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Effects of Organic Matter Retention and Other Soil Management Practices on Long-term Productivity of a Pacific Northwest Coastal Douglas-fir Site
Barry
Flaming, Graduate Students
College of Forest Resources, University of Washington
Within the past couple months, 48 tube lysimeters were installed in a total of 6 different treatments (times 4 reps) at the Fall River study site. At each installation location, lysimeters were put in at 20-cm and 100-cm depths. Soil solution will be sampled periodically in order to monitor nutrient concentrations and leaching at the two depths. Particularly, we are interested in how increasing levels of organic matter removal (3 levels), herbicide treatment, soil compaction, and tillage affect nutrient availability and leaching losses from the system. This study was partially funded by a grant from the Olympic Natural Resources Center.
Nurrition
Amy Sidell, Graduate
Students
College of Forest Resources, University of Washington
There is an emerging trend in the forest products industry to use nutrient cycling models coupled with growth and yield models in order to anticipate nutrient deficiencies and requirements and explore various nutrient management options (Luxmoore et al, 1999). However, it has been noted that the estimated mineralization rates don’t “match up” with the observed tree growth rates. The N uptake rate required to allow the observed growth often exceeds the estimated N mineralization rates. The discrepancy and apparent missing source of available N has been termed “occult N”(Johnson, 1999). A potential source of “occult N” may lie deeper in the soil profile. Most N mineralization studies consider only the forest floor and top 15-20 cm of mineral soil, based on the idea that the bulk of the soil N is found in the upper soil profile, and thus, N mineralization at depth will be negligible. However, the amount of N mineralization below the surface soil layers may have a greater effect on the N nutrition of the trees than is generally thought. Federer (1983) found that although net N mineralization generally decreased with depth, net N mineralization from deeper mineral soil horizons made a significant contribution to the total net N mineralization in 4 forest soil profiles in New England. Furthermore, it has been suggested that N fertilization increases the mobilization of soil organic matter to the subsurface soil layers (Luxmoore, 1999), potentially carrying with it a portion of available N. Recent work has suggested that there may be an increase in N mineralization rates, and thus, N availability, in the forest floor in the long-term following N fertilization of Douglas-fir stands in western Washington (Prietzel et al., unpublished). A study which examines changes in N availability with soil depth in the long-term following N fertilization of three of the SMC’s coastal Douglas-fir stands in Western Washington is currently being conducted by Amy Sidell, a graduate student of Rob Harrison’s, as a partial requirement for a Masters degree.
Nitrogen Carry-over
Gage Wagnor, Graduate
Students
College of Forest Resources, University of Washington
Of the ten proposed nitrogen carry-over sites, seven have been harvested and foliage collected (Installations 17 Little Ohop Creek, 53 Camp Grisdale, 134 Pack Forest, 156 Coyle, 167 Hank’s Lake, 168 Simpson Log yard, and 177 Overlook). Sites 17, 134, and 177 will have all lab work completed, and have initial characterization finished December 1999. Sites 53, 156, 167, and 168 will have soil and vegetation samples collected and analyzed spring/summer 2000 for initial characterization. All sites have had seedling growth re-measured at the end of September 1999. Installation 134 Pack Forest shows increased seedling height growth for the former fertilized versus control plot over three growing seasons. Growth data for the other sites will be available from the SMC soon.
We had the opportunity to present this study and data in a poster at the 1999 SSSA National convention in Salt Lake City this fall. We received positive feedback and considerable interest in this and other areas we are investigating with the SMC. This and other posters presented at the SSSA convention will be available for viewing outside of room 214 at Bloedel Hall at the University of Washington.