Effectiveness of Sentinel-2 imagery, apparent electrical conductivity and topography for delineating site-specific management zones in an olive grove in southern Spain.

Variable rate irrigation (VRI) shows attractive cost/benefit ratios, as compared to drip irrigation, when implemented in large orchards with suitable field and planting geometries. To evaluate the effectiveness of apparent electrical conductivity (ECa), elevation (Z), topographic wetness index (TWI) and time-series of Sentinel-2 NDVI imagery for delimiting VRI zones in olive groves, a study was conducted in a 40-ha commercial plot in southern Spain (Ecija, Seville), equipped with a linear move sprinkler irrigation system and with trees on a 4 × 7 m grid. Soil samples were collected at 140 points on a regular grid with depth intervals of 0.3 m down to 1.2 m and analyzed for soil texture. Relationships between soil texture, topography, ECa and NDVI were analyzed using correlation analysis and regression trees. Time series of correlation between ECa and NDVI showed a seasonal pattern because of the growth-decline pattern of the grass soil cover. The regression tree analysis showed that ECa and elevation were most relevant for classifying NDVI (R²=0.70). Fuzzy k-means classification using ECa+Z yielded 4 classes while for ECa, ECa+Z+TWI and ECa+Z+TWI+NDVI 2 classes were obtained. The zoning based on ECa+Z classified clay content and the 0.95 percentile NDVI successfully. This classification was adopted for VRI since the involved variables can be related to soil water availability. Confounding effects of coarse fragments and soil water content on the clay-ECa relationship could be resolved in future studies by measuring theses variables to improve further the classification.

Acknowledgement

This work is funded by the Spanish State Agency for Research through grants PID2019-104136RR-C21 and PID2019-104136RR-C22/AEI/10.13039/501100011033 and by IFAPA/FEDER through grant AVA2019.018.