Evaluation of normalized difference water index as a tool for monitoring pasture seasonal and inter-annual variability in a Mediterranean agro-silvo-pastoral system

Abstract

Extensive animal production in Iberian Peninsula is based on pastures, integrated within the important agro-silvo-pastoral system, named "montado" in Portugal and "dehesa" in Spain. Temperature and precipitation are the main driving climatic factors affecting agricultural productivity and, in dryland pastures, the hydrological cycle of soil, identified by soil moisture content (SMC), is the main engine of the vegetation development. The objective of this work was to evaluate the normalized difference water index (NDWI) based on Sentinel-2 imagery as a tool for monitoring pasture seasonal dynamics and inter-annual variability in a Mediterranean agro-silvo-pastoral system. Forty-one valid NDWI records were used between January and June 2016 and between January 2017 and June 2018. The 2.3 ha experimental field is located within the "Mitra" farm, in the South of Portugal. Soil moisture content, pasture moisture content (PMC), pasture surface temperature (T ir ), pasture biomass productivity and pasture quality degradation index (PQDI) were evaluated in 12 satellite pixels (10 m × 10 m). The results show significant correlations (p < 0.01) between NDWI and: (i) SMC (R 2 = 0.7548); (ii) PMC (R 2 = 0.8938); (iii) T ir (R 2 = 0.5428); (iv) biomass (R 2 = 0.7556); and (v) PQDI (R 2 = 0.7333). These findings suggest that satellite-derived NDWI can be used in site-specific management of "montado" ecosystem to support farmers' decision making.