Digestate and efficient nutrient management
The nutrient management represents an important item of the environmental impacts of modern agriculture: both the impact of the production of synthetic fertilizers (eg urea), and the management of nutrients contained in manure.
The introduction of anaerobic digestion in the livestock sector brings many environmental benefits that go far beyond the production of renewable energy, but are related to more sustainable management of animal manure: digestate, if managed properly, can significantly increase the efficiency of the units of nitrogen (the nitrogen which goes to the plant) and instead reduce the dispersion in water and atmosphere, decreasing environmental pollution.
In detail how the anaerobic digestion of manure can improve the environmental impact of agricultural production.
- Methane emissions and greenhouse gases: anaerobic digestion of manure and digestate use to the land, allow a significant reduction in methane emissions contributing to the reduction of emission of GHG National Scale
- Reduction of ammonia emissions: the factors influencing ammonia emissions in the field are the viscosity of the medium and the pH. The anaerobic digestion elevates the pH compared to the manure (greater possibility of volatilization), but digestate has lower viscosity, more evident in the case of use of the separated liquid A correct use of the liquid fraction of digestate ( “injection” ) allows the strong reduction of ammonia emission in atmospher.
- N2O emissions: the nitrogen oxide emissions are a function of the amount of nitrogen applied to the soil (Bowman, 1994) on the other hand, the presence of readily biodegradable organic substance make the emission potential, higher (Granly and Bockman, 1994). The digestate is a highly stabilized organic material, Furthermore, the use of the separated liquid, reducing even more the contribution of organic fraction, contributes to the reduction of N2O emissions.
- Reduction of nitrogen leached into the groundwater through a targeted distribution. The digestate, particularly the liquid fraction, contains a high amount of nitrogen in mineral form (ammonia). This form is immediately available for uptake by plants. So unlike manure, in which nitrogen can mineralize at different times of the year, the nitrogen of the digestate is immediately available for the plant and allows to make a very precise coupling between distribution and up-take by the plant . This greatly increases the utilization efficiency, reducing the quantities dispersed in the aquifer.
- Sanitation and reduction of pathogens
- Reduction of odour emissions
The environmental benefits of anaerobic digestion are related to the application of digestate management best practices
Below a summary:
• coverage of tanks in which digestate is stored
• split use of the digestate in pre-sowing and in coverage (time of increased nitrogen uptake by the plant)
• distribution od digestate for injection to zero emissions of ammonia
• distribution according crop nutrient budget