Elsevier

Field Crops Research

Volume 105, Issues 1–2, 2 January 2008, Pages 141-155
Field Crops Research

Transplanting young seedlings in irrigated rice fields: Early and high tiller production enhanced grain yield

https://doi.org/10.1016/j.fcr.2007.09.001Get rights and content

Abstract

Transplanting rice seedlings 20 days old or older has been commonly reported to generate an increase in grain yield as a result of higher tiller production. A series of experiments was conducted at the IRRI farm during the dry and wet seasons to quantify, in a range of plant types, the impact of even younger seedlings and contrasting nursery management on grain yield and to identify plant traits supporting high performance under a given establishment technique. Seedling age at transplanting, ranging from 7 to 21 days, and contrasting nursery types (seedling tray, dapog, mat nursery, and traditional wet-bed seeding) were evaluated for an elite line, a new plant type and hybrid rice. To avoid any confounding effect, sowing date in the nursery, seed rate and crop management in the main field were all the same. In the two seasons, and for all genotypes and nursery types, transplanting older seedlings induced a delay in the onset of linear dry matter accumulation and tiller emergence, while the rate of dry matter accumulation and tiller emergence was unchanged. This delay reduced nitrogen content in the seedlings. Plants recovered quickly, however, after transplanting. The delay also reduced maximum tiller number, and extended crop duration with delayed maximum tillering, flowering and maturity. Grain yield was consistently higher for younger seedlings, with, in some cases, a difference as large as 1 t ha−1 between 7- and 21-day transplanting. This result was valid for the four genotypes evaluated, with a higher impact during the dry season. In contrast, no significant difference was observed for the influence of nursery type on the timing of tiller emergence and on grain yield. Some differences in seedling vigor (plant dry weight, specific leaf area, N content), higher in the case of dapog and wet bed, and in maximum tillering, higher in the case of the seedling tray, however, were observed. But these differences did not have a significant impact on the late increase in crop dry matter and on panicle number at maturity. No significant interaction between seedling age and nursery management for all genotypes and for all the parameters measured was found. Promoting early tiller emergence as a response to transplanting young seedlings increased grain yield in all cases despite the associated decrease in tillering efficiency. Extended growth inside the nursery, rather than transplanting shock per se, appeared to be the main reason for delayed tiller emergence in late transplanting.

Introduction

Age of seedlings at transplanting most often depended on the availability of water, herbicides, labor and other inputs in farmers’ fields. In tropical lowland rice, farmers transplant seedlings at distinct ages, most of the time from 25 to 50 days after germination (De Datta, 1981, Wagh et al., 1988, Singh and Singh, 1999). Observations from scientific works, however, were quite contradictory but tended to support transplanting seedlings as young as 20 days. Some studies indicated a positive impact on grain yield by using seedlings not older than 25 days (Wagh et al., 1988, Mandal et al., 1984, Singh and Singh, 1998, Ashraf et al., 1999, Singh and Singh, 1999, Nandini and Singh, 2000, Rao and Raju, 1987, Thanunathan and Sivasubramanian, 2002, Kurmi et al., 1993, Chandrakar and Chandravanshi, 1988). On one hand, few others reported that the use of 30- and 60-day-old seedlings did not affect yield (Chandra and Manna, 1988), whereas, on the other hand, the use of 45-day-old seedlings proved to be better than those aged 30, 60 and 75 days (Khatun et al., 2002). Few analyses have been set up to understand these differences. Some attributed the significant superiority in 1000-grain weight and grain yield of younger seedlings (25 days old versus 50 days old) to the longer heading and maturity periods (NARC, 2004), while others attributed it to the longer vegetative growth (Chandra and Manna, 1988). The mortality of young seedlings (14 days) right after transplanting was reported as a reason for the lower yield compared to that with older seedlings (28 days) (Kewat et al., 2002). Recent studies on the System of Rice Intensification (SRI) showed, however, that transplanting seedlings as young as about 14 days old generated higher crop performance than transplanting 21- to 23-day-old seedlings (Makarim et al., 2002, Thiyagarajan et al., 2002). McHugh (2002) also observed in Madagascar that 8- to 15-day-old seedlings transplanted at 25 hills m−2 produced the highest yields, whereas in Sumatra the highest yields were obtained with 10-day-old transplanted seedlings. In North Sumatra, a 15-day-old seedling crop out yielded a 21-day-old one (Makarim et al., 2002). There were indications that the longer stay of seedlings in the nursery may have affected seedling growth pattern in response to high seedling competition (Mandal et al., 1984). Herrera and Zandstra (1980) also stated that transplanting old seedlings extended the overall crop duration.

Producing vigorous seedlings from desirable nurseries in order to increase grain yield was also the focus of recent work on improving nursery management with the assumption that high seedling vigor mostly depends on the kind of nursery the plants are grown in. Although seedlings are grown at 4000 seeds m−2 and transplanted at 20–25 days old under conventional wet-bed nurseries, or grown at 120,000 seeds m−2 and transplanted at 9–14 days old under dapog nurseries (De Datta, 1981), Rajendran et al. (2004) reported higher seedling vigor with regard to seedling dry weight and seed germination rate due to the development of an improved mat nursery. This nursery was, however, characterized by a highly fertile medium with urea supply, a low seed rate (2000–4000 seeds m−2) and the transplanting of 14-day-old seedlings in contrast to the conventional wet-bet nursery. These confounding effects did not allow quantifying the individual benefit of each component.

High seedling vigor, however, was not systematically reported to have a great impact on rice production. Quick tiller and leaf area production at the early stage, associated with high biomass production, was commonly observed in direct-seeded fields compared with transplanted fields (Dingkuhn et al., 1990a, San-oh et al., 2004). Despite the overexpansion of foliage in direct-seeding, grain yield was not higher in some cases (Dingkuhn et al., 1990b, Schnier et al., 1990b) due to the reduction in leaf N concentration and in the conversion of biomass into grain. Lower foliar N concentration, measured in direct-seeding conditions as a consequence of higher canopy CO2 assimilation and leaf area production, was assumed to have increased tissue death inside the canopy and respiration losses at booting and during ripening. The physiological cost of tiller abortion, in situations where tillers are considered to be overproduced during the vegetative stage, and the unfavorable assimilation/respiration balance induced by the foliar N deficiency, which limited subsequent tiller production, were proposed as the reasons for lower harvest index reported in direct-seeding conditions (Schnier et al., 1990b). Low harvest index was still observed even if an appropriate fertilization did compensate foliar N dilution (Schnier et al., 1990a). San-oh et al. (2004) even considered the effectiveness of assimilate remobilization from non-productive tillers toward reproductive ones.

Clear guidelines addressing optimum crop establishment to reduce yield gaps in transplanted fields under tropical conditions are lacking in the literature. (i) Preferable seedling age for transplanting did not appear as clearly identified from previous studies, even though it obviously depends on the economic status of the farm and growing conditions. (ii) Recent reports from SRI promoted the transplanting of seedlings not older than 15 days, whereas the main guidelines still advise transplanting 20- to 25-day-old seedlings grown at 4000 seeds m−2 in a wet-bed nursery (De Datta, 1981, Mandal et al., 1984). (iii) An improved mat nursery was considered in performance against a conventional one, whereas it was set up with regard to three modified characteristics: fertilization, seed rate and seedling age at transplanting without addressing their individual impact. (iv) A high tiller mortality rate, as a result of early seedling vigor and luxurious leaf area growth, was assumed detrimental to grain yield because of its potential impact on the increase in respiration loss and on the poor assimilate remobilization. Promoting high seedling vigor in transplanted fields in order to increase grain yield may then not always be considered as a relevant practice, even if appropriate N fertilization is applied. Crop establishment is also an actual issue with regard to genotype characteristics considering the recent development of improved lines, hybrids and new plant types, which might require distinct management in the seedbed as well as in the field if their strategy for growth varies. The objectives of this study were to quantify, across plant types, the distinct effect of seedling age at transplanting and nursery management on crop performance and to identify key components supporting the performance of the genotypes. In particular, the factors under study, seedling age (ranging from 7 to 21 days) and nursery type (wet bed, dapog, seedling tray and improved mat nursery), were evaluated using an elite inbred, an improved new plant type and hybrids in field experiments designed to limit confounding effects to the minimum.

Section snippets

Site description and growing conditions

Two field experiments were conducted in 2003 at the lowland experimental farm of IRRI, Philippines (14°11′N, 121°15′E), one in the dry season (2 January–24 April) and one in the wet season (17 June–14 October). The soil texture was clay (64% clay, 29% silt and 7% sand), with an average pH of 6.7, electrical conductivity (ECE) of 1 dS m−1, and cation exchange capacity (CEC) of 40–50 mequiv. 100 g−1. The soil was classified as Andaqueptic Haplaquolls. Variety IR72 (I1), a high-yielding elite cultivar,

Effect of seedling age on growth dynamics during the dry season

The increase in shoot dry weight (ShDW) of I1 plants transplanted at 7 days during the dry season was almost exponential until 30 DAS and then linear thereafter until maturity. This dynamics was delayed when transplanting was delayed by 7 days (14 DAS) and was even more delayed when transplanting was delayed by 14 days (21 DAS). As early as 28 DAS, ShDW of plants transplanted at 7 days was already about 19.4, while it measured 6.0 and 3.8 g m−2 for plants transplanted at 14 and 21 days (Fig. 1a,

Discussion

Grain yield was consistently higher with transplanting at seedling age as early as 7 days (3-leaf stage) compared with that at 14 days (5-leaf stage) and 21 days (7-leaf stage). The difference was as high as 1 t ha−1 in some cases. The positive effect of transplanting young seedlings over older seedlings observed in the present study was reported for a given genotype sown at the same date and rate in the same type of nursery, transplanted at the same plant density with the same plant arrangement,

Acknowledgments

We thank Pedro Gapas, Rene Carandang, Luis Malabayabas, Victor Lubigan and Andrew Revilleza for the setup of the experiments in the field, the process of the sampling and data collection. We also thank Rosalie Laude-San Antonio and Rechelle Angeles for their help in data encoding and graph and table rechecking.

References (35)

  • W.A. Herrera et al.

    Experiment in the use of old seedlings and their effect on the performance of transplanted rice

  • T. Horie et al.

    Can yields of lowland rice resume the increases that they showed in the 1980s?

  • International Rice Research Institute, 2006. Site-specific nutrient management. http://www.irri.org/irrc/ssnm. Accessed...
  • A. Khatun et al.

    Seasonal effect of seedling age on the yield of rice

    Pak. J. Biol. Sci.

    (2002)
  • M.L. Kewat et al.

    Effect of divergent plant spacings and age of seedlings on yield and economics of hybrid rice (Oryza sativa)

    Indian J. Agron.

    (2002)
  • K. Kurmi et al.

    Effect of seedling age on grain yield and yield components of ahu rice

    Oryza

    (1993)
  • Makarim, A.K., Balasubramanian, V., Zaini, Z., Syamsiah, I., Diratmadja, I.G.P.A., Handoko, Arafah, Wardana, I.P.,...
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