Nitrate leaching and productivity of some farming options in the Lake Taupo catchment

Abstract

To farm efficiently within a nitrogen (N) cap, Taupo farmers need to know the relative N-leaching potential of existing and potential farming enterprises. We quantified production and N leaching in four 'cut and carry' cropping treatments (Trial 1), and two cattle grazing systems (Trial 2), in replicated trials over 3 years. Annual crop systems Triticale and Maize, which included annual ryegrass as a winter cover crop, leached 104 and 222 (1 year only) kg nitrate-N/ha respectively, while perennial crops Lucerne and Pasture leached 19 and 12 kg nitrate- N/ha/yr respectively. In grazing systems, removing cattle between May and August reduced N-leaching from 13 to 5 kg nitrate-N/ha/yr and could be achieved by strategic selling and buying, grazing-off, or using feed-pad systems. N-fertilised annual crops, can lead to high N leaching whereas in cattle grazing systems, strategic destocking over winter can greatly reduce N leaching. Some enterprise choices based on quantified N leaching data can now be made. Keywords: cropping, lucerne, maize, triticale, cattle grazing, nitrogen leaching, environment