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).

KEYWORDS:

• Nitrate leaching
• arable production systems
• vegetable production systems
• drainage fluxmeters
• soil hydraulic properties

Acknowledgements

Sites A to F were initially funded through a collaborative initiative between the New Zealand Ministry for Primary Industries (Sustainable Farming Fund project #401484), the Foundation for Arable Research, HortNZ Vegetable Research and Innovation, Environment Canterbury, Horizons Regional Council, Hawke’s Bay Regional Council, Ravensdown Fertiliser Cooperative and The New Zealand Institute for Plant and Food Research Limited. Sites G to I were funded through a collaborative initiative between HortNZ Vegetable Research and Innovation, Auckland Council, Waikato Regional Council and The New Zealand Institute for Plant and Food Research Limited. Operational funding for Sites A to F and G to I ended in July and September 2017, respectively, with subsequent funding for the period ending 28 February 2018 provided by the Foundation for Arable Research, The New Zealand Institute for Plant and Food Research Limited and Ravensdown Fertiliser Cooperative. For the remaining time, the network was funded through another collaborative initiative between the Ministry for the Environment (Fresh Water Improvement Fund) and the same group of research, industry and regional council organisations.

Assistance with installation of the sites was provided by Shane Maley, Mike George, Moe Jeram, Paulo Zuccarini and Christina Finlayson.

We thank the collaborating growers for their support and interest in the project. We would also like to acknowledge Diana Mathers (Foundation for Arable Research) for her invaluable project management and collaborative engagement efforts.

We are also grateful for the helpful comments provided by reviewers.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by Auckland Regional Council; Foundation for Arable Research; Ministry for the Environment, New Zealand [Grant Number 22353]; Ministry of Primary Industries [Grant Number 401484]; Horticulture New Zealand; Ravensdown Fertiliser Cooperative; Horizons Regional Council. Hawke's Bay Regional Council; Environment Canterbury; The New Zealand Institute for Plant and Food Research Limited.