Archive for the category: Nitrogen budgets and calculators to aid decision making

S F Ledgard¹, J Rendel², S Falconer¹, T White¹, S Barton³ and M Barton³

¹ AgResearch Ruakura Research Centre, Hamilton 3240, New Zealand, stewart.ledgard@agresearch.co.nz

² AgResearch Invermay Research Centre, Mosgiel 9053, New Zealand

³ Farmer, Hingarae Road, R.D. 1 Turangi 3381, New Zealand

Abstract

Farms in the Lake Taupo catchment of New Zealand have a farm-specific nitrogen (N) leaching limit per hectare. A beef cattle finishing farm in the catchment was used as a case study to compare optimised scenarios with and without N constraints and with flexible supply to meat processing companies or a requirement for regular supply to restaurants based on a premium price for beef with a low N footprint. Scenario analyses included evaluation of sourcing surplus young beef cattle from breeding farms or from dairy farms. A life cycle assessment method was used to estimate all reactive N emissions through the life cycle of beef. Leaching of N from the finishing farm was <20 kg N/ha/year from N-constrained scenarios and 43 kg N/ha/year with no N constraint. Profitability decreased with N constraints and with regular beef supply requirements, which could be countered by a price premium. The N footprint from beef production ranged from 95 to 156 g N/kg meat, being least from the N-constrained scenarios. It was lower from dairy-derived beef and higher with regular beef supply requirements. The farm stage dominated the life-cycle N footprint (78% of total emissions) with the only other significant contributor being the final waste (sewage) stage at 21% of the total, based on a traditional urban waste water treatment system. Preliminary analysis indicated that the Taupo town sewage system of land application to pasture for silage production and feeding back to cattle can further decrease the N footprint over the life cycle of beef.

David Wheeler¹, Caroline Read ²

¹ AgResearch, Ruakura Research Centre, Hamilton, New Zealand, 3124, david.wheeler@agresearch.co.nz

² Overseer Management Ltd, PO Box 11785, Wellington, New Zealand, 6142

Abstract

OVERSEER^® Nutrient Budgets (OVERSEER) is a whole-farm nutrient budgeting tool using a yearly time scale. It calculates a nutrient budget for the farm, taking into account inputs, outputs, and some of the internal recycling of nutrients around the farm. The model integrates multiple animal enterprises (dairy, sheep, beef, deer, dairy goats) and different land uses, including pastoral, cropping (arable, vegetable, fruit), and cut and carry areas. Nutrient budgets are calculated for the nutrients nitrogen (N), phosphorus (P), potassium (K), sulphur, calcium, magnesium, and sodium. With an increased emphasis on water quality, the model is being used to assess N leaching from pastoral farms. This paper discusses some perspectives and emerging practices that are occurring as a result of using an integrated farm systems model like OVERSEER, with a focus on urine patch, irrigation, effluent management and fodder crops.

Cameron J P Gourley¹, Kerry J Stott² , Sharon R Aarons¹, Innocent Rugoho¹

¹ Agriculture Research, Ellinbank Centre, Department of Economic Development, Jobs, Transport and Resources, Ellinbank, Victoria 3821, AUSTRALIA

² Agriculture Research, Parkville Centre, Department of Economic Development, Jobs, Transport and Resources, 32 Lincoln Square North, Carlton, Victoria 3053 AUSTRALIA

Abstract

Nitrogen (N) inputs are critical for productive and profitable grazing-based dairy systems, but inefficient use can contribute to excess N in the broader environment. Whole-farm N balance (WFNB) provides the commonly used recovery metrics: N use efficiency (NUE), milk production N surplus and N surplus/ha; all recognised as environmental performance indicators. We determined annual WFNB for the Australian dairy industry over a 22 year period, and for a diverse range of 16 commercial dairy farms for the 2013/2014 production year. The industry as a whole demonstrated a long-term declining trend in all N recovery metrics, associated with ongoing intensification. Individual farms in a single production year had a wide variation in NUE, productivity N surplus and N surplus/ha, and a poorly defined relationship between NUE and N surplus/ha. At an industry level, the determination of average farm NUE, milk production N surplus and N surplus/ha provides a useful environmental performance indicator but total industry N surplus needs to be adjusted for changes in contributing land area. For individual farms in any production year, we suggest that in addition to quantifying annual N surplus, employing standardised indices that specifically target key N fluxes and utilisation efficiencies at the component level. These will establish more appropriate industry benchmarks for improving N recovery and inform and improve on-farm N management decisions.