NationalVOLUME 19 ISSUE # 32

How to cut post-harvest losses!

Agriculturists point out post-harvest wheat losses almost every year, and stress methods and techniques to minimise the losses. According to Food and Agriculture Organisation (FAO) estimates, about 25 million tonnes of wheat is lost during post-harvest stages, including storage and post-production, across the globe every year. About 46 percent of this loss is recorded in developing countries.
Various scientific studies indicate that post-harvest losses of major food commodities in developing countries are enormous. A study, conducted by the FAO some years back, reported food grain storage losses to the tune of 30% in South East Asia, 25-55% in South American countries, 8-25% in India. Even in the USA, 5% losses are on record.
In Pakistan, losses occur during harvesting, threshing, cleaning, drying, milling, storage, processing, cooking and consumption. The aggregate losses during various post-harvest operations in Pakistan are 17.1% in paddy, 15.3% in wheat, and 12.6% in maize. Post-harvest losses of wheat estimated by Indian workers are to the tune of 9.33%.
Some studies based on empirical evidence, carried out by the Department of Agriculture Entomology, University of Agriculture Faisalabad (UAF), showed 7.37% post-harvest losses of wheat, but it was on experimental scale only. The WFP reported approximately 12.5% of wheat is wasted on the way from the field to the consumer. Most Pakistani scientists strongly believe that 10% post-harvest losses of wheat are not at all uncommon in our country.
According to the official data, wheat is grown on about 37% of the cropped area and accounts for 76% of the total food grain production. It contributes 13.8% to the value-added in agriculture and 3.2% to the GDP.
Agriculturists say the post-harvest losses are estimated to be about 25% in Pakistan, which are very high compared with even neighbouring countries. The estimates put the total preventable post-harvest losses of food grains at about 20 million tonnes a year, which is nearly 10% of the total production. Food security experts believe food grains wasted during the post-harvest period could feed 17 million people for a year.
It must be a point of special concern for the authorities that over 60% of the crop is still harvested manually in Pakistan, using sickles or with types of knives leaving 3-6cm wheat straw above the ground level. The timing of the harvest is the most critical decision. If it starts late, the grain becomes too dry and the rate of grain shattering is high. The longer a ripe crop is left in the field or on the threshing floor, the higher will be the losses from natural calamities including hailstorm, fire, birds, or rodents. The moisture content of the grain will be high, making drying difficult if the harvest starts too early.
Wheat is harvested from March to May in Pakistan. The manually harvested wheat crop is tied into small bundles and stacked in 10-15 bundles, left in the field for one to three days to dry. Combine or mechanical harvesters yield a higher proportion of immature grains and pose a moisture hazard, leaving no time for the grain to dry.
However, around 60-80% of threshing is mechanical now. Tractor-driven threshers and at times combine harvesters are used. The design and maintenance of the thresher are central to reducing the broken grain percentage. Threshing by using animals is also common in many areas. Several animals continuously walk around a pole to crush the wheat straw and heads to separate the grains and convert the straw to husk.
Post-harvest handling, transportation and storage of grains also cause losses. Bags are used for transportation and problems arise when old torn bags are used which spill grains, causing losses. Other hazards are hooks which tear the bags, the rough surface of carts and trolleys and nails. The major factors influencing wheat losses during storage are insects, moulds, birds and rats. Biotic factors including temperature, humidity and type of storage all affect environmental conditions in storage. High temperatures cause deterioration, while low temperatures are good for storage.
Scientists say high temperatures accelerate the respiration of grain, which produces carbon dioxide, heat and water, conditions favourable for spoilage. Humidity equally impacts grain storage. Increasing humidity increases spoilage, while decreasing humidity is good for storage. The type of storage plays a fundamental role in storage efficiency. If a concrete or mud storage structure can absorb water or allow the water vapours to pass through, in the case of a jute bag, the biochemical changes and mould attack are minimal, but the risk of insect infestation increases.
It is necessary that the food departments of all provinces take special measures every year to minimise post-harvest losses of wheat grain. Farmers and people involved in the crop procurement process must be educated about the methods and scientific techniques to cut the post-harvest losses.