Hybrid Poplars in Natural Buffer Systems for Agricultural Pollution Reduction and Income Enhancement
The loess soils of the Palouse Region of eastern Washington and northern Idaho provide rich, fertile lands for dry-land agriculture. This high soil fertility has prompted maximum utilization of the land, and most of the original vegetation has been removed to make way for farms and homes. In this inland region, the combinations of farming and developments on steep slopes, vulnerable soils, and lack of vegetation have led to erosion rates among the highest in the country. Likewise, streams draining the Palouse region have been ranked by EPA as among the most degraded in Washington and Idaho.
Within this background, re-establishment of riparian vegetation has long been seen as an important component of restoring functional components of both terrestrial and aquatic ecosystems in the Palouse. Hybrid poplars offer a potential means of balancing the economic need for utilization of riparian areas with the ecological benefits of higher landscape diversity and water quality protection. In this project, we address some of the practical considerations as well as some of the unanswered questions regarding use of hybrid poplars in the Palouse. One major scientific question is the actual ability of poplars to trap or sequester phosphorus and other nutrients in riparian buffers. Likewise, the fate of phosphorus during harvesting is a prime practical operational consideration in management of riparian buffers.
The objectives of this proposal are to develop sustainable farming systems in the Palouse region by:
1 promoting use of hybrid poplar riparian buffers to reduce water pollution
2 enhancing ecological functions by increasing total landscape diversity in agricultural ecosystems
3 developing fundamental information on poplar nutrient requirements, nutrient recycling, and nutrient removal essential to proper design of riparian systems for pollution control
4 establishing a core cadre of Palouse farmers skilled in poplar cultivation and with linkages to corporate producers and markets.
In contrast to 2000, 2001 was a wetter year enabling collection of more water samples, particularly overland flows associated with storm events, and from piezometers located on our main site, the Boyd plot. Significant progress was made in 2001 in completing phosphorus analyses of current water samples, and in eliminating the backlog from previous collections. Phosphorus content of the water samples, along with flow data, will be used to quantify phosphorus in surface and subsurface runoff delivered to poplar buffer strips.
Extensive autumn leaf fall samples were collected this reporting year at the Boyd site. Leaf fall data and will be used to assess retention of phosphorus in winter tree tissues, return to soils, and potential export to adjacent streams.
In addition to the water samples, we also made much progress in the laboratory analysis of hybrid poplar plant tissue. The digestion process for these analyses involves a lengthy procedure to breakdown woody tissue. A number of hot acids are added in sequence; each sample requires two to three weeks to complete. Following the acid digestion process, the plant samples are analyzed for phosphorus content using methods similar to those used for water samples. One focus of our research will be to assess if there are significant differences between clones in their phosphorus content. This may be relevant for selection of best hybrids for water quality protection in buffers.
Data from the analyses noted above are being utilized in a mass balance approach to model phosphorus capture and sequestration in hybrid poplar strips. Growth and biomass data is being modeled using biomass equation provided by Jon Johnson (WSU-Puyallup).The modeling work has begun and will be the primary focus of our efforts for the upcoming year.
Impacts and Contributions/Outcomes
Quantification of the ability of hybrid poplars in riparian buffers to retain nutrients from edge-of-field runoff is the prime focus of this research. We are not directly addressing the potential economic benefits to farmers. However, we do anticipate that demonstration of the ecological potential of poplars in these riparian settings will stimulate both producers and regulatory agencies to recognize poplar-based systems as a viable replacement for existing monocultures while at the same time supplementing or enhancing farm incomes.