110 Min Huang, Xuefeng Zhou, Xiaobing Xie et al.
Soil orgaic matter and total N contents in this study were approximately
2 – 3 times higher than those in the study of Huang et al. (2008). These suggest
that improving soil fertility is critical to enhancing the crop productivity and
meanwhile reducing the dependence on external N inputs. It is further
supported by the results that the N uptake form soil and fertilizer occupied 81–
83% and 17–19% of the total N uptake (Figure 2). Consistently, Zou et al.
(2015) reported that grain yield without N fertilization was 73–79% of grain
yield with N fertilization in four rice cultivars, including Liangyoupeijiu,
across a wide range of regions.
The difference in retention of fertilizer-N in soil was not significant
among the three N rates (Figure 3a). Fertilizer-N loss significantly decreased
with decreasing N rate (Figure 3b).
These observations agree with those observed in other rice-based cropping
systems by Ju et al. (2009) and further emphasize the need to minimize N
application rates to reduce the impact on environments in rice production.
More importantly, our results indicate that long-term rice-oilseed rape rotation
may be a feasible way to achieve this goal. However, unexpectedly, fertilizer-
N loss rate (100×fertilizer-N loss/N rate) under the N rate of 150 kg ha–^1 is
about 10% higher in our study than in the study of Ju et al. (2009). One reason
for this difference was the fact that soil sampling depth is different between
the two studies.
Figure 3. Retention (a) and loss (b) of fertilizer-N applied at three rates to a hybrid rice
cultivar Liangyoupeijiu in a^15 N micro-plot experiment conducted on a paddy soil with
long-term rice-oilseed rape rotation in 2015. Vertical bars represent SE (n =3).