Aim: To make best use of nutrients and manures on the farm and reduce emissions.
Better targeting of fertilisers can cut waste and improve profits. For the majority, it will not be practical or economic to replace all fertilisers with manures, slurries, compost and digestates, but the aim should be to make maximum use of the manures and slurries that are available on the farm.
Practical Measures
- Soil testing will help you to know the pH and nutrient status of farm soils, allowing you to adjust lime and fertiliser inputs as required
- Make sure you know the nutrient value of your manures, slurries, compost and digestates; use this first then top up with bought in fertilisers
- Apply fertilisers at optimum rates for the crop
- Improve the timing of nutrient applications to meet crop requirements
- Make sure that you separate slurry and fertiliser applications
- Include clover in grass rotations
- Choose plant varieties which use less nitrogen or fix nitrogen more efficiently
For example:
Each 10m³ tanker of dairy slurry could contain the equivalent of £30 to £50 worth of fertiliser. How you apply slurry makes a difference – applying slurry close to the growing crop with a trailing shoe or similar reduces nutrients lost to the atmosphere when compared to a splash plate application.
Digestate
Anaerobic digestion (AD), is the process of biological decomposition in the absence of oxygen. The lack of oxygen inhibits the range of bacteria that would normally populate under aerobic conditions causing composting.
In their place are bacteria that thrive without oxygen, and in doing so convert the sugars in the feedstock into carbon dioxide (about 35%) and methane (about 60%). The methane can then be used to generate renewable electricity and heat in a combined heat and power (CHP) engine, burned directly to produce heat, be cleaned and injected into the grid or used to produce fuel. The material left over after digestion, known as digestate, can be used as a fertiliser and soil improver. However, this can only be effective if they are widely accepted by farmers who need to be properly informed about what they are and how to use them safely. Incentive programs and the need for some regulation in the sector has resulted in a complex market place where digestates with differing origin, certifications and characteristics are available.
The simple flow diagram within the Using Anaerobic Digestates on Farms in Scotland document provides the key questions and explanations at each step to allow farmers/landowners to determine if a given digestate is suitable for use on their land. A series of information notes are also available to download using the links below to provide more details.
- Digestate Information Sheet 1 – Introduction to digestate
- Digestate Information Sheet 2 – Points to be aware of
- Digestate Information Sheet 3 – Application methods
- Digestate Information Sheet 4 – Nutrient availability
- Digestate Information Sheet 5 – Total nutrient content liquid digestate
- Digestate Information Sheet 6 – Nutrient content of solid digestate
- Digestate Information Sheet 7 – Available Nutrient Content of Liquid and Solid Digestate Applied at Different Rates
- Digestate Information Sheet 8 – Available Nutrient Value (£) of Liquid and Solid Digestate Applied at Different Rates
These documents were created by SRUC, funded with support from the Universities Innovation Fund (UIF), from the Scottish Funding Council (SFC)
Other useful resources:
- FAS Technical Note TN:699 Agricultural use of biosolids, composts and anaerobic digestates and other industrial organic fertilisers.
- The Farmer’s guide to sourcing and using digestate and compost’ is a useful booklet produced by Zero Waste Scotland and NFUS
- Digestate and compost use in agriculture – a good practice guide for agri-contractors
- The renewable fertiliser matrix (adopted by Red Tractor, QMS, SQC and others)
