Reduced nitrate leaching from livestock in a large lake catchment in New Zealand

Lake Taupo, a major New Zealand tourist attraction, has declining water clarity due to increased phytoplankton levels. Increased phytoplankton levels are a response to increasing nitrate levels in groundwater and groundwater-fed streams entering the lake. Urine from grazing animals is the largest, manageable, contributor to ground water nitrates. As means of reducing nitrate emissions, changed management on, and changed use of, farmland are options explored in two trials reported here. Production and nitrogen (N) leaching from annual and perennial crops have been measured over 2 years. Similar measurements were made in a cattle grazing trial comparing all year grazing (AYG), no winter grazing (NWG) and no grazing (NG - baleage). Lucerne, pasture, triticale+annual ryegrass and forage maize+annual ryegrass yields were variable between years and lower than expected. Nitrate leaching from perennial crops was lower than from annual crops (I I 28 v 50-223 kg N0(3)-N ha(-1)). N utilisation was similar in NWG and AYG (177 kg N ha(-1) yr(-1)) but N03-N leaching losses in AYG were significantly greater than those in NWG and NG (16.6, 5.6, 2.4 kg N0(3)-N ha(-1) yr(-1) respectively). Management options incorporating the low nitrate emission systems are being evaluated for agricultural and economic feasibility and, using selected scenarios, will be extrapolated across the farmed landscape in the Taupo Catchment to predict potential nitrate leaching reductions.