Groundwater, Nitrogen and Dairy Farming in the Waikato

In the world, about 69% of freshwater is contained in snow and ice with about 30% in groundwater. Rivers and lakes only make up about 0.27% of the total world freshwater.

In the Waikato, groundwater ‘…makes up about 90 percent of the region’s fresh water resource’ (1). So while the focus may be on Lake Taupo, the Waikato, Waipa and Waihou Rivers, their tributaries and a number of small lakes, they only make up about 10% of the water in the region – the rest is in the ground.

Te Waihou Springs

Te Waihou Springs

Nitrogen pollution is the present key issue for groundwater quality. Nitrogen is one of the most important nutrients in our farming system. However if it not properly controlled, it can lead to nitrogen losses below the root zone of pastures and crops, and thence into the groundwater. This is commonly called nitrogen leaching.

Groundwater can exit from springs or flow into streams, rivers and lakes over a short period of time, but mostly it takes a number of years or decades (2).

‘Nitrogen levels in both rivers have been slowly but steadily rising over the last 20 plus years, and will continue to rise if nothing is done. Nitrogen in groundwater can take decades to emerge into surface water, and this indicator of water quality will probably worsen before it improves.’ (3)

Excess nitrogen is no only a groundwater problem, but can have a negative effect on soil micro-organisms (such as bacteria, fungi and larger organisms like worms). Soil micro-organisms play a key role in the storage of nutrients in the soil, making them plant available and creating and maintaining good soil structure. The application of excess nitrogen, and other nutrients, can destroy micro-organisms thus leading to a loss of soil structure, soil compaction, erosion and minimal soil water holding capacity.

According to the law, the adverse environmental effects of nitrogen leaching into groundwater arising from applying nitrogen onto land needs to be avoided, remedied or mitigated (see Section 5, Resource Management Act 1991 (‘RMA’)). Under the RMA, territorial authorities have the responsibility to apply this law, including WRC and Environment Canterbury (‘EC’).

EC has recently developed rules to address the adverse effect of nitrogen leaching into groundwater. A key part of these rules in the use of computer programs/modelling tools to calculate a farm’s nitrogen baseline. This is arrived at by a ‘nitrogen loss calculation’ which is the discharge of nitrogen below the root zone.

The most popular tool appears to be a freely available program called Overseer (4), developed and owned by the Ministry for Primary Industries , Fertiliser Association of New Zealand and AgResearch. Other programs have been approved by EC, WRC and other territorial authorities. A farmer inputs a whole lot of data about their farm (eg. relating to stock, fertiliser, soil/sub-soil types, pasture species, fertilisers applied, effluent systems, feed/stand-off pads, lactation period, crops, feed supplements) and the tool outputs reports relating to nutrients, energy, greenhouse gases, pasture production and other information. In relation to nitrogen leaching, the tool specifically does the nitrogen loss calculation which is expressed in kg/ha/yr ie. the amount of nitrogen discharging into the ground below the root zone.

So in relation to nitrogen leaching for any farm, with its specific soil/sub-soil types and farm management/system, Overseer can calculate a specific amount of nitrogen leaching into the groundwater from that farm. While I cannot comment on the science behind the tool, this is impressive stuff.

EC’s rules follow this process (5):

  • All farms (over specified sizes) calculate their nitrogen baseline, that is, the total nitrogen leaching on the farm expressed in kg/ha/yr.
  • Farmers find out which nutrient zone their farm is in. EC has divided the Canterbury region into five ‘nutrient allocation zones’, depending on the condition of groundwater. This ranges from the Lake Zone catchments which are sensitive to nutrient enrichment so increases in nitrogen leaching must be avoided, to Green/Blue Zone where there is capacity for the zone groundwater to absorb additional nitrogen.
  • Farms limit their nitrogen according to their baseline and zoning. There are detailed rules but generally the nitrogen leaching ranges from no increase in the nitrogen baseline (providing it is under 10kg/ha/yr), to 10kg/ha/yr , to 20kg/ha/year – all depending on the zone in which the farm is located.
    The year ending 30 June 2014 was a transition year for farmers to allow them time to implement compliance. So this season, 2014/2015, is the first year in which compliance is expected.

EC states:

‘OVERSEER® allows management of water quality effects to switch from control of inputs, as commonly occurs in Europe, to control of what is discharged below the plant root zone (and from there into the environment)’ (6).

In taking this approach EC is clearly focusing on avoiding, remedying, or mitigating the adverse effects of applying nitrogen to farm land. Further, it makes enforcement action very clear: farmers are required to assess, plan and keep specified records, and EC can examine these records to ascertain if the nitrogen baseline is being adhered to.

The approach WRC is presently taking in the Waikato regions is quite different to EC’s in the Canterbury region. WRC uses a mix of both regulatory methods and non-regulatory methods such as environmental education, development and application of industry good practice and guidance notes (7). For example:

‘The approach adopted in the policies in Section 3.9.3 is to reduce the adverse effects of nonpoint source discharges through the use of non-regulatory methods and permitted activity rules in this chapter while also relying on regulatory methods in other chapters …. Apart from within the Lake Taupo Catchment, Waikato Regional Council is taking a non-regulatory approach to management of non-point source discharges as it considers this is the most effective method for changing behaviour in the long term.’ (8)

Waikato dairy farmers are required to assess, plan and keep records of nutrient applications to land. This includes inputting data into the Overseer tool and using the output data to develop a nutrient management plan (9). There are only two specific rules relating to nitrogen leaching: a maximum application of 25mm of farm dairy effluent (‘FDE’) at any one time and a maximum application of 150kgs of nitrogen content in FDE per hectare per year (10). It is recommended that nitrogen loading from all sources (‘…fertiliser, biosolids and irrigated farm effluent…’) is limited to 150kgs/ha/yr but as a recommendation this is not a rule ie. it is not mandatory (11).

The information attempts to show farmers that by using tools such as Overseer and Nutrient Management Plans, and the information supplied by WRC, the nitrogen applied will be towards plant growth and little will leach into groundwater. In this way their FDE will be utilised as a resource, farmer’s nitrogen fertiliser costs will be minimised and nitrogen leaching will be minimised.
However there are a number of problems with the WRC Regional Plan in respect of nitrogen leaching:

  1. There is only about a 50% compliance with the requirement to assess, plan and keep records of nutrient applications to land. In 2010 WRC completed a phone based monitoring survey to assess compliance with farmer’s obligations to assess, plan and keep records (12). 350 dairy farmers were surveyed – a response rate of 51%. Of those who responded, 44% of them were required by WRC rules to develop a nutrient management plan. Of that 44%, 49% said that they had complied, 48% said they hadn’t; and 3 were unsure. These results were similar to a survey in 2007.
  2. Under the WRC Regional Plan rules, there is no legal limit to nitrogen application – the 150kg/ha/yr is only a recommendation. The WRC 2010 phone survey records an average rate of nitrogen application of 70kg/ha/yr, up from an average of 62kg in 2007 (12). This is less than a 2009/10 Ministry of Agriculture and Forestry Pastoral Monitoring Report which found the Waikato/Bay of Plenty average to be 95k/ha/year (12).
    As there is no legal limit to nitrogen leaching, the 2010 phone survey was of course silent on the measurement of this.
  3. The 25mm FDE spreading rule and the 150kgN/ha/yr recommendation applies to the whole Waikato region. WRC’s website provides considerable information and links to information about applying FDE. But the nitrogen leaching from 25mm applied to the pumice soils south of Tokoroa is going to be considerably different to that from the peats of Hauraki to the clays of Raglan to the loams of Cambridge. Further, a farmer on pumice can apply FDE and urea at any rate to achieve planned pasture production whereas a farmer on loam might only need a portion of this to obtain the same production.

It appears to me that, overall, the present nitrogen leaching provisions in WRC’s Regional Plan aren’t working – the non-regulatory approach hasn’t changed behaviour in the long term. Only about half are complying with the provisions relating to assessment, planning and record keeping. Nitrogen application rates are increasing. Farmers are not required to limit nitrogen leaching, whether or not they record it via Overseer. There is evidence that the WRC’s provisions are not working because WRC’s monitoring of nitrogen levels in groundwater show that this is increasing (13).

In July 2013, the Sustainable Dairying: Water Accord was signed which replaced the Clean Streams Accord 2003. Fonterra is one of the ‘accountable partners’ under the new Accord, with WRC and EC being ‘friends’, whereby they are supportive of the purpose of the Accord and committed to contribute to its success.

Fonterra reported in November 2013 (Environmental Sustainability On Farm) that they are assisting farmers to use the Overseer tool. A farmer can voluntarily provide data to Fonterra which they input into Overseer and provide the output data to the farmer, including the nitrogen leaching figure. In the first year of this programme, 3,700 farmers were provided with Overseer feedback, but it doesn’t detail how many of those farmers were in the Waikato.

Fonterra stated its aim in respect of nitrogen leaching:

‘Fonterra aims to be able to report nitrogen leaching risk and performance at both catchment and farm scale, and show change over time.’

A project similar to Fonterra is being funded by the Waikato River Authority and run by DairyNZ, which is in respect of Waikato dairy farmers. It is not clear what the links are between the Fonterra project and the Dairy NZ project.

While the aim of Fonterra is laudable, as is that of the DairyNZ project, it is really up to WRC as the regional regulator to specify rules governing nitrogen leaching.

It appears that WRC accepts their nitrogen leaching provisions aren’t working, and they are doing something about it:

‘ The Office of the Auditor-General’s 2011 report on freshwater quality highlighted that more is needed to manage the risks to water quality in the Waikato than the current mix of regulatory and non-regulatory methods.

A 2011 policy effectiveness review of the current regional plan suggests managing the effects of agriculture on water bodies is the most important matter to deal with and that the plan’s provisions are not enough to address the ongoing pressures.

A specific review of the extent to which the current regional plan gives effect to the Vision and Strategy is underway, as legally required, and is expected to further support the need for a plan change.’ (14)

If WRC accepts that mandatory rules are required, then the EC model is worth considering, with WRC’s new plan needing to:

  • have rules to make it mandatory to calculate a farm’s nitrogen leaching (using a tool such as Overseer)
  • classify the Waikato region to identify those zones where nitrogen in groundwater is already a greater problem than others
  • specify nitrogen leaching limits for each farm according to the Overseer output and farm zone

WRC also needs to establish that there is clear scientific evidence linking the nitrogen leaching levels it specifies to the maintenance of safe levels of nitrogen in groundwater. The Canterbury Medical Officer of Health has raised this issue in respect of farms in the Selwyn District, an area for which EC is responsible (15).

WRC anticipates that the plan changes will be in place late 2017. It is likely that in respect of nitrogen leaching, WRC policy will move from non-regulatory to regulatory. Consequently assessment, planning, record keeping and achieving specified nitrogen leaching targets are all likely to become mandatory. For those farmers who have already adopted the non-regulatory education, industry good practice and WRC guidelines, as well as support from their dairy company, compliance with the new rules may not be difficult. For others, considerable change to both their farming system and management may be needed. They might like to get on the phone to their mates in Canterbury for a bit of guidance.

Tony Banks
21 October 2014

(1) Groundwater
(2) WRC pamphlet ‘Nitrogen Leaching: Cow intensity and urine – a challenge to water quality’
(3) WRC ‘Healthy Rivers: Plan for Change/Wai Ora’—Plan-for-Change/Drivers-for-change/
(5) EC, ‘Information for Farmers’
(7) See for example:
Paragraph 3.9.7
‘Farmers Guide to Permitted Activities’
(8)Paragraph3.9.3, WRC Regional Plan
(9)Paragraph, WRC Regional Plan—Non-Point-Source-Discharges; and Paragraph, WRC Regional Plan—Farm-Effluent-Discharges/; for a sample Nutrient Management Plan see the Fertiliser Association of NZ’s Code of Practice for Nutrient Management –
(10) Paragraph, Waikato Regional Plan – see (9) above
(11) Waikato Regional Plan – Water Module 3.9 Non-Point Source Discharges*3.9.7 Guidance Notes for the Use of Fertiliser
(12) WRC ‘Fertiliser Compliance Survey 2010’
(13) WRC Report Card, Nitrate in Groundwater
(14) The WRC ‘Healthy Rivers: Plan for Change/Wai Ora’ plan change.—Plan-for-Change/Drivers-for-change/

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