Crop growth and development
The length of the ratoon growth season was 45–48% that of main season (Table 1). The lengths of the main and ratoon growing seasons were similar for the four years of the experiment. Hybrid rice cultivars with longer main growing seasons also had longer ratoon growing seasons. The total main season growth durations for the rice hybrids were 9–10 d longer than for the inbred rice cultivars. The longer total main season growth duration of the rice hybrids was mainly attributed to the longer growing time from sowing to heading. Similarly, the total growth duration for the ratoon season was longer for the rice hybrids than for the inbred rice cultivars by 4–7 d.
Table 1
Growth duration of four rice cultivars in main rice crop -ratoon rice system in 2017–2020
Cultivar
|
Year
|
SW-HDa (d)
|
HD-MH
(d)
|
Main crop duration (d)
|
MH-HDR
(d)
|
HDR-RH
(d)
|
Ratoon crop duration (d)
|
HHZ & JNSMb
|
2017
|
112
|
30
|
142
|
34
|
30
|
64
|
2018
|
110
|
30
|
140
|
32
|
32
|
64
|
2019
|
111
|
30
|
141
|
34
|
30
|
64
|
2020
|
111
|
30
|
141
|
34
|
31
|
65
|
NY103 & RY1015
|
2017
|
119
|
32
|
151
|
38
|
32
|
70
|
2018
|
117
|
32
|
149
|
38
|
33
|
71
|
2019
|
118
|
33
|
151
|
37
|
31
|
68
|
2020
|
117
|
33
|
150
|
39
|
33
|
72
|
a SW-HD, days from sowing to heading; HD-MH, days from heading to harvest of the main rice crop; MH-HDR, days from harvest of the main rice crop to heading of the ratoon crop; HDR-RH, days from heading of the ratoon rice to harvest of the ratoon crop. bHHZ, JNSM, NY103, and RY1015 are abbreviations for the cultivars ‘Huanghuazhan’ and ‘Jinnongsimiao’, and the hybrids ‘Nei6you103’ and ‘Rongyou1015’, respectively. |
Climatic condition
The maximum and minimum temperatures were slightly higher for the rice hybrids from sowing (SW) to heading (HD) and from HD to harvest for the main rice crop (MH) than for the rice inbreds during the main growing season (Table 2). However, the rice hybrids experienced lower maximum and minimum temperatures from MH to heading of the ratoon rice (HDR) and from HDR to harvest of the ratoon rice (RH) than did the rice inbred lines in the ratoon growing season.
Table 2
Maximum and minimum temperatures during the rice-growing season from sowing to maturity of ratoon rice from 2017 to 2020.
Cultivar
|
Year
|
SW-HDa
|
HD-MH
|
MH-HDR
|
HDR-RH
|
Maximum temperature (°C)
|
HHZ & JNSM b
|
2017
|
25.9
|
35.2
|
33.0
|
26.7
|
2018
|
27.5
|
34.1
|
34.6
|
24.3
|
2019
|
26.0
|
31.1
|
33.3
|
27.1
|
2020
|
26.9
|
30.7
|
33.8
|
24.6
|
Mean
|
26.6
|
32.8
|
33.7
|
25.7
|
NY103 & RY1015
|
2017
|
26.3
|
35.6
|
31.6
|
22.9
|
2018
|
27.6
|
35.1
|
31.2
|
21.5
|
2019
|
26.1
|
32.1
|
31.8
|
24.9
|
2020
|
27.0
|
32.4
|
30.8
|
20.8
|
Mean
|
26.7
|
33.8
|
31.3
|
22.5
|
|
Minimum temperature (°C)
|
HHZ & JNSM b
|
2017
|
18.0
|
26.2
|
24.6
|
21.0
|
2018
|
19.0
|
25.6
|
25.3
|
20.1
|
2019
|
18.4
|
23.9
|
24.4
|
20.2
|
2020
|
18.5
|
24.1
|
24.7
|
19.8
|
Mean
|
18.5
|
24.9
|
24.7
|
20.2
|
NY103 & RY1015
|
2017
|
18.4
|
26.2
|
23.8
|
18.4
|
2018
|
19.4
|
25.5
|
23.8
|
17.3
|
2019
|
18.6
|
24.7
|
23.5
|
18.3
|
2020
|
18.8
|
25.0
|
22.8
|
17.1
|
Mean
|
18.8
|
25.3
|
23.5
|
17.8
|
a SW-HD, days from sowing to heading; HD-MH, days from heading to harvest of the main rice crop; MH-HDR, days from harvesting the main rice crop to heading of the ratoon rice; HDR-RH, days from heading to harvest of the ratoon rice crop. b HHZ, JNSM, NY103, and RY1015 are abbreviations for the cultivars ‘Huanghuazhan’ and ‘Jinnongsimiao’, and the hybrids ‘Nei6you103’ and ‘Rongyou1015’, respectively. |
Grain yield and its attributes
The interactive effects of Y×T and Y×C were significant for main season yield, ratoon season yield, and annual grain yield (Table 3). There was no significant interactive effect of T×C on main season yield, ratoon season yield, or annual grain yield. The interactive effect of Y×T×C was significant for ratoon season yield and annual grain yield but was not significant for main season yield.
Table 3
Main season yield, ratoon season yield, and annual yield of four rice cultivars/hybrids grown under four cultivation methods from 2017 to 2020.
Variable
|
Grain yield (t ha− 1)
|
Main crop yield
|
Ratoon crop yield
|
Annual yield
|
Treatment (T)a
|
CTDS
|
9.34 a
|
3.21 b
|
12.55 a
|
NTDS
|
9.05 b
|
3.36 a
|
12.41 a
|
NTTP
|
8.65 c
|
3.20 b
|
11.85 b
|
CTTP
|
8.80 c
|
3.22 b
|
12.03 b
|
Cultivar (C)b
|
HHZ
|
8.43 b
|
2.93 d
|
11.36 c
|
JNSM
|
8.07 c
|
3.07 c
|
11.14 d
|
NY103
|
9.64 a
|
3.70 a
|
13.33 a
|
RY1015
|
9.70 a
|
3.31 b
|
13.01 b
|
Year (Y)
|
2017
|
10.59 a
|
3.34 b
|
13.93 a
|
2018
|
8.70 b
|
2.83 c
|
11.52 c
|
2019
|
8.26 c
|
3.30 b
|
11.56 c
|
2020
|
8.29 c
|
3.54 a
|
11.83 b
|
Interaction
|
Y×T
|
**
|
*
|
**
|
Y×C
|
**
|
**
|
*
|
T×C
|
ns
|
ns
|
ns
|
Y×T×C
|
ns
|
**
|
**
|
a CTDS, NTDS, NTTP and CTTP represent conventional tillage and direct seeding, no-tillage and direct seeding, no-tillage and transplanting, and conventional tillage and transplanting, respectively. b HHZ, JNSM, NY103, and RY1015 are abbreviations for the cultivars ‘Huanghuazhan’ and ‘Jinnongsimiao’, and the hybrids ‘Nei6you103’ and ‘Rongyou1015’, respectively. The means within each variable that share the same lower-case letter are not significantly different according to LSD at p = 0.05. * Significant at p < 0.05; ** Significant at p < 0.01; ns, not significant at p < 0.05. |
There were significant differences in main season yield, ratoon season yield, and annual grain yield among the four cultivation methods used in the experiment (Table 3). Grain yield of the main rice crop for the CTDS and NTDS treatments was 6% and 3% higher, respectively, than for the CTTP treatment, whereas grain yield of ratoon rice for the CTDS and NTDS treatments was equal to or higher than for the CTTP treatment. Consequently, the annual grain yield for rice grown using CTDS and NTDS was 4% and 3% higher, respectively, than for rice grown using CTTP. Main season yield, ratoon season yield, and annual grain yield for the NTTP treatment were slightly lower than for the CTTP treatment.
A large difference was observed in main season yield, ratoon season yield, and annual grain yield between the rice hybrids and the inbred cultivars (Table 3). The average main season yield and ratoon season yield for the rice hybrids was 9.67 and 3.51 t ha− 1, respectively, which were approximately 17% higher than the yields for the rice inbreds. Consequently, the hybrids had 17% higher annual grain yield than did the inbred cultivars.
The main season yields were 22%, 28%, and 28% higher in 2017 than in 2018, 2019, and 2020, respectively. The ratoon season yield was similar to, or slightly higher in 2017, than it was in 2018, 2019, and 2020. As a result, the annual grain yields were 21%, 21%, and 18% higher than in 2018, 2019, and 2020, respectively.
The interactive effects of Y×T, T×C and Y×T×C were significant for panicles per m2 and spikelets per panicle in the main season rice crop but were not significant for grain filling and grain weight in the main rice crop (Table 4). There was a significant Y×C interactive effect on panicles per m2, spikelets per panicle, grain filling, and grain weight in the main rice crop.
Table 4
Yield components of four rice cultivars/hybrids grown under four cultivation methods in the main crop season in 2017–2020.
Variable
|
Panicles per m2
|
Spikelets per panicle
|
Grain filling (%)
|
Grain weight (mg)
|
Treatment (T)a
|
CTDS
|
354.2 a
|
121.4 d
|
90.3 b
|
24.9 a
|
NTDS
|
327.9 b
|
130.2 c
|
91.3 a
|
24.9 a
|
NTTP
|
230.7 d
|
159.9 a
|
91.3 a
|
24.7 a
|
CTTP
|
242.8 c
|
154.6 b
|
91.5 a
|
24.8 a
|
Cultivar (C)b
|
HHZ
|
330.3 a
|
133.4 b
|
92.0 b
|
21.9 c
|
JNSM
|
263.0 d
|
176.7 a
|
88.6 d
|
19.6 d
|
NY103
|
287.1 b
|
121.9 c
|
93.2 a
|
29.6 a
|
RY1015
|
275.2 c
|
134.1 b
|
90.6 c
|
28.1 b
|
Year (Y)
|
2017
|
331.4 a
|
138.1 b
|
92.0 a
|
25.2 a
|
2018
|
279.1 b
|
140.3 b
|
92.6 a
|
24.6 c
|
2019
|
273.0 b
|
138.1 b
|
89.6 b
|
24.9 b
|
2020
|
272.1 b
|
149.6 a
|
90.2 b
|
24.6 c
|
Interaction
|
Y×T
|
**
|
**
|
ns
|
ns
|
Y×C
|
**
|
**
|
**
|
**
|
T×C
|
**
|
**
|
ns
|
ns
|
Y×T×C
|
**
|
**
|
ns
|
ns
|
a CTDS, NTDS, NTTP, and CTTP represent conventional tillage and direct seeding, no-tillage and direct seeding, no-tillage and transplanting, and conventional tillage and transplanting, respectively. b HHZ, JNSM, NY103, and RY1015 are abbreviations for the cultivars ‘Huanghuazhan’ and ‘Jinnongsimiao’, and the hybrids ‘Nei6you103’ and ‘Rongyou1015’, respectively. Means within each variable sharing the same letter are not significantly different according to LSD at P = 0.05. * Significant at p < 0.05; ** Significant at p < 0.01; ns, not significant at p < 0.05. |
The panicles per m2 in the main rice crop for the CTDS and NTDS treatments were 46% and 35% higher than for the CTTP treatment, respectively, and there were 22% and 16% fewer spikelets per panicle in the main rice crop for the CTDS and NTDS treatments than for the CTTP treatment, respectively (Table 4). The number of panicles per m2 in the main rice crop for the NTTP treatment was 5% lower than for the CTTP treatment; however, the number of spikelets per panicle for main rice crop was 3% higher for the NTTP treatment compared to CTTP. The differences in grain filling and grain weight in the main rice crop among the four cultivation methods were relatively small.
The inbred cultivar ‘Huanghuazhan’ had the highest number of panicles per m2 and ‘Jinnongsimiao’ had the most spikelets per panicle in the main growing season (Table 4). On average, the rice hybrids had 5% fewer panicles per m2 and 17% fewer spikelets per panicle than did the rice inbreds in the main growing season, while grain filling and grain weight were 2% and 39% higher, respectively, in the rice hybrids compared to the inbred cultivars.
The panicles per m2, grain filling, and grain weight in the main rice crop were higher in 2017 than in 2018, 2019, and 2020 (Table 4). The number of spikelets per panicle in the main rice crop was slightly lower in 2017 than in 2018, 2019, and2020.
The interactive effects of Y×T and Y×C were significant for yield components in the ratoon rice crop except for the interactive effect of Y×T for grain filling (Table 5). The interactive effect of T×C was not significant for number of panicles per m2, spikelets per panicle, or grain filling in ratoon rice but was significant for grain weight in ratoon rice. The interactive effect of Y×T×C was not significant for the number spikelets per panicle, grain filling, and grain weight in ratoon rice but was significant for the number of panicles per m2 in ratoon rice.
Table 5
Yield components of four rice cultivars/hybrids grown under four cultivation methods in the ratoon rice season in 2017–2020.
Variable
|
Panicles per m2
|
Spikelets per panicle
|
Grain filling (%)
|
Grain weight (mg)
|
Treatment (T)
|
CTDS
|
352.2 a
|
55.8 b
|
72.9 b
|
21.1 a
|
NTDS
|
327.3 b
|
59.3 a
|
73.4 b
|
21.3 a
|
NTTP
|
279.4 c
|
61.4 a
|
76.9 a
|
21.1 a
|
CTTP
|
288.7 c
|
61.0 a
|
76.9 a
|
21.1 a
|
Cultivar (C)
|
HHZ
|
338.7 a
|
58.0 b
|
76.3 b
|
17.5 c
|
JNSM
|
291.5 b
|
67.3 a
|
80.8 a
|
16.5 d
|
N6Y103
|
342.5 a
|
51.4 c
|
71.7 c
|
25.4 a
|
RY1015
|
274.9 b
|
60.7 b
|
71.2 c
|
25.1 b
|
Year (Y)
|
2017
|
385.4 a
|
64.1 b
|
72.0 b
|
21.3 b
|
2018
|
322.0 b
|
54.2 c
|
71.4 b
|
20.1 c
|
2019
|
337.2 b
|
45.6 d
|
78.6 a
|
22.0 a
|
2020
|
203.0 c
|
73.6 a
|
78.1 a
|
21.1 b
|
Interaction
|
Y×T
|
*
|
ns
|
**
|
**
|
Y×C
|
**
|
**
|
**
|
**
|
T×C
|
ns
|
ns
|
ns
|
*
|
Y×T×C
|
*
|
ns
|
ns
|
ns
|
a CTDS, NTDS, NTTP, and CTTP represent conventional tillage and direct seeding, no-tillage and direct seeding, no-tillage and transplanting, and conventional tillage and transplanting, respectively. b HHZ, JNSM, NY103, and RY1015 are abbreviations for the cultivars ‘Huanghuazhan’ and ‘Jinnongsimiao’, and the hybrids ‘Nei6you103’ and ‘Rongyou1015’, respectively. Means within each variable sharing the same letter are not significantly different according to LSD at P = 0.05. * Significant at p < 0.05; ** Significant at p < 0.01; ns, not significant at p < 0.05. |
The number of panicles per m2 in ratoon rice for the CTDS and NTDS treatments were 22% and 13% higher, respectively, than in the CTTP treatment, while there were 9% and 3% fewer spikelets per panicle, respectively, in ratoon rice in the CTDS and NTDS treatments compared to CTTP (Table 5). Grain filling in ratoon rice in the CTDS and NTDS treatments was lower than in the CTTP treatment by 5% and 4%, respectively. The differences in yield components of ratoon rice between the CTTP and NTTP treatments were relatively small, and there were no significant differences in grain weight among the four cultivation methods.
The hybrid ‘Nei6you107’ had the highest number of panicles per m2 and the cultivar ‘Jinnongsimiao’ had the most spikelets per panicle in the ratoon season (Table 5). On average, rice hybrids had fewer panicles per m2, fewer spikelets per panicle, and less grain filling than the inbred cultivars by 2%, 11%, and 9% in the ratoon season, respectively, while grain weight in the rice hybrids was 48.5% higher than in the inbred lines in the ratoon season.
The number of panicles per m2 was the highest in 2017, and the number of spikelets per panicle was the highest in the 2020 in ratoon season (Table 5). Grain filling in ratoon rice in 2017 and 2018 was 9% higher than it was in 2019 and 2020. The differences in grain weight in ratoon rice among the four years were relatively small or inconsistent.
Biomass production and harvest index
The interactive effects of Y×T, Y×C, T×C, and Y×T×C were significant for total dry matter and harvest index in the main season rice crop (Table 6). The total dry matter of the main rice crop in the CTDS and NTDS treatments was higher than in the CTTP treatment by 16% and 18%, respectively, whereas the harvest indexes of the main rice crop in the CTDS and NTDS treatments were lower than in the CTTP treatment. The NTTP treatment produced 5% less total dry matter in the main rice crop than the CTTP treatment; however, the harvest index of the main rice crop in the NTTP treatment was 2% higher than in the CTTP treatment. The rice hybrids had 13% higher total dry matter compared to the inbred cultivars in the main season. The difference in the harvest index for the main rice crop between the hybrids and the inbred cultivars was relatively small. The total dry matter was highest in 2017 and the harvest index was highest in 2020 in the main growing season.
Table 6
Biomass and harvest index of four rice cultivars/hybrids grown four cultivation methods in the main crop-ratoon rice system in 2017–2020.
Variable
|
Main season
|
Ratoon season
|
Total dry matter (g m− 2)
|
Harvest index (%)
|
Total dry matter (g m− 2)
|
Harvest index (%)
|
Treatment (T)a
|
CTDS
|
1767.0 a
|
52.9 c
|
654.6 a
|
42.8 c
|
NTDS
|
1748.6 a
|
53.2 c
|
660.9 a
|
43.2 bc
|
NTTP
|
1455.7 c
|
55.1 a
|
586.4 b
|
44.4 ab
|
CTTP
|
1524.5 b
|
54.2 b
|
603.1 b
|
44.7 a
|
Cultivar (C)b
|
HHZ
|
1581.2 c
|
54.0 a
|
600.4 b
|
42.4 c
|
JNSM
|
1474.1 d
|
53.4 b
|
544.9 c
|
45.7 a
|
N6Y103
|
1738.7 a
|
54.1 a
|
722.1 a
|
43.2 bc
|
RY1015
|
1701.8 b
|
53.9 ab
|
637.6 b
|
43.8 b
|
Year (Y)
|
2017
|
1884.0 a
|
53.4 b
|
763.9 a
|
47.4 a
|
2018
|
1581.1 b
|
53.4 b
|
576.4 c
|
42.6 c
|
2019
|
1488.3 d
|
53.1 b
|
629.2 b
|
41.0 d
|
2020
|
1542.4 c
|
55.6 a
|
535.6 d
|
44.1 b
|
Interaction
|
Y×T
|
**
|
**
|
**
|
**
|
Y×C
|
**
|
**
|
**
|
**
|
T×C
|
**
|
*
|
ns
|
ns
|
Y×T×C
|
**
|
**
|
**
|
**
|
a CTDS, NTDS, NTTP, and CTTP represent conventional tillage and direct seeding, no-tillage and direct seeding, no-tillage and transplanting, and conventional tillage and transplanting, respectively. b HHZ, JNSM, NY103, and RY1015 are abbreviations for the cultivars ‘Huanghuazhan’ and ‘Jinnongsimiao’, and the hybrids ‘Nei6you103’ and ‘Rongyou1015’, respectively. Means within each variable sharing the same letter are not significantly different according to LSD at P = 0.05. * Significant at p < 0.05; ** Significant at p < 0.01; ns, not significant at p < 0.05. |
The interactive effects of Y×T, Y×C, and Y×T×C were significant for total dry matter and harvest index in ratoon rice (Table 6). The interactive effect of T×C was not significant for biomass production or harvest index in ratoon rice. The total dry matter of ratoon rice in the CTDS and NTDS treatments was 9% and 10% higher, respectively, than in the CTTP treatment. The harvest index of ratoon rice in the CTDS and NTDS treatments were lower than in the CTTP treatment by 4% and 3%, respectively. The total dry matter and harvest index of ratoon rice in the NTTP and CTTP treatments were the same. On average, the rice hybrids had 19% higher total dry matter than the rice inbreds in the ratoon season; however, the harvest index was 1% lower for the rice hybrids than for the inbreds in the ratoon season. The total dry matter and harvest index of ratoon rice were the highest in 2017.