The performance of individual component crops was assessed in relation to
whole treatment planting density. Values for banana represent the mean over the
experimental period, i.e. up to 28 MAP (Fig. 2), whilst values for rubber are those
obtained at final harvest at 28 MAP because unlike banana, rubber growth increased
steadily with time and reached a maximum at 28 MAP (Fig. 3). Except in the low
density BR intercrop, treatments had a little effect on biomass productivity and leaf
area per plant of banana in high density systems and therefore, CPRs of BBR and
BBBR were similar and greater than that of BR (Fig. 2c). In the case of rubber,
biomass productivity and leaf area per plant were greater in the intercrops than the
sole crop, particularly under the high density system (Fig. 3). In general, the greater
the planting density, the greater the TDM and CPR of intercropped rubber.
Data from the second small-scale experiment at Pallegoda also indicated an
improved performance of banana when intercropped than when grown alone, with
CPRs (based on fresh weight at 28 MAP) greater in the higher density BBR and
BBBR intercrops than in the BR system (Table I). The magnitude and direction of
the growth response of banana was similar at both sites, despite widely differing
management and growth conditions.
Stem girth and height of rubber (Figs. 4 and 5) showed an improved
performance in the intercrops relative to the sole crop throughout the experimental
period. Likewise, intercropped rubber in the high density BBR and BBBR treatments
performed best in terms of both girth and height at the Pallegoda site (Table 1). The
onset of tapping is determined by the % of trees with a girth at a height of 90 cm
above the bud-grafted union exceeding 50 cm. After 5'/i years of growth, the high
density BBR and BBBR systems of the main experimental site showed an increase in
tappable trees with values of 69 and 72% respectively, compared with the sole (51 %)
and BR (60%) treatments.