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Soil Health Series: Multi-functionality and Management

In the final part of a four part series on soil health researcher Lilian O’ Sullivan takes a look at some principle soil profile development processes in Irish soils that drive some of the characteristics and present an integrated approach for soil management.

How do we define soil health?

Soil health has been defined as the continued capacity of soil to function as a vital living ecosystem that sustains plants, animals and humans. In light of this, developing knowledge and understanding of factors affecting soil health and monitoring the trends in soil health over time is required to better manage and protect our agricultural soils for future generations. This is the last part of the soil health series (see Teagasc Daily for introduction to soil health, physical, chemical and biological content). Here, we touch on some principle soil profile development processes in Irish soils that drive some of these characteristics and present an integrated approach for soil management.

Understanding soils

In 2014, researchers at Teagasc Johnstown Castle and the Spatial Analysis Group, with partners, launched the 3rd National Soil Map along with the Irish Soil Information System as part of the EPA Strive Programme 2007-2013. This consistent national legend of Irish soil types has increased our understanding of soils in Ireland. Irish soils are complex and although relatively young (<15,000 years), are highly diverse with soil characteristics that vary across small spatial areas as a result of glaciation. The following are some key soil profile development processes that affect intrinsic physical, chemical and biological characteristics that can be linked to management of Irish soils:

Soil profile developmentDescriptionManagement Options
Leaching Precipitation exceeds evapotranspiration in most parts of the country. As water infiltrates soil, soluble constituents are percolated downwards with soil texture affecting nutrient leaching potential (figure 1). Compaction management of heavier (high clay content) textured soils in wet conditions. See SQUARE project
Podzolisation (Iron and Aluminium) As iron, aluminium and humus are elluviated soils become more acid over time (figure 2). The translocated compounds are weathered and “podzolisation” is reflected by organic matter accumulation at the surface, a bleached elluviated horizon and an iron-rich subsurface layer.  pH management – liming to limit soil acidity
Gleying Mottling or gleying due to poor drainage of slowly permeable subsurface layer. Leaching is limited due to restricted water movement due to high clay content typically. Gleying also occurs where there is a high water table. Rainfall is a driver of gleying in soils. Context specific land drainage of mineral soils will enhance structural stability and productive capacity. All drainage operations require individual assessment.  
Illuviation (or argilluviation) This is the translocation of clay down the soil profile mechanically by moving water. Higher clay content means these are often good agricultural soils however drainage may be moderate or poor depending on soil texture.  On heavier clay rich soils calcium lime can keep soil particles apart to increase soil aeration and drainage.
Calcification In Irish soils, calcium carbonates are redistributed in the soil profile but not completely removed.  pH affects the availability of nutrients and targeted application of nutrients is essential depending on soil fertility and crop requirements.

Figure 1: Texture and leaching potential 

Figure 2: Evidence of organic matter accumulation at the surface and a bleached horizon indicating an elluviated E horizon on top of an iron-rich reddish subsurface horizon.

Sustainable soil management – an integrated approach

Increasingly, farmers are tasked with the complex challenge to simultaneously deliver services beyond production. Healthy soils support the production of food, feed and fibre but also re-cycle nutrients, sequester carbon & regulate our climate while purifying and storing water and are an important habitat for biodiversity.  The capacity of agricultural land to deliver these ecosystem services is determined by the intrinsic capacity of the soil, the climatic regime and the management practices deployed.  An integrated approach that considers not only production but also these other functions is required. Researchers at Teagasc Johnstown Castle (David Wall and Lilian O’Sullivan) recently participated in the development of a soil navigator decision support tool for assessing and optimising soil functions in the LANDMARK project (Figure 3).  Unlike most decision support tools, the soil navigator considers the five main land functions and aims to help improve the supply of multiple soil functions simultaneously. Future research will seek to tailor this tool further for Irish soils and land uses.  

Figure 3 - Fig 3 Soil Navigator Description (further information available at Soil Navigator DSS) developed in Landmark project funded from the European Union’s Horizon 2020 research and innovation programme under grant agreement no. 635201

Going forward

Going forward we will need a long term monitoring of soils to detect changes in soil health over time and to act as an early warning system before problems arise on farms. Simultaneously we need practical management solutions for protecting the health and quality of our agricultural soil or for remediating soils which have been previously damaged. This knowledge can be integrated with knowledge transfer services to provide advice to farmers and farm advisors. We have made a good start but we have a long way to go!