Simulation of mitigation strategies to reduce nitrogen leaching from grazed pasture

Abstract

Strategies to reduce nitrogen leaching losses from pastoral farming in the Lake Taupo catchment are required to address declining water quality in the lake. This study used a biophysical whole farm simulation model, EcoMod, to explore the potential for four mitigation strategies to reduce N leaching in a soil and climate typical of the region. The strategies were use of: a nitrification inhibitor (DCD); steers instead of heifers (STEER); salt as a diuretic (SALT) and; high sugar ryegrass (HSG). These were compared to a BASE scenario of grazed heifers. Each of the simulated mitigation strategies showed the potential to significantly reduce nitrogen leaching compared to BASE by 25 to 45%. All mitigation strategies reduced nitrogen fixation due to more efficient plant use of nitrogen from urinary and faecal sources. This also contributed to an increase in pasture intake for SALT, STEER and DCD, but not for HSG. These mitigation strategies were explored at a single-paddock level and planned experimental studies will further examine the effectiveness of the strategies. Keywords: nitrogen leaching, mitigation, Lake Taupo, simulation, EcoMod