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.