NGAUGE: A decision support system to optimise N fertilisation of British grassland for economic and environmental goals
ABSTRACT The poor efficiency with which nitrogen (N) is often used on grassland farms is well documented, as are the potential consequences of undesirable emissions of nitrogen. As fertiliser represents a major input of nitrogen to such systems, its improved management has good potential for increasing the efficiency of nitrogen use and enhancing environmental and economic performance. This paper describes the development, structure and potential application of a new decision support system for fertiliser management for British grassland. The underlying empirically-based model simulates monthly nitrogen flows within and between the main components of the livestock production system according to user inputs describing site conditions and farm management characteristics. The user-friendly decision support system (‘NGAUGE’) has a user interface that was produced in collaboration with livestock farmers to ensure availability of all required inputs. NGAUGE is an improvement on existing nitrogen fertiliser recommendation systems in that it relates production to environmental impact and is therefore potentially valuable to policy makers and researchers for identifying pollution mitigation strategies and blueprints for novel, more sustainable systems of livestock production. One possible application is the simulation of the phenomenon of pollution swapping, whereby, for example, the adoption of strategies for the reduction of nitrate leaching may exacerbate emissions of ammonia and nitrous oxide. Outputs of the decision support system include a field- and target-specific N fertiliser recommendation together with farm- and field-based N budgets, comprising amounts of N in both production and loss components of the system. Recommendations may be updated on a monthly basis to take account of deviations of weather conditions from the 30-year mean. The optimisation procedure within NGAUGE enables user-specified targets of herbage production, N loss or fertiliser use to be achieved while maximising efficiency of N use. Examples of model output for a typical grassland management scenario demonstrate the effect on model predictions of site and management properties such as soil texture, weather zone, grazing and manure applications. Depending on existing management and site characteristics, simulations with NGAUGE suggest that it is possible to reduce nitrate leaching by up to 46% (compared with a fertiliser distribution from existing fertiliser recommendations), and fertiliser by 33%, without sacrificing herbage yield. The greatest improvements in efficiency are possible on sandy-textured soils, with moderate N inputs.
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ABSTRACT: Ammonia volatilization from nitrogen (N) fertilizer applied throughout the year to two soil types was measured using a system of small wind tunnels. Losses from urea ranged from 12 to 46% of the applied N. Small losses, averaging <1%, were measured from ammonium nitrate (AN) and calcium nitrate applications. Factors influencing these losses are discussed. Using these results and those from other workers, emission factors for urea and AN applications to grassland in the UK were determined as 23.0 and 1.6% of the applied N, respectively. Emission factors for these fertilizers when applied to arable land were estimated as 11.8 and 0.8%, respectively. The emission factor for all other applied N (as straight and compound fertilizers) was assumed to be similar to that for AN. Calculations showed that fertilizer applications to agricultural land in the UK contributes 34 kt NH3-N per year, equivalent to 17% of the total annual NH3 emission.Environmental Pollution 01/1997; 95(2):205-11. · 3.73 Impact Factor
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ABSTRACT: Factors influencing the seasonal and daily variation in denitrification rates in grazed swards were examined at 5 experimental sites in England with wide ranging environmental/geographic conditions. There was a wide range of fertilizer inputs at each site. Rates of denitrification were estimated by a coring and field incubation technique using acetylene to inhibit the reduction of N2O to N2. Major features of the detailed results from two of the sites were: (i) the large ranges in rates of loss, (ii) the relatively low contributions to total annual loss during autumn and winter, (iii) the apparent association of high rates of loss with fertilizer additions made when the soil was wet or immediately preceding a rainfall event, and (iv) significant losses from soil at 10–30 cm in the profile. Multiple quadratic regression analysis of the effects of soil NO3 --N, soil temperature and water was used to explain variability in rates of loss. When separate regressions were fitted within each site × year × season × fertilizer level subset, 51% of the variation in loss was explained on a poorly drained fine loam/silt but only 38% on a freely drained loam.Plant and Soil 01/1991; 131(1):77-88. · 2.64 Impact Factor
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ABSTRACT: A simple, semi‐empirical model for estimating nitrogen (N) leaching losses and critical N application rates in dairy pasture systems is described. The model uses the annual rates of major N flux processes in the soil‐plant system to determine the potentially leachable N pool (mineral N and mineralisable N), and estimates the N leaching loss based on measured relationships between the N leaching loss and the potentially leachable N in the soil. The N flux processes considered in the model include fertiliser or effluent N applications, biological N fixation, soil N mineralisation and immobilisation, plant N uptake, animal N return at the urine patches, ammonium volatilisation, and denitrification. The impact of drainage on N leaching is taken into account by normalising the N leaching loss to a per 100 mm drainage basis. A quadratic equation is used to describe the relationship between the N leaching loss and potentially leachable N. Tests of the model predictions against other experimental data showed reasonable agreements between the estimated N leaching losses with those measured. The modelled critical N application rates which would cause the annual average N concentration in the drainage water to reach the drinking water standard (11.3 mg N r) are: 390–392 kg N ha for cut and carry, and 162–192 kg N ha for grazed pastures if urea is used; and 588–600 kg N ha for cut and carry, and 248–301 kg N ha for grazed pastures if dairy shed effluent is used.New Zealand Journal of Agricultural Research - N Z J AGR RES. 01/2000; 43(1):139-147.