Uses Of Variable Rate Application And Associated Benefits

Variable Rate Application (VRA)

Variable Rate Application in Precision Agriculture refers to the spatially regulated distribution of agricultural resources. Two types of VRA exist, map-based and sensor-based. Given its relationship with GNSS, map-based VRA will be the focus in this instance. Map-based VRA regulates resource application rate based on a ‘prescription map’. Prescription maps are developed around previously observed spatially referenced data containing information detailing at least one of the following environmental attributes: soil type, colour and texture, site topography, crop yield etc. Essentially, the rate of application can be varied according to any existing attribute that can be spatially referenced within the area of interest. Strategies of VRA exist to incorporate a combination of information sources, each to the users desired extent. The most commonly used materials for VRA include fertiliser, soil ameliorants (i. e. lime), pesticides, sowing, tillage and irrigation. As is the case with yield mapping and monitoring, the central objective of VRA is to advance both the economic and environmental output of a paddock as much a practically possible. With prior reference to yield mapping, it would be favourable if VRA was able to be implemented at the same or similar spatial density as to what yield is monitored. As of the year of 2006, the limiting factor of the scale with which a given resource can be variably applied is determined by the material itself as well as the speed at which a rate-of-change can be relayed to the equipment from the data source.

The core components of a map-based VRA system are:

• prescription map: georeferenced data file containing information regarding input rates of a certain resource at specific points within the area of focus
• actuator: component on machine with capability to vary application rate according to the prescription map in use
• GNSS receiver: determines position of machine machine guidance system: can automatically direct combine harvester using attached GNSS receiver (this is optional).

With this collection of equipment, variable rate application is made possible.

The most notable benefit of VRA is the ability it gives the user to better and more accurately manage sowing density, crop nutrition and protection and soil composition. Having optimised such practices, a number improvements across various aspects of the farm will result:

• minimisation of resource wastage: with the volume of material being applied having been optimised, misuse of such products can be minimised improving the user’s gross margins
• minimisation of ecological footprint: by reducing unnecessary use of potentially harmful materials such as herbicides and pesticides, damage to the local environment from agricultural practices can be curtailed
• potential yield increase: armed with a better understanding of the ideal conditions to improve yield, the suitable volume of seed to be sown per unit area (or any other chemical of interest to be applied) can be determined which in turn can boost profitably through increased yield.

Relevance to Site-Specific Crop Management

VRA represents a number of the central elements of site-specific crop management:• spatial referencing: use of GNSS

• attribute mapping: utilisation of prescription maps developed around previous collected spatially referenced data
• decision support systems: analysis of attribute maps and the magnitude of spatial variability across the area of interest to determine if VRA is necessary
• differential action: the use of VRA, that being the spatial variation of a particular action-in this instance the application of an agricultural material.
• The greatest results of variable rate application are seen where areas of high spatial variability of a measurable environmental component exists. The use of such a technique delivers cost and profit benefits, as well as potential improvements in crop yield.