SMT Lecture at BGS conference

SMT Lecture at BGS conference

Friday, September 18, 2009

Mark Shepherd, from AgResearch Ltd, Hamilton, New Zealand, recently addressed the BGS 9th Research Conference, giving the Stapledon Memorial Lecture on Balancing production and environment in New Zealand: an alternative approach to the UK? 

Mark was brought up in the UK and worked for ADAS before emigrating to New Zealand to take up a research post at AgResearch. His paper from the conference is below. Full copies of proceedings from the event are available on CD in the online shop (under the publications tab above).

BGS is grateful to the Stapledon Memorial Trust for their support. Find out more about the Trust at

Balancing production and environment in New Zealand: an alternative approach to the UK? 


New Zealand's economy is highly reliant on its agricultural sector; c. 50% of NZ's merchandisable exports are from agriculture.  NZ's economic reliance on agriculture brings with it many challenges, not least maintaining an industry that is sustainable both in terms of profitability and environment.

A brief overview of the pastoral sector

Pastoral based agriculture covers c. 75% of the accessible land area (i.e. excluding mountains etc).  Trends over the last 20 years show an increase in the national dairy herd (65%), a reduction in sheep numbers (35%) and a small decrease in beef cattle (10%).  Farmed deer is also an increasing sector (180% increase over 20 years). 

Traditionally, the NZ dairy production system has been based around low input grass/clover pastures, with animals left out all year round.   A drive for increasing productivity is resulting in increased used of N fertiliser (but still considerably less than in the UK[1]), higher stocking rates (average 2.8 cows/ha), larger farms (average herd size 350 cows) and the use of supplementary feeding.  Farms are starting to deploy restricted grazing, bringing the animals to feed pads for parts of the day during winter.

Environmental issues the same as in the UK

Greenhouse gas emissions from agriculture are calculated as 36 m tonnes co2-equivalent..  The vast majority of this derives from pastoral agriculture, either through methane from enteric fermentation or as nitrous oxide from dung and urine deposition.  Although less in absolute terms than from the UK (agriculture's contribution c. 46 m tonnes CO2-equivalent, 8% of national total), agriculture's contribution makes up c. 50% of NZ's national emissions, hence the need for action.

Lake and river water quality monitoring networks show that water quality is highly correlated with land use in the catchment, with farmed (livestock) catchments showing the worst water quality.  In these catchments there is generally a significant upward trend in nitrogen and phosphorus concentrations, though there are variations between individual catchments. Water bodies not in catchments dominated by agriculture are generally in excellent condition.

An example of New Zealand's policy response to water quality issues: Lake Taupo

The approach to tackling water quality issues is still under development and will vary from region to region because it is the responsibility of the Regional Councils.  The approach developed for Lake Taupo is worthy of special mention.

Lake Taupo, located in central North Island, is considered as one of New Zealand's 'iconic lakes'.  The Lake currently has excellent water quality but there is concern over a risk of declining quality, attributed to increased nitrogen (N) loads from development and intensification of the surrounding rural and urban land. There is a target to reduce N input to the lake by 20% over the 15 years by encouraging farmers to diversify from pastoral to alternative lower N leaching land uses through financial incentives and advisory services (MfE, 2004). 

A component of this strategy is using the OVERSEER® nutrient budget model (Overseer; Wheeler et al., 2003), to calculate a farm's historical annual N leaching loss, thus providing a baseline 'nitrogen discharge allowance' (NDA).  The NDA is the basis for a cap and trade policy mechanism to reduce N leaching. This is an early example of the use of a farm systems model to underpin water policy and this paper uses Lake Taupo as a case study to highlight the challenges of using a nutrient management tool in a regulatory role.

Overseer is a whole farm model that provides users with a tool to examine the impact of nutrient use and flows within a farm (product, fertiliser, effluent, supplements or transfer by animals) on nutrient use efficiency and possible environmental impacts. The model also provides a means to investigate mitigation options to reduce the environmental impact of nutrients within a land use (Anon. 2009).  Users range from farmers and their consultants through to policy makers and policy implementers.  The main assumptions underpinning the model are: uses long-term annual averages, i.e. the model assumes a 'steady state'; the system is in equilibrium; user supplies actual and reasonable inputs; any management practice implemented on the farm follows best practice.

The Taupo catchment and the allocation process

Farming currently comprises mainly dry stock, with a small number of dairy cow herds.  Funding for improvement is from a partnership of Ministry for the Environment, Taupo District Council and Environment Waikato (EW, the regulatory agency).  The Lake Taupo Protection Trust (LTPT) administers the funding.  The baseline N leaching (NDA) is assigned by EW.  Farms within the catchment work with EW staff to provide detailed farm records within the period 2001-2005.  Once deemed acceptable by EW staff, the data are passed to an independent third party (AgResearch Ltd) with the expertise to run Overseer based on these data.  The outcome is a calculated annual average farm N leaching loss (kg N/ha); the highest N calculated loss of the 4 years is allocated as that farm's NDA.  Future farming has to operate at or below this NDA, with scope to trade NDAs.  A key role of LTPT is to purchase NDAs, effectively removing from the catchment permit to leach N, and lowering the cap over time.


The approach adopted around Lake Taupo is innovative in that it is an output-based system, not simply relying on limiting inputs (fertiliser rates, stocking rates), for example as with the EU's Nitrates Directive.  It allows farms to develop novel approaches to limiting N losses, e.g. the use of nitrification inhibitors (Monaghan et al. 2006).  However, operating such a scheme is not without its challenges.  This presentation will discuss some of these issues.

[1] National use across all sectors in 2008 c. 350,000 tonnes N; this compares with c. 800,000 tonnes in England


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