Using drainage fluxmeters to measure inorganic nitrogen losses from New Zealand’s arable and vegetable production systems

ABSTRACT Commercial cropping farms in New Zealand (NZ) showed highly variable rates of nitrate-N leaching losses (13–148  kg/ha/year) across sites, cropping systems and seasons. Losses were measured at 1.2 m below the soil surface using a network passive-wick drainage fluxmeters (DFMs) which were installed across nine commercial farms between August 2014 and June 2016. Sites were located in the Canterbury, Manawatu, Hawke’s Bay, Waikato and Auckland regions and monitored for a period 51 to 72 months. Twelve DFMs were installed at each site and drainage volumes were validated using an established soil water balance model. At seven sites, losses were calculated using measured drainage and measured concentrations, and at two sites losses were calculated using modelled drainage and measured concentrations. Nitrate-N was the predominant form of inorganic N (96.7–99.9%) in drainage water and annual losses averaged 52  kg/ha/yr for mixed cropping systems with livestock grazing (n = 6) and 101  kg/ha/yr for mixed cropping systems with a focus on vegetable production (n = 3). While not broadly representative of all NZ cropping land uses, results from this study do, nevertheless, suggest that when drainage occurs, nitrate losses may be considerable under the land uses represented here (> 70  kg/ha/y).