Nitrogen fertilizer application increased grain yield of both
cultivars when 4 and 8 t ha1 CA were applied, but no yield response
to N application was observed when 16 t ha1 CA were applied.
Higher grain yields in 4 and 8 t ha1 CA plots with N fertilizer may be
due to the combined effects of the improved soil physical properties
and the alleviation of CA-induced N availability.
However, the high rate of 16 t ha1 CA application obviously caused N limitation even
with N fertilizer application, consequently leading to low grain yields.
No significant CA-related effects on grain yield were observed in
Exp. 2 for the combined ANOVA across all sites, but a t-test for
individual sites indicated that grain yields at LO2 and HK3 were
significantly higher in CA-treated plots than in untreated plots
(P < 0.05) (Table 3).
Although not significant, these trends were
also observed at other sites with low available phosphorus (P)
contents in the soil (LO3, SN; Table 1), whereas lower yields in CA
applied plots were observed at all sites with a high P availability
(HK2, SO, LS; Table 1).
A possible explanation is that CA increased
plant available P.
A similar effect of CA on P availability was
reported in previous studies (Lehmann et al., 2002; Glaser et al.,