106 Min Huang, Xuefeng Zhou, Xiaobing Xie et al.
In the single rice-growing season in 2015, a field experiment was
conducted on the long-term rice-oilseed rape rotation paddy field.
Liangyoupeijiu was grown under three N rates, i.e. 150 kg ha–^1 (recommend N
rate), 120 kg ha–^1 (80% of the recommend N rate) and 90 kg ha–^1 (60% of the
recommend N rate). N was applied in three splits (50% at basal, 30% at
midtillering, and 20% at panicle initiation) for each treatment. Plots were
arranged in a randomized complete block design with three replications, using
a plot size of 48 m^2 (8 m × 6 m). Pre-germinated seeds were sown in a
seedbed. Twenty five-day-old seedlings were manually transplanted at a
spacing of 20 cm × 20 cm with one seedling per hill. Phosphorus (90 kg P 2 O 5
ha–^1 ) was applied and incorporated in all plots at basal (1 day before
transplanting). Potassium (180 kg K 2 O ha–^1 ) was split equally at basal and
panicle initiation. The experimental field was kept flooded from transplanting
until 10 days before maturity. Insects were intensively controlled by chemicals
to avoid yield loss. At maturity, 10 hills were sampled to determine
aboveground total dry weight, harvest index, yield components, and
aboveground total N uptake. Plants were separated into straw and panicles.
Straw dry weight was determined after oven-drying at 70°C to constant
weight. Panicles were hand-threshed and the filled spikelets were separated
from unfilled spikelets by submerging them in tap water. Three subsamples of
30 g of filled spikelets and all unfilled spikelets were taken to count the
number of spikelets. Dry weights of rachis and filled and unfilled spikelets
were determined after oven-drying at 70°C to constant weight. Aboveground
total dry weight was the total dry matter of straw, rachis, and filled and
unfilled spikelets. Spikelets per panicle, grain-filling percentage, and harvest
index were calculated. N contents of straw, rachis, and filled and unfilled
spikelets were determined by using an autoanalyzer (Integral Futura, Alliance
Instruments, Frépillon, France). Aboveground total N uptake was calculated.
Grain yield was determined from a 5-m^2 area in each plot and adjusted to the
standard moisture content of 0.14 g H 2 O g–^1.
In the field experiment, two locations were selected in each plot to
conduct^15 N study in micro-plots to determine fertilizer-N fate. The micro-
plots (PVC cylinders, 40-cm long with 40-cm inner diameter) were inserted
into the soil to a depth of 20 cm with a collar of 20 cm aboveground. Except
for the N fertilizer using^15 N-labeled urea (abundance 5.18 atom%, producing
by the Shanghai Institute of Chemical Industry, China), the micro-plots were
managed in the same way as the main plots of the field experimemt. At
maturity, a mixed soil sample was taken from 5 randomly selected points
within each micro-plot, throughout the upper 20 cm of the soil, using a 1.8-cm