Variable rate spreader for real-time spot-application of granular fertilizer in wild blueberry

The results of calibration tests for the ACCU-RATE controller suggested <5% deviation when compared with the manually measured application rate. The results of response time revealed that the maximum of 2.38 s and 2.25 s were taken to dispense clay filler and fertilizer respectively, after detection of the target. In order to assess the real-time performance accuracy of modified variable rate granular (MVRG) fertilizer spreader grass and wild blueberry fields were selected. Artificial bare spots were made using orange colored tarps in the selected grass field and equal numbers of weighed rat catchers were placed on artificial bare spots and grass. The MVRG fertilizer spreader was operated on VR mode (detection and no application in artificial bare spots) and the rat catchers were collected and re-weighed. The same procedure was repeated for uniform (UN) application mode of the system (application on both grass and artificial bare spots). This test was repeated for wild blueberry field to detect bare spots and plants for spot-application of fertilizer only in plant areas. The results of paired t-tests showed significant difference (P-value < 0.0001) between VR and UN treatments when the clay filler weight collected from bare spots were compared for both fields. The results showed non-significant difference (P-value > 0.05) between VR and UN treatments in grass/plant areas. These results suggested that the MVRG fertilizer spreader was efficient and accurate for spot-application of fertilizer to increase farm profitability and reduce environmental risks.