Corn Production: Harvesting and Post Harvesting Operation
Right Time to Harvest
Timeliness is the most important consideration in harvesting corn. It may begin as soon as the corn plant is physiologically mature, which occurs when the grains contain approximately 30-40% moisture, depending on the variety used.
Large grain losses occur when corn is harvested below 18-20% moisture. Also, improper corn harvesting is one of the major contributory factors that affects corn quality.
When corn is harvested at the right stage, there is less lodging from stalk rot, less dropping of ear, better quality of grains and greater resistance to mechanical injury during shelling.
Indices of Maturity
There are several ways to determine the exact maturity of corn. One is through visual observation of the leaves, husks, ears and kernels. Corn is mature when the leaves and husks are dry and the kernels are nearly glazed.
However, the best sign of corn maturity is the existence of a black layer at the base of the kernel. To examine this, you have to remove the husks of the ears then remove the kernels from the cobs.
The black layer is an evidence that there is no more food movement from the mother plant to the kernel and, therefore, no increase in kernel weight.
Methods of Harvesting
Mature corn can be harvested by:
Manual method. Harvest corn either by cutting the stalk at the base and hand picking the ears or by picking the ears on standing plants. This method is applicable for small-scale corn production.
Mechanical method. Harvest corn with a mechanical corn harvester. This method is feasible for large-scale commercial corn production.
Post Harvest Operations
Shelling
Shelling is the process of separating the kernels from the cob. It is best done when the moisture content is 18-20%. In this range, the kernels are already hard and tough to resist damage or injury during shelling.
Shell corn either manually or by using mechanical shellers. Mechanical shellers are usually used for high-yielding varieties to reduce losses. This type of shellers is practical to use for corn farms 4 ha or more.
Drying
Drying is the most critical postproduction operation. The moisture content of harvested corn grains is still high. The excess moisture must be removed quickly before grain deterioration sets in. Drying is an effective method of preserving grain quality.
Ideally, corn grains must be dried down to 14% moisture content to maintain grain quality. Corn drying is done in two operations, regardless of the drying method used. These are drying the cobs with or without husks and drying the shelled grain.
Determining Moisture Content
Determine moisture content of corn grains a moisture meter.
In the absence of a moisture meter, use the formula below:
MC = FW - DW x 100 where:
MC is the percent moisture content FW is the weight just after harvest DW is the weight after drying
Drying Methods
Field drying
Extend the harvesting schedule beyond the maturity date to allow the corn ears to dry in the field. The moisture content is reduced to about 25%.
This practice is common in areas where wet and dry seasons are distinct. Schedule planting such that harvesting will fall on the dry months.
Conventional sun drying
This is the most common method of drying corn ears and shelled corn grains. It is considered cheap and practical for small-scale production.
Dry dehusked corn ears, as well as shelled corn, by spreading them evenly and thinly on concrete floors, plastic or canvass sheets, mats, etc.
This method takes 1-3 days to dry the ears or grains, depending on the initial moisture content and weather conditions.
The acceptable moisture content is 18-20% for the husked corn ears while shelled corn are dried down to about 14%.
Halayhay method
Bundle and hang corn ears, with their husks opened to expose the kernels, on bamboo poles. This method is commonly used for drying grains for seed purposes.
Drying by natural ventilation
This method is commonly used in areas of higher elevation. Construct holding structures called corn cribs and allow corn ears to dry by natural ventilation while in storage.
The rate and uniformity of drying the corn ears in the crib depend on the moisture content, relative humidity and wind velocity in the area.
Drying usually takes a longer period. Grain deterioration, sprouting and molding may occur even before drying is completed.
Artificial or mechanical drying
The uncertainty of weather conditions, coupled with increased production volume, make the sun drying method ineffective especially during the wet season. Use artificial or mechanical dryers as better alternatives. These are more flexible, reliable and allow faster drying.
An artificial dryer makes use of heated forced air for quick drying of corn grains. Basically, it consists of a holding bin. blower, burner and air ducts. Auxiliary equipment, such as elevators and conveyors, are also used for high-capacity units.
Storage
Storage is a vital component in corn postproduction operations. It is necessary to provide sufficient and continuous supply of the commodity even during off-seasons.
Corn can be stored as:
Unhusked ears
Corn in cobs
Shelled corn
Types of Corn Storage
Corn crib
This structure is used for storing corn ears. Small corn cribs may be used without a blower. A big corn crib is usually provided with a blower to dry corn ears high in moisture content. Big corn cribs when idle may also double as farm machine storage.
Jute sacks and bags
Pack shelled corn grains in jute sacks or bags, with a standard weight of 50 kg per bag. Pile the sacks one on top of the other inside a warehouse in such a manner that allows ample air movement between individual sacks and between rows. Provide spaces between piles for easy access.
Bulk storage
For large commercial set-up, use steel bins or concrete silos in storing corn grains. Bulk storage systems are usually provided with elevators, conveyors, aeration and fumigation facilities.
Moisture Limits for Safe Storage
14% or less for shelled corn
15-16% for crib storage (reasonably safe for bin storage)
17-21% for ordinary crib storage
22-24% for ordinary crib storage, but only when ventilation is provided