Measurement of nitrate leaching losses from lysimeters on a dairy farm following conversion from forestry

ABSTRACT

Nitrate (NO₃⁻) leaching losses from lysimeters on a dairy farm were measured using an automated monitoring system designed to reduce labour and analysis costs. Nitrate leaching losses were measured under two soil types on farm (moderately deep and moderately shallow, stony silt loam) and under both urine patches and non-urine areas. The moderately deep soil leached significantly less NO₃⁻-N than the relatively shallow soil in the 2016–17, 2017–18 and 2019–20 seasons. The NO₃⁻-N leaching losses, under urine patches, were higher in autumn (168.5–190.1 kg NO₃⁻-N ha⁻¹) than in spring (3.7–4.9 kg NO₃⁻-N ha⁻¹) and summer (28.2–35.1 kg NO₃⁻-N ha⁻¹). Paddock scale NO₃⁻ leaching losses were calculated using a semi-empirical model. The calculated NO₃⁻-N leaching losses ranged from 18.3 to 47.3 kg NO₃⁻-N ha⁻¹ year⁻¹, with a mean loss of 30.7 kg NO₃⁻-N ha⁻¹ year⁻¹. These relatively low leaching losses from free-draining dairy pasture soils may be due to the recent conversion from forestry to dairy, with the soil having a high soil C:N ratio that may have caused increased immobilisation and subsequently lower NO₃⁻-N leaching loss.

KEYWORDS:

• C:N ratio
• stony soil
• UV–visible spectrolyser
• nitrogen
• automatic monitoring system

Acknowledgements

The authors wish to thank Ngāi Tahu Farming for funding and collaboration on this project. The authors also wish to thank Tara Okan (Aquaero Ltd) (NZIWTF), S::CAN Oceania technical advisor and Dr MS Srinivasan (NIWA) for invaluable climatic data. The authors also thank Lincoln University for funding and for the technical staff involved in this experiment: Trevor Hendry, Roger Atkinson, Jeneth Hendry and Shelagh Bassett. The authors also wish to thank Dave Saville (Saville Statistical Consulting Ltd) for his advice and guidance with statistical analysis.

Disclosure statement

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

Additional information

Funding

This work was supported by Ngāi Tahu Farming Limited, Te Runanga o Ngāi Tahu Group.