Differentiated Management Center-Pivot Travel Speed Based on Soil Apparent Electrical Conductivity and Remote Sensing

Abstract

Climate change, in particular the trend towards global warming, will significantly affect the hydrological cycle leading to a general reduction of the available water for agriculture. In this scenario it is therefore essential that research could focus on the development of ‘water saving’ technologies and techniques. Conventional irrigation systems are based on the application of a homogeneous input over the field, considered as a uniform spatial unit. However, within the field, can be often recognized a spatial heterogeneity of soil characteristics, topography, microclimate, as well as of crop development. These factors result in spatial variability of irrigation efficiency and a non-uniform irrigation requirement. This work summarizes the methodology followed in a “Precision Irrigation” project for implementation of variable rate irrigation (VRI) systems in large scale application using center pivots. This is based on technologies for monitoring (i) soil electrical conductivity (ECa), (ii) soil moisture, (iii) vegetation indices (Normalized Difference Vegetation Index, NDVI) obtained from satellite images, and automatic pivot travel speed control technologies. The VRI was achieved by varying the pivot travel speed. ECa maps were the basis for the definition of irrigation management zones (IMZ) in an experimental corn field of 28ha located in Samora Correia (Portugal). NDVI time-series were used to establish the subsequent prescription irrigation maps. The main result of this study was the reduction of spatial yield variability achieved in the 2017 corn crop campaign with the VRI management compared to the conventional irrigation management. This study demonstrates how a relatively simple solution could be designed and implemented in large scale, showing that precision irrigation techniques are ready to provide tangible results that represent an important contribution to the sustainability.