weeds across all the crop growth stages. Concerning crop yield, the conventional till-wet Direct-seeded rice and 6 kg Zn ha-1 (basal application) recorded higher grain, straw, biological yield, and harvest index. Thus, it is suggested that conventional till-wet Direct-seeded rice and 6 kg Zn ha-1 (basal application) can be practiced for recording the higher yields and the effective management of weeds in DSR.