In Exp. 1, the grain yields at HK1 ranged between 2.2–3.2 t ha1
for Apo and between 0.5–1.5 t ha1 for Vieng.
They were two to three times higher at LO1 (4.8–5.9 t ha1 for Apo and 3.0–4.0 t ha1
for Vieng) (Table 3).
Lower yields at HK1 could have been caused by the very low available P and SOM content at this site (Table 1).
Surprising was the mostly negative effect of nitrogen application in
the plots without CA application; positive yield responses were
limited to some of the CA plots.
Combined ANOVA across sites
suggested that there were no significant CA-related effects on grain
yield, probably because severe lodging occurred in all plots at LO1,
increasing the experimental error at that site. The separate data
analysis for HK1 showed an interaction effect between CA and N at
P = 0.07 (data not shown). A single CA application (4 t ha1) resulted
in a decreased grain yield for Apo and no change in yield for Vieng.
That may be due to the CA-induced reduction of plant N uptake as
noted above