Interpretation of foliar nutrient concentrations in young Pinus radiata D. Don plantations on abandoned agricultural lands in Galicia

Abstract

The nutritional status of 14 4-5-yr-old Pinus radiata plantations on abandoned agricultural lands in Galicia (NW Spain) was studied. Nutritional status was assessed using macronutrient foliar analysis followed by the critical levels method, foliar nutrient ratios interpretation and the DRIS system. The relationships between foliar and soil nutrient levels and between annual growth and foliar and soil data were also analyzed. Mg and P deficiencies were the most common in foliage samples. Foliar N concentrations were always over the critical level and foliar N:P ratios were unbalanced in almost all sites. The annual height, diameter and volume growth were positively correlated with foliar P concentrations and negatively correlated with foliar N:P ratio. The P nutrition seems to play an important role in the plantation’s development. However, both, the high levels of available P in the soils, and the lack of a significant correlation between foliar and soil P levels, suggest that other factors, such the N excess or the soil pH, may interfere in the P assimilation. On the contrary, exchangeable soil Mg levels were not very high and were significantly correlated with foliar Mg. Thus, a positive growth response to Mg fertilization can be expected.