From the literature it appears that in the developing countries, crop harvesting equipment available with the smallholder farmers have changed very little over the years. The search for more efficient, cost-effective ways of harvesting and threshing the crop is significant because of the extreme labour intensity of these tasks. For example, up to 40 percent of the total labour required to grow this crop is expended in harvesting operations. At peak harvest periods labour shortages often occur, even in regions that normally have surplus labour available. This can either lead to higher costs of production or reduced yields. Several factors other than capital costs affect decisions on using harvesting and threshing equipment. The size of the farm in physical and economic terms influences the scale of machinery and the appropriate investment. If only a small amount of work is undertaken each season, then the capital cost per unit of work done may be so high that a machine may not be economical compared to alternative methods. Trade-offs can be avoided where multi-farm equipment use is possible, but this approach requires a high degree of organization and cooperation, especially when timely harvesting is critical.type of groundnut
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Figure 4: Manual harvesting and lifting of Spanish type of groundnut by hired labourers.
Harvesting usually consists of a series of operations comprising digging, lifting, windrowing, stocking and threshing. Some of these tasks can be combined or eliminated depending on the system applied. Among the field operations concerned with groundnut cultivation, harvesting is the most laborious and costly endeavour. The actual method of harvest employed depends upon the type of groundnut grown.
In bunch types, pod development is confined to the base of the plant and the pegs carrying the pods into the soil are thick and strong. Almost all the pods are recovered with the plants when they are pulled out of the soil (Figure 4). The bunch type of groundnut is mostly harvested by pulling out the plants with manual labour in India. The diversity of the labour employed to harvest the crop depends on the location. For instance male labourers are used in Tamil Nadu and in Gujarat both male and female labourers are employed. Usually 12 to 14 labourers can harvest one-hectare area of groundnut crop in one day.(type of groundnut)
Harvesting may sometimes become a problem especially when the crop has passed the stage of full maturity and the soil has hardened. In this case, it is customary to lift the plants by loosening the soil either by working a hand hoe, a plough or a blade harrow along the plant rows. If after lifting the crop manually it is observed that a good percentage of the pods have been left in the soil, the same implements may be used to pick the leftover pods. In the latter case, additional labour will be required. In the case of the spreading type, the process of uprooting the crop from the soil is a rather difficult operation as pod formation takes place all along the creeping branches of the plant. The pegs are comparatively thinner and more delicate. In Figure 5. a blade type digger is harvesting a runner type of groundnut (Figure 5).
Figure 5: Groundnut harvesting by a blade type digger being operated by bullocks and tractor.
As compared to manual uprooting, the performance of the bullock-drawn digger is satisfactory and economical. The digger lifts groundnut plants from a depth of 10 to 12 cm. Several models are available in the markets to be operated either by the animal draught or by the power tiller drive (3 to 6 hp). The capacity of various diggers ranges from 1.2 ha h-1 (animal drawn) to 1.5 ha h-1 (power tiller).
Harvesting bottlenecks in the less-developed regions are commonly caused by the logistics of lifting plants from the ground. This task is the most mechanized operation in developed countries and replaces the hard manual labour of digging. Many models of ploughs or digger blades can be used to up-root one or several rows. The design depends on whether the digger is animal operated or mechanically powered. It is essential that the blade or ploughshare be set deep enough to cut below all the pods, but not so deep as to increase draughts unnecessarily. Slow speeds and additional implements are preferable to higher speeds with fewer tools, especially when kernels are produced for table consumption. The gain in yield, quality and final price offsets the additional digging costs. Harvesting techniques can also affect milling quality of groundnuts. Sweeps or fingers may be necessary on the digging blades to ensure that the plants are left well to one side of the opened furrow and not covered with soil. Where it is necessary to combine several rows of plants into one, this operation must be carried out soon after lifting as practicable or pod loss can occur. Raking early in the day when plants are moist reduces this danger.
In certain areas, the vines are uprooted with country ploughs and the vines and pods are picked by manual labour (Figure 6). The pods left over in the soil are picked by hand. Groundnut diggers drawn by a pair of bullocks or by tractor are available in market. The bullock-drawn groundnut digger can harvest groundnut crops over an area of 0.75 hectares in 8 hours.
Some farmers use conventional 76 inch blades attached to cultivator frame to dig groundnut. A tractor-mounted digger-shaker-windrower is available in the Indian market. This equipment saves the loss of pods and reduces the cost of harvesting.
Figure 6: Manual lifting of groundnut vines.
Stripping of pods is performed manually by the small farmers (Figure 7) or by the strippers. There are two type of groundnut strippers, the drum type and comb type.
Figure 7: The women-farmers and hired female labours are doing manual stripping of groundnut pods. In the background bullocks are also enjoying the freshly harvested crop.
The description of the drum type stripper developed at Zonal Research Centre, Tamil Nadu Agricultural University, Coimbator. Drum type strippers consist of a hollow drum formed by two metal discs at the ends, connected on the periphery of 5 1/2 inch M.S. rods inserted inside and covered by thick and soft rubber tubes. This drum is mounted on pedestal bearings and is free to rotate. It is fixed on a framework at a conventional height so that the operator can stand and beat the root portion of handful of plants over the rubber-covered roads of the revolving drum.
To avoid scattering of pods, a hood frame is also provided. The roof as well as the three sides, i.e. other than the operator’s side is covered with a canvas or gunny bag. One man can carry the unit. A comb type groundnut stripper is used for stripping the pods from the wet groundnut vines. This has been developed at Zonal Research Centre, Tamil Nadu Agricultural University, Coimbator. The unit consists of a square frame of four verticalstandards with a strip of expanded metal fixed on to each of its side in the form of a comb. The stripping of the pod is accomplished by drawing a handful of vines across the comb with slight force. The structure facilitates use by four persons simultaneously.
Stripping of pods from the vines is done by several methods. In bunch type the plants are stacked in heaps with the pod end exposed. Please see Figure 8 and 9.
Figure 8: Comb type groundnut stripper. Source: NDDB
Figure 9: Drum type groundnut stripper. Source: NDDB
The pegs become brittle within a week and pods are stripped by hand. In some areas in India the pods are first lifted out of the soil, dried in the field and then the pod ends of the plant are knocked against a crossbar to dislodge the pods. In this process some pods
b../img/ch21/ecome damaged. This method of stripping is cheaper. A simple comb-type stripper and peddle-operated stripper are available and can be used for bunch types of groundnut.
In the case of runner types, the plants are first allowed to dry, then are beaten with flails and the pods are separated from the beaten mass by winnowing. The pods left over on the vines are handpicked. This method of stripping is not preferred as it is considered to reduce the fodder value of the vines. The Central Institute of Agricultural Engineering (ICAR) Bhopal, India has developed a CIAE Groundnut power stripper to strip the pods from green vines both runner and Spanish types, however, it need more testing and demonstrations to be implemented at the farmers level (Figure 10).
Figure 10: Groundnut stripper for stripping green vines developed by CIAE (ICAR), Bhopal.
Threshing operations also very both within and among the developing countries. It varies from the age-old procedure of using sticks and racks to the modern power threshers. In India the smallholder and marginal farmers do manual threshing using sticks and rakes. Variations also exist in stripping pods from the plant. After harvest bunch type plants are stacked in heaps with the pod-end exposed. After the crop has remained in this state for a week or so the pegs become brittle and the pods are plucked from the plants with labour. This operation is comparatively difficult as the attachment of peg to pod is stronger in bunch type than the runner types, but drying the plants for a few days facilitates this operation.
Sometimes the stripping of the pods is also performed side by side with the harvest when the crop area is small and labourers are available. In this case, the pods are dried immediately after stripping. In Pollachi (Tamil Nadu, India) the usual practice is to separate pods by beating the pod-end of the plants against a rough stone or a thick iron rod. This process damages a small percentage of the pods. Following this method the proportion of the damaged pods is not appreciable and is a considerable labour saving.
A pedal operated thresher based on the Japanese Paddy thresher tried in Tamil Nadu has proved useful for the bunch type in which the pods are clustered together at one end; however in spreading types pod are found all along the branches and have to be plucked individually. The attachment of peg to pod in runner types is also weaker. In this case none of the above methods would work satisfactorily in case of runner type, thus it becomes a laborious process. In most of the groundnut-growing areas in India for example the states of Andhra Pradesh, Maharastra and Gujarat, the harvested plants are allowed to dry well on the threshing floor, the dried mass is beaten with flails. After making sure that the pods have been detached from the plants, pods are separated from the beaten mass by winnowing. Threshing involves quite distinct operations including separating the pods from the vine, sorting the pods from the haulms and winnowing the chaff from the pods. In some parts of India. small farmers employ manual threshing. After drying the groundnut plants in sunlight in the field for 4 to 5 days they are collected at one place. Threshing is done manually by a wooden comb type structure with a long handle (Figure 11). Earlier in Gujarat farmers used to follow this procedure but now it has become an obsolete technology, mainly due to the availability of power operated opener or thresher in local markets.
Groundnut pods are properly picked either manually or by the thresher after sufficient drying. In Gujarat, the farmers, local artesian and traders have designed and developed efficient threshers. At adequate moisture content of groundnut plant, pods are harvested directly in a power thresher. Oil engines or electrical motor operated groundnut threshers can be used for higher land holdings. The capacity of the thresher ranges between 2 000 to 2 500 kg of groundnut pods day-1 and requires at least two people for operation. The first separation of groundnuts from all other material occurs during threshing and or combining. The threshers used in India are quite efficient and require skill to adjust it prior to threshing, otherwise losses like incomplete separation and breakage of pods may occur.
Figure 11:An old method of threshing groundnut pods.
The best threshing is obtained with minimum loses at pod moisture content between 18 and 20 percent. Groundnut threshers are generally designed as axial flow where the plant moves in a direction parallel to the beater axis. The pods are separated from the remainder of the plant in the threshing chamber so that the latter is expelled at the other end of the thresher. The impurities fall onto the sieve, where the leaves and light material are removed by air from the blower. The clean pods than fall through the sieve and are discharged through the pod outlet. The clearance between the bar and the screen is too small to admit the pods with the shell. The machine can be trickle-fed automatically or fed by handfuls. The JYOTI Ltd, Vadhodhra, (India) has developed a decorticator, which performs simultaneously decorticating and cleaning operations. The blower separates the hull and clean kernels are discharged through the grain outlet. Ball/bush bearings with oil cups are standard fittings. The capacity is 10 to 20 kg h-1. The thresher requires 10 hp and is operated by 3 to 4 people (Figure 12).
Figure 12:Threshing operations in the field, groundnut opener being operated with the help of tractor engine and another with a diesel engine.
Figure 13:Winnowing and cleaning operations are being performed by the farm family.
Curing and its interaction with the maturing process comprise the single most critical factor in establishing the basic flavour quality of groundnut after harvest. The terms curing and drying have been defined as two distinct phases marking the change in groundnut composition following harvest (Blatchford and Hall, 1963). Because of common usage, the terms curing and drying are often used interchangeably. Curing is the process of water removal such that groundnut biochemistry and physiology are optimum for food quality. Proper curing is essential for safe storage, milling quality and flavour quality. Extremely high temperatures, while the crop is in windrows, can promote far too rapid drying and may contribute to the development of off-flavours. The process of curing has not received much attention, especially in the developing countries, where the farmers lack education, quality consciousness or the proper facilities and knowledge. type of groundnut
During the curing process, groundnuts are dried to an average moisture content of approximately 10 to 15 percent. This means that some kernels are drier, measuring as low as 10 percent while others contain more moisture. The moisture content range of kernels in a lot is related to initial moisture and maturity of individual kernels. Immature groundnuts may contain twice the moisture as mature groundnuts at harvest. The difference in moisture content among the pods of various maturity groups during curing is sustained during the storage period.
type of groundnut
The word drying is often used to describe all phases of moisture removal, including those already referred to under curing. Speicifcally, drying is used only to describe the period when moisture is being removed after groundnuts have been threshed from the haulms. Groundnut after harvest is dried thoroughly either following the natural or the artificial methods. The equilibrium between the pod moisture content and atmospheric relative humidity during the drying process has been investigated by several workers. The results showed that the shell, the testa (skin of kernel) and the kernel have different equilibrium moisture contents at the same humidity (Table 7). The rates at which pods lose water to the air during curing and drying and the rate at which they change in moisture content during storage, depend on the physical structure of the pods as well as the temperature, velocity and relative humidity of the air.
Table 7. Equilibrium moisture contents of groundnut at various relative humidity
|Components of pods||Percentage relative humidity|
|Percentage moisture content (wet basis)|
Source: Blatchford and Hall, 1963
Blatchford and Hall, (1963) made extensive surveys of the literature on drying methods for groundnut in various countries. Some of the drying methods being followed in the developing countries are mentioned below.