From the soil to the table, harvesting peanuts
Peanuts are geocarpic leguminous plants, widely cultivated and particularly appreciated for appetizers, especially during festivities. The vast surface dedicated to this crop in some countries implies the importance of proper harvesting mechanization usually carried out in two stages. The first stage is the extirpation of the plant (followed by a short withering), then the separation of the pods carrying the seeds from the rest of the vegetable mass
Most of all, in wintertime, peanuts (Arachis Hypogea L.) are among the most popular and widely consumed types of dried fruit in the fruit and vegetable department of supermarkets. They are marketed primarily on a roasted form (or roasted and salted) as an appetizer, but also as seed oil (in a mix or pure) or as a spreadable cream (the so-called "peanut butter").
The leading producers are China, India, Nigeria, the USA and Israel. Peanut belongs to the Fabaceae family. The plant is herbaceous, and its morphology is similar to the chickpea's one. Originally from South America, it reaches a height between 30 and 80 cm. Yellow flowers are racemes. Pollination produces a rigid peduncle ending in the ovary.
The length of the peduncle and its stiffness are required for the ovary to be buried. As a matter of fact, it is geocarpic cultivation, that is, with fruits developing underground. In order to ensure good yields, this feature requires it to be cultivated in frank soils tending to sandy without or with very little skeleton, with good drainage, to prevent the onset of fungal diseases, which can often affect geocarpic crops.
Peanuts are usually sowed in rows with a 25-50 cm distance between single plants to facilitate mechanized weeding and harvesting.
Peanuts have a scalar flowering which affects the ideal time of harvesting: if harvested too early, part of the pods will not be ripe yet, whereas by delaying the harvesting process, there is the risk that at the uprooting of the plant, the pods will remain in the ground, therefore losing an essential part of the production.
Harvesting
The geocarpic characteristic of the crop requires a two-step harvesting, i.e., the uprooting from the ground of the hypogeal part (and the subsequent natural dehydration of the mass, left temporarily in the field) and then the separation of the pods from the rest of the plant.
As this phase is a crucial step for the profitability of the crop, it is only natural that different techniques have been developed over time for carrying out this work.
Machinery for product excavation
They are mostly towed machinery. They displace and lift the plants from the ground using a single-row or multi-row system, usually coupled to the tractor's rear with a 3-point hitch.
A series of discs with jagged edges, parallel to each other but placed on inclined and concentric axes, open grooves in the inter-row conveying the plant mass into a central heap.
The disks can uproot the plant from the collar with the attached pods grown in the soil thanks to their shape.
The entire plants are then conveyed onto a grating belt and meet a pair of bulkheads shaped in such a way as to rotate them by half a turn and place them in a windrow back in the field. This is a crucial step because, in this way, the epigeal part of the plant withers and the pods with peanuts dry out.
Harvesting machinery
After partial drying in the field, the crop is suitable for seed sorting. In this case, too, the machinery used is mainly towed and capable of collecting and processing two or more windrows simultaneously. The header is equipped with a pick-up with retractable fingers which, thanks to an upper reel, loads the material, while an auger placed behind conveys it to the center, making it flow into the elevator channel and then to a group of beaters and concave arranged in series, which separate the pods from the rest of the vegetation. Similarly to conventional cereal harvesters, there may be shaking organs and sieves with a fan to clean the product better.
Finally, the pods are stored in the primary hopper (generally of 3-4 t capacity, sometimes also in a tipping version), or they can be directed straight into a trailer pulled by the tractor alongside the harvester via an unloading belt. If dumped, the trailer body is subsequently loaded onto trucks for transfer to the final drying site.
The output of the models is proportional to the header capacity: those produced by KMC (USA) have 4 or 6-row headers, while Amadas, also from the USA, offers both trailed and self-propelled models, with headers up to 12 rows.
Without doubt (just like standard combine harvesters) that self-propelled machinery brings several tangible operational advantages. In this view, Amadas manufactures the 9980 model equipped with a John Deere engine and hydrostatic transmission. Harvesting heads are available with 6, 8, 10 or 12 rows.
Finally, the epigeal part of the plant and the hypogeal part of the waste can be chopped and scattered on the field through devices of different conformation.
The major peanuts producing countries
Several tens of millions of tons/year of peanuts are grown worldwide, but contrary to what one would think, the USA is not the leading producer of peanuts.
As a matter of fact, the major peanut producers are in order of quantity: China, India, Nigeria. The United States comes only fourth. Conversely, yields are 4.2 t/ha for the USA and 3.7 t/ha for China; lower yields are achieved in India (1.2 t/ha) and Nigeria (1.1 t/ha). However, the highest yields are achieved in Israel; Italy has a minimal production, with only 65 tons/year in total.
Peanut processing
Peanuts are among the most appreciated types of consumer nuts worldwide. These seeds have different uses in human nutrition, also depending on the specific characteristics of the different cultivars:
- consumption of the seeds as they are, after roasting and possible salting that makes them crunchy and more appetizing;
- production of oil from the pressing of seeds: it is frequently used in cooking, especially for frying, thanks to its high smoke point of more than 220°C (220°F);
- production of peanut butter: typical of the USA; it derives from the grinding of seeds until obtaining a dough rich in fats (for the specific nutritional characteristics of peanuts). The traditional recipe, only based on ground seeds seasoned with salt, has been adapted over time for industrial production by adding preservatives and other ingredients.
