On-the-go variable rate fertilizer application on vineyard using a proximal spectral sensor

Spatial variability represents a challenge for viticulture. Variable-rate fertilization is a promising technology to manage different vigor and yield zones within the. In this study, on-the-go variable rate fertilization system was implemented and tested, based on commercial spectral sensors. GreenSeeker Normalized Difference Vegetation Index (NDVI) sensor was mounted in front of a tractor and connected to the electronic control unit of a variable rate spreader. Fertilizer rate was based on threshold values of NDVI, calibrated previously in ten sampling points by a GreenSeeker handheld sensor. The sampling points were selected according to the agronomist expertise on vineyard variability. A couple of GreenSeeker sensors carried by tractor and connected to the fertilizer electronic control unit were used for fertilizer dosage definition. Fertilizer application was evaluated comparing the amount of fertilizer distributed in the sample points with the prescribed dose. Results showed good accuracy of distribution compared with the prescribed amount of fertilizer. Similarly, the fertilizer distribution showed a significant correlation (R
²
= 0.65, p-value <; 0.01) with the Leaf Area Index collected in the sampling points. The effects of variable rate fertilizer application on vine vigor were preliminary assessed measuring vine shoot length the day when fertilizer was applied and 14 days after fertilizer application. Linear regression for vine shoots growth rate based on applied fertilizer showed an R
²
of 0.6, suggesting a positive effect of the on-the-go variable rate fertilizer application on vines growth. Fertilization effects on field variability were then assessed considering three variability coefficients of NDVI (σ, Gini, and CV). The comparison between variability coefficients of the years before and after the fertilizer application showed a reduction of 37%, 43%, and 40% for ı, Gini, and CV, respectively. The results highlight the potential of proximal spectral sensors for on-the-go variable rate fertilization and reduction of in-field variability in vineyards.