Technical Guidance on Reducing Losses in Mechanized Wheat Harvesting was issued by the Ministry of Agriculture in 2015
This technical guidance applies to wheat harvesting operations using full-feed combine harvesters. Within a given area, wheat varieties and planting patterns should be as uniform and consistent as possible, and crop and field conditions should be suitable for mechanized harvesting. Operators should inspect and adjust the machinery in advance, determine the appropriate harvest time, follow the quality standards and operating procedures for mechanized wheat harvesting, and strive to reduce grain scattering losses during the harvest stage.
I. Pre-operation Machinery Inspection and Adjustment
Before operating a wheat combine harvester, thorough maintenance and adjustment should be carried out to bring the machinery to its optimal working condition, thereby reducing the failure rate and improving work quality and efficiency.
(1) Inspection and Maintenance Before the Start of the Harvest Season
Before the start of the harvest season, a comprehensive inspection and maintenance of the combine harvester should be carried out according to the product manual to ensure the machinery can work normally throughout the entire harvest period. For wheat combine harvesters that have been reassembled, maintained or repaired, a careful trial run should be conducted, first on individual parts and then on the whole machine, to carefully check the operation, transmission, control and adjustment of the traveling, steering, harvesting, conveying, threshing, cleaning, and grain unloading mechanisms, and to check for abnormal noises and leaks of oil, water and air. Any problems found should be resolved promptly.
(2) Pre-departure Inspection and Preparation During the Harvest Season
Before operation, check whether the functions of all control devices are normal; whether the free travel of the clutch and brake pedal is appropriate; whether the engine oil and coolant levels are appropriate; whether all indicators on the instrument panel are normal; whether tire pressure is normal; whether the drive chain and tensioning pulley are loose or damaged, and whether they move flexibly and reliably; whether bolts and nuts at important positions are loose; whether there is any water leakage or oil seepage; and whether the header, frame and other components are deformed. Prepare sufficient common field operation tools, spare parts, wearing parts and fuel, so that faults can be promptly remedied when they occur.
(3) Trial Harvesting
Before the formal harvest, select a representative plot for trial harvesting, so as to conduct a comprehensive on-site inspection of the technical condition of the machine after adjustment, and make necessary adjustments according to the operating conditions and the farmer's requirements.
During trial harvesting, operate at normal working speed for a distance of about 20 m, then stop the machine and check for losses after cutting, grain breakage, impurity content, and any abnormal conditions such as missed cutting, straw blockage or grain loss. If there are any problems, make necessary adjustments to the cutter clearance, threshing clearance, sieve opening and/or fan air volume as appropriate. After adjustment, conduct trial harvesting again and check the work quality until requirements are met before proceeding with normal operation.
During the trial harvesting process, attention should be paid to observing and listening to the machine's working condition, and any abnormalities should be resolved promptly.
II. Determining the Appropriate Harvest Time
Mechanized wheat harvesting should be carried out from the late dough stage to the full ripe stage, when yield is highest and quality is best. The main characteristics of wheat at maturity: at the mid-dough stage, the lower leaves are dry and yellow, the stems are elastic, the grains turn yellow, plump and moist, and the grain moisture content is 25-30%. At the late dough stage, the plant turns yellow, with only the leaf sheath base slightly green, the stems are still elastic, the grains are yellow and slightly hard, the contents are waxy, and the moisture content is 20%-25%. At the full ripe stage, the leaves are withered and yellow, the grains become hard, show the characteristic color of the variety, and the moisture content is below 20%.
When determining the harvest time, the harvest sequence should also be reasonably arranged according to the weather conditions at the time, variety characteristics and cultivation conditions, so as to adapt to local conditions, harvest promptly at the right time, and ensure that every grain is safely stored. Small-area harvesting should be carried out at the late dough stage, while large-area harvesting should be carried out at the mid-dough stage, so that most wheat is harvested within the suitable harvest period. Wheat fields intended for seed purposes should be harvested at the full ripe stage. If the rainy season is approaching, or if there is an urgent need to plant the next crop, or if the variety is prone to shattering, stem breakage, ear breakage or sprouting on the ear, harvesting should be appropriately advanced.
III. Quality Requirements for Mechanized Harvesting Operations
According to the requirements of NY/T 995-2006 "Operating Quality of Grain (Wheat) Combine Harvesters," the total loss rate of full-feed combine harvesters shall be ≤2.0%, the grain breakage rate shall be ≤2.0%, and the impurity content rate shall be ≤2.5%, with no obvious missed harvesting or missed cutting. The stubble height should be consistent, generally not exceeding 15 cm, and when leaving high stubble for return to the field, it should preferably not exceed 25 cm. After mechanical operation, there should be no grain and land contamination caused by fuel leakage. To improve the sowing and seedling emergence quality of the next crop, wheat combine harvesters are required to be equipped with straw chopping and spreading devices to ensure even distribution of straw on the ground surface. In addition, attention should be paid to timely communication with users to understand their quality requirements for harvesting operations.
IV. Measures to Reduce Losses in Mechanized Harvesting
During the harvesting process, correct operating parameters should be selected, and the machinery should be adjusted in a timely manner according to different natural conditions and crop conditions, so as to keep the combine harvester in good working condition, reduce mechanized harvesting losses, and improve work quality.
(1) Choosing the Operating Travel Route
Combine harvester operations can generally adopt three travel methods: clockwise inward spiral, counterclockwise inward spiral, and shuttle-shaped harvesting. In actual operation, the operator should flexibly choose according to the actual conditions of the plot. When turning, harvesting should be stopped, and either the reverse turning method or the loop method for right-angle turning should be used. Do not turn while cutting, to prevent the divider, walking wheels or tracks from flattening uncut wheat and causing missed-cutting losses.
(2) Choosing the Operating Speed
A reasonable operating speed should be selected based on factors such as the combine harvester's own feed rate, wheat yield, natural height, and degree of dryness or wetness. Under normal circumstances, harvesting should be carried out at normal operating speed. When wheat is dense, plants are large, yield is high, or crop moisture is high in the morning and evening or after rain, the operating speed should be appropriately reduced.
(3) Adjusting the Operating Width
When the load permits, control the operating speed well and work at full width or close to full width as much as possible, to ensure uniform crop feeding and prevent excessive feed volume from affecting threshing quality and increasing the breakage rate. When wheat yield is high, moisture is high, or the stubble height is too low, and low-speed operation is still overloaded, appropriately reduce the cutting width, generally to 80%, to ensure wheat harvesting quality.
(4) Maintaining an Appropriate Stubble Height
The stubble height should be determined according to the height of the wheat and the flatness of the plot, generally 5-15 cm is appropriate. If the stubble is too high, due to uneven wheat height or the header fluctuating up and down when the machine crosses field ridges, some wheat may easily be missed, and at the same time, the reel's gathering and pushing effect is weakened, which can easily cause losses from grain falling to the ground. While ensuring normal harvesting, the stubble should be as low as possible, but not less than 5 cm at minimum, to avoid cutting into the soil and accelerating cutter wear.
(5) Adjusting the Reel Speed and Position
The reel speed is generally 1.1-1.2 times the forward speed of the combine harvester and should not be too high. The reel height should be positioned so that the reel bats act at 2/3 of the height of the crop being cut. Its front-to-back position should be determined according to crop density and lodging degree. When crop plant density is high and the crop is lodged, it should be moved forward appropriately to enhance the lifting capability. If the reel speed is too high, or the position is too high or too far forward, it will easily increase the shedding of grain from the ears, thereby increasing operation losses.
(6) Adjusting Threshing, Cleaning and Other Working Components
The rotational speed of the threshing cylinder, the threshing clearance and the angle of the guide plate are important factors affecting the wheat threshing rate and breakage rate. On the premise of ensuring that the breakage rate does not exceed the standard, measures such as appropriately increasing the rotational speed of the threshing cylinder, reducing the clearance between the cylinder and the concave, and correctly adjusting the ratio of inlet to outlet clearance (which should be 4:1) can be adopted to improve the threshing rate and reduce threshing losses and breakage. Cleaning loss and impurity content rate are in opposition to each other, and both should be considered comprehensively during adjustment. On the premise of ensuring that the impurity content rate does not exceed the standard, cleaning losses can be reduced by appropriately reducing fan air volume, increasing the sieve opening, and raising the position of the tail sieve. During operation, frequently check the straw blockage inside the straw walker housing and clean it promptly. For axial-flow cylinders, the feed rate can be appropriately reduced and the cylinder speed increased to reduce separation losses.
(7) Harvesting Lodged Crops
Appropriately lower the stubble to reduce missed cutting; move the reel forward appropriately and tilt the reel tines backward 15°-30° to enhance the lifting effect. For severely lodged crops, adopt measures such as harvesting against the lodging direction, reducing operating speed, or reducing feed volume.
(8) Harvesting Overripe Crops
When wheat is overripe, the stems are too dry and easily broken, and the grains easily shed. After threshing, the increase in broken stems easily causes separation difficulties. During harvesting, the reel speed should be appropriately reduced to prevent the reel bats from striking the wheat ears and causing grain loss. At the same time, reduce the operating speed, appropriately adjust the cleaning sieve opening, and harvesting can also be arranged in the morning or evening when the stems have greater toughness.