Slurry is a source of nutrients for grass growth thus the use of slurry is important for reducing the demand for inorganic fertilisers. Spreading slurry when the conditions are favorable reduces greenhouse gas emissions.

Overview

Slurry is a mixture of animal excreta, water, and other wastes. Appropriate application of slurry allows farmers to recover maximum nitrogen (N), phosphorus (P), and potassium (K) on farms.

Why should farmers aim to spread slurry in Spring?

  • Spring has the most favourable conditions i.e. damp, cool, overcast days, however, farmers can spread some slurry in Summer if the conditions are appropriate.
  • Spreading slurry in Spring increases nitrogen availability by 65% in Spring compared to Summer when using Low Emission Slurry Spreading (LESS) equipment (Teagasc, 2020 ).

In the following video, the Teagasc advisor discusses the timing of the slurry application using LESS equipment.

How do you ensure the proper timing of slurry spreading?

  • Avoid spreading slurry when rain is forecast within the next 48 hours to avoid slurry being washed away into water sources. 
  • Soil temperature should be above 6°C.   
  • Spread when grass cover is low (up to 1200kgDM/ha) to reduce contamination of grass.
  • Spread using LESS equipment.
  •  Ensure there is enough storage space to avoid spreading slurry when conditions do not permit.

Economic and Environmental Benefits

Spreading all slurry in Spring ensures more nitrogen is recovered from the slurry and minimises fertiliser emissions. A summary of net savings and emission reductions for a typical 93-cow herd farm is presented in the Table below.

Table 6 Savings and emissions reduction from spreading all slurry in Spring

Scenario 1Scenario 2
Cattle slurry applied @ 33m3/ha/hour50% Spring 50%Summer1Spring
Total slurry produced (m3)552552
Available nitrogen( kg /m3)20.801
Total nitrogen saved (kg)–110
Fertiliser savings per farm (€)134
Environmental impact
Total emissions (kg CO2-eq / kg FPCM)0.9600.955
Reductions in emissions (%)–0.52
 kg CO2-eq / kg FPCM is the carbon footprint per kg of Fat and Protein Corrected Milk.
93 cow herd producing approximately 0.33m3 of slurry/cow/week.
 1Spring in Scenario 2 signifies spreading in the right conditions i.e., damp, cool, overcast days. Some slurry can be spread in Summer under right conditions.
2When 100% of slurry is spread in Summer using LESS equipment recovery rate is 0.6kg/m3 and 1kg/m3 in Spring( Lalor et al., 2011; (Teagasc, 2020).

Research

Currently, at FZC, 80% of slurry is spread during Spring and 20% in Summer. Compared with national average figures of 50:50 for Spring and Summer, this saves Shinagh approximately 177kgs of nitrogen per year. The aim is to ensure all slurry is spread during favourable environmental conditions.

Other research

The key findings of  previous research on the timing of slurry application include:

  • Testing different equipment for slurry spreading, researchers in Ireland found that more nitrogen can be retained for use if the slurry is spread in Spring rather than in Summer.
  • Farmers could retain 8.7 units of nitrogen per 1000 gallons of slurry in Spring using a trailing shoe as compared to 5.4 in Summer (Forrestal et al., 2021).
  • If  farmers use a splash plate in summer they can retain as low as 3.3units nitrogen/1000 gallons of slurry (Forrestal et al., 2021)
  • Farmers should aim to spread at least 75% of their slurry in Spring.

Links to more research

Manure and its Management in cattle

Slurry timing for protecting the environment

The slurry-spreading calendar

Effect of increasing the time between slurry application and first rainfall event on phosphorus runoff

Regulations

The Nitrates and Water Directive Ireland–  The nitrates directive states that the maximum stocking rate on a farm is 170kg/ha (1.9LU/ha) unless the farmer applies for and is approved for a nitrates derogation.

  • Slurry cannot be spread on land from 8th October 2022 and 1st October from 2023 onwards to January 12 / 15th / 31st (depending on which part of the country a farm is located).
  • Farmers are prohibited from spreading slurry when heavy rainfall is forecast within 48hrs and also when temperatures are very high. 

The Nitrates Derogation – For derogation farmers, they should adhere to all slurry spreading timing and use LESS equipment for slurry spreading.

Suppliers

This is a management strategy that requires no information on suppliers.