Waikato Regional Council monitors soil quality to provide information about how particular land uses are affecting soils in the long-term. Some land uses and land management practices may affect soil properties and reduce soil quality over time.
Some reductions in soil quality, such as lost organic matter, can take many decades to remedy. This can mean that future landowners are unable to grow crops or pasture of the same quality or need to use greater amounts of fertiliser to achieve the same result as previously.
The better the measured soil characteristic matches the guideline value for its current land use, the better the soil quality. Scores for individual soil quality characteristics are grouped together for each land use to give the percentage of the Region’s land area that meets (or fails) soil quality guidelines. This is expressed as satisfactory soil quality and soil quality that is ‘of concern’.
We can get an idea of what the soil quality issues are for certain land uses by looking at which key soil quality characteristics don’t meet guideline values for that land use. For example, fertility imbalance and soil compaction are currently the main concerns identified for pastoral farming soils.
Good quality soils are those where key soil characteristics are in good condition for the current land use. Waikato Regional Council measures soil quality for four main land use types in the Waikato region:
About 9 per cent of the region's productive soils had satisfactory soil quality for their current land use in 2016. This compares with 12 per cent being satisfactory in 2010 and 16 per cent in 2005.
Over 90 per cent of the land under dairy farming has soil quality that is of concern, with excessively high fertility and/or soil compaction affecting about 80 per cent of the sites.
Similarly, more than 95 per cent of the land under drystock farming has soil quality that is of concern. About 70 per cent of the sites are affected by soil compaction, 70 percent are affected by excessive fertility, while about 20 per cent are affected by low fertility.
Nearly 90 per cent of the land under cropping and horticulture has soil quality that is of concern. More than 75 per cent of the sites are affected by excessively high fertility. About 50 per cent of the sites under cropping show loss of soil prganic matter and have low stability of aggregates.
Approximately 70 per cent of the land under forestry has soil quality measurements outside targets. Around 30 per cent of sites are considered loose. Loose is the opposite of compaction and many of the region's soils are naturally loose.
Trees reduce the risk of erosion so forestry land use allows production on what would otherwise be unproductive land. However, care is needed at harvest or conversion to another use where the land is made bare as a result. Conversely, sites where logging occurred showed evidence of compaction from dragging logs and machinery.
The indicator is updated annually.
Soil Scientist - Science and Strategy Directorate