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Conventional rice planting method (CRP) includes transplanting in poddled soil with permanent flood irrigation method. This method consumes a lot of water, energy and labor. In recent years, despite the lack of irrigation water and restrictions in most rice-rich areas of the country, the area under rice cultivation has increased due to high economic income. One of the ways to reduce water consumption in rice production is direct sowing of seeds in dry-bed conditions in the main land. This study was conducted to select a suitable method for rice dirrect seeding in dry-bed condition (RDD) in Golestan, Khuzestan, Isfahan and Golestan provinces for one year and in a randomized complete block design with three replications. Six planting methods include: RDD in flat bed with grain drill machine (P1), RDD on the ridge bed (P2), RDD on the ridge bed with hill-drop seeding (P3), CRP or control (P4), RDD in flat bed with hill-drop seeding (P5) and pot seedling cultivation on on the ridge bed (P6) in terms of index Economic, technical, crop yield and water consumption were compared. P5 were excluded from the experiment due to the unpreparedness of the special seeser and P6 treatment due to the loss of all seedlings in the field (despite the immediate irrigation of the post from transplanting). In Isfahan and Golestan, Firoozan and Tarom cultivars were cultivated, respectively, and in Khuzestan, Champa, Anboury and Aerobic rice cultivars were cultivated. Irrigation method was intermittent in RDD treatments and permanent flooding in control treatment (P4). Seed consumption per hectare of main land in P1 and P2 was 100 kg.ha-1, in P3 it was equal to 5 seeds per hill and For P4 (control) in Khuzestan and Isfahan provinces were 40 and 100 kg.ha-1, respectively. In P3, P4 and P5, the distance between seedlings (planting arrangement) was according to the instructions provided by the Agricultural Research Center of that province. The dimensions of each experimental plot were 10×4m. In addition to economic comparison of treatments, indices of required time and field capacity of planting method, amount of water consumption and productivity, number of sprouted plants per square meter, percentage of seed germination, number of spikes per square meter, number of seeds per spike, weight Thousand grains and paddy yield were measured.
The results showed that the time required for P1 to P4 (control), were 1.2, 1.7, 1.4 and 265.9 h.ha-1, respectively. In the RDD methods, farmers do the planting operation by machine, but in the conventional method, farmers are forced to hire large numbers of workers at a high cost to plant seedlings on time on their farm. During one working day (10 h), in P1 to P3, 9.0, 6.4 and 7.3 hectares can be cultivated, respectively, while in the conventional method of transplanting (P4) with effort and high cost only 400 m2 can be cultivated.
In terms of agronomic indices (yield and its components), the difference between Khuzestan, Isfahan and Golestan regions was very significant due to large climatic differences and differences in cultivars planted in these regions. In terms of grain yield, there was no significant difference between cultivars and planting methods in Khuzestan. The highest grain yield was obtained for Champa and aerobic cultivars at 4095 and 3974 kg/ha in P3 and for Anboury cultivar at 4070 kg.ha-1 in P1. Also, in the conventional transplanting method, the highest grain yield of Anbouri, Champa and aerobic cultivars were 3808, 3667 and 2927 kg.ha-1 , respectively. In Isfahan, the difference between planting methods in terms of all crop indices (yield and its components) was very significant and the highest grain yield of 4000 kg.ha-1 was obtained in the transplanting in poddled soil with permanent flood irrigation method (CRP). Grain yield in RDD methods (P1 to P3) decreased by 56, 61 and 61%, respectively, compared to the control. In Golestan, the highest grain yield of 5238 kg.ha-1 was obtained from the conventional transplanting method with permanent flood irrigation, but this index was reduced by about 98% in RDD methods. In this province, contrary to the conventional method, in rice planting in summer, plant density in RDD methods decreased due to inefficient weed control and intense weed competition. Grain yield was also severely reduced due to late sowing (July 1) and hollowing of the seeds due to the collision of the filling stage with the cooling of the air in October.
The results of this study showed that in terms of irrigation water volume index and its physical productivity, there was a significant difference between the studied areas, planting methods in each region and the levels of interaction between the region and rice planting methods. In Khuzestan, the volume of irrigation water in conventional transplanting method with permanent flood irrigation was 35221 m3.ha-1, while this index for P1 to P3 RDD methods with intermittent irrigation cycle once every four days, compared to control (P4) decreased by 34, 49 and 49%, respectively. In Isfahan province, the volume of water used in the control treatment with severe poddling conditions was 17883 m3.ha-1, while in the RDD methods P1 to P3 (with intermittent irrigation cycle of three days in among), the volume of water consumed increased by 57, 55 and 55% compared to the control, respectively. Physical water productivity (FWP) in Khuzestan was 0.10 kg.m3-1 for conventional planting method and 0.15, 0.23 and 0.20 kg.m3-1 for RDD methods P1 to P3, respectively. But in Isfahan, unlike Khuzestan, SWP in the CRP was about 0.22. This index in seed drying methods in the main land decreased by 73% to about 0.06 kg.m3-1 and in the methods of RDD in the main land decreased by 73% and reached about 0.06 kg.m3-1.
Economic comparison of different planting methods also showed that for rice production in Khuzestan, the use of aerobic cultivar with RDD on the ridge bed with hill-drop seeding and intermittent irrigation, due to the highest net income of 730 $.ha-1 (9.4 times the conventional transplanting method), the highest income-to-cost ratio of 2.62 and the lowest volume of irrigation water at 17,800 m3.ha-1 (50% less than the control) is the best option. After that, planting Champa cultivar by RDD on the ridge bed method with intermittent irrigation, due to net income of 720 $.ha-1 and irrigation water consumption of 17849 m3.ha-1 (49% less than the CRP), is suggested. In Isfahan province, for Firoozan cultivar, the gross income of farmers in all three methods of RDD methods (P1 to P3) was about 50% of production costs, which was economically unprofitable and rejected. In general, Despite earning a net income of 610 $.ha-1 and a net profit of 36% in the conventional transplanting method with permanent flood irrigation, from a national perspective, due to lack of water resources and widespread drought in recent years and high water consumption to 17857 cubic meters per hectare, rice planting in Isfahan is not recommended. In Golestan province, late summer planting of Tarom cultivar in RDD drying methods (after emptying the field from the previous crop), due to severe reduction of rice plant density in conditions of inefficient weed control and high reduction of grain yield due to coinciding with the grain filling stage with the decrease in temperature in October and the emptying of the grains is economically unprofitable and is not recommended.
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