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The strategic position of wheat and the role of protecting agricultural inputs (especially water resources) in food and social security of the country on the one hand, and on the other hand, the expansion of adverse effects of climate change in the country and the severe wind and rain in the growing season of wheat, increase the need for monitoring grain losses and planning to reduce it in the country. The national research project conducted in the year 97-96 in order to determine the type and source of grain losses and the contribution of each human, technical and crop factors affecting the amount of wheat grain losses in harvesting with new and common types of John Deere, New Holland and class combines, in the country. The research was carried out with the participation of the Agriculture Directorate (wheat plan office and Agricultural Mechanization Development Center) in 21 provinces of the country. The number of studied combines was 536, which were randomly selected and visited and sampled while working on farmer's fields. In addition, crop and farm conditions, including cultivated wheat cultivar, Field area and soil tillage-planting method were recorded in special forms. Also, farmers, experts and drivers of combines were interviewed face to face and completed questionnaires. Sampling of combines was used to determine the percentage of seed loss in the platform and processing unit (back combine) and sampling from a combine tank to determine grain moisture content and impurities in harvested grains. Sampling was done at unharvest areas for determining the grain yield and percentage of natural loss. Type, age, forward speed, and field capacity of combines were also measured. The results of this study showed that the average total loss of wheat harvest stage was 3.75% in the country, of which 1.26% was natural loss and 2.49% was combine losses. The sum of combine and natural losses in rainfed and irrigated wheat fields was 3.34% and 4.40%, respectively. The mean loss in rainfed and irrigated wheat fields was 2.86% and 2.30%, respectively. The average natural loss in irrigated and rainfed wheat was estimated to be 1.04 and 1.54% respectively. In the year of this research, the amount of natural losses of grain in Tehran province due to exceptional circumstances and lodging wheat in the farms due to heavy wind and rain was 27.1%, but the combine losses in this province was 2.88%. The results of this study showed that the wheat grain loss by combines in the country dropped by 0.88% over the past 13 years to reach 2.49%. According to available data of wheat grains harvested in 2018, the calculations in this study showed that the total wheat produced in the country's irrigated and rainfed fields was 13824481tons, of which 13300000 tons were harvested and and the remainder 519864 tons was lost at the harvesting stage (277219 tons of irrigated wheat and 242645 tons of rainfed wheat), of which 338999 tons (65%) were lost by combine and 180864 tons (35%), due to natural loss. If the price per kilogram of wheat (17000 Rials) is estimated at 0.142 USD, the total damage to farmers and the country due to the total loss of wheat grain is about 74 million USD, which is estimated to be about 48 and 26 million USD, due to grain loss by combine and natural loss respectively. Also, assuming an average production of 4280kg ha-1 and water consumption of 5800 cubic meters per hectare for irrigated wheat, the amount of wasted water for producing grain lost in irrigated and rainfed fields and total of grain losses are equal to 376, 329 and 705 million cubic meters of water (1.8, 1.6 and 3.4 times more than the Amir Kabir dam reservoir of Karaj) respectively. Other results of this study showed that with each percentage reduction in wheat losses, farmers' income in irrigated and rainfed fields would increase by 5.9 and 2.3 USD per hectare, respectively. Grain losses was 2.9%, 2% and 1.8%, respectively, by common types of John Deere (955, 1050 and 1165), class (Tucano 320, S80 and Medion 310) and New Holland (5060, 5070 and 5080). The use of New Holland and class combines with John Deere combines (955, 1055 and 1165) increased the farmers' income in irrigated wheat field, due to the reduction in grain loss, by 3.8, 7.1 and 6.9 USD per hectare. Also, seed loss in fields with a yield of less than 4 tons per hectare, 3% and in farms with a yield of more than 8 tons per hectare, was 1.6%. The data of this study showed that for farms with an area of less than 10 hectares, there is not a strong correlation between the amount of combine losses and the field area, but With an increase in the area of the farm to more than 10 hectares, the average drop in combines dropped by 0.7%. Of the combine losses in wheat grain in the country (2.49%), 74% of it was created by the platform and 26% by the processing units (back combine). His finding highlights the importance of monitoring the performance of the combin’s platform to reduce combine losses in the country. Average of grain moisture content at harvest time was 9.7% and 10.1%, respectively, which was less than optimum moisture content (12 to 14 percent). The loss caused by native and migratory combines was estimated to be 2.72 and 2.36 percent, respectively. The average age of the combines in the country was 14 years and For each year of the increase in the age of the combine, the amount of combine loss increased by 0.26%. In general, to compare zones and determine critical points in crop losses, the percent of grain loss and the amount of grain lost per hectare alone is not sufficient and attention to the total amount of grain lost is more important. At the moment, with the increase in the use of advanced combines, the acceptable wheat grain combine loss in the world is between 1% and 2%, and its reduction below 1% is targeted. In the past decade, the expansion and modernization of the agricultural machinery (especially harvesting machines) has been paying great attention in the country. To reduce wheat losses by combines to an acceptable range of 1% to 2% and to achieve ideal conditions (less than 1%), it requires planting of wheat varieties resistant to seed falling, use of advanced combines, timely delivery and sufficient combines, timely harvesting of wheat, use of modern technologies and monitoring systems and automatic control of grain losses in designing and manufacturing domestic combines, basic leveling and reducing roughness on the farm (due to the due to the large number of borders and irrigation streams), Combine driver training for detecting and controlling crop losses and training farmers to monitor seed loss in the field.Key Words: combine harvester, wheat, graine losses, solutions
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