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Nitrogen leaching under grazed lucerne
Malcolm McLeod, Manaaki Whenua - Landcare Research
Completed March 2020
Introduction
Lake Taupō Protection Trust (LTPT), the Sustainable Farming Fund (SFF), Pāmu, Fertiliser Association of New Zealand, and Waikato Regional Council funded a field trial on N-leaching under grazed lucerne on a Taupo Lake Care member's farm. The project objective was to use lysimeters to quantify nitrogen leaching due to livestock urine from autumn-grazed lucerne or ryegrass/clover pasture.
Grazing was simulated by the application in autumn of ewe lamb or cow urine collected from animals whose diet included lucerne. Results showed that a single autumn urine application (simulated grazing) significantly increased N leaching compared to controls, but no significant differences were found between pasture or lucerne vegetation. When expressed at the paddock scale, assuming urine patches cover 3% of the paddock during a single grazing, the three-year average nitrogen leaching loss from the autumn grazing was approximately 2 kg TN/ha/yr under cow grazed lucerne and approximately 3 kg TN/ha/yr under cow grazed pasture. Controls (no grazing) showed leaching losses of approximately 1 and 2 kg TN/ha/yr for lucerne and pasture respectively.
"Studies like these are critical to understanding the nutrient flows in different farm systems," says Greg Sneath, Executive Manager, Fertiliser Association of New Zealand.
"It helps provide the information needed for building the tools for management and mitigation of nitrogen losses in productive farm systems."
