Proximal sensing for monitoring the productivity of a permanent Mediterranean pasture: influence of rainfall patterns

Abstract

Site-specific management (SSM) is a form of precision agriculture whereby decisions on resource application and agronomic practices are improved to better match soil and crop requirements as they vary in the field. These subfield regions consist of areas that have similar permanent characteristics. Traditional soil and pasture sampling and the necessary laboratory analysis are time-consuming and cost prohibitive, not viable from a SSM perspective. The main objective of this work was to evaluate, in two years (2015 and 2016), technologies which have potential for monitoring aspects related to spatial and temporal variability of soil nutrients and pasture yield and support to decision making for the farmer. Three types of sensors were evaluated in a 7ha pasture experimental field: an electromagnetic induction sensor (“DUALEM 1S”, which measures the ECa), an active optical sensor ("OptRx®", which measures the NDVI) and a capacitance probe ("GrassMaster II" which estimates plant mass). The results indicate the possibility of using a soil electrical conductivity probe for monitoring the characteristics of the soil, which could represent an important aid in simplifying the process of sampling and support SSM decision making. On the other hand, the significant and very strong correlations obtained between capacitance and NDVI and between each of these parameters and the pasture productivity shows the potential of these tools for monitoring the evolution of spatial and temporal patterns of biodiverse pasture in Alentejo dry-land farming systems, in two consecutive years with different rainfall patterns affecting the pasture vegetative cycle. These results are relevant for the selection of an adequate sensing system for a particular application and open new perspectives for other works that would allow the testing, calibration and validation of the sensors in a wider range of pasture production conditions, namely the extraordinary diversity of botanical species that are characteristic of the Mediterranean region.