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Land

• Land cover
• Land use
• Soil health
• Soil intactness

Soil health

Healthy soils support agricultural and forest productivity, help prevent contamination of waterways, and provide for resilient soil and land ecosystems.

Intensive land uses can put pressure on soil. Compacted soil may inhibit pasture growth, cause soils to become water logged and increase runoff. Phosphorus fertilisers are the major source of cadmium (a heavy metal) to agricultural soils. Cadmium can build up in soil and cause problems for human health as well as market access and trade if it makes its way into food products. In contrast, land managers can help improve or maintain soil health, for example through the prudent use of fertiliser, soil tillage and/or crop rotation, and at the same time increase productivity and economic value.

Soil health is reported from sampling at approximately 740 sites in 12 regions, sampled by regional councils between 1995 and 2009. Close to 300 of these sites were re-sampled to determine changes over time. The samples represent soils under indigenous land cover and under five productive land uses:

• drystock (ie, sheep and beef farming)
• dairy
• forestry
• cropping
• horticulture.

Seven soil measures were monitored to provide information about the organic reserves, fertility, acidity and physical status of our soils. Collectively, these measures can tell us about the health of our soils. These soil measures also allow changes in soil health due to land management to be detected.

Soils under productive land uses were assessed as either meeting, or not meeting target ranges for all of the seven soil measures. The target ranges are indicative of the optimal soil health needed for production under each land use. Note that the target ranges for cropping and horticulture land uses are not well defined because of the diversity of soil requirements for these land uses, but they represent the best available guidelines to illustrate soil health at present.

Soils under indigenous land cover tell us about soil health in the absence of human activity. Although target ranges were not applied to soils under indigenous land cover, the findings provide a valuable reference to unmodified natural conditions.

Current Situation

Just over one-third of monitored soils under productive land uses meet all soil health target ranges. Of these productive soils, soils under drystock and dairy land uses are least likely to meet all ranges, while horticulture soils are most likely to meet all ranges. The health of soils under drystock and dairy land uses are particularly important for an overall assessment of soil health, since grassland, likely to be used predominantly for grazing, covers half of New Zealand’s total land area.

These monitoring results differ from public perceptions surveyed in 2008 (11 Mb download). About 80 per cent of New Zealanders surveyed perceive soil health is adequate, good or very good and about 70 per cent perceive soil is adequately, well or very well managed. The main causes of damage to soil were perceived to be hazardous chemicals, solid waste and farming. More New Zealanders in 2008 perceived farming to be a cause of damage than in 2000. While soil monitoring results and the public’s perception of soil health may differ, the public are aware of the major causes of damage to soil health in New Zealand.

Figure 1: Percentage of productive land use sites meeting and not meeting target ranges for soil health measures, latest available year

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Land use	Percentage of productive land use sites meeting all target ranges	Percentage of productive land use sites not meeting all target ranges
Drystock	24	76
Dairy	30	70
Forestry	39	61
Cropping	45	55
Horticulture	60	40
All productive land uses	35	65

Note: This figure represents the latest data for each site, determined from monitoring over a number of years.
Data source: Ministry for the Environment

Table 1: Average soil health measures arranged by land-use categories, 1995-2001 and 1995-2009

Key findings by land use

Soils on approximately half the dairy and a third of the drystock sites do not meet target ranges for physical status, predominantly because of compaction from livestock.

Dairy and drystock soils are generally less acidic and have higher organic reserves, fertility and cadmium than soils under indigenous land cover. This is indicative of intensive land use and the use of fertilisers and lime. Organic reserves (particularly nitrogen) and, in some cases, fertility are above target ranges on dairy sites and some intensively managed drystock sites. In contrast, other drystock sites are below fertility target ranges. Long-term grazing on those low fertility soils could lead to overgrazing, decreased pasture production, invasion by weeds, and soil compaction and erosion.

Monitoring sites under horticulture and cropping land uses generally have similar soil health, but a higher proportion of cropping sites do not meet target ranges for organic reserves and fertility. Intensive cultivation can result in the loss of soil carbon. In addition, nitrogen and phosphorus fertilisers are generally used, sometimes to excess. These land uses may also place other pressures on soil health (eg, pesticide and chemical use), that are not measured by the soil health indicators reported here.

About 40 per cent of sites under plantation forestry meet all the target ranges. Plantation forestry often occurs on erosion prone soils and its physical status is often below the target range. Forestry can be a useful management option for reducing erosion, although harvesting and replanting must be carefully planned and executed to avoid soil erosion and nutrient loss. About a third of forestry sites have low fertility, although Olsen phosphorus (the measure used for fertility) is not as critical for tree growth as for other productive land uses reported.

Figure 2: Percentage of productive land use sites not meeting target ranges for soil health indicators, by productive land use, latest available year

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Soil health indicator	Organic reserves	Fertility	Acidity	Physical status
Land use
Drystock	24	44	6	38
Dairy	29	15	4	53
Forestry	8	33	0	48
Cropping	15	36	2	23
Horticulture	2	29	0	23

Note: This figure represents the latest data for each site, determined from monitoring over a number of years.
Data source: Ministry for the Environment

Trend

Overall trend

Overall, the soil health at monitored sites has improved slightly for all productive land uses. Between 1995 and 2009, there was an increase in the number of re-sampled sites meeting target ranges for fertility and physical status. Fertility improvements are likely to be due to decreasing fertility in those soils that had earlier levels above target ranges. These monitoring results match the public perception that soil health is now better than in the past.

Figure 3: Percentage of re-sampled productive land use sites meeting target ranges for soil health indicators, by sample period

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Soil health indicator	All indicators	Organic reserves	Fertility	Acidity	Physical status
Sample time
Initial sample	33	84	68	99	54
Re-sample	38	84	77	98	57

Note: This figure represents the latest data for each site, determined from monitoring over a number of years.
Data source: Ministry for the Environment

Trend by land use

While more sites are now meeting all target ranges, re-sampled soils under drystock and dairy land uses generally showed average annual increases in organic reserves and fertility. Increases in organic reserves, particularly nitrogen, may indicate deteriorating soil health when organic reserves are already above target ranges. However, increases in fertility, up to a point, can be interpreted as an improvement in soil health, particularly in soils below target ranges, as is the case for many drystock and some dairy sites. Physical status continues to deteriorate in soils under drystock land use due to livestock grazing.

Re-sampling did not show statistically significant changes in soil health for sites under horticultural or forestry land uses.

Table 2: Average annual changes in soil measures for re-sampled sites

Notes:
(1) ▲ = Increasing, ▼ = Decreasing.
(2) The statistical strength of the trend is indicated by the number of arrows. ▲▲= P<0.001, ▲= P<0.01.
Data source: Ministry for the Environment

Move to the next land indicator: soil intactness on erosion prone land.

Last updated: January 2011