Chapter 12

Variable-Rate Technology in Precision Agriculture

Variable-Rate Dry Chemical Technology

Variable rate technology (VRT) in agriculture allows farmers to apply different rates of inputs, including dry chemicals like granular fertilizers and pesticides, at specific locations within a field rather than a uniform application across the entire area. This targeted approach is based on the principle that soil and environmental conditions vary significantly across a field, and a single, uniform application rate may not be optimal everywhere.

Types of Spreaders

Granular dry chemicals can be applied with a fan or pneumatic spreaders. Fan spreaders can apply more than one product at a time via one or two spinning disks at the rear of the applicator, which allows for quick application rate changes. In fan spreaders, a flow divider apportions product, which drops on spinning discs for spatial distribution. Pneumatic applicators have centrally located bins or hoppers, and air tubes leading from a metering unit to the point of discharge.

Spreader Operation

Granular dry fertilizer can be applied in a separate operation with a fan or pneumatic spreaders or in conjunction with planting using seeding equipment. Each option uses an in-cab controller, a GPS receiver, and a variable-rate option to adjust the application rate. Fan-type fertilizer spreaders use a variable-rate electric or hydraulic motor to adjust the speed of the feeding apron or conveyor belt.

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