Getting the most from your slurry

Organic manure is a valuable source of plant nutrients. The key aim is to maximise the value of slurry. This means getting the most from the phosphorus (P) and potassium (K) content, as well as the nitrogen (N). This will be achieved by making sure that it goes to the right place at the right time and is spread at the right rate.

How does using slurry reduce greenhouse gas emissions?

By making the best use of slurry on the farm there is a saving in chemical N fertiliser use. By reducing chemical N use, there is a reduction in nitrous oxide (N₂O) emissions, which is one of the main greenhouse gases we are concerned with. Using low-emissions slurry spreading (LESS) also reduces ammonia emissions by up to 30%.

What do you need to do?

Step 1: Know the nutrient content of your slurry

Knowing the N, P and K content of your slurry is a useful starting point to planning your fertiliser programme for the year. There are two options for getting this information:

• Send a sample to a laboratory for analysis.

There are four steps involved in taking a slurry sample.

1. 1. 1. Agitate the slurry tank.
      2. Suck up a load of slurry into the tanker.
      3. Take the sample from the fill point of the slurry tanker.
      4. Place the sample in a sealed plastic container.

• Use a hydrometer to estimate the nutrient content of the slurry

This can be done using the table below as a guide.

Slurry dry matter %	N Units/1,000 gallons	P Units/1,000 gallons	K Units/1,000 gallons	Value €/1,000 gallons
2% (very dilute)	4	2	13	16
4% (watery)	6	3	21	25
6% (typical)	9	5	32	39
7% (thicker)	10	6	36	45

Table 1: Value of Slurry (Cattle)

Step 2: Ensure you have adequate slurry storage

It is important to apply slurry at the correct time to maximise its fertiliser replacement value, N, P and K. Having adequate storage gives you flexibility to match slurry application timings with grass growth, enabling a better use of nutrients when grass is growing.

Assessing your slurry storage

In order to best assess whether you have adequate slurry storage, you should ask yourself the following questions:

• Were all slurry stores empty at the beginning of the last winter?
• Have you had to go out to spread slurry during the closed period?
• Depending on the zone you are in, had you enough storage from the start of the winter housing period?
• Are you concerned that this is an issue on your farm?
• When did you first spread slurry this winter?
• If you spread slurry between the end of the closed period and the 15 February, it is an indicator of storage shortage or issues within the farmyard?
• Where are your dairy, parlour, collecting yard, pit washings stored on the farm?
• Have you excessive straw bedding in your storage calculations that is not actually used in practice?
• Have you considered or planned any solutions to rectify any storage shortage?

Farmers who have insufficient slurry storage to meet the requirements of 16, 18, 20, or 22 weeks may be in reach of the nitrates regulations. It is strongly recommended that all farmers plan for a minimum buffer of 20% or an additional two to four weeks storage over and above the minimum nitrates regulation requirements.

Step 3: Apply slurry at the right time

The third step to increasing slurry N efficiency is optimising the time of applications. Spread when potential N losses are low and uptake by a growing crop is high, for example, February to April. Spring applications of cattle slurry typically have a higher recovery of N, by up to 50%, compared to summer applications. Weather conditions in spring will be more favourable to improving the recovery of N from the slurry. For example, during cool, damp, overcast days, with temperatures for less than 13°C, N loss through ammonia emissions is lowest.

There are some points to take note of when applying slurry.

1. Apply the slurry where ground conditions are suitable, for example, apply to soils that are trafficable.
2. Umbilical slurry spreading systems should only be used where ground conditions are suitable. Using this system where soils are saturated to avoid soil damage from tankers poses a risk to water quality. When using umbilical spreading systems, ensure slurry is not over-applied.
3. Slurry should not be spread if heavy rainfall is forecast. High rainfall levels can lead to soils becoming saturated and water flowing over the surface of fields, bringing with it the nutrients applied.

Step 4: Applying slurry in the right place

Planning

It is important to have a slurry application plan. The spreading of organic manure has boundaries which must be respected and adhered to. These include not spreading organic manure within:

• 5 meters of surface waters. This extends to 10 meters for the first two and last two weeks of the spreading season.
• 10 meters of surface waters where the slope towards the water exceeds 10%.
• 15 meters of exposed cavernous or karst features such as swallow holes and exposed rock.
• 20 meters of a lake shoreline.
• 25-200 meters of a water abstraction point for human consumption.

Where?

Spread on fields or paddocks where fertility is low and nutrient demand is highest, for example, silage fields. It is important to direct watery slurry to grazing plots.

Silage Ground

Maximise the use of slurry on silage ground as 3000 gallons per acre makes up the majority of P and K requirements, as well as up to 30kg N. Target thicker, or higher dry matter slurry to silage fields.

Step 5: Using the right equipment

Spring applications using Low Emissions Slurry Spreading, LESS for short, further increase N availability by up to 65% compared to summer applications. For example, where a grass silage crop receives 33m³ per hectare in spring, this will supply 33kg N per hectare; however when applied in summer it will only supply 20kg N per hectare. 

Get more information on Low Emissions Slurry Spreading here.

Calibrating your slurry spreader

Teagasc has created a simple online calibration calculator to eliminate the guess work. The tool can be used with any type of slurry tanker, no matter what applicator is being used on the back. It works on your smartphone, so it can be accessed from the tractor seat. It is simple to use through the following method:

• Sliders allow you to input the size of the tanker, spread width, and the time taken to empty the load.
• Select your desired application rate.

Use the Slurry Calibration Tool below.