IDENTIFYING THE DECISION MAKING PROCESSES FOR APPLICATION OF N FERTILISER TO AN INDIVIDUAL PADDOCK M. Shepherd1 1
AgResearch Limited, Ruakura Research Centre, East Street, Private Bag 3123, Hamilton 3240, New Zealand
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Introduction Traditionally, the use of nitrogen (N) fertiliser in New Zealand pasture systems has been small, with a greater reliance placed on the use of legumes to supply N through fixation of atmospheric N. However, N fertiliser use has doubled over the last 10 years (MAF, 2009). Sound guidance on N fertiliser use on farms is required to ensure economic returns are optimised while minimising potential environmental impacts. Parker et al. (1994) observed that the combination of factors influencing pasture response to N fertiliser is so large that there is usually insufficient experimental evidence alone to develop an N Decision Support System (DSS) and they suggest one approach should be to use expert opinion to supplement the response data when developing a DSS. Therefore, a web-based questionnaire was used to gather the opinions of experts from the fertiliser industry and independent consultants to identify the main decision processes when planning a fertiliser application to a paddock, as a first step in developing a DSS for N fertiliser applications. This paper reports on the findings from the survey of advisors. Approach A web-based questionnaire was developed, asking general questions on what factors experts take into consideration when planning when, where and how much N fertiliser to apply to a paddock on a dairy or dry stock farm. The questionnaire was circulated throughout the industry. There were 83 responses to the questionnaire, comprising fertiliser industry (53 responses), independent consultants (21 responses) and ‘others’ (9 responses). In total, this equated to over 1000 person-years of experience. Results and discussion In terms of typical N fertiliser use, c. 75% of respondents estimated annual N application rates to be 200 kg N/ha or less on dairy farms, with about 35% applying 150-200 kg N/ha/year. Annual N use was much less on dry stock farms, with over 90% of replies suggesting annual use of 100 kg N/ha/year or less. For an individual N fertiliser application to pasture, over 70% of replies suggested that the typical single application for a dairy farm fell into the range 26-45 kg/ha. For dry stock farms, the 26-35 kg/ha rate was the most common response, but there was also a tendency for lower application rates compared with dairying; c. 30% of responses suggested a rate of < 25 kg/ha N. The wide range of answers presented on factors that influenced these rates suggests that, not surprisingly, economics is a key driver in the decision making process. However, it seemed that there was no consistent method employed across-farms for developing an N fertiliser recommendation, and factors taken into account differed markedly between some experts. Analysis of these responses allowed a flow chart describing the decision process to be tested (Fig. 1). In summary, the key decisions appeared to follow this pattern: ‘Is feed required; ‘Will the grass respond?’; ‘How much N’; Economics, i.e. return on investment in N fertiliser; Environment, i.e. some recognition and concern over potential environmental effects, particularly on nitrate leaching.
Fig. 1. A representation of the decision process for a single N fertiliser application to a paddock.
The flow chart could serve as a useful starting point for structuring N fertiliser advice by providing a framework for the provision of more detailed information to support decision making. However, a key component of a DSS would be the provision of robust guidance on rate of N to apply. Sun et al. (2007) reviewed factors affecting pasture N response, many of which were also identified by the experts in this survey (Box 4, Fig. 1). There is a need now to focus on populating the framework with detail and especially linking to a recommendation system that is able to provide advice on rates of N fertiliser to apply. Acknowledgements Funding for this project from New Zealand’s Foundation for Research, Science and Technology is gratefully acknowledged. References MAF (2009). Amount of fertiliser applied in New Zealand, 1981 to most recent. MAF website: http://www.maf.govt.nz/statistics/fertiliser/ Parker, W. J., et al. 1994. Risk management for tactical nitrogen fertiliser applications in pastoral farming. Proceedings of the New Zealand Grassland Association 56: 223-227. Sun, X. et al. 2008. Fertiliser nitrogen and factors affecting pasture responses. Acta Agretica Sinica.
