Soil quality and land use

  • Image, Soil health and land use.

    Soil supports the productivity of agriculture, horticulture, and forestry, and filters water to help prevent waterways from becoming contaminated. Different land uses put pressure on the land environment and can change soil quality. We assess soil quality for four types of land uses – forestry, cropping and horticulture, dairy, and dry stock – by measuring these soil properties: acidity (pH), fertility (Olsen P), organic reserves (total carbon, total nitrogen, mineralisable nitrogen), and physical status (macroporosity and bulk density). Soil scientists have identified the target range for each of these indicators for maintaining production while managing risk to the environment.

    We classified Soil quality and land use as a case study.

    Key findings

    Trend not assessed

    Surveys conducted between 2014 and 2017 found 83 percent or more of assessed sites were within target range for five of seven soil quality indicators (soil pH, total carbon, total nitrogen, mineralisable nitrogen, bulk density). However, for the remaining two indicators (macroporosity and Olsen phosphorus), more than 48 percent of assessed sites were outside target ranges.

    • For the seven indicators, the percentage of assessed sites within target range were:
      • mineralisable nitrogen – 98.4 percent of sites
      • soil pH – 97.8 percent of sites
      • total carbon – 95.0 percent of sites
      • bulk density – 93.0 percent
      • total nitrogen – 83.0 percent
      • macroporosity – 51.6 percent
      • Olsen phosphorus (Olsen P) – 49.2 percent
    • For Olsen P, 17.8 percent of sites were below target range, indicating less than optimal levels of soil phosphorus; 33.0 percent of sites were above target range, indicating higher than optimal soil phosphorus, which can present a risk to water quality.
    • For macroporosity, 43.7 percent of sites were below target range, indicating soil compaction, which can present a risk to water quality.

    By land use:

    • Olsen P levels were above target range in 51.3 percent of dairy sites, and 37.2 percent of cropping and horticulture sites.
    • Macroporosity levels were below target range in 65.0 percent of dairy sites.

     

    Figure 1

    Note: Some sites did not have a recorded value for all indicators. We excluded soil sites with missing indicator measurements from the analysis.

    Data from Northland, Waikato, Bay of Plenty, Hawke's Bay, Manawatu-Wanganui, Wellington, Canterbury, Southland regional councils; Marlborough and Tasman district councils; and Auckland Council were collated by Manaaki Whenua – Landcare Research.

    Figure 2

    Graph, Soil sites within target range for given soil quality indicators

    Note: Some sites did not have a recorded value for all indicators. We excluded soil sites with missing indicator measurements from the analysis.

    Data from Northland, Waikato, Bay of Plenty, Hawke's Bay, Manawatu-Wanganui, Wellington, Canterbury, Southland regional councils; Marlborough and Tasman district councils; and Auckland Council were collated by Manaaki Whenua – Landcare Research.

    Figure 3

    Graph, Soil phosphorus, by land use

    Note: Values above the red dashed lines are of most concern. The ends of each ‘box’ in the box-plot are the upper and lower quartiles (25 percent of the sites are either higher or lower than these values). The top and bottom ‘whiskers’ represent the highest and lowest value. The middle line of the box represents the median (middle) data point (half the sites are above and half below this value). The target range for soil phosphorus, measured in micrograms of Olsen P per gram of soil, varies for land uses on different soil types. The red and blue lines indicate the highest and lowest recommended levels of soil phosphorus for each land use, respectively (Mackay et al, 2013).

    Data from Northland, Waikato, Bay of Plenty, Hawke's Bay, Manawatu-Wanganui, Wellington, Canterbury, Southland regional councils; Marlborough and Tasman district councils; and Auckland Council were collated by Manaaki Whenua – Landcare Research.

    The units 'µg' are micro (one millionth) grams.

    Figure 4

    Graph, soil macroporosity levels by land use

    Note: Values under the red dashed lines are of most concern. The ends of each ‘box’ in the box-plot are the upper and lower quartiles (25 percent of the sites are either higher or lower than these values). The top and bottom ‘whiskers’ represent the highest and lowest value. The middle line of the box represents the median (middle) data point (half the sites are above and half below this value). The target range for macroporosity varies for land uses on different soil types. The blue and red lines indicate the highest and lowest recommended levels of macroporosity for each land use, respectively.

    Data from Northland, Waikato, Bay of Plenty, Hawke's Bay, Manawatu-Wanganui, Wellington, Canterbury, Southland regional councils; Marlborough and Tasman district councils; and Auckland Council were collated by Manaaki Whenua – Landcare Research.

    Definition and methodology

    Soil quality is informed by seven indicators:

    • acidity, measured by soil pH is how hospitable the soil is for plants and other organisms and is important in determining the amount of nutrients available to plants
    • organic reserves, measured by total carbon, total nitrogen, and mineralisable nitrogen is how much organic material is available to provide nutrients, to and hold soil together and to allow air and water movement
    • fertility, measured by Olsen P is the amount of nutrients (phosphorus) in the soil and available for supporting plant growth
    • physical status, measured by bulk density and macroporosity is how dense the soil is and how many pore spaces it has – these are important characteristics for air and water movement through soil

    Soil quality is subjective to land use or environmental issues – what's considered a good quality for growing potatoes is different to what's good for a pine forest. This means the target ranges used to determine if soil is of good quality are different, depending on the land use or if the targets are related to farm production or environmental risk. The target ranges for each indicator are derived from Sparling et al (2008) as amended by Mackay et al (2013).

    Data from the 2014–17 survey period come from 11 regional and unitary councils, surveyed at 461 sites down to 100mm deep. Data are from Northland, Waikato, Bay of Plenty, Hawke's Bay, Manawatu-Wanganui, Wellington, Canterbury, Southland regional councils; Marlborough and Tasman district councils; Auckland Council.

    A national perspective on the long-term trends on the quality and condition of our soils is currently limited by the coverage and consistency of soil quality data.

    We classified Soil quality and land use as a case study.

    Relevance

    Image, Direct relevance. This case study is a direct measure of the 'Land and soil condition' topic.

    Accuracy 

    Image, Medium accuracy. The accuracy of the data source is of medium quality.

    See Data quality information for more detail.

    References

    Mackay, A, Dominati, E, & Taylor, MD (2013). Soil quality indicators: The next generation (PDF, 3MB). Retrieved from www.envirolink.govt.nz.

    Sparling, G, Lilburne, L, & Vojvodić-Vuković, M (2008). Provisional targets for soil quality indicators in New Zealand (PDF, 1.26MB). Retrieved from www.landcareresearch.co.nz.

    Archived versions

    See Soil health and land use (archived April 2018)

    Updated 19 April 2018

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