Nitrogen leaching, 2011

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).



References:

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.
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