Environmental Reporting, Ministry for the Environment and Statistics New Zealand
"Nitrogen is an essential nutrient for plant growth. It occurs naturally, but in agricultural systems more nitrogen is commonly added to soils as fertiliser or from livestock waste. Not all the additional nitrogen can be taken up by plants. Some nitrogen will drain (leach) as nitrate from the soil and can enter waterways, potentially causing ecological harm. The amount of nitrate leaching from the soil varies around the country, as a result of different land uses, climates, and soils. This dataset relates to the ""Geographic pattern of agricultural nitrate leaching"" measure on the Environmental Indicators, Te taiao Aotearoa website. "
Source: Landcare Research
Method: "The amount of nitrogen that leaches from the soil (nitrogen leachate) is a fraction of the total amount that is added to land. The amount of nitrogen leached depends on the rate of plant uptake, the amount of rainfall, and the texture and type of soil (McDowell et al, 2008). It is also affected by individual farm characteristics such as the stocking rate of grazing animals. Nitrogen leachate is defined as the mass of nitrogen drained through the soil and below the plant root zone. Typically, leached nitrogen is in the form of nitrate, which drains away easily through soil compared with other forms of nitrogen. As it leaves the plant root zone, nitrate can enter groundwater, eventually feeding into rivers, streams, lakes, and, ultimately, the sea. The nitrate-nitrogen leaching rates for the map were estimated from version 5.4 of the OVERSEER® Nutrient Budgets model (AgResearch, 2011) for combinations of soil and climate, using the method outlined in Dymond et al (2013).
AgResearch (2011). OVERSEER®. Available from www.overseer.org.nz. Dymond, JR, Aussiel, A-GE, Parfitt, RL, Herzig, A, & McDowell, RW (2013). Nitrate and phosphorus leaching in New Zealand: A national perspective. New Zealand Journal of Agricultural Research, 56(1), 49–59, doi: 10.1080/00288233.2012.747185. McDowell, RW, Houlbrooke, DJ, Muirhead, RW, Müller, K, Shepherd, M, & Cuttle, SP (2008). Grazed pastures and surface water quality. New York: Nova Science Publishers. "