March 19, 2007
Wheat harvesting losses
By Hafeez Ur Rehman, Dr M. Farooq & Dr Shahzad M.A. Basra
OVER four per cent of wheat produced in the country is lost due to inefficient farm operations, inappropriate agriculture technologies followed at harvesting, threshing, drying, storage and other post-harvest factors at the farm, village and commercial levels, though losses in excess of 40 per cent for other cereals are not uncommon. Harvesting of the crop includes cutting, stacking and handling, threshing, drying and storage.
Harvesting can be done manually by sickles or mechanically by threshers or combine harvesters. Most problems in harvesting are attributed to irregular wheat ripening. Early harvesting results in shrinkage of grain and late harvesting may cause shattering of grain in field.
Optimum time for wheat harvesting is physiological maturity, when moisture percentage in grains ranges from 20 to 40 per cent. However, moisture percentage is not a good predictor of physiological maturity as it varies with varieties and environments.
There are many visual indicators that predict maturity of the crop. Loss of green colour from the peduncle, kernel and glumes is an important sign of maturity of the grain. Generally, the glumes at the bottom of the spike are the last to lose its green colour that is easily observed across the field. At this stage grain moisture is around 16-17 per cent.
Grain that shatters before and during harvest yields no return and may cause additional expense as a volunteer crop, but in case of semi-dwarf improved varieties harvesting should be done two to three days earlier. Harvest of the crop should be started as soon as the crop has field dried and can be handled safely.
Modern and traditional methods of wheat harvest technology often depend upon the scale of production. Self-propelled mechanical threshers may be found in use all over the country. However, reaping by hand-pulling of plants or cycling, stooking, shocking and stacking of straw followed by threshing, upon need of grain for food or sales, by stationary mechanical threshers or on oxen-trodden mud-packed threshing floors is common in many small-scale farming situations. On-farm storage of grain is common for smaller scale farmers, whereas direct sales to cooperative, government or private elevators are the norm for larger producers.
Harvesting by combine is mostly used for early harvest, provided the crop can be dried safely. Adjustments in combine cylinder or speed of fan in the field improve threshing and cleaning. Lower cylinder speeds reduce damage of kernel. Increased fan speed cleans wet chaff more easily, but more grain can be blown out.
Another harvest technique is to cut wheat with a swather and allowed to field dry in the swath (or windrow) until it can be threshed with a combine. This technique requires specialised equipment usually a swather and pickup device.
Several types of weeds, such as common lambs quarters and rag weeds, can interfere with wheat harvest. With wheat nearing maturity, some producers may want to consider applying a pre-harvest herbicide treatment to control weeds that could make harvesting operations difficult. Only a few herbicides are cleared as harvest aids for wheat, including clarity, glyphosate, and some formulations of 2, 4-D.
In all situations, grain must be harvested timely, before shattering, pre-harvest sprouting, bird damage or weathering, to minimise pre-harvest losses and it must be dry enough for storage. During threshing, cracking and breaking of the grain should be avoided since damaged grain invites greater damage from storage moulds and insects, and reduces marketability.
Drying: After harvesting, grain should be dried to a certain moisture level for safe storage. The procedure depends upon the grain moisture contents and method applied for drying. For high-moisture wheat i.e. greater than 15 per cent moisture can be dried with both high-speed and bin drying equipment. Wheat has a higher resistance to airflow than other cereals. For commercial wheat, drying air temperatures should be below 140ðF to avoid damage to milling quality. Seed wheat should be dried at 110ðF or lower.
High temperature batch or continuous flow dryers usually have adequate airflow capacity for drying wheat. These units typically have high airflow rates, so supplemental heat may not be required for daytime drying when harvesting in the moisture range of 18 per cent to 20 per cent.
Heat is required when drying high moisture wheat during periods of high humidity (above 70 per cent at night or during cloudy days).
Storage: Freshly harvested wheat should be dried to a moisture content 8-10 per cent for storage or 13.5 per cent for immediate sale. Sanitation, aeration, and monitoring are the watchwords to remember when storing grain during the summer months.
Totally remove the old crop before placing newly harvested wheat into a bin. Thoroughly sweep the bin wall and floor to remove grain kernels that may contain insect larvae or mold spores. Apply an approved insecticide both inside and outside the bin to delay insect population development before placing wheat in the bin.
Aeration should be used to cool wheat after drying with heated air. To a small degree, aeration will control grain temperature if it starts heating during storage, but this may only be a short-term solution. If heating cannot be controlled by running the fan, the crop must be moved to another bin, if possible to break up hot spots in the bin that usually cause the problem. Check the condition of stored wheat once a week during hot weather to guard against deterioration from molds or insects. Run the fan for a few minutes to check for off odour of the air from the grain pile.
Unfortunately, many resource-poor farmers use grain storage structures that are inadequate to protect grain from rain or dampness and rodent or insect infestation. Recently, appropriate storage structure technology, through support from the Food and Agriculture Organization of the United Nations (FAO), has been introduced.
These airtight grain stores are made from clay and straw, are simple in construction, are low cost and have the potential to reduce significantly post-harvest grain losses.
For damage to stored grain due to rodent infestation, prevention is better than a cure. Contrary to damage caused by insects or fungi, rodents can infest stored grain regardless of temperature or humidity, the only requirement being access to the grain store. Storage structures should be built with rodent-proof air vents, roofs and door jams. In addition, surrounding areas should not be considered general storage areas and should be kept clean from debris. Use proper fumigants and rodenticides if necessary.
Maximum grain yield and to minimise damage and quality deterioration is only possible by good harvest. These losses can not be easily reduced in the absence of well-integrated policies and plans to develop the total system of production, marketing, storage and distribution.
http://www.dawn.com/2007/03/19/ebr4.htm
Wheat harvesting losses
By Hafeez Ur Rehman, Dr M. Farooq & Dr Shahzad M.A. Basra
OVER four per cent of wheat produced in the country is lost due to inefficient farm operations, inappropriate agriculture technologies followed at harvesting, threshing, drying, storage and other post-harvest factors at the farm, village and commercial levels, though losses in excess of 40 per cent for other cereals are not uncommon. Harvesting of the crop includes cutting, stacking and handling, threshing, drying and storage.
Harvesting can be done manually by sickles or mechanically by threshers or combine harvesters. Most problems in harvesting are attributed to irregular wheat ripening. Early harvesting results in shrinkage of grain and late harvesting may cause shattering of grain in field.
Optimum time for wheat harvesting is physiological maturity, when moisture percentage in grains ranges from 20 to 40 per cent. However, moisture percentage is not a good predictor of physiological maturity as it varies with varieties and environments.
There are many visual indicators that predict maturity of the crop. Loss of green colour from the peduncle, kernel and glumes is an important sign of maturity of the grain. Generally, the glumes at the bottom of the spike are the last to lose its green colour that is easily observed across the field. At this stage grain moisture is around 16-17 per cent.
Grain that shatters before and during harvest yields no return and may cause additional expense as a volunteer crop, but in case of semi-dwarf improved varieties harvesting should be done two to three days earlier. Harvest of the crop should be started as soon as the crop has field dried and can be handled safely.
Modern and traditional methods of wheat harvest technology often depend upon the scale of production. Self-propelled mechanical threshers may be found in use all over the country. However, reaping by hand-pulling of plants or cycling, stooking, shocking and stacking of straw followed by threshing, upon need of grain for food or sales, by stationary mechanical threshers or on oxen-trodden mud-packed threshing floors is common in many small-scale farming situations. On-farm storage of grain is common for smaller scale farmers, whereas direct sales to cooperative, government or private elevators are the norm for larger producers.
Harvesting by combine is mostly used for early harvest, provided the crop can be dried safely. Adjustments in combine cylinder or speed of fan in the field improve threshing and cleaning. Lower cylinder speeds reduce damage of kernel. Increased fan speed cleans wet chaff more easily, but more grain can be blown out.
Another harvest technique is to cut wheat with a swather and allowed to field dry in the swath (or windrow) until it can be threshed with a combine. This technique requires specialised equipment usually a swather and pickup device.
Several types of weeds, such as common lambs quarters and rag weeds, can interfere with wheat harvest. With wheat nearing maturity, some producers may want to consider applying a pre-harvest herbicide treatment to control weeds that could make harvesting operations difficult. Only a few herbicides are cleared as harvest aids for wheat, including clarity, glyphosate, and some formulations of 2, 4-D.
In all situations, grain must be harvested timely, before shattering, pre-harvest sprouting, bird damage or weathering, to minimise pre-harvest losses and it must be dry enough for storage. During threshing, cracking and breaking of the grain should be avoided since damaged grain invites greater damage from storage moulds and insects, and reduces marketability.
Drying: After harvesting, grain should be dried to a certain moisture level for safe storage. The procedure depends upon the grain moisture contents and method applied for drying. For high-moisture wheat i.e. greater than 15 per cent moisture can be dried with both high-speed and bin drying equipment. Wheat has a higher resistance to airflow than other cereals. For commercial wheat, drying air temperatures should be below 140ðF to avoid damage to milling quality. Seed wheat should be dried at 110ðF or lower.
High temperature batch or continuous flow dryers usually have adequate airflow capacity for drying wheat. These units typically have high airflow rates, so supplemental heat may not be required for daytime drying when harvesting in the moisture range of 18 per cent to 20 per cent.
Heat is required when drying high moisture wheat during periods of high humidity (above 70 per cent at night or during cloudy days).
Storage: Freshly harvested wheat should be dried to a moisture content 8-10 per cent for storage or 13.5 per cent for immediate sale. Sanitation, aeration, and monitoring are the watchwords to remember when storing grain during the summer months.
Totally remove the old crop before placing newly harvested wheat into a bin. Thoroughly sweep the bin wall and floor to remove grain kernels that may contain insect larvae or mold spores. Apply an approved insecticide both inside and outside the bin to delay insect population development before placing wheat in the bin.
Aeration should be used to cool wheat after drying with heated air. To a small degree, aeration will control grain temperature if it starts heating during storage, but this may only be a short-term solution. If heating cannot be controlled by running the fan, the crop must be moved to another bin, if possible to break up hot spots in the bin that usually cause the problem. Check the condition of stored wheat once a week during hot weather to guard against deterioration from molds or insects. Run the fan for a few minutes to check for off odour of the air from the grain pile.
Unfortunately, many resource-poor farmers use grain storage structures that are inadequate to protect grain from rain or dampness and rodent or insect infestation. Recently, appropriate storage structure technology, through support from the Food and Agriculture Organization of the United Nations (FAO), has been introduced.
These airtight grain stores are made from clay and straw, are simple in construction, are low cost and have the potential to reduce significantly post-harvest grain losses.
For damage to stored grain due to rodent infestation, prevention is better than a cure. Contrary to damage caused by insects or fungi, rodents can infest stored grain regardless of temperature or humidity, the only requirement being access to the grain store. Storage structures should be built with rodent-proof air vents, roofs and door jams. In addition, surrounding areas should not be considered general storage areas and should be kept clean from debris. Use proper fumigants and rodenticides if necessary.
Maximum grain yield and to minimise damage and quality deterioration is only possible by good harvest. These losses can not be easily reduced in the absence of well-integrated policies and plans to develop the total system of production, marketing, storage and distribution.
http://www.dawn.com/2007/03/19/ebr4.htm
