Loss of rice in either the pre- or post-harvest stages is a national concern and scientists are aware of this. Crop loss during the growing period due to some biotic and abiotic stresses is a pre-harvest loss.The occasional extreme events like flood, flash flood, cyclone, and drought sometimes incur a huge pre-harvest loss to the standing crop. The loss from harvesting to the moment of human consumption is considered as a post-harvest loss. The shattering loss in the field is considered as the post-harvest loss in this write-up. As a whole, these losses are considered as a quantitative loss. There is also substantial qualitative loss during storage in some cases but is not my concern today. My consideration is only the quantitative loss for the sake of this article.
We need 24 million MT (metric tonnes) of rice (clean rice and hereafter rice) just for our consumption purpose. The requirement for the non-consumption purpose (seed and some relevant purposes) is 8.7 million MT. So the total requirement we estimated last year was 32.8 million MT of rice. But we had a total production of 34 Million MT means we have produced 2 million MT extra. We have to produce some 0.34 million tonnes extra rice per year to satisfy extra people every year. And I think we have the ability to produce that amount provided the other requisites go well. So we are self-sufficient in rice. However, this sufficiency is still shaky as we have to encounter a lot of climatic adversaries like flash flood and pest insurgency like this year at least in some areas of the country. That might cost a huge amount of rice. This is pre-harvest loss used to occur occasionally and a matter of grave concern to everybody from media to mass. In contrast, the post-harvest loss – a kind of loss mentioned above is an under-reported issue occurring from field to farm in every step of the processing and storing of rice crop, every day. The amount is 14 per cent equivalent to an amount of 4-5 million MT presumably, several folds higher than the loss suspected due to flash flood. But nobody cares about this loss.
Scientists belief that the significant amount huge loss could be avoidable to some extent only by awareness build up in every step of activities like harvesting, stacking, carrying, threshing, drying, storing, parboiling, drying again, milling, cleaning, cooking etc.
Out of all these activities storing is a long term process. So there is an enough opportunity to save a lot during the storage of rice. According to BRRI scientists, the conditionalities for proper storing are
* Rice should be dried up to a certain level (Moisture content <12 per cent)
* The container must be airtight.
Rice can be stored for properly provided the grain moisture is reduced to 12 per cent. But the grain moisture ≤9.0 per cent for long-term storage under the ordinary condition is not good for seed as the viability gets down. But the quality of food is not deteriorated. In contrast, moisture beyond 12 per cent might invite pests. The moisture is a critical issue for grain storage and depends on the air moisture. Because most of the farmers are habituated to store their seed in gunny bags or in the container where airtight is not ensured. Thus the quality of seeds sometimes not ensured too.
The seed and the rice for the most of the family consumption in the rural area are coming from their own stocks. But the process of storing of seed paddy and rice to be used for family consumption is different. Seed must be viable to produce at least 80 per cent germination and must not be damaged by insects. Rice exclusively for consumption purpose, viability is not a factor. But the factor is rice must not be stinky or damaged by stored grain pest. The quality and quantity must be more or less intact. The grain loss during storage is done by various agents like fungus, mites, insects, rats, and birds even by man (thief). The abiotic environment of the storage structure is important. Rice is generally stored in the big earthen pot (MoTka, Kola), gunny bag, polythene bag, barrel, plastic drum, tin container, bamboo structure, gola,, beri etc. in the rural areas. But the large amount rice is stored in the huge structure like warehouse, silo etc. The quality of rice is dependent on the temperature, thermal property of rice and moisture content of rice and the environment. So intensive care is needed to protect the stored rice from various kinds of stored grain pests. The stored pests are born and brought up within stored grain. These insects are voracious eater. They could eat the amount more than their body weight. However, their eating behaviour varies with the species. Some love to eat intact grain or embryo, some the broken ones, some prefer the powdery mass. Not only that; insects spoil the grain with their excreta, slough of their larvae, pupae, dead body etc. They create stink within the storehouse or the container they live.
Their activities generate heat within the heap of rice. This heat comes up in the form of hot air and interacts with the relatively cool air to generate a damp environment within the upper portion of the heap. So the noxious fungi like Aspergillus flavus, Aspergillus ochraceus and Aspergillus parasiticus etc. grow on the seed surface to create aflatoxin, injurious to human health. The critical safety level of the toxin is 30 micro gramme per Kg. The main store grain pests are Angoumois moth, lesser grain borer, borer rice weevil, Khapra beetle Trogoderma granarium) below.
As indicated above the stored grain pests attack in three stages as per their nature of the attack.
Primary stage stored grain pest (insects): Angoumois moth (Corcyra cephalonica, Sitotrogacerealella) lesser grain borer (Rhizopertha dominica) and rice weevil (Sitophilus oryzae, S. zeamais) are the pests of the primary stage. They bore the hard coat of paddy to lay their eggs inside the grain. The larvae feed on the rice inside the husk.
Secondary stage stored grain pest (insects): This group of insects (Saw-toothed beetle: Oryzaephilus surinamensis: Red grain beetle Tribolium castaneum, T. confusum, Flat grain beetle: Laemophloeus minutus) confine their activities on the left over broken grains by the Primary group of insects. They do not attack undamaged ones.
Tertiary stage store pest (grain): They attack the left over broken and powdery mass of the secondary stage grain insects. They are considered as the tertiary stage grain pest for unhusked rice but primary stage grain for husked rice. These insects are popularly called flour beetle.
Rat is considered one of the most noxious pests of rice. There are different species of rats are seen to be active from field to house and warehouse. They are house rat (Rattusrattus), Brown rat (Rattusnorvegicus) ), Pacific rat (Rattus exulans) ), Mice (Musmusculus, M. booduga), Black field rat(Bandicota bengalensis) .
Pest resurgence depends on the temperature and moisture. The appropriate temperature ranges from 27-37C and the moisture from 12-15 per cent. The insects cannot survive beyond 37C.
Seed storage deserves more attention. The procedure starts right before the harvest of the crop. Rice must be harvested at the appropriate stage. It should not be left in heap for several days to allow the pests to lay eggs which must be hatched out during storage.
Before storage rice should be dried properly and then be allowed to cool down slowly. The traditional storage structures like dole, beri, motka etc.
(good for small amount of storage) must be made air tight before storing rice by overlaying with cow dung paste or bitumen as per suitability of the structure made off. The opening of the structure must be covered with polyethene sheet having a layer of rice husk or dry sand. In the case of seed occasional sun-drying is good to maintain the quality. In the case of huge storage facility like warehouse the maintenance of temperature, humidity, sanitation, treating with pesticides is needed. There is another kind of storage structure often found at the farmyard of a rich farmer is called Dhaner Gola. The capacity ranges from 2-4/5 tonnes. For large-scale storage, the warehouse must be well built with airtight floor and wall. It is better to stack the sacks on a wooden platform. In the case of gunny bags, polyethene lining is desirable. A reasonable distance should be maintained between the wall and the stack, and stack to stack even from to ceiling above the stack.
Seeds stored at the grass root level should be sun dried frequently to drive out the insects grown and to reduce the moisture built up in between the two drying period. Many of the insects and pathogens might die during the sun drying too. In the case of warehouse storage, automated system of controlling temperature and moisture is better. Sometimes spraying insecticides inside the warehouse is recommended 1 to 3 weeks before storing the seeds. Fumigation is another way but quite risky needed an expert hand to handle. Generally, methyl bromide, Ethylene dichloride carbon tetrachloride (EDCT), or phostoxin are recommended. Phostoxin is quite popular. 4-5 tablets is recommended per tonnes of rice. Five days is enough for fumigation treatment.
Rice or paddy is stored in Dole, Bedi or motka with the dry leaves of Neem (Azadirachtaindica), Nishinda (Vites regunds), Bis Katali (Polygonumhydropiper) etc. is a traditional practice. The conventionally rat is controlled by trap or by poison bait. But the method is not much effective as the rats become aware of their danger within a few days. So it is better to have cats to control rats.
Anyway, we are very much concerned about the loss due to early flash flood and some extreme events in some particulars corner of the country.
But we are not much concerned about the loss occurring consistently within the farmyard. The loss due to the extreme event is apparently beyond our direct control. But the loss within our farmyard could be managed to a large extent. We have to take care of these losses. Because the cumulative amount of this kind of post-harvest loss is more than those of the extreme events. Therefore, the scientists from BRRI, BAU and some relevant institutions have to work to develop more appropriate technologies with respect to reduce the post-harvest loss of rice. More so, the extension agents should work in the field to motivate the farmers and the grass root level workers associated with the rice storage activities.
The writer is the Director General (PRL), Bangladesh Rice Research Institute, Gazipur