Abstract:
This study was conducted with the objective of quantifying the effect of zero
grazing on the biogas and slurry production in Fogera woreda through
grouping cattle in to two main categories, i.e., zero grazers and free grazers
having four cattle in each groups and collecting data accordingly. Both biogas
and slurry production were measured by taking two biogas plants that fed with
manures of zero grazing and free grazing cattle separately. The parameters on
which data were collected are manure production, manure fed to biogas
plants/influent, slurry and biogas production. The interpretation and
discussion were carried out based on descriptive statistics through comparing
and contrasting the data/ the parameters between zero grazing and free
grazing. The result shows that zero grazing has significant effect on the
production of manure, slurry and biogas. There was significant (P<0.05)
difference between manure and slurry from zero grazing cattle and that of free
grazing ones, i.e., the manure collected from zero grazing cattle was about
38% larger in amount than that of free grazers. This difference results the
same amount of slurry and 36.4% of biogas productions. More over, it was
investigated that the dry matter content of manure and slurry of zero grazing
cattle is significantly greater than that of the same amount of manure and
slurry from free grazers. On the other hand, there was no significant (P>0.05)
difference between the amount of liquid manure fed to the two biogas plants
which resulted equivalent amount of biogas production per a unit of manure
from the two groups. Therefore, it can be concluded that, in addition to the
direct impact through over grazing and over stocking, free grazing
management system of cattle has significant indirect impact on the
environment by affecting the production of slurry and biogas which may be the
silent impact of cattle management systems on the environment.
Key words: Biogas, slurry/bio-slurry, feedstock/influent, zero/free grazing