Stem bending force and hydraulic system pressure sensing for predicting napiergrass yield during harvesting

Napiergrass, which resembles sugarcane in stature and cultivation practices, is emerging as a candidate bioenergy crop. However, limited studies investigating harvesting and yield sensing of napiergrass are available. This study investigated stem-bending force, and the hydraulic pressures of basecutter, chopper and elevator drives in a John Deere 3522 sugarcane billet harvester as indicators of napiergrass yield. The coefficients of determination (R²) between napiergrass yield and hydraulic pressures were 0.73, 0.88 and 0.81, respectively for the basecutter, chopper and elevator drives. The highest correlation (R²=0.92) was found between stem-bending force and napiergrass yield. The yield prediction errors were 4.9% and 8.6% for the calibration and validation plots with the stem-bending force yield sensor. Cross-validation, in which each harvested row was treated as a data point, showed that the average yield prediction errors were 10.9% and 11.8% for the calibration and validation data sets. Yield maps were also generated employing the stem-bending yield sensor. In addition, it was expected that the stem-bending yield sensor could be utilized to control harvester operation such as travel speed. Further studies would be needed to extend the stem-bending concept to other thick stemmed crops.