Mekelle University The School of Graduate Studies Faculty of ...

2.6 Palatability of the Substrata to EarthwormOrganic debris is more palatable to earthworms if it is fresh or incubated for up to 2weeks. The particle size of organic matter does not matter. In Martin et al. (1992) it wasshown that when fresh material is compared to incubated material, worms prefer freshorganic matter as in undecomposed plant debris or debris incubated for 2 weeks.Incubation of the material fed to earthworms for 2, 5 and 10 weeks caused an increase ingrowth rate and yield efficiency. With fresh plants (or plants incubated for 10 weeks orless) worms eat less and gain more weight than with material incubated for more than 10weeks.Martin et al. (1992) states that worms prefer leaves to roots: When leaves are incubatedfor more than 10 weeks however the material becomes only as beneficial as fresh rootmaterial: plant material decomposed for a long time has less nutritive value. When rootsare incubated for 2-5 weeks they increase growth rate, but without a change in yieldefficiency. This was explained by the fact that fresh OM has a higher water-solublecontent and more N availability. Also in the same study all plant materials have the samevalue after a long incubation time since all easily assailable compounds are gone. Whenlegumes and grass were compared they gave different yield efficiency results althoughthey both have same N content because legumes have higher nitrogen assimilability. Asto the particle size effect, a fraction of soil OM was replaced with labeled C - OM. Theresults showed that worms ingested similar amounts of coarse OM (young OM – 250 –200 µm) and fine OM (0.20µm). This indicates that particle size does not matter (Martinet al., 1992). Palatability of different types of litter to earthworms may also depend onnitrogen and carbohydrate content, and the presence of polyphenolics such as tannins23