Haymaking, the machinery for drying forage in the field
Forage drying is crucial to produce hay with good nutritional qualities and free from external contaminants. Specific machinery such as rakes and tedders are used for this type of work. On the market, different types are offering different performances as to speed and precision of work
The production of high-quality hay begins with field drying, through which a large amount of water is extracted from fresh fodder to ensure its preservation over time. In fact, freshly mowed fodder has an average water content of about 80%, while in good hay, only 20% of water remains. These percentages show that it is necessary to evaporate 60 kg of water for each quintal of mowed grass. Usually, this work is carried out in the field, rarely intervening elsewhere, mainly exploiting energy sources other than the sun. Remaining within the field of traditional processing, it is possible to operate with different types of machinery: some of these can only turn and spread the forage, while others make the "swath." In the first case, we deal with hay tedders, while in the second case with rakes. However, this distinction is almost obsolete, since unlike in the past, today almost all machines can be adjusted in such a way as to be able to profitably perform both functions. Both can be mounted or towed and almost always derive the motion of their working parts from the cardan shaft connected to the PTO of the tractor, while - in some cases - the same is transmitted hydraulically or derived from the wheels of the operating machine that are placed on the ground.
However, the type of machinery used, how field operations are carried out, including the adjustments made to the machine, have a very significant influence on the quality of the forage obtained, especially as regards contamination by foreign substances such as stones and earth. The adjustments made on the machine are essential both for the efficiency of the forage stirring action and for the eventual formation of the swath. They are also crucial for their role in causing contamination of the forage by foreign bodies. However, it is less well known that the type of machinery chosen has a particular influence on this aspect.
It should be borne in mind that the repeated handling of hay during the drying phase is also helpful in reducing the presence of coarse foreign bodies (stones and clods of turf) that may be inserted into it during mowing. The continuous turning and windrowing operations favor the accumulation of dust in the hay that is generated when the gripping parts (springs) come into contact with the ground. In order to limit this phenomenon, it is necessary to privilege the use of machines that have a lower possibility of contact between the working parts and the ground. Since the clostridia content is closely correlated to the pollution of the forage with soil particles, especially if coming from the surface, this issue is more important to consider the more the forage is destined for milk production.
Turning, spreading, and windrowing
The rake, i.e. the machinery used to swath the hay, removes from the soil surface the forage scattered over its entire surface and composes the swath, i.e. a longitudinal heap created in order to protect the product from excessive night-time dampness or to facilitate subsequent baling. In the days following mowing, the hay is periodically turned in the field, if necessary also spreading on the field the forage windrowed the night before, and usually using the same machinery, but with an inverted mode of operation.
It is clear that correct and careful adjustment of the working parts during these phases of haymaking is essential: Ideally, the rakes and tedders' tines, as well as those of the balers' pick-up trucks, should touch the ground without ever coming into contact with it. However, this is a theoretical condition because, despite the development of recent laser leveling technologies, agricultural plots are never perfectly level.
The different solutions
Therefore, in ordinary operations, it is advisable to minimize the interference of the working parts with the ground. The technical solutions proposed are varied, both by foreign and Italian manufacturers, with the latter often producing machines branded with the names of the best-known world market leaders. From a technical point of view, rakes can be divided into the following main categories: those with idle wheels (also called star rakes), those with rotary wheels (also called spinning top or walker rakes), and finally, those with belts and with combs.
This type of rake is the most problematic in reducing dust pollution, as the working parts must necessarily maintain as continuous a firm contact with the surface of the ground as possible since they are made to rotate precisely because of the reaction due to contact with the ground. Each "star” is made with a series of teeth arranged to form a radial wheel. The teeth are made of a rather harmonic steel rod and are therefore very flexible. Since the rotation plane of the stars is oblique with respect to the direction of advancement, the flexible tines, by rotating, lift the forage to move it laterally. The advantages of this type of construction are its low cost, reduced maintenance requirements, and the possibility of maintaining a very high working speed in the field (from 12 to 20 km/h). This type of rake makes excellent swaths but is a little less effective than the other types in its spreading function and is not very comfortable to use in small plots or where it is not possible to operate at sufficiently high speeds.
Rotary rakes (spinning top or walker)
This is a rather varied category. Various models are entirely dissimilar from each other but have in common the type of working parts, which are basically large forks with flexible steel rod tines. The forks are mounted on a series of arms (generally from 4 to 6) that are arranged in a radial pattern on one or more drums rotating on a vertical axis. The rotation of the drums is usually derived from the power take-off of the tractor, or alternatively from the wheels of the operating machine, while a series of cams placed inside the drum performs a partial lifting of the forks, aimed at intercepting the forage and moving it laterally to form the swath. By reversing the rotation of the drums, it is possible to use the same equipment as a hay tedder. Typical working speeds for this type of machinery vary between 9 and 15 km/h. Although they handle the forage more gently than idler models and can be carefully adjusted to skim the ground (obviously in optimal field conditions), they still drag the crop along the ground, caused by a very open cycloid movement of the flexible tines, which places them very close to the ground for about one-third of each rotation they make.
These machines usually lift the hay with the classic pick-up, while a conveyor belt then moves it sideways to form the windrow. These machines can also be used for turning and morning windrow unraveling, although they perform these operations with reduced efficiency. Their working widths are usually limited, as increasing the length of the conveyor belt, the width of the same must also be increased - proportionally - to avoid clogging. However, this is a very interesting technical solution to limit the contamination of the forage with soil particles as much as possible since the working unit lifts the forage layer from the ground, which is then transported to the swath, thus avoiding the risk of further contamination. However, they have a reduced operating capacity, considering the low forward speed (4-7 km/h) that they can generally maintain in the field. Their limited size and the type of collecting organ make them suitable for working on uneven terrain and/or characterized by significant slopes.
Comb rakes are based on a working reel equipped with toothed combs that rotate on a horizontal axis, which is arranged transversely with respect to the direction of advancement. There are both mounted and towed models on the market, driven by wheels on the ground, by a cardan shaft connected to the tractor, or even hydraulically. In any case, the reel carries 3 or 6 combs parallel to each other (usually 5), which keep a constantly vertical orientation during the reel rotation. The adjustment of the rotation axis determines the machine's functionality as a tedder (when the axis is normal with respect to the direction of advancement) or as a rake (when it is oblique). Thanks to the very narrow cycloid traversed by the tines with respect to the ground on which they pass, the product can be lifted from the ground with an almost imperceptible drag. The combs' teeth enter the forage mass vertically and lift it with a short horizontal movement which takes place a few mm from the ground surface, then retracting as the rotation continues. The limited forward speed allowed by this machinery, typically between 6 and 8 km/h, related to a working width that rarely exceeds 3 m for single-rotor models, does not allow to obtain high working capacities. To overcome this drawback, 2 or 3 reel comb rakes have been developed.
The importance of adjustments
The most critical adjustment is the correct working height, limiting contamination of the forage by dust (and clostridia) and limiting losses in the field (especially when creating the swath). The correct adjustment must avoid ground contact between the working parts by positioning them at the height of at least 1-2 cm. Obviously, this adjustment cannot be made with idle wheel rakes. Given that losses in the field, especially with leguminous crops, are directly proportional to the degree of drying and the number of forage handling operations, it is logical that in order to limit losses (and production costs), when possible, hay turning in the field should be kept to a minimum. During standard operations, it is necessary to avoid trying to increase working capacity by increasing the rotation speed of the working parts in order to increase the forward speed, because doing so inevitably causes greater mistreatment with a consequent increase in product losses in the field, mainly due to the detachment or breakage of leaves.
Most hay tedders and rakes on the market today have well-defined rotation and advancement speeds. If they are exceeded, they negatively affect both the reliability of the machinery and the quality of the product obtained. To maintain the highest quality, it is usually advisable to go slightly below the manufacturers' values, also because the market is progressively selecting forages with increasingly higher quality requirements.