Variable Rate Tecnology

VRT, or Variable Rate Technology. In the flood of acronyms which for some time have flooded us, this one has often recently been mentioned in many domains concerning the world of agriculture.

It is one of the cornerstones of the by now well known ‘precision agriculture’. In practice, any plant protection products or fertilizers are not constantly spread any longer over the entire surface, but just in varying amounts, according to specified parameters previously established or even in real time. Irrigation is not carried out indistinctly any longer, but proportionally, where it is more needed. Neither pruning nor defoliations (e.g. vine) are univocally carried out, but in a more or less decided way where it is appropriate, again according to well-defined agronomic needs.

And so on…

It is a very intelligent operating system, under many respects, to do agricultural activities, rationalizing the use of resources, improving the quality of both cultivation and crop, while reducing at the same time the environmental impact.

In this context, machines obviously play a key role. Both truck machines, tractors in the first place, and above all operating machines, which must be equipped with devices and mechanisms able to change, within the broadest possible limits, the quantity of product that must be spread (or removed).

But this is just the final part, the implemental one. The variable rate becomes ‘intelligent’ if it actualizes itself on the basis of prescription maps previously realized with care and attention, and / or in relation to sensors that define, in real-time, the needs of the cultivation.

Some examples: mineral fertilization, especially the nitrogen one, given in variable rate in relation to NDVI maps, which ‘read’ the intensity of green in vegetation, interpreting it as an indication of greater or lesser need for nitrogen; mechanized harvesting of the grapes, which is realized by carrying the product in separate tanks, in function of its degree of ripeness, and then the process is directed towards distinct workings, in order to obtain wines characterized by different value; again, always in viticulture, variable rate defoliation is realized by means of a sensor that detects the density of the surface of the leaf and then intervenes in a more or less decided way.

However, these operating methods are successful to a very specific condition, which is the real key for the whole VRT: the detail of the prescription map must be adequate to both speed and quickness of the actuator to adjust the amount of product that must be spread (or removed or collected). As a matter of fact, if this does not happen, and the values show high variations, it is possible that a double mistake is committed, that is, for example, to spread  too much product in some areas and too little in other ones compared to the real needs.

Concretely, with the typical present work speeds, the possibility of having a map with only a few centimetre definition for meshes (obtainable without any problem with the new opportunities of use consisting in drones, which allow localized and much more detailed analysis than those based on satellite) reveals to be in fact useless, because at present there are not so fast actuators available that can faithfully follow the continuous proposed changes.

In these cases, it is necessary to perform an interpolation in order to bring the degree of map detail to an appropriate level for variable-rate working. Usually a few meters definition is considered as acceptable for meshes.

On the other hand, the environmental impact is not the same for all the activities: it is one thing to carry out variable rate defoliation, another one to perform this way a phytosanitary treatment. It is clear that in the latter case the impact is definitely superior, both on cultivation (because if too much product is spread phytotoxicity occurs, while if too limited irrigation is realized it is impossible to control the pathogen agent as it would be necessary). In both cases, reduced income is obtained, for a production characterized by lower value, in both quantitative and qualitative terms.

The environmental impact, then, cannot be certainly underestimated: if the distribution of plant protection product considers the presence of vegetation, besides health state, avoid spraying the surface of the leaf and then spread the product where there is nothing would be simply disastrous.

The hope is that the manufacturers of equipment in compliance with VRT technology are well aware of this key step, and will take this into due account right from the design stage of their machines.

Otherwise, VRT technique, although innovative, frugal and environmentally friendly on paper, would not simply work…

By Prof. Domenico Pessina

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