Nitrogen leaching losses from forests in New Zealand

Abstract

Regional governing organisations in New Zealand are developing new policies to assess and manage the effects of land use intensification on water quality. Such policies require an assessment to be made of potential nitrogen leaching losses from different land uses, particularly where land use may be becoming more intensive. This review compiles the information on nitrogen concentrations and fluxes in stream and soil water drainage from indigenous and planted forests in New Zealand. Nitrogen concentrations and losses in streams from undisturbed indigenous forests and from planted forests established on land that has not been developed for agriculture are low. Nitrogen concentrations and losses in streams draining forests established on pasture land are commonly higher than in streams from indigenous forests and from forests planted on non-agricultural land, however most of the values for planted forests on pasture land were influenced by high volcanic nitrogen inputs. The impact of afforestation of pasture land on nitrogen leaching is described, as are the effects of planted forest management practices including fertilisation, harvesting and herbicide use. Nitrogen leaching is generally not greatly affected by forest management practices, however fertilisation can cause large leaching losses in coastal sand forests. While nitrogen leaching from planted forests is normally less than from other major land uses, there are key times during the forest rotation when nitrogen leaching may occur, particularly in forests planted on coastal sands or pasture land. It is advantageous to minimise leaching at these key stages to limit adverse effects on the environment and maintain nitrogen in the soil for the benefit of crop nutrition. Measures to reduce nitrogen leaching losses in forests are discussed, as are practices to minimise nitrogen leaching of forest plantings in catchments with high nitrogen soils, where forests may be planted specifically to reduce nitrogen loss to sensitive waterways.

River water quality changes in New Zealand over 26 years: response to land use intensity

“…With a 28-year mean age of harvest, NZ will experience its greatest coverage and intensity of forest disturbance around 2025. When combined with drought and intense storms, the potential for nutrient and sediment mobilization is high, especially given that approximately 45 % of these plantings occurred on high-producing grasslands (NZFFA, 2014) where many of the legacy nutrients will be exported to rivers during forest harvest (Davis, 2014). If carbon prices continue to stay low, there will be a high likelihood that many of the harvested forests will be converted to pasture, adding even more nutrients to NZ rivers (PCE, 2013).…”

Water quality in New Zealand’s planted forests: a review

“…Furthermore, underlying natural processes and legacies from historical land-use practices can sometimes have a greater influence on some aspects of water quality in planted forests than the current land use itself (Davis 2014;Parkyn et al 2006;Quinn et al 1997).…”

“…For example, total phosphorus (TP) and dissolved reactive phosphorus (DRP) concentrations declined within 4-5 years of planting a small (34 ha) pasture catchment in the Central North Island in P. radiata in comparison with an adjacent pasture stream (Cooper et al 1987). Nitrate-nitrogen (NO 3 -N) response in the afforested catchment varied over time, but long-term records showed a decline in NO 3 -N within 5 years of planting (Davis 2014).…”

“…The reasons for the higher levels of nutrients recorded in some studies were not always obvious, but underlying lithologies and associated soils, previous land-use practices and localised inputs of atmospheric N are possible contributing factors (Davis 2014;Macaskill et al 1997;Parkyn et al 2006).…”

Effect of Pine Waste and Pine Biochar on Nitrogen Mobility in Biosolids

“…In both cases, NO 3 − -N may be leached. Excessive loadings of mineral N are associated with high levels of NO 3 − -N leaching, which can contribute to eutrophication of lakes, rivers, and groundwater (Davis, 2014) and thus, should be prevented.…”