Trees Used As Effluent Sponge
6 May, 2002
Effluent from dairy shed is in the spotlight. Run off into waterways is causing problems throughout the country. A solution is needed and HortResearch is helping.
A team of HortResearch scientists, making use of willows and poplars, has created a trial site to act as an effluent sponge. An area of coppice style trees are being used to soak up the effluent, with the added benefit that the foliage can be fed back to the stock.
Poplar and willow trees establish large root systems and use large amounts of water. As they can repeatedly be coppiced, and grow again quickly, they can be used to remove the nitrogen in dairy shed effluent.
The team, led by Val Snow, has established a three-year demonstration trial incorporating willows and poplars along with a pasture control area on a southern Wairarapa dairy farm where nitrogen-rich effluent is directly irrigated onto the trees.
The project, supported by MAF’s Sustainable Farming Fund, New Zealand Dairy Research Institute and the Poplar and Willow Research Collective, will determine the efficacy of using poplars and/or willows in a self-renewing, coppicing system to reduce the amount of nitrate leaching. It will also determine the potential nutritional value of the coppiced material for dairy cows or other livestock.
Dr Snow said measurements are taken of the amount of nitrogen in the effluent irrigated onto the pasture and trees. Measurements of nitrogen are also taken from the coppiced trees and harvested pasture, and the amount accumulated in the soil and leached from the pasture and tree systems.
An outcome of this project will be the ability to assess the usefulness of such a system for dairy farms. It will provide information on how to match the area of trees to herd size, along with tree management information and potential uses for the coppiced foliage as well as outlining practical management issues in relation to soils and climates.
Should this system prove effective it could be extended to cover all the major dairying regions of New Zealand, and will help with land management and river protection. The project is run in close collaboration with AgResearch, New Zealand Dairy Research Institute, Wellington Regional Council and Environment Waikato.
Other expected benefits will be reduced levels of nitrate contamination in the environment and improved profitability compared to other riparian plantings. Perhaps more importantly, it will contribute to cleaner waterways.