- Kraske, Charles R.
University of Maine, Orono, Forestry
Intensive forestry practices intended to increase growth rates and yield of wood result in an increased demand on the nutrient supplying capacity of forest soils. Determining the ability of specific soils to provide available nutrients for seedling and tree uptake will play a vital role in the success of these intensive practices. The objectives of this study were to examine differences between soil properties and nutrient availability of major soil horizon materials (O, AP, B), determine the effect of soil horizon material and nutrient availability on conifer seedling growth, identify nutrient availability indices most directly related to conifer seedling growth, and to determine which seedling characteristics best correlated with nutrient availability.
Bulk Samples of Two Horizons of three typical forest soils were collected. Soil pH, organic matter content, and total N and C contents were determined with each soil type. N, P, K, Ca, Mg, Mn, and Na availability, along with Al and Fe concentrations, were measured for each soil type using a variety of availability indices.
As a result of organic matter content and soil pH, there were significant differences between the levels of available nutrients, Al, and Fe found in the major horizon types. These results emphasize the need to assess nutrient availability in Northeast forest soils for morphologically distant horizons separately. Nitrogen and phosphorus appeared to be the growth limiting nutrients in this study, as N and P foliar concentrations were int eh critical to deficient range for most of the seedlings. Base cations did not appear limiting nutrients since foliar concentrations were adequate and regressions between extractable cations and conifer seedling growth were not significant. Soil N values determined by the one and two week anaerobic and two week aerobic incubations were more closely related to seedling characteristics than values determined by any chemical index. Soil P values as measured by NH4OAc extractions (pH 4.8 or 7.0) and the Mehlich 3 extraction were also closely correlated with seedling growth. P extracted by the Bray method was poorly correlated with seedling characteristics. Foliage nutrient uptake and seedling growth. P extracted by the Bray method was poorly correlated with seedling characteristics. Foliage nutrient uptake and seedling dry weights were the characteristics best related to available nutrient levels. Because of the limited data of the study, further evaluation of the nutrient availability indices should be conducted, both in the lab and field, to corroborate the conclusions of this study.