Thesis
A Capture Mark Release (CMR) study was carried out at the Sokoine University of
Agriculture, Solomon Mahlangu Campus in Morogoro, Tanzania from April 1999 to
August 2001 to investigate the effect of slash and bum versus tractor ploughing on the
population of rodents in agricultural fields subjected to either monocropping (maize
alone) or intercropping (maize and beans). Mastomys natalensis was the most abundant
species in the different treatments (97.8%). The spatial distribution of individuals was
significantly affected by land preparation methods. The coefficient of dispersion values
(based on variance-to-mean ratio calculations) indicated that before land preparation,
animals were randomly distributed everywhere, but after land preparation and the
consequent stages of maize growth, more animals clustered around the edges in tractor
ploughed fields whereas in the slash and bum fields, animals were randomly distributed.
Rodent population abundance increased in slash and bum fields during the crop growth
stage in the short rainy season (yuli) as a result of higher recruitment of new individuals
than in the tractor ploughed fields (for both mono and intercrop) (P = 0.004) suggesting
that slash and bum fields are more attractive for colonization from the surrounding
fallow fields. Tractor ploughing, slash and bum, mono and intercropping systems
significantly (p< 0.05) affected the home range and movements of rodents. Home range
was smaller in the tractor ploughed fields (Wald stat = 57.03; df=l; p<0.001). Females
occupied smaller home ranges than males (Wald stat=18; df =1 p< 0.001), but the
reasons were not clear. Significant variations in rodent population density due to soil types also occurred, with lowest populations in sandy clay soils (F=(2.5)= 8.42;
p=0.025). These variations could be attributed to differences in the suitability of soils for
burrowing. The level and distribution of crop damage in the fields indicated higher and
uniform rodent damage in the slash and bum but lower and random damage occurred in
tractor ploughed fields (Variance to mean ratio calculations). This suggests that seed
retrieval was easier in the slash and bum fields. The current study suggests that slash and
bum practice does not affect rodent population distribution in crop fields while tractor
ploughing does affect rodents, probably by reducing cover and food availability or even
by killing some individuals. Yet, it seems useful as a management tool when it is
practiced over a large area and the surrounding fallow lands, which act as donor habitats,
are cleared.
Furthermore, land preparation methods should not be assumed to be
adequate and effective on their own in controlling rodents but instead, they should be
integrated with other strategies to reduce crop damage.
SUA- VLIR