6 Soil health, ecosystem services and environmental health

Back to: Soil health for Victoria's agriculture - context, terminology and concepts

6.1 Soils and animal and human health | 6.2 Soil erosion | 6.3 Land contamination and soil health | 6.4 Climate and soil health

Ecosystem services have been broadly defined in other literature (for example by Binning et al. 2001) but most of them have some relationship to soil and soil health. Table 3 provides example of the functions that soil performs to support more general ecosystem services.

Table 3 Ecosystem services (from Binning et al. 2001) and relationship to soil functions and soil health.

Ecosystem Service	Relationship ot soil functions and soil health
Pollination	Soil does not have a direct role in pollination, although undisturbed soil can provide habitat for many insect pollinators that pupate, nest or raise larvae underground.
Fulfilment of people’s cultural spiritual and intellectual needs	Soil provides general ecological functions that sustain diverse vegetation, habitats, gardens and sports fields.
Regulation of climate	Soil plays an integral role in the global climate, indirectly through supporting vegetation and C–fixation, and directly through C–sequestration in soil and gaseous emissions from soil. The latter are significant in some agroecosystems. Soil also influences the microclimate close to the ground through albedo and heat storage which are affected by surface soil conditions, organic matter and moisture content.
Insect pest control	Soil borne insect pests may be regulated through complex biological systems in soil. Airborne pests (eg Aphids) may be encouraged or discouraged depending on soil fertility and plant nutrition.
Maintenance and provision of genetic resources	Soil health has an indirect role in supporting genetic variety of plants and animals, but is itself also a store of unique genetic resources, many of which are undocumented at this time.
Maintenance and regeneration of habitat	Soil supports vegetation as habitat. Soil health (or soil quality) is critical in the restoration of habitat. Management of soil for ecological restoration after mining operations, urban reclamation and post agricultural land use change is a critical area for the science of soil and soil health.
Provision of shade and shelter	Through supporting and maintaining vegetation, soil serves a primary function in the provision of shade and shelter.
Prevention of soil erosion	‘Resist erosion’ is a primary function of soil described in the soil health / soil quality literature. Soil structural stability and strength, ground cover, roots and vegetation all interact to provide this ecosystem service.
Maintenance of soil fertility	‘Store and cycle nutrients’ and ‘support plant growth and productivity’ are two primary functions of soil described in the soil health / soil quality literature.
Maintenance of soil health	This becomes tautological, however that ‘maintenance of soil health’ is recognised as a primary ecosystem service only serves to emphasise the importance of soil and soil health. This ecosystem service links the soil back to the ecosystem as a whole or the agro–ecosystem and a requirement for appropriate system dynamics that serve the objective ‘soil health’.
Maintenance of healthy waterways	‘Filter and absorb wastes’, ‘act as an environmental buffer’, ‘resist erosion’, and ‘partition and regulate flows of water’ are all primary functions of soil that assist in the provision of the ecosystem service, ‘maintenance of healthy waterways’.
Water filtration	Comments made with respect to healthy waterways apply here too.
Regulation of river flows and groundwater levels	Comments made with respect to healthy waterways apply here too.
Waste absorption and breakdown	The soil ecosystem is the single most important processor of waste in the environment and this is recognised in the soil quality literature through primary functions such as ‘filter and absorb wastes’ and ‘store and recycle nutrients’.

There are many ways in which soil health and environmental health are linked. Examples relating to salinity and impacts on urban infrastructure are well known and documented sufficiently elsewhere.

6.1 Soils and animal and human health
Soil quality affects animal and human health directly and indirectly. Reviews by Oliver (1997) and by Abrahams (2002) have summarised the many impacts that soil can have on human health. Relationships can be identified between soils and human health, but these might not depend on soil health. Biological, chemical and mineral components of soils can either be directly beneficial or detrimental to human health if ingested, inhaled or absorbed through the skin. The detrimental impacts do not necessarily represent ‘unhealthy’ soil, but this serves to illustrate some of the difficulties surrounding the ‘health’ terminology and positive functions of soil (supporting animal and human health). Serious contamination (for example, lead in urban soils in the UK) can result in severe human physical effects.

In the course of this project I have been unable to find any review of direct relationships between soil and animal health, although there is certainly a large body of knowledge in the veterinary and animal husbandry professions that could be summarised. Deficiencies and toxicities resulting from nutrient imbalances in forage are the most common soil health factors affecting animal health. Soil ingestion may be of concern (e.g. long–term persistence of sheep dip spillage) or of benefit (e.g. salt licks). Animal lameness is often related to soil conditions, particularly to waterlogging and to uneven ground following soil surface disturbance or damage (pugging and poaching by hooves or wheels). Flukes and other parasites may persist in ponded soil. Spores of lethal bacteria can persist for decades in soil (e.g. Anthrax) and can be directly ingested. Prions, the infectious agents thought to be responsible for transmissible spongiform encephalitis, can contaminate soils, being absorbed onto clay surfaces where they persist in a viable state (Rigou et al. 2006).

One of the much debated issues around soil and animal health concerns the ratio of exchangeable calcium or potassium and magnesium in soil. While hypomagnesemia or grass tetany in cattle is a common effect of low Mg in forage, the occurrence of this is not precisely predictable from the Ca to Mg or K to Mg ratios in soil. For example, there is little refereed research in the Ca to Mg topic but the importance of a ratio in the order of 6.5–7:1 is strongly promoted by ‘biological’ farmers. Different species of plants have different nutritional requirements and there is no evidence that yield is affected by soils with widely different Ca to Mg ratios.

Animals may amplify any effects of soil chemistry by reacting to imbalance in their nutrition but there is little reliable guidance to link measurable soil fertility factors to animal health. Trace and macro element deficiencies or toxicities are more reliably determined from animal blood tests than from soil tests.

6.2 Soil erosion
Soil erosion by wind or by water has major environmental health and economic impacts. Loss of topsoil has onsite consequences for soil health which, in some instances (loss of weed seed load in wind erosion), has been seen as positive by the landholder, but is invariably also an economic loss due to loss of nutrients and soil fertility. The offsite impacts of wind erosion in the form of human health due to dust, and obstruction of infrastructure due to drifting sand, have been estimated as ten times greater than the economic losses due to fertility losses from wind–affected paddocks (John Leys, personal communication⁶).

Loss of soil organic matter from erosion can lead to degraded surface structure and consequent problems of reduced water infiltration and impaired seedling emergence. Water erosion has major consequences on river health and on silting of infrastructure. Both wind and water erosion are significant soil health issues in Victoria.

6.3 Land contamination and soil health
Soil and land contamination has resulted from agricultural chemicals, poor handling of overburden during mining operations and poor rehabilitation and soil reinstatement following trenching operations and installation of infrastructure. Soil management is a critical component throughout all urban, industrial or mining operations if soil is to be satisfactorily reinstated in a healthy condition. Soil scientists and agronomists therefore have important roles to play in planning and supervising soil handling and rehabilitation. The soil management issues and unique classification systems for non agricultural soils are summarised well in ‘Soils and the Urban Environment’ (Bullock and Gregory 1991).

Soil contamination may be assessed through chemical analyses and there are many registered laboratories able to provide this service. However, multi–parameter screening of soil contaminants is expensive and there may be more economic ways to assess the potential impact of contaminants by assessing plant health and soil biota.

Madejón et al. (2006) argue that the use of plants as biomonitors of soil quality has advantages over soil analyses, particularly on a large scale. Their emphasis is on contaminants and metals associated with mined land, but they suggest that plants with a high root–shoot transfer would be important biomonitors for land destined for agriculture, as the worst case scenario for risks to health would be indicated by such plants. In an ecological restoration project the most significant primary producer (start of the food chain) would be the most appropriate biomonitor.

Hatcher (2002) describes a health index approach using abiotic and biotic factors to assess contaminated sites and their remediation. Abiotic assessment includes parameters likely to affect organisms’ physical tolerances (for example; pH, EC and texture). The biological assessment encompasses responses of species at different trophic levels (microbes, plants, invertebrates, and community processes such as CO₂ evolution). Different media are also tested. Solid phase tests expose test organisms to soil as received. Aqueous extracts indicate water soluble toxicities. Methanol extracts test for non–polar hydrophobic organic contaminants that would not be detected in aqueous extracts. Each test result is ranked on a normalized scale of 1 to 5 (1 non toxic, 5 worst case), values are averaged and a single health index between 1 and 5 reflects all the components of the health index.

6.4 Climate and soil health
Climate has a direct impact on soil health and has its most severe impacts in extremes of dryness leading to wind erosion and, in extremes of wetness leading to sheet, rill and gully erosion. Soil health is also linked to climate benefits on a global scale because soils can store carbon, improving soil quality and reducing greenhouse impacts. Studies on the actual storage of carbon in different systems, and modelling to predict the amount of C that can be sequestered in soil, present a somewhat limited prospect for a net long–term positive impact on climate. Soil management practices underpin the capacity of these activities to sequester carbon. However, under Australian conditions, soils have a poor capacity to store large quantities of carbon and, once soil carbon has been built up, practices must be put in place to prevent its release (AGO 2002).

Chan, Heenan and So (2003) have reviewed sequestration of carbon in relation to conservation tillage in light–textured soils in Southern Australia. They found that significant improvement in carbon levels were only found in the higher rainfall (>500 mm) cropping areas. They also suggest that data from trials over 3–19 year periods indicate that carbon levels continue to decline under continuous cropping even where conservation tillage is used. They concluded that other soil quality attributes associated with conservation tillage (macroporosity, aggregate stability, infiltration and water holding capacity) depend on organic carbon levels, and therefore these attributes may also have limited long–term sustainability. They advocate that long–term continuous monitoring of soil carbon and soil quality is needed for different agro–ecological zones.

A more significant and potentially manageable relationship between soil quality and climate impacts resides in the production of nitrous oxide, a major greenhouse gas. N₂O production is related to soil moisture, N levels and soil temperature, and is therefore a feature of irrigated pastures. Recent work by DPI at Kyabram indicates that some of the modelling used up to now overestimates N₂O in temperate irrigated agriculture by about 70%. A better understanding of the dynamics of N₂O in these systems can lead to positive outcomes for soil fertility, water and fertiliser management and greenhouse mitigation. Dalal et al. (2003) stress the need for long term research into the relationships between CO₂ and CH₄ emissions and sinks and N₂O emissions as these interact strongly.

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