Quantification of nitrate-N losses under intensive vegetable production systems in New Zealand

Abstract

Nitrogen leaching under intensive vegetable production is a major concern in New Zealand, yet measurements remain scarce. The main aim of this study was to quantify the amount of nitrate-N leached from representative soils and vegetable crops of the Lower North Island of New Zealand.

Nitrate-N concentrations in soil and drainage losses were measured from 2020 to 2022 at two vegetable crop sites. One site had a potato-fallow rotation with six N fertiliser treatments: control, standard practice, split liquid, controlled release, good practice, and excess fertiliser. The second site, a lysimeter study, evaluated a beetroot-Pak choi rotation under similar treatments, including a reduced rate and chicken manure.

High nitrate-N concentrations were observed in topsoil (9.3–18.3 mg kg−1), subsoil (7.3–9.6 mg kg−1), and drainage water (33.8–61.9 mg L−1), with leaching losses reaching 225 kg N ha−1, particularly during fallow periods. Alternative fertiliser strategies reduced soil nitrate-N but did not consistently maintain or increase yields. Excess fertilisation did not significantly increase potato yields but greatly increased nitrate-N losses.

This study provides essential data on soil nitrate-N concentration and leaching from intensive vegetable farms.