Relationship among soil parameters, tree nutrition and site index of Pinus radiata D. Don in Asturias, NW Spain

The relationships among soil parameters, tree nutrition and site index were examined in Pinus radiata D. Don stands in a climatically homogeneous area of NW Spain. Thirty-eight even-aged stands, ranging from 10 to 54 years, were sampled. In each stand, a representative plot of 0.1 ha was selected and different stand variables and parent material were considered. The soils in the study area are strongly acidic, with high proportions of organic matter, high C/N ratios, and low exchangeable base cation and available P concentration extracted by Mehlich 3 method (PM3). Although foliar N was sufficient in every stand studied, widespread deficiencies of K, P and, to a lesser extent, Mg and Ca were diagnosed. The foliar concentrations of P were positively correlated with PM3 and effective cation exchange capacity. The SI values ranged between 9.5 and 28.8 m and were positively correlated with foliar P and extractable K in soil. In the stands developed on quartzite and sandstone lithologies, the SI was negatively correlated with slope and foliar N respectively. The results suggest the importance of site selection and fertilizer treatment in reforestation programmes.