Organisation:Food and Agriculture Organization of the United Nations (FAO), AGST
Author: Danilo Mejía, PhD, AGST.
Edited by AGST/FAO: Danilo Mejía, PhD, FAO (Technical), Emanuela Parrucci (HTML transfer)

CHAPTER XXIII MAIZE: Post-Harvest Operation

3. Maize Overall Losses
3.1. Definitions of terms
3.2. Level of loss during maize post-harvest system

3. Maize Overall Losses.

Notwithstanding losses is a concept which is difficult to define it, however quantitative losses eventually give a broad picture of where the losses were occurring and their relative scale, and how a specific crop is handled during the post harvest operations. So that, some assessment have been done in order to determine total post-harvest losses for maize. For example, losses are estimated based on post-harvest losses of each stage and assuming that each loss found is a percent age of the amount remaining from the previous stage. Otherwise, if losses are determined on the basis of the original weight of the crop, it can lead to an overestimation of losses.

On the other hand, there are others losses which are difficult to determine and these losses consider include: time, manual labour, agricultural inputs, opportunity cost, illusions and hopes. For these reasons many post harvest specialist agree that the post harvest losses measure concept has changed. However and for practical reasons, still exist some methodologies which give up an idea about the main quantitative and qualitative losses occurring during the postproduction system.

3.1. Definitions of terms.

3.1.1. Loss: in this context denote a measurable decrease of food grain which may be quantitative, qualitative, nutritive or economic.

3.1.2. Damage: It mean superficial evidence of deterioration (e.g. holed grain by insects pest, broken grains.

Quantitative loss: denote reduction in weight and can be defined, quantified and valued, For instances, a portion of grain eaten by insects, rodents, or lost during spillage or transportation

· Qualitative loss: damage or contamination of the grain. It is difficult to assess or quantify because is a subjective criteria, but can be described by comparison with quality standards

· Nutritional loss: reduction of the food value of the crop. It can be qualitative and quantitative loss and is also difficult to identify

· Germinative loss: represent a reduction in germination ability. Methods of laboratory exists to measure the degree of viability of a sample of seeds

· Economic loss: reduction in monetary value of the product due a reduction in quality and quantity. Since quality loss is difficult to quantify it is also difficult to quantify economic loss.

3.1.3. factors and causes of grain loss.

The maize post harvest system or pipeline in figure 38, shows several stages at which losses of food can occur. So the main agents or factors responsible for the losses can be grouped as:

3.1.3.1. Physical factors

· Temperature

· Moisture

3.1.3.2. Biological factors

· Produce properties or characteristics

· Insects and mites

· Birds, rodents and other wildlife

· Microorganism: fungi, moulds and bacteria

· Man

3.1.3.3 Mechanical factors

· Type and efficiency of on-farm transport

· Speed and ground conditions of use

3.1.3.4. Engineering factors

· Type and efficiency of harvesting tools, equipment and machines

· Primary processing equipment and machines

· Drying and storage structures

3.1.3.5. Socio-economic factors

· Financial status of the farm household

· Farming system and level

· Storage and marketing system and level

Fig. 38. The post-harvest pipeline for maize.
(AGROTEC/UNDP/OPS, 1991)

3.2. Level of loss during maize post-harvest system.

3.2.1. Field drying and harvesting.

The magnitude of losses at this segment is very likely the highest in the entire post harvest system for maize, and it influenced by:

· The time of harvesting which affects subsequent the storage quality of the grain

· Genetic characteristics of the varieties of maize. Generally traditional varieties are better adapted

· Weather conditions wetting condition from rain and hot sun in the day may result in lodging, sprouting, moulding, decolouration and fissure, and loss of quality and viability, etc.

· Harvesting practices, especially referred to by hand, machine and when

· Long field exposure of the crop may result in heavy infestation by insects pests and damage by rodents, monkey, baboons, bush pigs, elephants, hippos, etc

The effects above indicated occurs normally to the storage phase as the crop is made more vulnerable to infestations in storage by pests. Wildlife is more common in tropical areas and the savanna belts and less in drier areas. The magnitude of losses in traditional methods of field drying and harvesting varies greatly from country to country. It could be as less as 5 percent for relatively drier areas, to 50 percent or more in places heavily infested by baboons, monkeys or wild pigs. Average loss rank from 7 to 12 percent.

3.2.2. Transport.

Losses due to transport of the crop to, within, and off-farm depend on:

· Type of transport facility used

· Efficiency of transport facility

· Quantity of crop transported

· Ground conditions and surface of the terrain, etc.

Transport losses are generally small, ranking 1 to 2 percent.

3.2.3. On-farm drying.

Depend on how much the maize has been dried in the field. The drying methods and climatic conditions during drying are main factors which affects losses.

Traditional drying methods can cause:

The crop is exposed to proliferation of fungi, moulds and bacteria and soil reducing its quality

The crop is also exposed to attacks of domestic animals and birds causing qualitative and quantitative losses. Some time farmers do not consider crop eaten by livestock as loss.

Estimation of losses in traditional drying and storing in a raised barn for up to 4-5 months has been between 7 to 14 percent. Improved drying technique, as the crib, can reduce losses losses mainly due to fungi and insects in approximately 2 percent. Average on-farm drying losses are 3 -6 percent.

3.2.4. Threshing/shelling and cleaning.

Damage from these operations is proportional to the moisture content of the grain and depend of the method used.

Traditional shelling of maize made by hands causes minimum losses

Use of flails to beat the grain off of the cobs can damage the kernel, and the unseparated grain of the cob can be lost with the chaff

Modern equipment not properly used can also cause damage to kernels

Hand shelling: loss average 1 percent

Machine shelling: considering broken kernels and grain lost with chaff into the soil from 2 to 5 percent.

3.2.5. Storage.

Storage losses depend upon the following:

· Physical factors, e.g. damage during harvesting, transportation and shelling. This make maize susceptible to attacks by insect pests, mites and moulds

· Temperature and humidity may encourage mould formation and create conditions for insect population growth. The losses could be: minimal in cool dry areas, marked in hot dry areas, high in cool damp conditions and very high in hot damp climates.

· Type of storage structures or containers used

· Duration of storage

· The storage management effected prior to and during storage.

Some researchers identify that losses of grain stored at the farm level are in the order of 8 to 10 percent. In some studies done in eastern and southern Africa it indicates that when the losses are computed considering the actual amount of crop present in the store, at the time of each assessment (other the initial quantity of crop in the store), then the "weighted storage losses" may be in the order of 3 to 8 percent (average 5-6 percent ) over a storage season.

3.2.6. Marketing.

Before marketing and consumption, maize is subjected to a whole range of loss-agents discussed above as a result of which the following attributes get affected:

· Reduction in Quantity and quality of the crop

· Reduction in nutritive and germinative attributes

· Reduction in commercial and economic value

The following figures 39 gives some indicators of the post-harvest losses in maize at the small-holder level in eastern and southern Africa.

Fig. 39. Indicators of maize post harvest losses by segment at small holder level.
(AGROTEC/UNDP/OPS, 1991)

Organisation:Food and Agriculture Organization of the United Nations (FAO), AGST Author: Danilo Mejía, PhD, AGST. Edited by AGST/FAO: Danilo Mejía, PhD, FAO (Technical), Emanuela Parrucci (HTML transfer)