By Henning Lyngsø Foged, Organe Institute, and Christopher Ciantar, FCCS
The practices of discharging pig and cow slurry in Malta comes across as highly inappropriate. This is also the case for the way solid manures are handled. An important concern of current practices is that significant quantities of organic matter are lost at the cost of soil fertility and climate. The gravity of this is furthermore emphasised by the fact that Malta’s crop farming happens entirely on mineral soils, since the country is without cropping patterns that would allow the accumulation of soil organic matter, as is the case in grasslands and forests.
Currently, slurries are disposed into the overloaded wastewater treatment plants. After a mechanical separation process, the liquid fraction is discharged to the Mediterranean Sea. In this way, significant amounts of organic matter in slurries are lost.
The conventional way of handling solid manures is to store it in a heap for some time and spread it on the fields in the late summer. In this way, there happens a (typically uncontrolled) compositing process, whereby up to two thirds of the organic matter is lost as carbon dioxide (CO2) and methane (CH4) (both are potent greenhouse gases), rather than being returned to the soils.
When speaking about carbon sequestration in soils, different parameters are used. Organic Matter (OM) constitutes typically 80% of Dry Matter (DM) in livestock manures. Soil Organic Carbon (SOC) constitutes 40-60% of manure’s OM, most in solid manure, and less in liquid manures. Effective Organic Matter (EOM) is OM multiplied with a Humification Coefficient (HC), that represents the proportion of OM that is converted into stable, more resistant humus in soil. Soil humus contains about 50% Carbon.
The following table shows the amount of Effective Organic Matter and Effective C sequestration as Humus as an impact of three different scenarios:
- the current situation,
- with a country wide implementation of the SYNECO concept for liquid manures, and
- with a country wide implementation of the SYNECO concept if extended to also handle solid manures.