RESULTS AND DISCUSSIONS
The results of the effect of rubber based cropping
systems on rehabilitated rubber plantation on the
physico-chemical properties of the soil are presented in
Table 1. There was no significant effect of intercropping
on the particle size distribution (percentage sand, silt and
clay) and pH (H 2 O) of the soil. However, generally, the
pH of the soil in all the treatments increases from the pre-
cropping value, except for R + C and R + M systems.
Kang [11] reported that, this was as a result of continuous
cultivation in intercropping systems. The increases in the
pH values in sole systems compared with the
intercropping systems, demonstrates that intercropping
lead to reduction in soil acidity compared with sole
cropping, because of higher organic material generation.
This is consistence with the submission of [6,7] who
observed higher pH in soil under intercropping compared
with soil under sole cropping. The lower pH values in the
R + C intercropping system, may be attributed to the
longer duration of crop interactions in R + C compared to
R + M. While the higher pH values in R + M + C systems
compared to the R + M and R + C, can be attributed to
the higher level of organic matter production. Yasin et al.,
[12] argued that, decomposition product of organic matter
(maize) in the soil can play a role as soil pH regulator.
The concentration of exchangeable bases increases
above the pre cropping values except in Mg where there
was a decline R+C treatment due to cassava. This is
attributable to the effect of removal of vegetation
involving clearing burning during land preparation which
triggers the breakdown of organic matter and nutrient
mineralization. Nye and Greenland [13] reported that
continuous land cultivation leads to nutrient
mineralization and nutrient release in the soil. The result
showed a significant effect of intercropping on the organic
carbon concentration in the soil. The sole cassava and
sole rubber treatments showed significantly higher organic
concentrations compared with the other treatments due
to higher Litter production and residue addition under the
cropping systems involving cassava leading to increase
in organic carbon content in the soil. Furthermore,
compared with the control, all the treatments recorded
higher organic carbon concentration except R+C and
R+M+C treatments. This result is similar to the study of
earlier results of intercropping studies with cassava [7].