Leaf SPAD values measured in Exp. 1 and Exp. 2 are shown in
Table 3. The main effect of CA and the interaction effects of S CA
and S CA N were significant in Exp 1, while only the effect of
S CA was significant in Exp. 2 (data not shown). In contrast to the
positive effect on SHX and XSF, CA resulted in decreased leaf SPAD
values. The decrease was most prominent at HK1, where leaf SPAD
values for treatments without N fertilizer application were lowest
at the 16 t ha1 CA-level for Apo and at the 8 t ha1 CA-level for
Vieng. Similar trends in leaf SPAD values were observed at LO1, but
the differences were not statistically significant. These results
indicated that CA decreased plant N uptake, which confirms the
results of Lehmann et al. (2002), who also described a decrease in
plant N uptake and attributed the effect to N immobilization
caused by the high C/N ratio of the applied biochar.
The N fertilizer treatment in Exp. 1 alleviated the CA-induced
decrease in leaf SPAD values. However, leaf SPAD values in Nfertilized
plots also decreased as the CA amount increased,
indicating that excessive CA may offset the effect of N fertilizer.
3.2.