Soil Acidification The unseen threat to soil health and productivity

www.ces.vic.gov.au February 2009 Fact Sheet No. 7

This fact sheet is one of a series, developed from material presented in Victoria’s first comprehensive State of the Environment Report. The Report is a major undertaking of the Commissioner for Environmental Sustainability and covers a broad range of environmental issues affecting the State. Its purpose is to improve community understanding of Victoria’s environment, and through the use of recommendations, to ensure its protection for present and future generations. The report was released in December 2008 and is available at www.ces.vic.gov.au

Key findings Acidification is also linked to erosion, salinity, and loss of soil biodiversity. Bacteria, earthworms and other soil organisms are • The cost of lost productivity to Victoria due to soil generally sensitive to soil pH and tend to decline as soils become acidification is estimated at $470 million per year. more acidic. • Soil acidification is accelerated by some land management practices and the area of acid soil is increasing. Victoria has up to 8.6 million ha of acidic soils including • Naturally acidic soils can’t be distinguished from soils 4–5 million ha of strongly acidic soils, which mostly occur acidified by agriculture. naturally and are indistinguishable from those with accelerated • The use of acidifying fertiliser, to support more intensive acidification. agriculture, is increasing in Victoria. • Only 5.5% of the area requiring treatment with lime to restore Coastal acid sulfate soils are a different category of acid soils and critical soil pH levels is sufficiently treated. are described in SoE Fact Sheet #16 - Coastal Modification. • The last statewide assessment of soil pH was made in 1994. Victorian soils becoming more acidic Soil acidification is natural but can be accelerated Soil acidification is becoming more widely recognised as a Soil acidification is a naturally occurring soil chemical process. significant land degradation issue in Victoria, with potentially This process occurs very gradually in undisturbed ecosystems major impacts on agricultural productivity and sustainable but can be accelerated by agriculture. Soil acidification is an farming. Almost half of Victorian farm businesses reported soil environmental issue because it can: acidity as a land management issue in 2006/2007. • reduce plant growth and productivity; • decrease the availability of essential plant nutrients and Acidity is measured on the pH scale, which ranges from zero increase the impact of toxic elements; (strongly acid) to 14 (strongly alkaline). pH is measured on a • restrict soil biological activity; and logarithmic scale so a change of 1 pH unit represents a 10-fold • increase risks of soil structure decline, erosion and salinity. change in acidity. Most plants grow best in neutral soils with pH in the range 6–8 because the availability of essential nutrients is Productivity losses due to accelerated soil acidification are usually optimal in this pH range. estimated to cost Victoria $470 million per year. Lost agricultural productivity also means that less land is available for other purposes, such as revegetation. Prolonged acidification can also cause irreversible damage to soil structure.

Commissioner Environmental Sustainability Figure 1. Victorian surface soil pH map Victoria Soil pH in Victoria has changed as a result of vegetation clearing This inquiry led to the emergence of the ‘soil health’ concept, and modern farming practices. For example, soil pH in north- which takes a holistic approach to the management of soil- eastern Victoria declined by approximately one pH unit in the related issues. Victorian Catchment Management Authorities have 30–40 years following the introduction of modern agricultural developed soil health strategies to guide investment in programs practices. In the absence of lime application to neutralise acid to improve overall soil condition. Soil acidification is recognised soils, up to 13.5 million hectares of Victorian soil could be too as a problem in several regions. The investment priority given acidic for optimal plant growth by 2020. The regions most at risk to acidification depends on whether it is viewed primarily as of soil acidification are: North East, Goulburn Broken, Glenelg a limitation on agricultural productivity or whether broader Hopkins, West Gippsland, southern parts of the North Central implications for native vegetation management, soil carbon region and the southern Wimmera. accumulation and control of salinity and erosion are identified.

The current map of surface soil pH in Victoria provides broadscale information about the occurrence of strongly acid soils but doesn’t indicate changes in soil pH over time.

Acidification acceleration

While many soils in Victoria are naturally acidic, soil acidification is accelerated by some land management practices. Leaching of nitrate through the soil profile is the most widespread cause of soil acidification. This is related to rainfall and the efficiency of use of water and nitrogen by plants. There are three other primary causes of soil acidification: • removal of alkaline products such as wool, grain, meat, hay and wood; • use of ammonium-based fertilisers, which acidfy soil as they are converted to nitrate by soil bacteria; • build-up of plant-based organic matter.

Increases in agricultural productivity in Victoria have been driven by increased use of fertiliser and water. Greater productivity also Figure 3. Area sown to annual and perennial agricultural plants means that more products (grain, meat, wool, hay) are removed, contributing to soil acidification. What the Commissioner says Vegetation type is also important. Perennial plants generally use water and nitrogen more efficiently than annuals, which helps “Soil pH in Victoria has not been mapped since 1994. Land reduce nitrate leaching. The area of Victoria sown to perennial managers need up-to-date information about trends in soil plant species has increased in the last decade, but annual crops pH to encourage best management and preserve agricultural and pastures still dominate. Continued adoption of farming productivity. systems based on perennial plants will help to reduce rates of soil acidification, in addition to the benefits provided by “Farming systems based on perennial plant species can provide perennial systems for salinity and carbon capture. benefits for soil health and pH as well as salinity and carbon storage, but can be difficult to manage. Victoria should continue research and development of perennial-based farming systems, to provide farmers with cost-effective solutions.” Reducing the impacts of soil acidification

Soil pH management on private land is largely in the hands of individual land managers, who make business decisions about What you can do lime application and other relevant land management practices. The Government can assist by supporting research and providing • If you are involved in agriculture, know the pH of your soil information to land managers, to promote management practices and the critical pH for the plant species you grow so that you that reduce acidification. can make informed management decisions. • Investigate options for switching to less acidifying crop A Parliamentary Inquiry into the Impact and Trends in Soil rotations and nitrogen management (e.g. split applications of Acidity by the Environment and Natural Resources Committee nitrogen). of Parliament was undertaken in 2003/2004 with the aim of • Return plant material to the paddock, e.g. by retaining crop reviewing and reducing projected impacts of soil acidification. stubble and feeding hay in the paddock where it was cut. • Investigate options for farming systems based on perennial plants, to improve water- and nitrogen-use efficiency.

alkalinity Product removal For more information

State of Environment Report Victoria 2008, Land and Biodiversity – www.ces.vic.gov.au. Crop/pasture/animal products Biological Nitrogen N fixation f ertiliser

State of the Environment Victoria 2008 Fact Sheet Series Soil surf ace Organic matte r brea k down Published by the Commissioner for Environmental Sustainability Melbourne, Victoria, 2009 Plant ©The State of Victoria, Commissioner for Environmental Sustainability 2009 This publication is copyright. No part may be reproduced by any process except in accordance with the roots Organic provisions of the Copyright Act 1968. nitrogen Authorised by the Victorian Commissioner for Environmental Sustainability, 16/570 Bourke Street, Melbourne, Victoria 3000 ammonia nitrate Soil nitrate For further information contact the Office of the Commissioner for Environmental Sustainability, phone +61 38636 2197 or visit http://www.ces.vic.gov.au/SoE acidity nitrate leaching acidity Disclaimer This report may be of assistance to you and every effort has been made to ensure that the information provided is correct. It is based largely on data and information provided by the Victorian Government. The Commissioner for Environmental Sustainability does not guarantee that the report is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this Figure 2. Processes contributing to soil acidification publication.