Saturday, 15 July 2006

Nitrate Leaching from Gorse A Study from New Zealand.

Guna Magesan1, Hailong Wang1, Peter Clinton1, and John McIntosh2. (1) Ensis, 49 Sala Street, Rotorua, New Zealand, (2) Environment Bay of Plenty, Private Bag, Whakatane, New Zealand

Nitrogen (N) is often the most growth-limiting nutrient in both terrestrial and aquatic systems. Widespread concern about increasing concentrations of nitrate in surface and ground water has focused attention on nitrate leaching in recent years. Identification of the source and extent of nitrate leaching losses on a catchment scale has been difficult. Many studies in the past have examined the contribution of N from various sources such as agricultural lands, fertilizers, grazing animals, and land application of wastes. However, no detailed work has been carried out on the contribution to surface water quality in terms of N loading of invasive, leguminous weeds such as gorse and broom, although such weeds have invaded large areas of New Zealand's agricultural and forested lands. Egunjobi (1969) studied nine ecosystems in New Zealand, involving gorse (Ulex Europaeus L.) and associated shrubs and trees. He found gorse was superior to other species in its ability to accumulate dry matter, litter and nitrogen content. The dry matter accumulation of gorse stands was at an average annual rate of between 10,000-15,000 kg/ha/yr when the stands were young (less than 10 years old). During the period of rapid dry-matter accumulation, nitrogen accumulated at a rate of 100 to 200 kg/ha/yr in gorse stands. Egunjobi (1969) also reported that the N concentration was high in the soils under gorse stands because of its nitrogen-fixing ability and the large quantities of litter it produced. In another study, Dyck et al. (1983) studied nitrate losses from different disturbed ecosystems. They found that under controlled conditions more nitrate was leached from sites under gorse, than from sites under other species. For example, nitrate-N concentrations from the gorse area averaged 5 g/m3 whereas nitrate from Radiata pine averaged 0.006 g/m3. This paper gives the literature review on the contribution of nitrate leaching to ground water and a detailed methodology of the current work carried out both under laboratory and field conditions. References: 1) Dyck, W.J., Gosz, J.R., and Hodgkiss, P.D. 1983. Nitrate losses from disturbed ecosystems in New Zealand - A comparative analysis. New Zealand Journal of Forestry Science, 13(1): 14-24. 2) Egunjobi, J.K. 1969. Dry matter and nitrogen accumulation in secondary successions involving gorse (Ulex Europaeus L.) and associated shrubs and trees. New Zealand Journal of Science, 12: 175-193.

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