Potential for differential potassium fertilizer application in permanent pastures in Alentejo – case study

Abstract

Alto Alentejo region in Portugal has over 200,000 ha of grazing permanent pastures. Here, the soils do not generally need potassium (K) fertilization due to the bedrock richness. The objective of this study was to evaluate the spatial and temporal soil K dynamics, over ten years, in an agro ecosystem and the potential for implementing site specific fertilizer management. The evolution of mean soil K concentration in the experimental field study suggests that grazed pastures, as far as the K cycle is concerned, are a steady state system. This study, however, shows that the experimental field is dominated by a large spatially anisotropic trend. It can be stated that the combined effects of an undulated landscape, with sparse trees and animals with selective grazing and heterogeneous deposition of dung and urine, provide a notable spatial variability of soil K concentration. The K temporal stability is confirmed by the predominance of stable areas in experimental field. Within these, around 45% shows soil K concentrations below average soil K concentration. Based on recommendation of K in the soil, this study demonstrates the interest and the potential for using variable rate technology (VRT) for site-specific K management in pastures in Southern Portugal.