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Organisation: Pakistan Agricultural Research Council (PARC)
Author: Umar K. Baloch
Edited by AGSI/FAO: Danilo Mejia (Technical), Beverly Lewis (Language&Style), Carolin Bothe (HTML transfer)

CHAPTER VI WHEAT: Post-harvest Operations


3.1 Wheat loss factors

3.2 Public sector storage loss

3.3 Farm storage loss


3. Overall losses

Depending on level of the self-sufficiency of the country the marketable surplus of food grain varies by factors comprising farm and family size, productivity and other parameters. In Pakistan, it is generally estimated that approximately 65 to 75 percentage of total wheat produced is stored at the farm. Smaller farms generally keep more grain for consumption. It is estimated that the quantity of wheat entering commercial channels from farms up to maximum 4.5 ha in size is negligible. Nationally, the 4.5 ha farm is worked by about 65 percentage of the farmers, who occupy 35 percentage of the cultivated land.

The major food grains are usually stored at the farm in specially constructed mud bins, protected by a cover, inside the house or in the open courtyard. Wheat may also be stored as a heap covered by straw, mud and dung plastered, loose in a room, or in bags, metal bins, baskets and pots. These widely contrasting storage practices may explain the range of storage loss in Asian countries.

The global emphasis on increased food production has been on the development of modern technologies relevant to the pre-harvest activities. The emphasis on achieving a significant reduction in post production food loss gained momentum from the World Food Conference in 1974 and the resolution passed at the 7th special session of the United Nations General Assembly in 1975.

Reports by a FAO Food Security Mission in 1980 and a World Bank Grain Storage Project Mission in 1981 in Pakistan, drew attention to the potential seriousness of farm storage loss, particularly for wheat. It was noted that considerable loss caused by insects, and to a lesser extent by rodents and fungi, occurs when grain is stored for three months or longer. Relatively low levels of insect damage may result in the rejection of a large amount of potential food material at the cleaning/food preparation stage. FAO, therefore, has been instrumental in developing action plans to reduce loss in grain after harvest through loss assessment, technology transfer and development of expertise via information dissemination.

3.1 Wheat loss factors

Loss is defined as a measurable decrease of the food quantity and quality. Loss should not be confused with superficial damage generally due to deterioration. Quantitative loss is physical and can be measured in weight or volume, while qualitative loss can only be assessed. Quantitative loss, qualitative loss, nutritional loss, seed viability loss and commercial loss may gauge this reduction.

The major biotic factors influencing wheat loss during storage are insects, moulds, birds and rats. The major insect species known to infect wheat include Khapra beetle, Trogoderma granarium Everts; Lesser grain borer, Rhizopertha dominica (F); Rice Weevil, Stitophilus oryzae (L.) and Red flour beetle, Tribolium castaneum (Hbst). All these insects may be found extensively in most developing countries to different extremes. Other insect species are recognised storage pests that also infest stored wheat like Angoumois grain moth, Sitotroga cerealella (Oliv.); Rice moth, Corcyra cephalonica Straint; Saw toothed grain beetle Oryzaephilus surinamensis (L.); Long headed flour beetle Latheticus oryzae Wat.; Flat grain beetle Cryptolestes pusillus (Schoen).

Biotic factors including temperature, humidity and type of storage all affect environmental conditions in storage. High temperature causes deterioration, while low temperature is good for storage. High temperature accelerates 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 bio-chemical changes and mould attack are minimal, but the risk of insect infestation increases. Sun drying or turning of food grain has many advantages as it provides an opportunity for inspection and precautionary measures to avoid spoilage. Aeration greatly minimises mould growth, insect activity, and respiration of the seed. Further aeration provides a cooling action and equalises the temperature throughout the mass of the grain stored. Bad odours developed by stored grains can be easily and effectively removed.

Climate conditions, grain conditions at storage (presence of infestation, moisture content, foreign matter content), the period of storage, grain and pest control practices all contribute to the rate of loss caused by insects and mould growth. As these factors interact, it is difficult to isolate them or identify one factor, which has a direct influence on loss. Average statistics for loss, whether for store types, areas, or quantities of grain stored are inconclusive. An average figure for loss for a region or a country holds no significance unless a decision regarding a new system of storage, or new pest control techniques is required. Nevertheless average loss figures are always sought. The loss figures consist of the following:

-The weight loss which occurred during storage = The difference between the condition of grain at the end of the storage period, compared to the condition at initial storage

-The weight loss, which happened before the grain was stored (Note: some of the grain under study had been stored elsewhere for an unspecified time).

3.2 Public sector storage loss

A preliminary review of public sector storage facilities in Pakistan by the author during 1984-85 confirmed the widely held view that loss due to insect infestation, mould growth and the activities of birds and rodents were often serious. The review also concluded that insect pests are most important. The survey of storage loss during 1984-85, therefore, focussed upon the measurement of weight loss caused by insects and mould growth (Table 5)

Table 5: Estimates of Storage Loss in various Provinces of Pakistan

       

Province

Average Storage
Period (months)

Loss percentage

Total

   

Insect

Moulds

 
   

Pre-storage

Storage

   
           

Sindh

6.4

0.1

2.9

0.3

3.3

Punjab

6.3

0.1

1.8

0.3

2.2

NWFP

6.5

2.9

2.6

0.7

6.2

Baluchistan

2.6

0.5

1.2

0.5

2.2

Pakistan

5.4

0.9

2.1

0.4

3.5

Source: Baloch, U. K. et. al . 1994, Loss Assessment and Loss Prevention in Wheat Storage ... in Pakistan.

in Stored Product Protection ed. Ed Highley, CAB. International. Pp 906-10

Loss due to insect infestation occurs in all regions, but is higher in grain stored at Karachi in Sindh and in Peshawar in NWFP. The higher loss at Karachi may be caused by generally favourable temperature and relative humidity, which are also conducive for insect growth combined with the difficulties in fumigating such large sheds. When the additional loss is taken into account from Peshawar (NWFP), the average loss due to insect pests during storage in two-year-old wheat was 8.9 percentage, with loss in individual cases as high as 15 percentage.

Mould damage is not a serious problem in countries like Pakistan, where wheat stored at procurement is usually dry at 10 percentage moisture content or less. During the rainy season the moisture content of stored grain may rise, but the average moisture content is rarely above 13.3 percentage. The loss figure due to mould measures the amount of grain, damaged so badly that it was regarded unfit for human consumption. Mould damage in tropical or humid countries is indicative of defects in storage structures and moisture migration due to insect activities.

Grain stored in the open covered with tarpaulin sheets, is always at risk and such stocks of grain suffer heavily. Some stacks of grain inside the shed are also damaged by mould because of rainwater. Occasionally rain enters through open or broken windows or through doors opened to allow ventilation and not closed in time. Wheat stored in bins is susceptible to localised mould damage, particularly in the surface layers. This results from condensation on the inner side of the metal manhole covering the top of the bin. Moisture migration following the activity of insects is common in bulk stored grain, but it is also noted in bag stacks.

3.3 Farm storage loss

A 1983 review by the author in Pakistan confirmed a broad variability in the reported estimates for wheat loss at the farm level and the need for quantitative data to base a loss reduction program. Following this was a preliminary survey, which provided an excellent record and understanding of the operation of post-harvest activities at the farm and village level. It also clearly demonstrated that farmers are concerned about the loss of grain occurring during long-term storage. While there was a need to establish reliable estimates of storage loss, there was already evidence to suggest that certain farm households were losing considerable quantities of grain to insects. The survey drew attention to the urgent need to formulate a suitable extension package on good storage management directed to both men and women.

Loss assessment surveys were conducted to determine the harvest loss from shattering of grain, loss of panicles and other effects, threshing loss and the amount of grain lost to rodents in the period between harvesting and storage. Based on the total quantity of wheat harvested, 0.35 percentage was lost during harvesting, 1.24 percentage was lost during threshing and 0.15 percentage was lost during temporary storage. Losses during harvesting are related to the degree of maturity of the crop at harvest and to delays in harvesting. Such losses are difficult to reduce. Although this represents a private loss to the owner, some of this grain will be recovered by those permitted to pick wheatears in the harvested field. Losses during threshing are operations-related and may be eliminated with a better adjustment of the thresher to limit the amount of grain lost with the straw.

3.3.1 Loss assessment survey

A socio-economic survey in Pakistan in 1984-85 confirmed that insect infestation was the most significant cause of loss in storage. Approximately 55 percentage of the households sampled regarded this as a major problem, while 15 percentage responded that it was a minor problem. There was inconsistent information provided when data from the farmers about perceived loss was compared with that provided by women. According to women respondents, the perceived storage loss due to insects in rain-fed and irrigated areas are about 4.0 percentage and 3.6 percentage, respectively, similar to the results obtained in the loss assessment survey. However, the actual food loss is likely to be far greater, since more than 80 percentage of the respondents admitted to discarding damaged grain. Of this group, approximately 30 percentage stated that the grain would be destroyed while others questioned would use the grain for animal feed.

The perception of losses by those directly concerned with storage management is a useful indicator to assess motivation for adopting new techniques for loss reduction. The results of the survey indicated that motivation is high. Most of the respondents felt that there was a need for additional advice on better pest control methods. Few suggestions were made for new types of storage containers; those who did referred to metal or concrete bins. Financial constraints limit the adoption of new storage structures.

While the traditional storage systems restrain loss to a low level, the introduction of new varieties of grains has placed an extra burden on those responsible for grain conservation, specifically the women members of the community.

3.3.2 Loss assessment studies

In Pakistan, wheat is commonly stored in jute bags, bharolas (containers of mud, plaster and straw), kothis (rectangular grain stores of mud, cow dung and straw) and open rooms. In the rain fed area, 90 percentage of farmers use jute bags, whereas, in the irrigated area, 42 percentage use jute bags and 44 percentage use mud bins. A small number of farmers in both areas use metal bins. The losses in the different storage types range from 0.1 percentage to over 10 percentage. Such wide variations are not unexpected, as the extent of loss will depend upon the quantity stored, the storage period, the consumption pattern, the condition of the grain at storage and the pest control methods used. The levels of insect infestation and of damaged grain were highest in jute bags. The average weight loss recorded in the different storage facilities is given in Tables 6 and 7.

Table: 6 Average weight loss (%) in different types of stores

Type of storage

Rain fed area

Irrigated area

     

Jute bag

3.1

6.6

Mud bin

2.3

6.1

Open Room

2.2

5.5

Metal bin

2.1

2.0

Source:Baloch, U. K. et. al . 1994, Loss Assessment and Loss Prevention

in Wheat Storage ... in Pakistan. In Stored Product Protection ed.

Ed Highley, CAB. International. Pp 906-10

Table: 7 Storage containers used by farmers (%)

     

Storage Container

1984-85

1985-86

 

Irrigated

Rain fed

Irrigated

Rain fed

         

1. Sacks

43.04

90.00

32.50

78.83

2. Metal Bin/Box*

3.37

4.59

4.08

13.75

3. Bharola/Mud bin

27.00

2.92

28.75

2.00

4. Other Storage

26.59

-

32.25

4.59

Source:Baloch, U. K. et. al . 1994, Loss Assessment and Loss Prevention in Wheat Storage ... in Pakistan. in Stored Product Protection ed. Ed Highley, CAB. International. Pp 906-10

*As a result of the project activities the trends of adoption of improved storage techniques (metal bin) in rain fed areas have increased as compared to irrigated area during 1985-86.

In India the Pansay Committee estimated post harvest loss at 9.3 percentage, of which an estimated 6.6 percentage was attributed to storage loss The breakdown of storage loss for food grains was 2.55 percentage for insects, 2.50 percentages for rodents, 0.85 percentage for birds and 0.68 percentage for moisture. The Administrative Staff College of India (ASCI) Hyderabad in August 1976 calculated the following storage loss estimates (Table 8).

Table: 8 Estimated Storage Loss (%) of Food-grains

Cause

Farm level

Trade

Public Agencies

     

Sheds

Silos

Insects

3.4

3.4

0.5-1.0

0.5

Rodents

0.5-1.0

0.3-1.0

Neg.

Nil

Birds

Neg.

0.2

0.2

Nil

Moisture

Neg.

0.2

0.2

0.2

Others

-

0.3

0.3

Neg.

Total

5

6

1.3-1.7

0.7

Source:Sawhney, K. L. 1988. Post Harvest Handling and Storage of Food Grain in India. Workshop on Bulk Storage of Food Grains. FAO. Hanzhu, China.

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