Determination of some agronomic characters in different age groups of traditional rice cultivars in Sri Lanka under fertilized and non-fertilized conditions

Yields of traditional rice cultivars are typically low. The objective of this study was to understand the yield and agronomically important phenotypic traits of some traditional rice cultivars with different days to maturity at fertilized conditions. A field experiment was done at Faculty of Agriculture, University of Ruhuna, Mapalana, Kamburupitiya, Sri Lanka during Maha 2011 to 2012 and Yala seasons in 2012. The recommended fertilizer dose for improved rice cultivars was applied for the study. Effect of fertilizer on agronomic characters namely plant height (cm), number of tillers/plant and number of leaves/plant were measured during the experiment. Grain yield (g/plant) and harvest index were calculated at the end of the experiment. All the evaluated parameters were significantly higher at the fertilized conditions than those of at non fertilized conditions except the plant height in 161 to 165 days to maturity age group and number of leaves/plant in 110 to 115 days to maturity age group. At fertilized conditions the lowest significant plant height (97.5 cm) was recorded in the 161 to 165 age group while 151 to 155 age group recorded the significantly highest plant height (138.4 cm). The number of tillers/plant ranged from 6.0 to 9.8 while the highest significant number of tillers/plant (9.8) was recorded in 110 to 115 age group. However the highest grain yield/ plant (23.0 g) was recorded in the shortest days to maturity age group (110-115). Supporting this, the highest average yield/plant (10.1 g) at non fertilized conditions was also recorded in early maturing cultivars belong to 110 to 115 days to maturity age group.


INTRODUCTION
The rice plant usually takes 3 to 6 months from germination to maturity, depending on the variety and the environment under which it is grown.The optimal growth duration for maximum yield of inbred Indica varieties in the tropics is about 120 days (Tanaka et al., 1976).There was a linear increase in total biomass as growth duration increased from 95 to 135 days whereas maximum grain yield of about 8 to 9 t/ha was constant in varieties of 110 to 130 days (Akita, 1989).Varieties of shorter growth duration usually give lower yields at typical hill spacing in transplanted rice due to insufficient vegetative growth for maximum yield levels (Yoshida, 1976).Pandey et al. (2012) reported that late maturing and taller rice genotypes had high spikelet fertility contributing towards higher grain yield.The real situation of individual rice cultivars in traditional rice gene pool in Sri Lanka is no informative.Discovering factors such as yield potential, response of traditional rice cultivars to fertilizer, *Corresponding author.E-mail: lankaranawake@hotmail.com.
behavior of yield potential of the rice cultivars at fertilized condition must be depleted in systematic way in the process of utilization of none utilized or under-utilized rice cultivars for the improvement of rice cultivars by interrogation of favorable trait from traditional cultivars in to the modern rice cultivars.
Traditional rice cultivars in Sri Lanka were evaluated for some abiotic stress tolerance in systematic way (Ranawake et al., 2010(Ranawake et al., , 2011;;Rodrigo et al., 2012;Weragodavidana et al., 2012).The selected abiotic stress tolerance rice cultivars have a potential of direct introduction in to farmer fields (Djilianov et al., 2005;Xiang et al., 2007) or utilization of them in the breeding programs (Djilianov et al., 2005;Xiang et al., 2007;Ashfaq et al., 2012) of development of abiotic stress tolerance rice cultivars.In such a process, poor yield potential of traditional rice cultivars is a great problem to be overcome (Jennings, 1964;Saito et al., 2006;Amarasinghe et al., 2013).Some of the Sri Lankan traditional rice cultivars have also been evaluated in different fertilizer levels in Sri Lanka (Amarasinghe et al., 2012;Dharmasena 2012).Taking in to consideration of crop nutrition, nitrogen plays an important role in crop life.It is one of the most important nutrients needed in large quantities for the plant growth and development (Arif et al., 2010).The best level of fertilizer applications for the maximum benefit is among the most important strategies in rice crop management (Arif et al., 2010).
Plant height, number of tillers per plant, panicle length, flag leaf area, primary branches per panicle, days to heading, and days to maturity are more effective as compared to other traits in boosting yield performance of rice (Ashfaq et al., 2012;Osman et al., 2012).Among these characters plant height and days to maturity showed the highest variations among the genotypes in rice (Ashfaq et al., 2012).The degree of correlation among the characters is an important factor especially in economic and complex characters such as yield (Akinwale et al., 2011;Khan et al., 2009).Akinwale et al. (2011);and Panday et al. (2012) observed a positive and non significant correlation in between grain yield and days to maturity.Harvest index and days to maturity have also exhibited very high positive direct effect on grain yield (Panday et al., 2012).
In the present study rice cultivars with different days to maturity were analyzed to understand the fertilizer response of them at the field conditions.In the same time some of the agronomic characters were evaluated to see the contribution of them to yield increment under fertilized conditions.

METHODOLOGY
Fifty traditional rice cultivars (Table 1) were geminated and planted in nursery beds.Ten day old seedlings were transplanted in the field at Faculty of Agriculture, University of Ruhuna in rows with 15 × 20 cm spacing.Experiment was conducted as a randomized complete block design with four replicates.Each replicate consisted 3 rows of 20 rice plants.The recommended fertilizer dosage for modern rice cultivars (Basal Dressing: Urea 50 Kg/ha, TSP 62.5 Kg/ha, MOP 50 Kg/ha and Top Dressing: Urea 37.5 Kg/ha -2 Weeks after planting and 8 Weeks after planting) was applied in recommended intervals.Control experiment was carried out without any fertilizer applications.
Plant height (cm) of individual rice cultivars was measured at reproductive stage in the middle row plants of the three-row-grown rice cultivars.Here, plant height was considered as the length in cm from the plant base to the tip of the highest leaf (or panicle, whichever was longer) (Ashfaq et al., 2012).Number of tillers/plant was counted at the age of 12 weeks of rice cultivars.Number of leaves/plant was counted at the vegetative stage before flowering, after second top dressing was applied in to the field.Grain yield (g/plant) was measured in individual rice cultivar after harvesting and removing unfilled grains.Harvest index was calculated according to Li et al. (2012)

RESULTS AND DISCUSSION
Harvest Index, yield/plant, and number of tillers/plant in traditional rice cultivars were significantly increased by inorganic fertilizers in all the age groups (  (1976) has revealed that varieties of shorter growth duration usually give lower yields at typical hill spacing in transplanted rice due to insufficient vegetative growth for maximum yield levels.However the earliest maturity group has responded in different way in the present study; the highest yield has been reported in the earliest maturing group (Table 2).Peng et al. (1994) has reported that rice cultivars those take 110 to 120 days to maturity were considered as medium growth duration varieties those can produce higher total yield.Finding of Peng et al. (1994) is aligned with the findings of the present study (Table 2).Moreover, the lowest harvest index was recorded in the longest age group (Table 2) at fertilized (0.11) and at non fertilized (0.09 ) conditions providing evidence on the effect of other factors rather than days to maturity on the yield determination of the studied rice cultivars.Under fertilized conditions the average number of tillers/plant ranged from 6.0 to 9.8 in the analyzed traditional rice cultivars.The highest average number of leaves/plant (15.5) was recorded in the 131-135 age group (Table 2).The highest grain yield/ plant (23.0 g) was recorded in the 110-115 age group, which included the cultivars with shortest days to maturity while the lowest grain yield/plant (5.0 g) was recorded in the 161-165 age group, which consisted of the cultivars with comparatively longer days to maturity.Further, the highest number of tillers/plant (9.8) was also recorded in the early maturing age group (110-115 days to maturity) while the lowest average number of tillers/plant (6.0) was recorded in 116-120 days to maturity age group (Table 2).
Harvest indices (HI) ranged from 0.11 to 0.35 in the cultivars used for the present study.This value in modern rice cultivars is more than 0.4 (Li et al., 2012) while it is varied from 0.4 to 0.6 in modern rice cultivars in Sri Lanka (De Costa et al., 2003;Wickramasinghe, 2011).The highest value of HI (0.35) in the present study was found in the 126-130 days to maturity age group.Panday et al. ( 2012) concluded that the harvest index, days to maturity and the effective tillers/plant as the major contributors for rice yield.So the rice cultivars with higher magnitude of these traits could be favorable for better yield in farmer field.
Under non fertilized conditions the average number of tillers/plant ranged from 3.9 to 5.3.The highest number of tillers/plant (5.3) was recorded in age groups; 121 to 125 and 151 to 155 while the lowest number of tillers/plant (3.9) was recorded in late maturing age group; 161 to 165 (Table 2).The highest number of leaves/plant (13.7) was recorded in the same 151 to 155 days to maturity age group which recorded the highest number of tillers/plant (Table 2).The highest grain yield/ plant (10.1 g) was recorded in the 110 to 115 early maturing age group, while the lowest grain yield/plant (2.1g) was recorded in the longest age group; 161 to 165.Harvest index (HI) ranged from 0.09 to 0.32 in the cultivars at non fertilized conditions.The HI values of the age groups with days to maturity 126 to 130 (0.35) was closer to the lower limit of the reference HI values of Sri Lankan modern rice cultivars (0.4 to 0.6) according to De Costa et al. (2003) and Wickramasinghe (2011).However the HI of age groups of 110 to 115 (0.3), 116 to 120 (0.33), 121 to 125 (0.33), 131 to 135 (0.32), 151 to 155 (0.3) and 161 to 165 (0.11) recorded the lower values than that of in modern rice cultivars in Sri Lanka.

Conclusion
All the evaluated parameters were significantly differed with the fertilized conditions than those of at non fertilized conditions except the plant height in 161 to 165 days to maturity age group and number of leaves in 116 to 120 days to maturity age group.The highest significant grain yield/plant can be obtained by planting cultivars in 110 to 115 days to maturity age group at fertilized conditions and at non-fertilized conditions as well.However for the highest harvest index, cultivars in relatively short days to maturity age group (126 to 130) are more suitable.
same letter are not differ significantly; No F= No fertilizer; RD = Recommended fertilizer.

Table 2
(106.5 cm)was recorded in the 110 to 115 days to maturity age group and the highest significant average plant height (133.3 cm) was recorded in the 151 to 155 days to maturity age group.According to Panday et al. (2012) late maturing and taller rice genotypes had higher spikelet fertility contributing towards the higher grain yield.Yoshida

Table 1 .
PGRC accession numbers and names of fifty traditional rice cultivars.

Table 2 .
Agronomic characters of traditional rice cultivars at non-fertilized conditions and at fertilized conditions.