Can fertigation increase nitrogen use efficiency in NZ dairy pastures? : A thesis submitted in partial fulfillment of the requirement for the Degree of Masters of Agricultural Science at Lincoln University

Abstract

From September 22nd 2019 - June 6th 2020, two field experiments were conducted on perennial ryegrass/white clover pastures within Lincoln University. Experiment 1 compared monthly application of urea (25 kgN/ha) in solution (fertigation) against the conventional/ recommended practice method of monthly 25 kgN/ha solid urea application with either immediate irrigation or irrigation applied after two days on production and quality of the pasture. This experiment aimed to determine if fertigation will increase nitrogen use efficiency (dry matter yield and nitrogen off taken relative to nitrogen input) when compared with the standard recommended dairy farm fertilisation methods. Experiment 2 tested the application timing of 25 kgN/ha/month of urea dissolved in water. The 25 kgN/ha was applied once per month or once per week (6.25 kgN/ha/week) to determine if smaller gaps between application timing increased nitrogen use efficiency. The two experiments had a zero-nitrogen control and were repeated across two field sites (autumn renewed pasture and permanent pasture). In the initial and repeat experiment 1, application of N regardless of treatment gave similar yield and pasture quality (dry matter digestibility, metabolisable energy, crude protein and neutral detergent fibre) at all harvests throughout the growing season. In the initial and repeat experiment 2, application of N in solution once per month or once per week gave similar yield and pasture quality throughout the growing season. In the initial and repeat experiment 1 and the initial and repeat experiment 2, the control gave lower yields to the N application treatments at the first two harvests, but similar yields and quality to the N application treatments at all later harvests. It is concluded that fertigation, as defined here, produces similar yields and quality to the standard/recommended dairy farm fertilisation methods regardless of timing frequency within a month. Areas for further research are discussed.