|Abstract or Summary
- Soil physical, chemical, and biological components as well as climate and
physiographic characteristics can interact to have a great effect on forest regeneration
and seedling growth response to different establishment activities. The objective of
this project was to increase the understanding of the interactions between soil type,
controlled-release fertilizers, and soil water content on Douglas-fir [Pseudotsuga
menziesii (Mirb.) Franco] seedlings.
Douglas-fir seedlings were sown in late February 2001 and transplanted into
pots at OSU in mid-May. Two forest soil types (Jory and Apt) were mixed with five
different controlled-release fertilizer (CRF) treatments (Customblen®, Wilgro®,
Osmocote®, and two Apex®), and one control unfertilized treatment. Three moisture
regimes were randomly assigned to each of the soil/fertilizer treatments (12, 18 and
24% soil water content based on soil dry weight). The same volume of soil was put
into each pot. The same weight for each soil (2700 g of Jory and 2300 g of Apt) was
used based on volume. The study design was a factorial completely randomized block
design with five replications.
Seedlings differed greatly by fertilizer treatment, soil type, and moisture
regime in many of their morphological and nutritional characteristics. Seedlings grown
in the wettest moisture treatment were larger than those grown in the drier treatments,
and had the greatest nutrient concentrations and contents.
Unfertilized control seedlings were larger in the Apt soil than in the Jory soil.
These differences were also apparent with the application of fertilizers. Among the
fertilizers, Wilgro® tended to have the greatest effect on seedlings, especially under
the wettest moisture regime. Vector analysis showed that for some nutrients, Apex®
(Amn), Apex® (Nit), and Osmocote Plus® had antagonistic or toxic effects. For these
fertilizers, a higher P concentration remaining in the prills, correspond to the lower
soil total and available P concentration. FESEM pictures suggested that a large
proportion of nutrients were still inside the prills. Wilgro® and Customblen® were
mostly dissolved at the time of sampling, and corresponded to greater total and
available soil Phosphorus with these two fertilizers.
The use of CRF in the Pacific Northwest offers potential to optimize resources
and meet seedling nutritional requirements. The study results suggest that CRF
application must consider soil moisture availability with more conservative
applications on dry sites.