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Impact of early transplanting on tillering and grain yield in irrigated rice

Estela Pasuquin1, Brenda Tubana1, Jessica Bertheloot1 and Tanguy Lafarge1, 2

1IRRI, DAPO Box 7777, Los Baos, Laguna, Philippines Email epasuquin@cgiar.org
2
CIRAD, TA 70/01, avenue Agropolis, 34398 Montpellier, France Email tlafarge@cgiar.org

Abstract

Appropriate crop management in rice is required for newly selected genotypes to match with their growth potential. In irrigated areas, transplanting is the most widely accepted method to obtain high yield. Even though the nursery management, and particularly seedling age at transplanting, is expected to have a great impact on plant growth through potential seedling competition in the nursery, research on its adaptation to the characteristics of promising genotypes has not gained much focus. The impact of early transplanting on rice growth and grain yield of four contrasted genotypes, including hybrid, new plant type and improved inbred line, was compared in the wet and dry growing seasons in IRRI, Philippines. Seedlings were grown in seedling trays and wet-bed nurseries at 3000 seeds m-2 and were transplanted 7, 14 and 21 days after sowing at 25 pl m-2. Late transplanting delayed tiller emergence by 15 days for all genotypes in all the studied situations through a delay in main tiller leaf emergence observed before transplanting. Leaf emergence started again as soon as the seedling was transplanted. Early transplanting then induced higher tiller production and higher plant shoot dry matter accumulation at early stage. Compared to later transplanting, early transplanting generated a significant positive effect on grain yield, up to 10% of hybrids and IR72 when seedlings were transplanted at 7 days, and up to 78% of the new plant type when seedlings were transplanted at 14 days. Early transplanting appears to be a relevant practice to improve yield in irrigated rice.

Media summary

Transplanting rice seedlings as early as possible can significantly increase grain yield in irrigated areas.

Key Words

Seedling age at transplanting, grain yield, tillering dynamics, shoot dry matter, rice.

Introduction

Crop management in rice needs to be adapted to newly selected genotypes to express most of their growth potential. In irrigated areas, transplanting is widely practised as a way to improve weed control and to grow a well designed canopy with homogeneous and healthy seedlings. Its grain yield advantage over direct-seeding rice has often been reported. The high-yielding ability of this practice is strongly dependent on transplanting age (Om et al 1989; Hossain et al 2001). Even if transplanting 20 to 40 days old seedlings is recommended, farmers may transplant seedlings as old as 80 days (Khatun et al 2002). Long stay of seedlings in the nursery may, however, affect seedling growth pattern in response to high seedling competition (Mandal et al 1984). The objective of this study was to quantify the impact of transplanting age, as early as 7 days, on plant growth and grain yield.

Materials and methods

Field experiments were conducted in 2003 at the lowland area of the IRRI experimental farm, Los Baos, Philippines. IR72 and two hybrids, IR75217H (H1) and IR68284H (H2) in the dry season, IR72, a new plant type IR72967-12-2-3 (N4) and H1 in the wet season, were grown in nurseries at 3000 seeds m-2, either in wet-bed (WB) or seedling trays (ST) and transplanted after 7 (WB07 and ST07), 14 (WB14 and ST14) and 21 days (WB21) at 25 pl m-2 in 4 replications. The seeds were sown in the nursery on 26 December 2002 (dry season) and 10 June 2003 (wet season). Water and nutrient management was optimum. Destructive plant measurements were performed weekly from transplanting until maximum tillering, then every second week until flowering and at mid-grain filling (dry season only). Measured plant growth parameters included tiller number, leaf and stem dry weight, yield components, from 2 locations per plot of 0.12 m2 area, and grain yield from a 5m2 harvest area.

Results

Tiller emergence of IR72 was delayed by 15 days with 21-day transplanting in the wet season (Fig. 1a). This reduced the maximum tiller number per plant from 34 to 29 and delayed the time of maturity by almost 10 days by delaying time of panicle initiation (Table 1). The same trend was observed in the dry season for IR72 and H2 (Figs 1b and 2b) and in the wet season for N4 (Fig. 2a). The increase in leaf number of the main tiller for IR72 in WB07 was linear with time until 10-leaf stage, but was delayed from 10 days after nursery sowing (DAS) in WB21 and even stopped between 18 to 21 DAS (Fig. 3a). It then resumed just after transplanting at the same rate as in WB07. This delay in leaf appearance in WB21 probably caused the delay in tiller emergence, as the primary tiller number per plant and the branch tiller number per plant were both related to the leaf number of the main tiller, whatever the transplanting date was (Fig. 3b). This gives little credit to the occurrence of a transplanting shock affecting plant development. From tiller emergence until flowering (80 DAS), these observed differences in tiller emergence with early transplanting induced higher shoot dry matter accumulation by at least 10g for the three genotypes whatever the growing season was (Figs 1c and d, 2c and d). The difference in shoot dry weight from flowering to maturity was still appreciable when comparing 7-days and 14-days transplanting but was, however, non-existent soon after flowering for all varieties when comparing 14-days and 21-days transplanting.

The consequences on plant growth of 7 over 14 days transplanting generated a significant higher grain yield of hybrids by 10% (considering rat damage occurrence in plots where H1 was transplanted after 7 days in the dry season) and of I1 by 7% in the dry season (Table 1). For hybrids, this positive effect was mainly due to the higher shoot dry weight per productive tiller, as the productive tiller number per plant was either not affected, or even lower with early transplanting (in the wet season), and the harvest index was unchanged, as both stem and filled grain dry weight per tiller increased similarly (Table 1). For I1, this positive effect was rather due to the slight increase in productive tiller number per plant, knowing that the small advantage in shoot dry weight per tiller observed in the dry season with early transplanting mainly generated an increase in stem dry weight (Table 1). This early transplanting (7 days) did not affect, however, grain yield of N4, as productive tiller number and shoot dry weight per productive tiller were almost unchanged (Table 1). The consequences on plant growth of 14-days transplanting over 21-days generated a significant higher grain yield for N4 by 78% partly due to a significant higher harvest index (HI). The plant mobilised more assimilate for stem growth thereby reducing grain number per tiller, filled grain fertility and grain size (Table 1). The grain yield of hybrids and their shoot dry weight measured at maturity were similar for plants transplanted at 14 and 21 DAS. The plants transplanted at 21 days seemed to have maintained 1 to 2 productive tillers more, but with lower shoot dry weight per tiller at maturity (Table 1). This trend was similar for I1 in the wet season (Fig. 1c and Table 1). In the dry season, the grain yield of I1 was significantly higher by 5% when transplanted 14 DAS than 21 DAS, even though the productive tiller number per plant was significantly lower by 2 tillers (Table 1).

Conclusion

Early transplanting favoured tiller emergence of three different genotypes grown in two nurseries during the wet and dry season : tiller emergence was affected by long stay of seedlings in the nursery as leaf emergence of the main tiller was delayed (after 14 days) and even stopped (after 21 days) in these nursery conditions. As soon as the seedling was transplanted, leaf emergence resumed, tiller emergence started and occurred according to the dynamics of leaf emergence on the main tiller (Davies and Thomas, 1983). Nursery management, rather than transplanting shock, appears to be the reason for this delay. Early transplanting then increased plant shoot dry matter accumulation and reduced crop duration in all situations studied. It significantly increased grain yield here in three cases: (i) hybrid rice transplanted as early as 7 days, for which shoot dry weight per productive tiller, grain number per tiller increased, even though HI remained unchanged; (ii) IR72 transplanted at 7 days, for which a higher productive tiller number at maturity was observed; (iii) N4 transplanted at 14 days, for which assimilate partitioning to stem was lower than at 21 DAS. As grain yield was either increased or unchanged by early transplanting as also observed by Mandal et al (1984), early transplanting, as early as 7 days, appears to be a promising way to improve grain yield in rice.

Fig. 1. Change, with days after sowing, in tiller number per plant in the (a) wet and (b) dry seasons, and in shoot dry weight per plant in the (c) wet and (d) dry seasons, of IR72 plants as affected by different nursery management.

Fig. 2. Change, with days after sowing, in tiller number per plant for (a) N4 in the wet and (b) H2 in the dry seasons, and in shoot dry weight per plant for (c) N4 in the wet and (d) H2 in the dry seasons.

Fig. 3. (a) Increase, with days after sowing, in leaf number of the main tiller, (b) tiller number per plant as a function of leaf number of the main tiller.

Table 1. Variation in crop duration (C dur, days), duration from sowing to panicle initiation (S-PI, days), grain yield (GYield, t ha-1) and main yield components between I1, N4, H1 and H2 for contrasted growing periods and nursery management. PtilNb for productive tiller number per plant, ShDW for shoot dry weight per productive tiller (g), HI for harvest index, StDW for stem dry weight per productive tiller (g), FGrDW for filled grain dry weight per productive tiller (g), FGrNB for filled grain number per productive tiller.

VAR

TRT

Crop dur

S-PI

GYield

PTil

ShDW

HI

StDW

FiGrDW

FiGr

days

days

(t ha-1)

NB

g

g

g

NB

Wet season 2003

I1

WB07

108

50

5.32a

15.21a

4.12a

0.35a

1.72a

1.42a

62.76a

I1

WB14

111

53

5.14b

14.42a

4.16a

0.34ab

1.77a

1.40ab

60.22ab

I1

WB21

115

55

5.18b

15.64a

3.93a

0.32b

1.72a

1.24b

55.91b

N4

WB07

118

57

4.56a

12.39a

5.96a

0.28a

2.69a

1.65a

61.71a

N4

WB14

121

60

4.62a

11.31a

5.77a

0.26a

2.63a

1.52a

56.62a

N4

WB21

126

63

2.60b

12.04a

5.90a

0.21b

2.90a

1.12b

46.06a

H1

WB07

104

44

6.62a

11.88a

5.18a

0.42a

1.86a

2.18a

93.42a

H1

WB14

106

47

6.02b

13.06a

4.70ab

0.41a

1.72b

1.92a

76.96ab

H1

WB21

111

50

5.89b

14.36a

4.50b

0.35b

1.88b

1.57b

66.52b

Dry season 2003

I1

ST07

108

51

6.99a

17.08ab

4.32ab

0.43ab

1.51a

1.87ab

80.95bc

I1

ST14

109

53

6.55b

16.19b

4.04bc

0.45b

1.39ab

1.83b

78.42a

I1

WB14

108

51

6.34bc

15.77b

4.38a

0.46ab

1.48ab

2.00a

84.61ab

I1

WB21

109

55

6.06c

17.88a

3.94c

0.46ab

1.28b

1.82b

76.91c

H2

ST07

115

55

7.58a

13.06a

6.96a

0.42a

2.50a

2.94a

105.95a

H2

ST14

117

58

6.98b

12.94a

5.98b

0.43a

2.07b

2.58b

95.56ab

H2

WB14

117

56

6.81c

12.36a

6.51ab

0.43a

2.23b

2.81a

104.16a

H2

WB21

118

62

6.99b

12.96a

6.32ab

0.40b

2.24b

2.51b

91.88b

H1

ST07

106

46

7.75a

14.79ab

5.52a

0.53b

1.64a

2.91a

121.11a

H1

ST14

107

48

7.59a

14.81ab

4.72c

0.52b

1.27b

2.47b

103.12b

H1

WB14

107

47

6.98a

14.13b

5.21ab

0.55a

1.42b

2.88a

117.60a

H1

WB21

107

50

6.97a

16.08a

4.81bc

0.51b

1.45ab

2.45b

102.57b

† In a column means followed by a common letter are not significantly different at P< 0.05 based on LSD.

References

Davies A and Thomas H (1983). Rates of leaf and tiller production in young spaced perennial rye grass plants in relation to soil temperature and solar radiation. Annals of Botany 57, 591-597.

Hossain MF, Bhuiya MSU and Hasan MA (2001). Effect of age of seedling and method of transplanting on the yield and yield components of aus rice. Bangladesh Journal of Agricultural Sciences 28, 359-365.

Khatun A, Mollah MIU, Rashid MH, Islam MS and Khan AH (2002). Seasonal effect of seedling age on the yield of rice. Pakistan Journal of Biological Sciences 5, 40-42.

Mandal BK, Sainik TR and Ray PK (1984). Effect of age of seedling and level of nitrogen on the productivity of rice. Oryza 21, 225-232.

Om H, Joon RK and Singh OP (1989). Effect of time of transplanting and age of seedling on growth and yield of dwarf rice. Indian Journal of Agronomy 34, 325-327.

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