Small scale soil variation and its effect on pasture yield in Southern Portugal

The general objectives of this study were to evaluate the specificity of the dynamics of soil parameters and to identify the determinant factors of pasture dry matter yield (DM) in a Mediterranean shallow soil. A topographic survey of the 6 ha experimental field was carried out using a real time kinematics GPS. Soil samples, geo-referenced with GPS, were collected in a depth range of 0 m to 0.30 m in 2004, 2005, 2006, 2007 and 2010. The apparent soil electrical conductivity (ECa) was measured using a Dualem 1S sensor under dry and wet conditions (2007 and 2010, respectively). Pasture samples, also geo-referenced with GPS, were collected between 2004 and 2007 to measure the pasture dry matter yield. A series of quantitative data analyses of soil and pasture parameters over the sampling years were carried out to identify the temporal stability as well as the inter-annual and inter-parameter correlations. The results demonstrate that the relative field elevation (RFE) has a significant influence on the dynamics of soil nutrients and, consequently, on the pasture yield variability. Also, it was possible to confirm, that, in Mediterranean shallow soils, RFE affects the spatial distribution of the soil moisture content (SMC) and bedrock depth, determinant factors of DM in dry-land pastures. A significant multi-variate regression was established between DM and bedrock depth, ECa, clay and SMC (r= 0.84; P < 0.001)