Fertiliser use on farms

Why we monitor fertiliser use on farms •
What's happening? •
How we monitor •
Data and trends •
Download the data file •
When this indicator is updated

Why we monitor fertiliser use on farms

Waikato Regional Council monitors changes in pasture fertility and nutrient losses to get information on the trends and risk nutrient losses are likely to have for water quality. Monitoring also helps us identify policy responses to avoid or remedy damage to our soil and water resources.

It is important to know whether the region's soils are being mined of nutrient reserves or if excess fertiliser is being applied and risking water quality. Monitoring nitrogen and phosphorus inputs and changes in soil phosphorus levels provides information about the balance of these nutrients in pastoral soils.

We regularly monitor nitrogen and phosphorus concentrations in surface and groundwater throughout the region. Our monitoring information, together with predictive modelling based on stock density and terrain, can be used to help explain any observed increases or decreases in nutrients.

Nutrient levels in water are linked to algal growth. Increasing trends in nutrient levels can be used to predict and manage 'hotspots' where nitrate concentrations in water are approaching or exceed critical limits.

This indicator estimates the average amounts of :

nitrogen (N) fertiliser added to pastoral soils
nitrogen fertiliser leached from pastoral soils
phosphorus (Olsen P) levels in dairy farm soil
phosphorus lost through runoff.

Losses of these nutrients affect water and air quality.

Total nutrient inputs should be close to total nutrient losses. If the inputs are greater than outputs, the soil nutrient levels will increase and higher losses to water bodies are more likely. Alternatively, soil nutrient levels will decrease if the inputs are less than the losses. This is not desirable because over time the soils will become 'exhausted' and unproductive.

What's happening?

The Waikato region contains some of the most productive land in New Zealand and the world.

In 2019-20, average dairy farm nitrogen fertiliser use was 128 kg N/ha/yr. Previously, dairy farm nitrogen fertiliser use had varied from 36 kg N/ha/yr in 1997-98, 160 kg N/ha/yr in 2002-03 and 109 kg N/ha/yr in 2011-12. Yearly nitrogen fertiliser use on sheep/beef farms was 6 kg N/ha/yr in 1997-98, 9 kg N/ha/yr in 2002-03, 4 kg N/ha/yr in 2011-2012 and 19 kg N/ha/yr in 2015-2016.

Nitrogen leaching results have been consistently about 40 kg N/ha/yr. In 19-20, nitrogen leaching for dairy was 39 kg N/ha/yr. Previously, dairy farm nitrogen leaching was 44 kg N/ha/yr in 1997-98, 35 kg N/ha/yr in 2002-03 and 42 kg N/ha/yr in 2011-12. Nitrogen leaching for sheep, beef and deer farms has also been stable, between 11 to 17 kg N/ha/yr.

On average, phosphorus fertility on dairy farms is near the maximum for a high producing farm. Since 1997, about half of the soil samples from volcanic and sedimentary soils have shown excessive phosphorus fertility, compared to about one-fifth in 1988-1996.

The results for farms on volcanic soils have remined constant but the results for dairy farms on sedimentary soils have improved after being considerably worse compared to those on volcanic soils. Between 2002 and 2011 about two-thirds of the soil samples from these farms had excessive Olsen P (phosphorous) compared to about half in 2012-2013.

Sheep and beef farms with excessive Olsen P levels have fluctuated between 6-26% on sheep and beef farms. About 8-14 percent of soil samples had excess phosphorus fertility in 2013, compared to 15-25 percent in 2010. Olsen P data in 2013 was similar to the data from 2002 (about 9-18 percent). In 2017, 14-16 percent of sheep and beef farms had excessive Olsen P.

Yearly phosphorus run-off is similar for dairy and sheep and beef farms, fluctuating between 0.9 and 2.4 kilograms of phosphorus per hectare. The value for sheep and beef reflects the hilly nature of these farms; the steeper the slope, the more phosphorous is likely to run off. In comparison, dairy farms have higher Olsen P levels than sheep and beef farms. More P in the soil means more P in the runoff.

How we monitor

Data were collected from MAF's farm monitoring surveys (20 sheep/beef farms) and Dairy NZ (formerly Dexcel) profit watch surveys (150 dairy farms) between 1997/98 and 2011/12. However, due to delays caused by Covid 19, some data has not arrived in time to be used in this update. The data that was used was sourced from Beef and Lamb NZ’s annual economic survey, the evidential brief of Dr Jane Chrystall presented to the Plan Change 1 commissioners (Chrystall 2019) and the report of Journeau et al. (2020). Chrystall (2019) modelled data from 38 farms dry stock farms in the Waikato region. Journeaux et al. 2020 was commissioned by the Fertiliser Industry to assess the value of N fertiliser to the New Zealand economy. For this purpose, they defined “model” or “typical” dairy and dry stock farms, in various regions in New Zealand, one of which was for the Waikato/BoP region. Both these sources of information are in the public domain and considered to be of high quality. This update of the indicator may be in turn updated if the delayed data comes in.
Fertiliser data, along with other data needed in the Overseer Nutrient Budget model, were used to estimate nitrogen leaching and phosphorus runoff losses.
Olsen P soil test results for tens of thousands of samples from farms throughout the Waikato region were subdivided by land use, soil type and year.
This indicator is updated five yearly.
Monitoring for nitrogen fertiliser use and leaching and phosphorus run-off losses uses data collected since 1997/98. Soil levels of Olsen P uses data collected since 1988.
The Fertiliser Code of Practice provides guidelines and technical advice on the best management practices for fertiliser use.
Fonterra through their Market Focussed initiative requires that all dairy farms undertake nutrient budgeting.
The World Health Organisation has set the standard of not more than 11 ppm nitrate in potable waters.
Target ranges for soil Olsen P are those listed in Fertiliser use on New Zealand Dairy Farms, A.H.C. Roberts and J.D. Morton (eds) revised edition, 1999, published by Dairying Research Corporation, AgResearch and Fert Research.
The sample size for previous samplings has been smaller than desirable, e.g. sheep/beef data (n=20). Changing the methodology for the 20215/16 sampling may cause unintended shifts in trends. Further data may yet come in requiring further update of the indicator. For these reasons, these data and the resulting comments and conclusions must be treated as tentative. Also, the nitrogen and phosphorus losses in this indicator are predicted, not measured, estimates using base data from farm surveys. These limitations need to be considered when using or extrapolating these estimates.
No information was available from the Olsen P results to determine whether the samples submitted to the laboratory represented the entire range of soil fertility status found in New Zealand or within the various soil groups. We also had no information on whether there was a bias towards low or high fertility sites being sampled. However, the data did conform to what is known about soil fertility trends in general and thus this bias may be minimal.
This indicator may be refined when nutrient management plans that include a nutrient budget become part of usual farm practise and are made available to Waikato Regional Council.
Quality control procedures
All data collection, interpretation and reporting was done by AgResearch and methodologies are presented in Waikato Regional Council's Technical Reports 2004/09 and 2004/19 (see Resources)