Giving Spreaders the Right Spin For Precision Agriculture

Tony Grift Assistant Professor of Biosystems Automation Department of Agricultural Engineering (217) 333-2854; grift@illinois.edu

Figure 1. Single disc fertilizer applicator fitted with optical sensor.

The application of granular fertilizers has been carried out using spinner-type spreaders for decades. This intuitive design mimics the sweeping arm of a human being, but the pattern uniformity of these types of spreaders (particularly the single spinner type) is very limited. Calibration, using bins to collect and weigh the material, can produce a reasonable uniformity as long as the rate is constant. However, in precision agriculture, we need to be able to change the application rate in real time. Under these conditions, spinner-type spreaders perform very poorly, and for this reason they are gradually being replaced by pneumatic boom-style spreaders, which are more expensive and not as simple in design.

Researchers in the Department of Agricultural Engineering have developed a system where an optical sensor is used to control the uniformity of a spinner-type spreader. The sensor, as shown in Figure 1, measures the velocity and diameter of individual fertilizer particles. This information is used to predict where the particles will land on the ground. The measured pattern can be overlapped for multiple passes in a computer program, and the application rate and uniformity can be determined for any given swath width. Once the swath width is chosen, the pattern is adjusted in real time, such that the desired application rate and an optimal uniformity are achieved. When a different application rate is required, the process is repeated; the spreader permanently carries its own calibration tool.

Figure 2. Predicted spread pattern from single disc fertilizer applicator.

Figure 2 shows the spread pattern as measured with the optical sensor. It is clear that the pattern is very heavy on the right side, although the two feeding gates were set to the same value.

The sensor concept is used here under the assumption that particles pass the sensor individually. When clusters of particles are passing the sensor, the lengths of these clusters are measured. The cluster lengths contain enough information to statistically estimate the number of particles per cluster; in other words, a mass flow can be computed. This means that the concept can also be used in higher density mass flows, such as the aerial application of fertilizer. In fact, it can be used for any kind of mass flow, as long as the particles are opaque and nearly spherical. This side effect might, in the end, be more important than the original application.

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