Relationships of Selected Soil Parameters and Natural Pastures Yield in the Montado Ecosystem of the Mediterranean Area Using Multivariate Analysis

Chemical, physical and biological soil parameters (OM, total N, pH, P2O5, K2O, Mg, B, WHC, free–living nitrogen fixing and rhizobial microflora properties) and pastures yield were characterized and used to determine relationships in 40 locations covering different growth conditions of the "montado" ecosystem. Soil samples were collected in Spring. Reasonable soil fertility was found. The soils presented, in general, intermediate values for OM, K2O, Mg, and Bo and low values for pH and P2O5. Populations of free-living nitrogen fixing bacteria were high, with an average of 4.2 x 107 CFU g-1 of soil, being nitrogenase activity highly variable, with an average of 34 nmoles of C2H4 g-1 of soil h-1. Rhizobial population associated to Trifolium subterraneum was high, with an average of 106 bacteria g-1 of soil, having adequate nitrogen fixing potential for the majority of the soils. Rhizobial population associated to Medicago polymorpha was low, with an average of 6.5 x 104 bacteria g-1 of soil, an insufficient value for a good nodulation, having low nitrogen fixing potential for the majority of the soils. Annual yield of natural pastures varied highly among locals, with an average of 3245 kg ha-1, a usual value for this ecosystem. In general, soil properties were independent of the soil samples. The chemical parameters OM, P2O5, K2O and total N were important factors to pasture yield. A great variability, even in soil samples collected within a short distance, was observed. A relationship between geological origin and productivity was found, being the granitic soils more productive in non-legume plants