Seasonal Nutrient Dynamics and Vertical Nutrient Distribution in Loblolly Pine (Pinus taeda)

Abstract

Nutrient deficient stands may respond favorably to nutrient additions. However, deficient stands must be efficiently identified. Leaf area has been shown to diagnose gross nutrient deficiencies while chemical analysis of foliage can provide more specific nutritional data. Nutrient levels fluctuate throughout the year and vary with crown position. Therefore, it is important to know the proper time and location for foliage sampling.

The effects of nutritional treatments and time on foliar nutrient status were studied at SETRES. SETRES is a 2X2 factorial study of optimum nutrition and water additions in Scotland County, North Carolina, USA. Monthly foliage samples were collected and nutrient concentration and contents were determined for each sample for examination of seasonal variation. Foliage samples were collected in 1994, 1996, and 1998 and nutrient concentration and contents were determined for each sample for examination of vertical distribution patterns.

Fertilization significantly increased the nutrient content of all nutrients added. Copper concentrations increased on fertilized plots even though no Cu was added. Fertilization caused changes in seasonal nutrient dynamics of added nutrients, especially B. Retranslocation efficiencies of N, P, and K decreased with fertilization while retranslocation rates of several micronutrients increased. Concentrations of mobile nutrients increased with crown height while concentrations of immobile nutrients decreased with crown height. Distribution patterns also changed with fertilization. For example, boron concentrations on fertilized plots increased with crown height while concentrations on control plots decreased with crown height.

The ability to detect differences among sites and stability in concentrations are two criteria used to develop appropriate sampling protocols. Greatest sensitivity to detect site difference may occur at the times of year when the largest treatment differences occurred in this study. Unfortunately, concentrations are highly dynamic during those periods making the sampling window so small that it is impractical to use these periods for operational sampling. We recommend that foliage be sampled during the dormant season when nutrient concentrations are stable and there appears to be reasonable opportunity to detect difference among sites as indicated by significant treatment differences in this study. Greatest sensitivity to detect site difference may occur in the upper crown, where the largest treatment differences occurred in this study. Therefore we recommend that foliage be sampled from upper crown positions.