From the field to the table, harvesting bulbs, tubers, and roots
Roots, bulbs and tubers need sowing (or transplanting) beds without skeleton, well refined, ventilated, and drained. In order to harvest the product preserving its quality, it is necessary to have dedicated machines, which differ for the harvesting bar, which can be adjusted to the specific needs of different species
Bulbs, tubers, and roots are crops at the base of many diets spread worldwide. These three categories of plant species can be grouped in the so-called "hypogeal crops” (i.e., they develop the edible part under the soil surface) and have a high variability of products, with different nutritional and organoleptic characteristics, different farming systems, and quite different economic yields. Examples are potatoes and sunchokes, which belong to the same category of tubers, despite having different uses and selling costs.
All underground crops need homogeneous soil structure, with limited or no skeleton presence, well refined, ventilated, and drained. These characteristics are crucial for the product to be able to develop in an optimal way inside the soil without being damaged and/or deformed. Therefore, the ideal soil texture is sandy-loamy with strong draining capacities to minimize water stagnation, cause of possible molds or rottenness, which would make the product unmarketable.
The removal or deep burial of most of the skeleton and, more generally, all those operations aimed at improving the "soil system" are therefore necessary practices to ensure the best production.
Hypogeal products are harvested using self-propelled machinery for large areas, or employing semi-mounted or towed equipment, for smaller plots.
Harvesters are generally made of two main modules, i.e., the harvesting header (which differs according to the type of crop and the needs of the sixth planting) and the transport, cleaning, and conveying unit, which features a rather similar structure in all models.
The header is usually used to extract the product from the soil, carry out an initial cleaning, separate clods of earth and other residues and convey them into hoppers or bins for temporary storage or transfer to the processing center. Below the extraction organs, described later, there is a transport group composed of conveyor belts and sieves, with the possible addition of rotating brushes or air jets to remove foreign residues.
Most of these models handle the complete product of the epigeal part, which is then cut during the cleaning phase and unloaded in the field. In some cases, it is possible to use other machinery, which, through a set of hydraulically driven discs, cuts the epigeal part beforehand to facilitate cleaning the product after harvesting.
Harvesting bar for roots
Among the most widely cultivated roots in Italy, there are undoubtedly carrots (Daucus Carota L.), which are widely used in fresh consumption and industrial processing.
Carrot harvesting machinery can be either self-propelled or towed, with technical solutions that are pretty similar. The German company Grimme has developed a header in which gripping arms encircle the leaves, orienting them between a pair of rollers, which extract the roots without damaging them and then send them to a series of rubber flagella which remove any residual soil. During this phase, on some models, water is also sprayed on the product in order to eliminate fine residues of soil and dust.
It is well known that carrots can be marketed either with the "tuft" or with the leaves trimmed, which, if necessary, are cut directly on board with a device with rotating knives.
Finally, the roots are placed on a conveyor belt, which carries them downstream of the collection unit into a hopper or accumulated directly in bins by the operators on board.
Harvesting bar for bulbs
Among the crops whose bulbs are harvested, the most popular ones in Italy are garlic (Allium Sativa L.), shallot (Allium Cepa, var. aggregatum L.), and onion (Allium Cepa L.). The latter is an annual crop harvested in the summertime, usually when the epigean part of the plant has already dried. For this reason, contrary to what happens for roots, it is not possible to extract the bulbs by pulling on the epigeal part of the plant (because it would easily break). Instead, it is necessary to use a machine that digs and collects the product, moving the superficial layer of soil on the row employing a set of disks, rollers, and hoes.
U.S.-based TopAir manufactures trailed models for harvesting onions, driven by the tractor's PTO so that more than two rows can be harvested in a single pass. The lower part of the header is equipped with a grated conveyor belt, which works under the ground's surface, removing the bulbs and, thanks to a counter-rotating drum with bulkheads placed in a circle, conveys them towards the conveyor belt. The conveyor grid facilitates an initial rough separation between the bulbs and any clods of soil taken with the product. In some machinery, such as Grimme's onion harvesters, the drum with ragged bulkheads is replaced by plastic cylinders that facilitate the loading of the newly harvested material onto the conveyor belt.
Harvesting bar for tubers
Tubers are enlarged underground stems, with a function of starch accumulation (such as potatoes, Solanum Tuberosum) and/or soluble sugars (such as sugar beet, Beta Vulgaris var. Saccharifera). Similarly, to onions, it is not possible to use the epigeal part of the plant for the harvesting of tubers because, in the most favorable period, this part is senescent, and therefore not suitable for extraction.
The tuber harvesting machinery, both trailed and self-propelled, is usually characterized by large dimensions. The equipment for unearthing and harvesting the product is usually made up of a variable number of plowshares, according to the working width of the machine and a system of feelers that adjust their depth of intervention to extract the tubers conveniently. Sometimes a defoliation apparatus is added, which separates the tubers from any vegetative material still present. The tubers are then subjected to an initial cleaning, using sieves and/or brushes, to separate the product from any clods of soil and residues. After that, the product is either conveyed into the machine's storage hopper or conferred into the boxes of special trailers for transport.
The onion digger
If mechanical harvesting is not possible, it is at least possible to facilitate onion harvesting with an onion digger. The machine is equipped with a header that unearths the onions and directs them onto some grated conveyor belts, which separate the product from the soil residue. Meanwhile, a compactor roller placed under the conveyor belts recompacts the soil after the bulbs have been dugout. After cleaning, the onions are arranged in a windrow thanks to a pair of concentric flexible bulkheads.