Reducing nitrogen losses from Lake Rotorua dairy farms

Farm productivity and profitability and a healthy environment are not mutually exclusive.

Tanira Kingi from AgResearch’s Land and Environment Group, along with Stewart Ledgard and the Nutrient Management and Environmental Footprinting team, has been working with dairy farmers in the Lake Rotorua catchment area for the past three years, measuring and modelling different nitrogen applications and nutrient mitigation scenarios, with the aim of encouraging farmers to reduce nitrate leaching levels.

Modelling by NIWA and the University of Waikato have shown that nitrogen from agricultural activity around the Lake Rotorua catchment is a major contributor to the lake’s poor water quality.

Nitrate leaching from sheep, beef and dairy cattle farming affects water quality and encourages toxic algal blooms and aquatic weed growth. To achieve better water quality and a healthy lake nitrate leaching levels need to be reduced.

The Bay of Plenty Regional Council (BoPRC) has just completed  consultation with rural landowners, industry and iwi on draft rules that will set nitrogen limits for rural land in the Lake Rotorua catchment. These rules are being developed by the Rotorua Te Arawa Lakes Programme, a partnership between Te Arawa Lakes Trust, the Rotorua District Council and BoPRC. The consultation period ended on October 31, 2014.

The Lake Rotorua Stakeholder Advisory Group was established in 2012 and Dr Kingi chairs that group as an AgResearch science advisor under contract to BoPRC. The advisory group has been working with BoPRC to design the rules framework.

The current nitrogen load on Lake Rotorua is 755 tonnes, and a sustainable nitrogen limit of 435 tonnes-a-year has been determined by modellers at NIWA using their ROTAN model, to achieve a water quality target set by the community and BoPRC. That means an annual reduction of 320 tonnes of nitrogen is required for the catchment. Of that, losses from rural land needs to be reduced by 270 tonnes, about half its current amount level of 526 tonnes.

Many farmers in the region have already done much to reduce nitrogen leaching but further nitrogen reductions are required to achieve the nitrogen limit for the lake rules.

Dr Kingi also advised BoPRC in the establishment of a Land Technical Advisory Group (established September 2014), which will commission research to provide technical advice to BoPRC. AgResearch’s Dr Neels Botha (People and Agriculture) and Dr David Houlbrook (Nutrient Management and Environmental Footprint team leader) are members of that group.

Dr Kingi is developing a framework for nitrogen reduction through management options and land-use change for dairy farms in the Lake Rotorua catchment through a three-year project funded by the Ministry of Agriculture and Forestry’s Sustainable Farming Fund (SFF) along with BoPRC, DairyNZ and Ballance Agrinutrients.

The project, which involves modelling, measuring and engaging with farmers, started in July 2011 and will be complete by March 2015 (a nine-month extension was granted to enable three full years of trial data).

Field trials are being undertaken on the project’s monitor farm Parekarangai Trust, one of the Rotorua catchment’s largest dairy farm owners. Nitrogen applications have been reduced by 50 per cent and zero in comparison to the status quo applications on trial plots and nitrate leaching measured, the farm mapped, and the impacts modelled in Overseer and Farmax.

Discussion groups and ‘field days’ are run by DairyNZ to present the findings to farmers in the Lake Rotorua catchment and wider region. Being able to see the impact, for example, of reducing nitrogen fertiliser application on specific soil types in the catchment, helps farmers make better decisions for both their farm and the environment.

“We’ve been able to improve awareness in the Lake Rotorua catchment with farmers on mitigation options for their farms, to reduce nitrogen leaching,” says Dr Kingi.

In the future maintaining and improving the health of fresh waterways through sustainable farming practices will require collaboration and a commitment from all landowners and stakeholders.

Achieving the 2032 sustainable nitogen limit for the catchment will require farmers to have farm nutrient plans by 2017 that show managed reduction to each farm’s NDA to be set under the proposed rules framework.

“The reduction is significant, but it is over a 20-year period so farmers do have time to work towards the final and interim targets,” says Tanira.

“Over the next eight years to 2022, 180 tonnes of nitrogen will be taken out of the catchment under a regional council and central government agreement costing $48m. This includes 100 tonnes of nitrogen being purchased under a land use change or ‘incentives’ programme that has $40m to fund permanent land use change”.

Dr Kingi has been appointed to the Incentives Board along with Dr Tony Petch, formerly of Waikato Regional Council, and Judith Stanaway, deputy chair of Scion and chair of BDO Ltd.