Foliar nutrient status and tree growth response of young Pseudotsuga menziesii Mirb. (Franco) to nitrogen, phosphorus and potassium fertilization in Galicia (Northwest Spain)

Abstract

The nutritional status of 14 young Pseudotsuga menziesii plantations on abandoned agricultural land in Galicia (Northwest Spain) was studied and related to growth response to N, P and K fertilization. Nutritional status was assessed using macronutrient foliar analysis followed by the critical levels method and foliar nutrient ratios interpretation. Douglas fir showed high N levels in control foliage samples. Foliar N:P and N:K ratios were greatly unbalanced in many sites. Foliar Mg concentrations were below the satisfactory levels in all cases and P, K and Ca were deficient in several cases. Height growth of untreated plants correlated positively with foliar P, K and Ca concentrations and negatively with total soil N in the surface soil. Thus, P, K and Ca were classified as favorable parameters for Douglas fir growth, whereas N was classified as an unfavorable parameter. According to this, the application of urea significantly reduced the Douglas fir growth in several trials. However, there was a lack of consistence between the foliar diagnosis and the growth response to superphosphate and potassium sulphate applications at the end of the first growing season following fertilization. This response was much lower than expected after the foliar diagnosis. The low fertilization rates used, the short time passed between fertilization and response measurements or other factors such as Mg nutrition and other nutrient interactions, could be the cause. In conclusion, N fertilization is not recommended in young P. menziesii plantations on abandoned agricultural land in Galicia whereas further research is needed to generate a fertilization recommendation for the other nutrients.