Methods - 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). All farms were within the Waikato region.
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 the Waikato region were subdivided by land use, soil type and year.
Monitoring sites are the MAF Farm Monitoring farms and Dairy NZ Profit Watch farms in the Waikato region. Olsen P results are from farms throughout the region.
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 the sheep/beef data is small (n=20). For this reason these data and the resulting comments and conclusions must be treated as tentative. The nitrogen and phosphorus losses in this indicator are predicted, not measured, estimates using base data from farm surveys. This, together with the small number of farms in the survey, needs to be taken into account 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)