Harvesting, Threshing and Storage - Harvest and Post Harvest Operations, Crop Production | Crop Production Notes- Agricultural Engineering PDF Download

Harvesting

Most harvesting problems in Sierra Leone can be attributed to the fact that irrigated rice tends to ripen irregularly. At the end of the rainy season, when most varieties mature, frequent rains and a lack of continuous sunshine protract the grain ripening process and make difficult proper timing of harvesting, since grains even on the same panicle ripen at varying rates. If the crop is harvested too early, many green grains will be lost, because the high water content will lead to rotting. If, on the other hand, the crop is harvested too late, the rice will over-ripen and easily shatter. Furthermore, the unnecessary delay will expose the grains to increased bird attack, which can be devastating.

As harvest time approaches, the plants should be inspected daily, particularly the panicles on the most mature tillers. The proper time to harvest is when approximately 85% of the panicles are ripe. "Ripe, means that 90% of the spikelets are golden and hard, yet not so dried out as to shatter easily. The lowermost spikelets on each panicle will ripen last, but even they should be at least at the hard dough stage. The color of the leaves and stems should not be used as an indicator of the ripeness of the grains, since many varieties tend to have some green stems and leaves even when the grains are fully ripened.

Although grain ripening cannot be fully controlled by the farmer (climate and varietal characteristics will always be the major determinants), drain the plots 7-10 days before anticipated harvesting, i.e., when most of the grains are at the hard dough stage. This will contribute to even drying and facilitate harvesting by making it easier to walk inside the plots.

The traditional method of harvesting practiced throughout most of Sierra Leone involves panicle cutting. Harvesters grasp each stem several inches below the lowermost spikelets and cut it with a small straight knife. The panicle is retained and added to the growing bundle held in the hand. When the bundle becomes awkwardly large, it is tied together with a wisp of straw and carried out of the swamp. The chief advantage of panicle cutting is that the straw remains behind in the field. Bundles of rice produced by panicle cutting are easy to transport, easy to store, and easy to thresh. However, panicle cutting has several distinct disadvantages: it is very time-consuming, and since each panicle is handled frequently many grains shatter (fall to the ground).

In some areas of Sierra Leone, harvesting is done with the sickle. Sickle harvesting, popular in Asia, is very fast, since entire bunches of stems are grasped and cut in one swift motion. However, sickle harvesting requires the use of threshing machines - either the pedal thresher or the threshing table. At present few farmers possess threshing machines or know how to build them, so sickle harvesting remains relatively unpopular.

Threshing

Rice that has been harvested by traditional panicle cutting is very easily threshed, since very little straw remains with the grains. The harvested bundles of rice are placed on a clean, hard surface and beat with sticks to separate the grains from the straw (dried leaves and stems). Frequently the threshers will walk over the bundles to speed the process. If any grains remain clinging to the straw, they are separated by pounding in wooden mortars.

Rice that has been harvested by sickle cutting must be threshed by other means, since the grains must be separated from a relatively large amount of straw. Usually a threshing machine is used to increase efficiency. The pedal thresher is a revolving drum (often an old oil drum) studded with nails or wire hoops which strip the grains from the panicles when bundles of rice are held against the moving drum, The pedal thresher is effective and fast, and it can be moved from plot to plot to eliminate extensive transportation of the cut plants. The mayor disadvantage of the pedal thresher is its price (about Le 150, or $150), which makes it too expensive for individual private ownership. However, farmers associations have been known to share pedal threshers with good results, since in most cases each individual's entire crop can be harvested and threshed in a few days. Another threshing device, the threshing table, is a slatted table constructed of bamboo, wood, or any suitable locally-available materials. Sheaves of rice are beaten against the table surface, dislodging the grains to drop through the slats into the collection area below. Threshing tables work best with those varieties in which the grains separate easily from the panicle, but the crop must be extremely dry for threshing to be effective.

Storage

Rice harvested by panicle cutting traditionally is stored up in the rafters of the farmhouse or kitchen. The bundles are transported from the fields and stacked on reed mats high up off the ground, often over the cooking area so that smoke will sift in among the grains to assist drying and discourage insects. Where bags are readily available, the rice is often threshed and bagged for storage.

Rodent attack is generally a major problem. Since storage facilities are constructed of mud adobe and/or wood, rats easily gain access to feed on the rice. It is difficult to estimate accurately the annual crop loss to rodents, but 15% seems reasonable. In some instances, the loss is probably a good deal higher.

The key to effective grain storage lies in the construction of proper storage facilities. A good storage facility should be:

- plastered inside and out
- well ventilated
- well lit
- dry
- clean
- cool
- rat-proofed (heavy screen over windows and ventilation shafts)

After proper drying, threshed rice should be packed in bags and stored on wooden pallets in the storage facility. Instruct the farmer to stack the bags so as to allow good ventilation, since free air movement between the bags will prevent mildew and/or spoilage. Do not allow the bags to come into direct contact with the floor or walls, since moisture tends to condense where there is contact. If they are available, set rat traps (or get a cat!). Encourage the farmer to check the rice periodically for signs of spoilage and/or pest infestation.