Opinion: the science behind the relationship between soil health and water quality is highly complex

By Mary Ryan, Teagasc and Cathal O'Donoghue, NUI Galway

Ireland has a largely human-influenced landscape, formed over millennia of settlement and agriculture. This lush landscape is a major selling point for our agri-food and tourism sectors and the conservation and enhancement of our rural environment is a major policy objective. 

But when you dig beneath these pleasant images, there are significant complex interactions underpinning the notion of the rural environment. One of the most visible and pressing areas of current environmental concern is the risk of loss of nutrients to water as a result of human activity (disposal of human waste) and land use (application of fertiliser to increase agricultural and forest production).

In relation to food production from livestock agriculture, plants need nutrients such as nitrogen, phosphorous, potassium and other organic compounds to grow. Some of these nutrients feed into soil naturally as animal waste is deposited on land or as plants decay and decompose. When animals eat plants (grass, hay, feed), they ingest some of these nutrients and products such as milk, meat and crops are sold from the farm at the end of a production cycle, thus removing nutrients.

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Without the replacement of these nutrients, the food production potential of soil is reduced. Supplementary nutrients in the form of industrially manufactured inorganic fertilisers may be needed to increase grass growth to produce dairy or meat products. The development and use of industrial fertilisers was a critical part of the Green Revolution research, development and technology transfer initiatives and for which Norman Borlaug won the Nobel Peace Prize in 1970. This together with the development of high-yielding varieties of cereal grains, expansion of irrigation infrastructure, the modernisation of management techniques, distribution of hybridised seeds and pesticides to farmers, has allowed the world to feed its growing population.

There is an increasing focus on environmentally sustainable food production. A key part of farming sustainably is the optimisation of agricultural production by using "just enough" of the most appropriate nutrients so that grasses and plants get all the nutrients they need. The challenge is to apply enough nutrients to facilitate food production, without applying excess nutrients that are not taken up by the grasses/plants and are thus at risk of being lost to water either through surface run-off to drains and watercourses or through seepage to ground water.

The science under-pinning the relationship between soil health and water quality is highly complex. For instance, the hydrological processes by which nutrients are lost from agricultural fields to waterbodies are influenced by the level and type of agricultural activity, the amount and intensity of rainfall and the slope, soil type and underlying geology of particular fields. Excess nutrients in water (eutrophication) results in more vegetation growth that increases the demand for oxygen in the water by plants, leaving less oxygen for aquatic life, which can lead to fish kills. This is an example of how imbalanced interactions between land productivity, soil fertility and water quality can have negative consequences.

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The pollution of drinking water by animal and human waste can also bring with it harmful microscopic organisms like Cryptosporidium and E-coli that can cause illness in humans and animals. Although there have been specific areas with sub-standard drinking water quality, as in the case of the Cryptosporidium outbreaks in Galway and Roscommon, Ireland’s water quality is above average by and large compared to other European countries.

Over time, we have seen an improvement in water quality. The European Union Water Framework Directive sets targets for Irish water quality to achieve good status in all water bodies and to maintain the areas with high water quality. The Environment Protection Agency (EPA) monitors water quality across over 3,000 water quality sampling points and uses a five point scale from Poor (1) to High (5) to measure ecological quality. In 1991, about one quarter were unsatisfactory and this fell to one sixth in 2011. By 2011, two thirds of water quality sampling points had a status of good. However, gains have been flat since then and the fall in the share of Q5 pristine water quality points is of particular concern.

In relation to sources of pollution such as household waste-water treatment plants or septic tanks, the relationship has remained fairly static over time. This is against a backdrop of a higher pollution load as the population has increased, balanced by considerable investment in urban waste water plant upgrades.

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But when we examine the relationship between agriculture and water quality, we find an improvement in the relationship over time. In other words, the downstream impact was better in 2011 than in 1991 for a given level of agriculture in a catchment. During this period, the intensity of agriculture declined, while we have seen an increase in the density of septic tanks with the increase in rural populations.

What has driven this improvement? For over 20 years, there has been a strong push for farmers to farm in a more environmentally sustainable fashion. Agri-environment programmes have incentivised farmers to implement changes, while regulations such as the EU Nitrates Directive have imposed legally binding constraints in relation to animal numbers and fertiliser use.

In addition, subsidy payments to farmers are conditional on compliance with the Nitrates Directive, while tax incentives were also provided for farmers to improve manure storage facilities. However, in recent years agricultural intensity has reversed again, due to the government strategy to increase agri-food production (Food Wise 2025) and the removal of restrictions on dairy cow numbers in 2015.

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In order to study these processes to improve agricultural practices, Teagasc funded by the Department of Agriculture, Food & the Marine has established a large research programme in agricultural water catchments in which sensors monitor the source of nutrients in water bodies and track these nutrients through to ground water and surface water bodies. The Agricultural Catchments project also monitors agricultural activity and localised weather events.

The main finding is that hydrological and weather conditions can have a greater impact on water quality than the level of intensity of agricultural activity. Thus in some areas where hydrological conditions are such that nutrients reach water sources quickly, water quality is worse than in areas that have "better" hydrological conditions with more intensive agriculture. Similarly, extreme weather events are associated with higher run-off and can worsen the situation.

However, the increasing global population and consequent demand for greater food production mean that we need to balance agricultural intensification with maintaining soil fertility and maintaining or improving water quality. This is a complex scientific challenge, which is made more complex and politically challenging by differences in soil and weather conditions across the country, which increase the risk to water quality and may restrict farm management options. In response, farmers are becoming more conscious of optimising the use and timing of application of nutrients. Current agri-environment policies compensate farmers for mitigation measures in specific risk areas. Future measures might compensate in a more nuanced fashion according to the level of risk at particular points in time.

The agri-food sector as a whole may need to change to bring water quality protection up the priorities list

While technical solutions exist, one of the biggest challenges in achieving environmental objectives is behavioural. The appropriate use of fertilisers is a win-win for farmers (as it can save money if expensive chemical fertilisers are not needed) and for the environment (as the risk of loss of nutrients to water is reduced).

However, farmers need to understand the soil fertility and nutrient balance on their farms to enable them to adopt a right measure in the right place at the right time approach. Farmers also need a better understanding of the level of risk of loss of nutrients that applies to their farm and how this can be reduced. The science provides the scientific approach but the challenge lies in getting widespread adoption of these approaches.

But it is not merely about getting farmers to change behaviour. The agri-food sector as a whole may need to change to bring water quality protection up the priorities list. Farmers’ management practices are influenced by agricultural advisors, by marketing and sustainability initiatives and by the regulatory and Common Agricultural policy environment in which they operate.

Teagasc, NUI Galway and UCD are bringing together a multi-disciplinary team of environmental scientists, social scientists and psychologists under the WaterMARKE umbrella to examine behavioural drivers from policy level to farm level. This has been done in conjunction with the National Rural Network, the Local Authority Waters & Communities Office (LAWCO) and the Agricultural Sustainability and Support Advisory Programme (ASSAP). WaterMARKE is funded by the EPA and Department of Agriculture to co-design and implement new policy instruments and levers to improve water quality.

Dr Mary Ryan is a Research Officer with the Rural Economy and Development Programme at Teagasc. Professor Cathal O’Donoghue is Dean of the College of Arts, Social Sciences and Celtic Studies at NUI Galway


The views expressed here are those of the author and do not represent or reflect the views of RTÉ