Minimising harvesting, post-harvest losses

TRADITIONALLY, April 1 marks the start of the marketing season. Farmers are, therefore, expected to start harvesting their crops and preparing them for sale. It is also a month away from the start of the winter wheat planting season.

Farmers are, therefore, faced with the harvesting and selling of their crops.

However, as this process takes place, farmers experience pre-harvest, harvest and post-harvest losses, which will need to be minimised at all costs.

Pre-harvest losses occur before the process of harvesting begins, and is mainly due to pests and weeds.

This year, there were outbreaks of the fall armyworm and the incidences of maize stalk borer were more prevalent.

If not controlled, these pests will continue to attack mature maize cobs, resulting in severe grain losses. Most pre-harvest losses have already been incurred at this stage of the crop.

Harvest losses occur between the beginning and completion of harvesting, and are caused by a number of factors that include the method of harvesting, the condition of the crop at harvesting and how the harvested crop is managed between the field and the storage or marketing point.

Most farmers with big hectarages to harvest normally resort to the use of combine harvesters.

The Agriculture, Mechanisation and Irrigation Development Ministry recently estimated that 195 combine harvesters will be needed for this year’s Command Agriculture maize crop.

However, the challenge is that only a few of these combine harvesters are in working order.

Government and owners of the equipment should start working on repairs to avoid compromising the harvest.

Combine harvesting works well where the crop is still standing and can be picked by the combine harvester.

A maize or soya bean crop that has fallen to the ground will be difficult to harvest using a combine harvester.

A substantial part of the crop is likely to be missed by the combine heads and farmers will normally have to put workers to pick whatever the combine would have missed.

Therefore, whilst the use of a combine harvester will quicken harvesting, care should be taken to ensure a substantial crop is not left in the field.

Farmers with small areas to harvest normally resort to hand harvesting.

Workers remove the cobs from the standing stalks using 50kg bags, and once a bag has been filled, they drop it to the ground for a tractor driver and assistant who will be following with a trailer to pick and take to storage.

This method minimises chances of leaving some maize behind.

Some soya bean farmers use sickles to cut the soya beans stalks and then take the crop to a hard surface for thrashing and winnowing. However, there is always the danger that the beans might shutter and scatter the seed on the land as it is being cut. It is important, therefore, that farmers who decide to use this method do so very early in the morning whilst the pods are still a bit moist from the morning dew and, therefore, unlikely to shatter easily.

The dryness of the crop will determine how much a crop shatters or shells whilst being harvested.

Farmers are, therefore, urged to continue monitoring their crops prior to harvesting so that they do not over dry whilst still in the land.

An over dry soya bean crop will shatter easily whilst an over dry maize crop will easily shell grain with minimum handling.

Post-harvest losses, on the other hand, occur between harvesting and the moment of sale or human consumption.

They include on-farm losses such as when grain is threshed, winnowed and dried, as well as losses along the chain during transportation, storage and processing.

It is estimated that in Africa, post-harvest losses from the time harvesting starts to the marketing stage amount to 10-20 percent.

Another 40 percent of these losses occur during storage at the farm whilst 30 percent occur during processing that includes drying, threshing, and winnowing.

About 20 percent is lost in transportation from the field to the homestead, and the remaining 10 percent occurs during transportation to market.

Most farmers prefer to store harvested maize cobs in driers that are located near their homesteads as a way of reducing further damage if the crop had been kept on the land.

They also do this in order to minimise theft of the crop by neighbours or in the case of farmers, from their own workers.

Theft by humans constitutes major post-harvest losses for many farmers.

The best that farmers can do is to increase their security as well as the storage structures so that outsiders find it difficult to access the crop.

There is also potential for grain loss during shelling.

Some shellers can damage the grain, making it easier for insects to penetrate that grain once it is stored.

Post-harvest losses can also occur when mechanical shelling is not followed up by hand stripping of the grains that would have been missed, especially at the maize tips.

For crops like soya beans, threshing losses occur because of spillage, incomplete removal of the grain or by damage to grain during the threshing.

They can also occur after threshing due to poor separation of grain from the chuff during cleaning or winnowing.

Incomplete threshing usually occurs where hired labour is used and, therefore, farmers should inspect the chuff to ensure the threshing was done well.

Some farmers prefer to bag their crops before sending them to the market, whilst others prefer to combine harvest whilst lorries are on standby to take the produce straight to market.

Those who prefer to bag, the justification is that they would want to clean the crop of chuff and remove rotten grain before sending it to the market.

However, it is also true that all this extra handling will result in further grain losses as well as thieving by workers.

It is also important to note that there are companies that can receive the maize or soya beans straight to their storage facilities where they can further clean the crops.

These companies can also further dry a crop like maize so that it reaches the desired 13 percent moisture content that the Grain Marketing Board requires before accepting a delivery.

This is especially critical to those farmers intending to grow wheat on lands that currently have maize crops and they happen to have grown long season varieties like SC 727 or SC 719.

These varieties take up to 156 days to reach physiological maturity.

At that stage, the crop will still have 30 percent moisture content.

The challenge then will be how to reduce the moisture content from that 30 percent to the desired 13 percent.

Natural drying is said to reduce the moisture at a rate of approximately 2 percent per week and, therefore, a further 10 percent moisture is likely to be lost in a month whilst the crop continues to be in the land.

After that, it makes sense to put the maize, hopefully now at 20 percent, through a drier and get it to 13 percent.

Post-harvest losses also occur during transportation of grain from the farm to the market.

Quite often lorries laden with maize or soya beans scatter grain on the roadside as the grain is moved to silos in towns. Farmers should, therefore, make sure they have sealed truck sides with sacks to minimise such losses.

As the lorries travel, the materials used to seal the sides might move with the shaking of the truck, hence, drivers should make regular checks along the way.

For those farmers who wish to keep their grain for use until the next season, it is important that the grain be protected against weevils and rodents.

Several grain protectants are available on the market; however, I should hasten to say, phosphide tablets are poisonous and should not be applied to a crop that is stored where humans will inhale the fumes from the fumigant.

Separate measures will need to be put in place to control rodents.

Grain that is stored in moist places is likely to rot and develop aflatoxin, which can be poisonous to human beings.

Farmers should, therefore, make sure their grain storage facilities are dry at all times by letting enough air circulate in the facilities.

Livestock should not be fed rotten grain as aflatoxin can be poisonous to it as well.

As farmers embark on their harvesting, transportation and selling grain, care should be taken to reduce grain losses as much as possible by paying attention to the many factors that contribute to those losses. Mr Peter Gambara is an agricultural economist/consultant based in Harare. He wrote this article for The Sunday Mail.