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Utilising Nitrogen Inputs Efficiently

Tuesday March 23rd 2021

Teagasc and Co-op ASSAP advisors provide information on nitrogen with the help of researchers from Johnstown Castle. Information includes how nitrate interacts with soil and what farmers can do to minimise diffuse nitrate losses form their farms. Videos will include;

N interactions with soil – how N leaching occurs

Nitrate leaching can occur during times of heavy or prolonged rainfall. Free draining soils are particularly susceptible to nitrate loss as it's very mobile in soil and readily leaches groundwater. The highest risk is in winter and early spring, as Prof Owen Fenton, Teagasc Researcher explains

The highest risk is at the shoulders of the year in winter and early spring due to unfavourable weather and where the nitrogen is not being used by the plant due to poor crop growth.

Source, Pathway, Receptor

We often hear of the term source, pathway and receptor now when discussing nutrient losses from the farm but what does it mean?

When looking at nitrate leaching from the soil, the source describes where the nitrogen has come from. Nitrogen on a farm can be deposited onto soil in many different ways such as fertiliser, slurry and animal deposits on the land to name a few.

Nitrogen in the soil can take a number of different forms, such as nitrate and ammonium depending on what you spread and also natural conversions happening in the soil through microbial activity.

CAN is made up of half ammonium and half nitrate, after spreading CAN a large pool of nitrate is placed in the soil  open to being leached away if unfavourable conditions occur.

Protected urea converts to the ammonium form of nitrogen when applied to soil. Ammonium is more stable in soil than nitrate and less susceptible to leaching due to its positive charge. Soil microbes convert ammonium to nitrate almost like a steady conveyer belt; plants take up both nitrate and ammonium as required for growth.

Where does leached nitrate go?

The pathway for leached nitrate is down through the soil into groundwater, the groundwater eventually ends up in the river (receptor) and the river carries the nitrate to the estuary.

Time Lag – how long does it take

In free draining areas, nitrate can move from the soil to the river from months to years but as we move to moderately drained areas it can take up to decades. Remember, the landscape is rarely uniform but in reality it is a tapestry of freely-moderately or poorly draining areas. Therefore, the transfer of nitrate to surface waters is not uniform on our landscape.

The changes we make today to reduce nitrate leaching on the farm will be seen for years to come.

Prof Owen Fenton, Teagasc researcher at Johnstown Castle tells us more in this short video clip below.

Nitrate mitigation advice, Nitrogen use efficiency, N use in spring & autumn 

Deirdre Glynn, Teagasc ASSAP Advisor and Dr. David Wall, Teagasc Researcher both define Nitrogen Use Efficiency (NUE) here. They discuss losses of Nitrogen and how we can avoid this going forward through soil testing, nutrient planning, responsible fertiliser and slurry spreading and more

Nitrogen use efficiency (NUE)

Nitrogen use efficiency (NUE) is the quantity of nutrient recovered by a crop relative to the nutrients supplied from soil, applied fertilisers, manures and ultimately how much is recovered in the end product we are selling in terms of milk, meat or crops. Efficient use of nitrogen is essential to achieving maximum crop growth and achieving a greater return on each kg of fertiliser you invest in.Planning helps to optimise the use of farm nutrients, maintain and improve soil health, reduce excessive nutrient build up and lessen environmental losses.

Losing from the system

Grassland based systems of production are “Leaky” by nature in terms of N loss. Current National Farm Survey Sustainability reports put Irish dairy farms at 25% NUE in terms of their ability to recover N from their N imports (feed, fertiliser etc.) via milk sales, cattle sales and grass/crop yield. With an industry target of 35% looming there is scope for improvement.

Application rate and application date of fertilizer nitrogen (N) are important factors in determining grass production response and N recovery. Applying nitrogen fertilizer ‘little and often’ during the growing season gives most efficient response in terms of grass growth and economic return.

What can we do in 2021?

  • Soil Test and develop a nutrient management plan with you advisor
  • Monitor soil temperature, provided conditions are suitable, nitrogen application should coincide with the onset of spring growth – this happens once soil temperatures reach 5.5 degrees C or above and climbing
  • Ensure heavy or prolonged rain is not forecast when spreading fertiliser/slurry and don’t spread if machine is tracking ground
  • Adhere to buffer zones
  • LESS (Low Emission Slurry Spreading) increases the amount of N recovered for slurry and allows for a reduction in applied fertiliser N
  • Use of grass-clover systems. White clover can increase the tonnes dry matter grown (+ 1 – 1.5 t DM/ha) increase animal performance as it is a higher quality feed, and it can reduce the need for chemical nitrogen which increases the nitrogen use efficiency (NUE) on farms
  • Calibrate your fertiliser spreader, this makes sense financially and environmentally

No farmer wants to pollute a waterway or well water under their land that their family or neighbours are drinking and improving nitrogen use efficiency on your farm will reduce nitrogen losses to water. In this short clip, Dr. David Wall, Teagasc, goes through what you can do to prevent this such as soil testing and developing a nutrient management plan with your advisor; monitoring soil temperature (5.5 degrees C or above and climbing); ensuring heavy or prolonged rain is not forecast when spreading fertiliser/slurry and not spreading if machine is tracking ground; adhering to buffer zones; using LESS; using grass-clover systems and calibrating your fertiliser spreader.

Protected Urea 

Protected urea allows farmers to spread urea based nitrogen during the growing season without the worry of nitrogen (N) being lost from the field through ammonia emissions. It also reduces greenhouse gas emissions and nitrate leaching when compared to CAN Cathal Somers gives more information

Teagasc trial work shows that protected urea achieves the benefits of protecting nitrogen (N) loss and reducing greenhouse gas emissions while yielding as well as CAN over the growing season (Figure 1), a win-win outcome both economically and environmentally.

Figure 1. Protected urea consistently matching CAN grassland yields in Teagasc trials

Reduce Nitrate Leaching:

Nitrate leaching can occur during times of heavy or prolonged rainfall. Free draining soils are particularly susceptible to losses as nitrate is very mobile in soil and can be readily leached to groundwater. CAN is made up of half ammonium and half nitrate. After spreading CAN a large pool of nitrate is placed in the soil is open to being leached away if unfavourable conditions occur.

Protected urea converts to the ammonium form of nitrogen when applied to soil. Ammonium is more stable in soil than nitrate and less susceptible to leaching due to its positive charge. Soil microbes convert ammonium to nitrate almost like a steady conveyer belt; plants take up both nitrate and ammonium as required for growth and have access to a steady flow of available nitrogen as soon as the protected urea granules begin to melt.

Ammonia Emissions & Water Quality

Some farmers do not like to use traditional urea (even during 1st application) as they are concerned that grass growth is poorer with this N source. This is because the use of traditional urea leads to ammonia (N) losses after spreading, even in spring. The amount of ammonia loss can be substantial and is dependent on weather conditions. The highest losses tend to occur during warm and/or windy conditions; however losses can also readily occur in cooler drying hash conditions.

Ammonia in the atmosphere is then deposited into water bodies or other sensitive habitats causing deterioration in water quality and poor grass production on the farm.


  • Protected urea will reduce Ammonia/GHG emissions and reduce nitrate leaching
  • Protected urea similar to urea has a lower density than CAN and other compounds, for this reason the fertiliser spreader settings and vane selection may need to be adjusted to achieve the required spread width
  • For the greatest protection use protected urea within 12 months as the urease inhibitor will degrade over time in storage
  • Potassium and sulphur mixes with protected urea can be purchased, however currently phosphorus (P) blends result in shelf life problems for the protection
  • Protected urea is cheaper per unit of N to spread than CAN
  • Consult the Teagasc Protected urea fertiliser list 


Ever thought of increasing the diversity in your swards? This can be simply and profitably done across the whole farm over 3 years adding to the health of the soil, animals and consumers as well as reducing losses to water and emissions to the atmosphere. Lane Giles, ASSAP Advisor tells us more.

White Clover

White clover, common in Mediterranean regions, holds moisture close to the ground and helps retain carbon dioxide (increasing photosynthetic efficiency) which would otherwise escape more easily from the open canopy of grass-only swards. It also has rhizobia bacteria in nodules on its roots that “fix” nitrogen from the air and make it available for plant growth. The extra diversity in the sward also leading to greater microbial activity in the soil.

Livestock like diversity in their diet. Cows grazing grass-white clover swards eat more, producing in the region of 20-50 kg extra milk solids per year, found to be worth an extra €12,000 in milk sales per 100 acres at Darrara College Clonakilty. Recent research in Clonakilty has shown that white clover can increase herbage production by 1 – 1.5  tons DM/ha/yr and can contribute to the reduction of N fertiliser application thus improving N use efficiency.

Research in Moorepark has shown conclusively that white clover in the sward can replace 40% chemical nitrogen (100 kg N/ha) and not affect herbage production compared to a grass-only sward receiving 250 kg N/ha. This saving of 80 units N/acre is worth about €4000 per 100 acres.

Establishment programme

  • Aim to have weeds under control and soil in good health, balanced for nutrients and lime ahead of sowing.
  • A programme of reseeding 10% per year and over sowing 30% per year can achieve the target of 20-25% average annual sward clover content within 3 years.
  • Reseed at 1.5 - 2 kg clover per acre sowing in April – June. Sow at a depth of 1 cm or less, rolling afterwards. If a paddock drops below 10 - 15% clover it may be one to consider oversowing. Oversow at 2 – 2.5 kg clover per acre. For best results bare the paddock first before surface seeding and rolling just ahead of rain.
  • Grazing off covers of 700 - 900 kg DM/ha helps the clover seedlings to establish.
  • The extra growth comes the following year, approximately 8 kg DM/ha/day is grown between mid-April and end of September. Reduce chemical nitrogen from the third rotation in early May when the clover increases in the sward.

Key management techniques

  • Avoid letting animals into high clover contents hungry or else restrict the amount they consume. This can easily be done by letting all cows into the paddock together so each gets a comparable amount.
  • In Autumn aim to graze off paddocks with least clover first, these will grow more grass over winter and can be the first to graze in spring. Graze those with the most clover last in November coming back to them last again in spring.
  • Aim to avoid poaching.
  • Flexibility is the key, managing according to clover content, as well as total cover.

Most of all, enjoy the diversity!

In this short video clip Lane Giles talks about why you should use White Clover 


Slurry N and LESS 

Slurry application on Irish farms was often seen as a chore, done to relieve pressure on slurry storage systems in late winter / early spring, traditionally spread by splashplate. Today this is changing fast with the use of low emission slurry spreaders (LESS), as Eamonn Lynch Dairy Advisor,explains

The traditional method of spreading slurry for the last 30 to 40 years was by means of slurry tankers with splash plates. However things are changing at a very fast rate which is part due to knowledge built up through some excellent research and the use of low emission slurry spreaders (LESS) techniques by innovative farmers. Another factor which is also having a large effect is regulation and the largely publicised percentage of ammonia emissions which is attributed to Agriculture (98%).

Ammonia is a form of nitrogen lost during slurry spreading, is then often redeposited to other sensitive habitats such as watercourses, the use of LESS technology can reduce this loss.

To achieve these targets we need to know and understand the benefits.

  • LESS increases the Nitrogen (N) recovered from Slurry. This allows farmers to reduce chemical N applications on the farm. There is a large loss of nitrogen when using a splash plate as the slurry is spread over a large area which leads to bigger losses from the weather, wind and the effect of the sun. The process of loss is mainly through Ammonia volatilization, the nitrogen in the form of ammonia is potentially a dangerous pollutant to both human health and the environment as well as being a substantial economic loss from the farm. LESS reduces the spread width by minimising the surface area to which slurry is applied and puts the slurry directly on the ground/soil.
  • Research shows that by changing to LESS technology that the overall ammonia N losses can be reduced by up to 60%. 
  • In terms of the fertiliser value compared to the traditional splash plate based system, one thousand gallons with LESS will give on average 50% extra nitrogen compared to a splash plate. Financially the extra nitrogen alone is worth €5 per one thousand gallons. So at two thousand gallons per acre, this is equal to €10 per acre just for the extra fertiliser before you factor in the savings on chemical fertiliser application. 
  • Another large benefit is the flexibility of slurry applications on grazed pasture with lower levels of contamination and faster recovery of grass / silage swards. 
  • More accurate application with LESS give farmers the confidence to replace expensive compounds with home sourced organic fertilisers. 

In summary, you can make way better use of your slurry, reduce your chemical usage and improve the environment all in one application!

Hear more from Teagasc advisor Eamonn Lynch in this video clip below


Cover and Catch Crops

There are multiple benefits to using catch or cover crops in a tillage system. In terms of water quality it is the ability of catch crops to reduce nitrate (NO3-N) leaching that makes it a valuable tool for all tillage farmers.

Catch or cover crops in a tillage have a number of benefits for the tillage farmer these include:  

  • improved soil structure
  • reduced compaction
  • increased water infiltration
  • reduced risk of soil loss in periods of heavy rainfall

Catch Crops to prevent Nitrate Loss?

Nitrate leaching is a process that happens naturally, it occurs when nitrate leaves the soil in drainage water. Nitrate is soluble and mobile particularly in free draining soils. Nitrate leaching occurs when nitrate is present in our soils during periods of low or no crop demand for growth. If soils are saturated or subjected to heavy rainfall, nitrate can leach down through soils and into groundwater.  When the N is utilised by the plant there isn’t a problem but once it goes below the root zone of the plant and into the ground water it can find its way into the stream and river network. This can impact on water quality in the stream and river at high levels but can also have a big impact at the river estuary.

In a tillage system, the period post-harvest is the highest risk time for nitrate leaching. If soils are left fallow in the autumn/winter period with no growing crop in place, there is an increased risk that nitrate present will leach into ground waters. Simply put, catch crops will create a demand for nitrate in the soil and convert it into a growing crop rather than allow it be lost from the soil. The catch crop scavenges available nitrogen and other nutrients from the soil preventing this nitrate being leached into ground waters.

Catch crops can trap up to 60 – 120 kg N/Ha/yr that would otherwise be at risk of leaching into our groundwater.

Catch Crop Establishment

Sowing a catch crop in autumn or winter can reduce nitrate leaching losses, many cover species need to be sown before mid-August with sufficient moisture and good seed-to-soil contact been essential. The earlier the crop is established, the greater the potential to reduce nitrate leaching. The key to maximising nitrate capture is establishing a cover crop immediately after harvest. August-sown crops will provide more green material (dry matter) for grazing or incorporation, than September-sown crops. A variety of catch crops can be used to capture nutrients to build soil fertility and protect water resources.

There are a variety of targets to select from, mitigating nutrient loss and reducing soil erosion, including managing weeds and pests, environmental goals such as creating habitat building soil fertility and building soil structure.

Plan ahead

Plan ahead to incorporate legumes or grasses as a catch crop at the end of the summer season. Select catch crop species mixtures carefully with regard to the functionality required and the impact they may have on crop rotation being practiced. It is essential to clear fields of straw as soon as possible after harvest so sowing can take place.

  • Decide how catch crops fit into the arable rotation 
  • Selecting the right species and varieties will be dictated by the site and preceding crop.
  • Consider the balance between cost effective establishment and appropriate seedbed conditions for the catch crops
  • Be organised, purchase seed, have on site ready to go
  • Establish as early as possible, clear any preceding crop and prepare the ground.

There are many advantages to using catch crop in any tillage system – both from soil health and environmental point of view and well worth the time and effort in planning their establishment. Successful catch crop establishment is one of the most important tools available to tillage farmers in helping to reduce the risk of nitrate leaching from their lands.

In this clip, Fiona Doolan, Teagasc ASSAP Advisor tells us more.

ASSAP Overview

The Agricultural Sustainability Support and Advisory Programme - ASSAP is in existence since 2018. Advisors are working with farmers in Priority areas for action (PAA) across the country to improve water quality. ASSAP advisors Deirdre Glynn and Cathal Somers give information about the programme

The EPA have identified 190 PAA’s  where water quality needs some improvement. There are multiple pressures across the PAA’s such as industry, waste water treatment plants, septic tanks, forestry, agriculture and urban pressures. A lot of good work over the last 20-30 years yet we are falling short in achieving 'good status'for our water. Water quality has remained mainly static with no significant improvement in recent years. ASSAP advisors are focused on addressing agricultural pressures in the 190 identified PAAs. 

20 advisors from Teagasc and 10 advisors from the dairy CO-OP’s are working closely with farmers in a free and confidential advisory service. The aim is to work together in identifying threats to water quality on the farm and develop a plan to put measures in place to reduce nutrient, sediment and other agricultural losses to our waterbodies. All farmers can avail of this service within the PAA’s.

ASSAP advisors are supported by a team of catchment scientists from the Local Authority Waters Programme (LAWPRO), who assess rivers in a PAA and identify the main pressures in the waterbody. Where agriculture is the pressure, ASSAP advisors can use this information to provide targeted advice to farmers, ‘the right measure in the right place’.

Both a community and a farmer engagement meetings are held in a PAA when starting work in an area. LAWPRO organise the community meeting to update locals on the water quality and pressures in their area. Following this, ASSAP advisors host a farmer meeting generally on a local farm to discuss the service and how to tackle the agricultural issues in the area.

When on a farm visit, the 3 main things ASSAP advisors will discuss with a farmer are:

  • nutrient management planning
  • farmyard losses
  • land management.

The purpose of the visit is to identify issues on the farm that may affect water quality and form a plan. The local knowledge of the farmer plays an important role in identifying solutions. The practical advice will be designed to ‘break the pathway’ and prevent nutrients from entering water. Small changes on a farm, can make a big difference to water quality.  


Find out more about ASSAP here