Advanced distribution for centrifugal fertilizer spreaders
In addition to an excellent control of distribution with traditional solutions, the new technologies related to fertilizer spreaders allow a profitable application even adopting the Variable Rate Tecnique, one of the cornerstones of precision agriculture. On the best models, different ways to control the distributed dose are available
The aims of the two alternatives differ since organic fertilization in many cases improves not only the nutritional potential of the soil, but also its structure, and finds profitable (and sometimes unique) application in organic farming. On the opposite, the so-called “chemical” fertilization is limited to providing a certain quantity of elements (basic: nitrogen, phosphorus and potassium) useful to plants through the circulating solution, after having been transformed into absorbable and assimilable forms.
There is no doubt that mineral fertilizers are still much more frequently used than organic ones, and therefore that the corresponding machines for their distribution, in most cases of the centrifugal type, have been the object of considerable technical evolution, oriented towards an increasingly environmentally friendly operation and a rational use of the product with a view to precision agriculture, with its implementation oriented to site-specific distribution, through the so-called “variable rate technique” (VRT, Variable Rate Technique).
The machines
In a nutshell, the operating principle of fertilizer spreaders for mineral fertilizers is based on the centrifugal force imparted to the granules which, dropped on one or more rotating discs at high speed, come into contact with some radially mounted blades on each disk, so that the impact gives them a strong tangential acceleration (and therefore a considerable speed) enough to be launched at certain distances from the point of fall, ending on the ground by gravity after having traveled a parabolic trajectory transverse to the direction of progress of the equipment.
The aims of the traditional performance of the operation are basically two, that is a contribution of nutrient principle on the surface unit (eg unit of nitrogen per hectare) according to the agronomic prescription and a distribution that is as uniform as possible on the whole treated surface. In the first case the result is achieved traditionally by consulting specific tables for each model, through which, depending on the feed speed, the opening of the fertilizer free fall light on the disc is practically adjusted, while in the latter it is necessary to carry out a determined overlapping of the applications, since, with the solution described, the distribution diagram of the product has a typically triangular course.
The adjustment of the proper dose
There is no doubt that the dose regulation is the key indicator of good mineral fertilization. On this subject, to manage the width of the free fall light, Maschio Gaspardo on the Primo model has adopted an advanced solution for two overlapping side partitions, managed by linear actuators (on request powered by electric motors controlled by an electronic control unit) that allows significant operational advantages. In short, the lower partition adjusts the dose by varying the area of the free fall light, while the upper one acts as a quick closure, in order to avoid waste where the product does not have to be distributed (typically on the headland). Moreover, the fertilizer is conveyed from the hopper to the drop point through a rotating head with an optimized conformation, for a delicate but constant action on the product, without excessive rotation which would lead to a marked crushing of the granules and ultimately to a non-uniform distribution.
The speed of rotation of the disc, as well as the position and the length of the paddles mounted on it determine the characteristics of throwing the granules. On the Amazone fertilizer spreaders distributed in Italy by SAVE from Agrate Brianza, the SBS (Soft Ballistic System) was implemented, based on a stainless steel disc (on request also with hard metal coating, to increase its service life) equipped with spreading vanes with adjustable angle of incidence and length to obtain a precise distribution in each sector. In addition, the disc rotates at a relatively low speed (720 rpm) in order to guarantee a uniform and constant “filling” of each paddle. For more precise dose adjustments even in hard operating conditions, the most advanced models use some interesting measures, among which the automatic weighing has been widely used. In practice, one or more (usually up to 4) strain gage load cells placed between the spreader frame and the overlying hopper (or on one of the tractor attachment points, for models attached to the 3-point attachment) are able to measure the rate of distribution, sending to the inevitable electronic control unit changes in weight over time, or the amount of fertilizer distributed. For example, some models of the Vicon brand, the Kverneland Group (which has its Italian branch in Castiglione delle Stiviere) fit 4 load cells integrated with an inclinometer, to create a weighing system with automatic slope correction, useful in case of working on hilly terrain and/or irregular profile and with frequent speed changes
Avoiding waste and pollution
In this sense, one of the most important aspects concerns the limitation of the distribution of borders (towards roads, cycle paths, waterways, etc.) and the edges of the field. For this purpose, devices are installed on the latest models that allow the spreading width to be divided.
The limiter is based on a lamellar block that slides on a special frame within a very wide tilting field, varying the throwing direction of a part of the fertilizer flow.
Electronic management
On the most complete models, there are different ways to control the distributed dose, which may use or not some detectors supplied. In short: manual: the operator sets the distribution parameters before the field intervention, completely excluding (if necessary) the electronic controls; stored: the distributed dose is adjusted by a previously predefined distribution curve, and as in the previous situation it does not use sensors that may be available on the machine. It is a mode suitable for working on soils with steep slopes and with an irregular terrain; semi-automatic: after having set the desired dose, the flow regulation is automatically adjusted according to the speed, measured by GPS. If the soil is very uneven (for example after plowing), the rate is fixed with the fertilizer spreader stopped; automatic: in addition to monitoring the speed, the quantity of product distributed is controlled according to the weight detected. The control unit continuously calibrates the dose according to the type of fertilizer in use.
Electronics + information technology = agriculture 4.0
The most recent evolution obviously concerns the fully automatic management and specific site (that is to say variable rate) by exploiting also the new technologies on the subject, such as ISOBus, which allows a profitable “dialogue” between the tractor and the equipment (and now also viceversa). On the Kuhn fertilizer spreaders of the Axis range, the Quantron control units regulate the opening position of the dosing nozzles and consequently the flow volume according to the feed speed, while the Varispread Dynamic gradually adapts in a completely automatic way both the working width and the dosage, on the basis of the plot shape. Electrically powered actuators ensure high reactivity to changing operating conditions. The “Pro” version of the device has in fact 4 electric engines, which act 2.5-5 times faster than the hydraulic drive, to obtain an almost instantaneous modulation of the dose, a greater readiness for changes in the forward speed and an even more precise opening/closing at the end of the field. The most recent evolution has brought to the appearance of terminal devices very similar to tablets (even in size) on which you can fully manage the machine, even using a joystick connected to it.
