Management zones delineation on grazed permanent pastures using low cost geophysical surveys

Abstract

Spatial variability of soils used for grass-based livestock production is as high as soils used for agricultural production. Thus, site-specific management (e.g., fertilisation or grazing intensity) might be implemented after assessing the spatial distributions of the main soil properties (e.g., texture and macronutrients). However, to do so, cheap and reliable techniques are needed to delineate zones of similar production potential in order to improve profitability of low-income farms. In this sense, the use of soil apparent electrical conductivity (ECa) measurements from a contact sensor is one of the most promising approaches. ECa technique was evaluated for a grassland site (2.3 ha) in Évora (Portugal), where important soil properties, such as clay, silt and content, cation change capacity, organic matter and macronutrients content, related to soil fertility and topography were known. For comparison, 10 soil samples were taken throughout the field at different sites, in a depth range of 0–0.30 m, considering the maximum depth of the roots in the pasture, approximately 0.2–0.3 m. Analyses showed that ECa results as independent variable, were significantly correlated to some of the main soil variables, allowing to visualise the spatial distributions in a geographical information system (GIS). Moreover, the delineation of management zones through a clustering algorithm revealed, after a principal component analysis, that the most important contributing properties to soil variability were elevation and clay content. Accordingly, the proposed approach, using a low-cost ECa surveys, can be used to implement precision farming for permanent pastures. This may allow to apply more cost-effective field management and additional environmental, economic, and energetic benefits.