2.
THE EFFECT OF SEEDLING AGE, SPACING, AND SEASON ON PHYLLOCHRON, YIELD, AND YIELD COMPONENTS OF RICE, USING THE PRINCIPLES OF THE SYSTEM OF RICE INTENSIFICATION (SRI) Dobech Enquayehush Mulu, MSc University of the Philippines, Los Baños Major Adviser: Oscar B. Zamora, PhD Professor, UPLB

3.
<ul><li>Scientific reasons supporting SRI practices: </li></ul><ul><li>1. Water should be managed so that during </li></ul><ul><ul><li>the period of vegetative growth, there is no </li></ul></ul><ul><ul><li>continuously standing water creating </li></ul></ul><ul><ul><li>hypoxic soil conditions. </li></ul></ul><ul><ul><li>When rice plants are grown in flooded paddies, their root cortex disintegrates to form air pockets, known as aerenchyma . This permits oxygen to travel through the root system to keep the root tissue alive. </li></ul></ul>

4.
<ul><li>Unfortunately, little research has not been done on the impact of aerenchyma formation on the growth and development of rice plants. </li></ul><ul><li>The formation of aerenchyma causes the disintegration of 30-40 % of the roots’ cortex, and this disintegration can be ‘almost total’ (Kirk and Bouldin, 1991). This must have some adverse effects on the transport of nutrients to the rest of the plant system. </li></ul><ul><li>Under continuous flooding, up to 3/4 of the roots can degenerate by PI (Kar et al., 1974). </li></ul>

5.
<ul><li>With SRI methods, paddies are allowed to dry out for several periods of 3-6 days during the vegetative growth period, and the soil is kept moist, not continuously saturated. </li></ul><ul><li>When rice plants are grown under unsaturated conditions, their roots tend to grow longer to seek out water. Consequently, the root system becomes larger and more massive. </li></ul>

6.
<ul><li>Such roots can capture greater amounts of essential nutrients and other trace elements from the soil. </li></ul><ul><ul><li>With a full root system, the plant can better access the “balanced diet” needed for the healthy and vigorous growth of rice plants. </li></ul></ul><ul><ul><li>If plants have healthy and vigorous growth, they are better able to tolerate diseases and pest attack. </li></ul></ul>

7.
<ul><li>2) Seedlings should be transplanted </li></ul><ul><li>singly and with optimally wide spacing </li></ul><ul><li>Seedlings are transplanted just one per hill and in a square pattern at wider spacing (at least 25 x 25 cm, and even up to 50 x 50 cm when the soil is very fertile). </li></ul><ul><ul><li>When seedlings are planted with wider spacing, their roots and shoots have more space to grow. </li></ul></ul>

8.
<ul><ul><ul><li>Then, the root systems become larger and more massive so that they can access greater amounts of nutrients from the soil, and also </li></ul></ul></ul><ul><ul><ul><li>Plants can absorb more air and solar radiation, resulting in high amounts of dry matter production with greater tillering and ultimate grain yield. </li></ul></ul></ul>

9.
<ul><li>3. Soil management </li></ul><ul><li>With SRI, organic fertilizers are recommended instead of chemical fertilizers so as to: </li></ul><ul><ul><li>Optimize the biological activity of the soil, </li></ul></ul><ul><ul><li>Improve soil structure , </li></ul></ul><ul><ul><li>Assure the continual release of nutrients into the soil, and </li></ul></ul><ul><ul><li>Provide a balanced supply of essential plant nutrients. </li></ul></ul>

10.
<ul><li>4. Seedlings should be transplanted while still very young </li></ul><ul><li>Seedlings just 8-15 days old are transplanted, before they reach their fourth phyllochron growth, in order to maintain the tillering potential of rice plants and to avoid any loss of tillers due to late transplanting (de Laulanie, 1993). </li></ul><ul><li>Katayama (1951) discovered the tillering pattern of rice and other gramineae plants. Nemoto et al. (1995) have reviewed his work and reported the same findings. </li></ul>

11.
<ul><li>Nemoto (1995) found that the root and tiller development of a rice plant are closely, with synchronized emergence of leaves on the main stem. </li></ul><ul><ul><li>This pattern of growth and development is described in terms of phyllochron. </li></ul></ul><ul><ul><li>“ Phyllochron” is the time interval between the appearance of two successive leaves on the main stem. </li></ul></ul>

12.
<ul><li>If rice plants are grown under favorable environment and agronomic management practices, a rice phyllochron can be completed quickly, within 5 days. </li></ul><ul><li>With this rapid growth rate, a dozen phyllochrons could be completed before panicle initiation begins, with a possible total of 84 tillers on a single plant (de Laulanie, 1993). </li></ul><ul><li>If a rice plant can enter into a 13th or 14th phyllochron of growth before panicle initiation, the number of its tillers can be even larger. </li></ul>

13.
<ul><ul><li>The length of phyllochrons is influenced by : </li></ul></ul><ul><ul><ul><li>temperature </li></ul></ul></ul><ul><ul><ul><li>day length, </li></ul></ul></ul><ul><ul><ul><li>light intensity, </li></ul></ul></ul><ul><ul><ul><li>soil moisture, </li></ul></ul></ul><ul><ul><ul><li>soil fertility, </li></ul></ul></ul><ul><ul><ul><li>soil compaction, </li></ul></ul></ul><ul><ul><ul><li>planting spacing, </li></ul></ul></ul><ul><ul><ul><li>genotype (Cao and Moss, 1989; Nemoto et al., 1995), and </li></ul></ul></ul><ul><ul><ul><li>seedling age at transplanting (de Laulanie, 1993). </li></ul></ul></ul>

14.
<ul><li>What are the benefits of transplanting younger seedlings before they reach the fourth phyllochron? </li></ul><ul><li>Because tillering from the main stem and the start of root proliferation does not begin until the 4th phyllochron. Thus, the 2nd and 3rd phyllochrons represent a ‘window of opportunity’ to transplant the rice plant with minimum trauma, especially to its root system </li></ul>

15.
Figure 1. Tillering dynamics of rice shoot based on Katayama`s rice growth rule. Source: Vallois, 1997.

16.
<ul><li>The attainment of higher yields with SRI management practices has led to the need for better understanding of the physiological and agronomic factors underlying the SRI yield. </li></ul>

17.
MATERIALS AND METHODS Location and Timing of Study: <ul><li>Two experiments were conducted at the Central Experiment Station at UPLB during the dry and wet seasons of 2003 </li></ul><ul><li>Note: there was significant water stress during the dry season in 2003 </li></ul><ul><li>Varieties Used: </li></ul><ul><ul><ul><li>High-yielding variety: PSBRc-82 </li></ul></ul></ul><ul><ul><ul><li>Traditional variety: Elon-Elon </li></ul></ul></ul>

18.
<ul><li>Cultural Practices Used for Experiments </li></ul><ul><li>Nursery bed </li></ul><ul><li>Seedlings were established on well-aerated and fertile dry seedbeds. </li></ul><ul><li>Land preparation </li></ul><ul><li>Experimental fields were plowed and harrowed twice. </li></ul><ul><li>Before planting, the field was leveled and dikes were constructed around the seedbeds. </li></ul>

19.
<ul><li>Eight ton/ha compost was applied for each experimental field in both seasons . </li></ul><ul><li>Seedlings were carefully uprooted from the seedbed and were transplanted with a shallow depth, by placing their roots horizontally like “L” shape so resumption of growth would not be impaired. </li></ul><ul><li>Water management </li></ul><ul><li>After establishment, the field was irrigated at 5-day intervals throughout the vegetative growth period until panicle initiation. </li></ul>

20.
<ul><li>During the wet season, whenever there is high rainfall, fields were immediately drained. </li></ul><ul><li>After panicle initiation began, an average of 2 cm depth of water was maintained in both experimental fields and seasons. </li></ul><ul><li>At 15 days before harvest, the fields were drained and kept dry. </li></ul>

21.
<ul><li>Weed and pest management </li></ul><ul><li>A weed-free condition was maintained by using a mechanical weeder (rotating hoe) throughout the duration of the experiments up to flower initiation. </li></ul><ul><li>No commercial pesticide was applied in either season. </li></ul>

22.
<ul><li>Experiment 1 </li></ul><ul><li>The Effect of Seedling Age on Phyllochron Length, </li></ul><ul><li>Yield, and Yield Components of Rice Using the </li></ul><ul><li>Principles of the System Rice Intensification </li></ul>Objective To determine the best age for seedling transplant in terms of phyllochron length, number of leaves per culm, yield, and yield components of the two rice varieties in the two cropping seasons.

23.
<ul><li>Experimental Design and Treatments </li></ul><ul><li>Split plot design with three replications in both seasons </li></ul><ul><li>Main Plot: Varieties (Elon-Elon and PSBRc-82) </li></ul><ul><li>Sub-Plot: Four seedling ages (8, 15, 20 and 25 days). </li></ul><ul><li>Sub-plot size: 4 m x 4 m (16 m 2 ) </li></ul><ul><li>Seedlings were transplanted singly per hill at 45 cm x 45 cm spacing in both cropping seasons </li></ul>

24.
Table 1. Phyllochron length as affected by seedling age in the dry and wet seasons 2003 Phyllochron Length (days/leaf) Seedling Age Dry Season Wet Season 8 5.3 c 4.7 b 15 4.9 d 4.5 c 20 6.0 b 5.6 a 25 6.5 a 6.2 a CV 4.9 % 4.8%

25.
Table 2. Phyllochron length as affected by variety in the dry and wet seasons 2003 Phyllochron Length (days/leaf) Variety Dry Season Wet Season Elon-Elon 5.7 a 5.5 a PSBRc-82 5.1 b 5.1 b CV 4.9% 4.8%

26.
<ul><li>The longer phyllochron observed in the older seedlings was apparently because the older seedlings had longer roots to be managed during transplanting as compared to younger seedlings. </li></ul><ul><li>When these older seedlings were uprooted, more roots were cut off from their primary roots . This increased the stress to the seedlings during their period of re-establishment and decreased the subsequent growth and development of the plants. </li></ul>

27.
Table 3. Number of leaves on main stem (after transplanting) of rice as affected by the interaction of seedling age and variety in the dry season 2003 Number of Leaves on the Main Stem Variety Seedling Age (days) 8 15 20 25 Elon–Elon 13.0 a 13.0 a 10.0 c 9.0 d PSBRc-82 12.0 b 12.0 b 10.0 c 9.0 d

28.
Table 4. Number of leaves on the main stem (after transplanting) of rice as affected by the interaction of seedling age and variety in the wet season 2003 Number of Leaves on the Main Stem Variety Seedling Age (days) 8 15 20 25 Elon–Elon 15 a 15 a 12 c 11 d PSBRc-82 14 b 14 b 12 c 11 d

29.
Table 5. Number of productive tillers per hill of rice as affected by the interaction of seedling age and variety in the dry season 2003 Number of Productive Tillers per Hill Variety Seedling Age (days) 8 15 20 25 Elon–Elon 30.5 a 30.1 a 29.6 a 16.6 c PSBRc-82 22.0 b 22.2 b 21.6 b 18.2 c

30.
Table 6. Number of productive tillers per hill of rice as affected by the interaction of seedling age and variety in the wet season 2003 Number of Productive Tillers per Hill Variety Seedling Age (days) 8 15 20 25 Elon–Elon 68.0 a 68.6 a 40.4 bc 38.0 d PSBRc-82 53.6 b 49.7 bc 42.4 cd 35.6 d

31.
<ul><li>The lower productive tillers per hill obtained from older seedlings was attributed to the stress or death or setback of primary tillers (first tillers off the mainstem) during their uprooting from the nursery. </li></ul><ul><li>Primary tillers are responsible for contributing more tillers to the total number of tillers of the rice plant. </li></ul><ul><li>Conversely, when seedlings are transplanted early, before the emergence of the first primary tiller, seedlings can re-establish themselves in the field with little or no stress. Thus, plants can produce more tillers per plant than those transplanted later (Enyi, 1963). </li></ul>

32.
Table 8. Number of productive tillers per hill of rice as affected by season, 2003 Season Number of Productive Tillers per Hill Dry Season 23.84 b Wet Season 50.68 a CV 11.4%

33.
<ul><li>The lower productive tiller obtained in the dry season was attributed to the soil moisture stress and the unfavorable climate that prevailed during the early and critical tillering stage of the rice crop in that season. </li></ul>

34.
Table 9. Number of filled spikelets per panicle of rice as affected by interaction of seedling age and variety in the dry season 2003 Number of Filled Spikelets per Panicle Variety Seedling Age (days) 8 15 20 25 Elon–Elon 265.7 a 234.9 b 233.5 b 212.9 c PSBRc-82 98.80 d 112.8 d 99.9 d 94.3 ed

35.
<ul><ul><li>Table 10. Number of filled spikelets per panicle of rice as affected by interaction of seedling age and variety in the wet season 2003 </li></ul></ul>Filled Spikelets per Panicle Variety Seedling Age (days) 8 15 20 25 Elon–Elon 290.80 a 288.30 a 263.40 b 249.20 b PSBRc-82 109.20 c 108.90 d 107.3 d 102.40 ed

36.
<ul><ul><li>The higher number of filled spikelets per panicle in younger seedlings in both varieties and seasons was because the transplanting of younger seedlings leads to little or no delay in root and shoot development. </li></ul></ul><ul><ul><li>This in turn enhanced the growth of proliferated and extensive roots systems which supported an accelerated leaf production rate that can in turn support the subsequent grain filling stage. </li></ul></ul>

37.
Table 11. Grain weight per panicle of rice as affected by seedling age in the dry and wet seasons 2003 Grain Weight per Panicle (gm) Seedling Age Dry Season Wet Season 8 4.0 a 4.1 a 15 3.7 b 4.2 a 20 3.7 b 3.5 b 25 3.4 b 3.1 c CV 6.3% 9.0%

38.
Table 12. Grain weight (t ha- 1 ) of rice as affected by seedling age in the dry and wet seasons 2003 Grain Weight (t ha -1 ) Seedling Age Dry Season Wet Season 8 3.9 a 7.8 a 15 3.83 a 8.1 a 20 3.6 a 6.1 b 25 2.5 b 5.9 b CV 14.9% 3.6%

39.
<ul><ul><li>The increase in final grain yield was associated with the number of leaves on the main stem, number of productive tillers per hill, filled spikelets, and grain weight per panicle. </li></ul></ul><ul><ul><li>Regression analysis revealed that 99% of the total variation among treatments in yield is explained by these agronomic traits in both the dry and wet seasons. </li></ul></ul>

40.
<ul><ul><li>The regression model for dry season yield was: </li></ul></ul><ul><ul><li>Yield = 4.81+ 0.15 (number of productive tillers/hill) + 0.0122 (number of filled spikelets/panicle ) + 0.86 (grain weight/panicle) + 0.34 (number of leaves/culm) </li></ul></ul><ul><li>For the wet season, it was: </li></ul><ul><li>Yield = 5.90104 + 0.53 (number of leaves on the main stem) + 0.11 (productive tillers/hill) + 0.053 (filled spikelets/panicle + 0.0.61 (grain weight/panicle) </li></ul>

41.
Experiment 2 The Effect of Planting Distance on Phyllochron Length, Yield, and Components of Yield Using the Principles of the System of Rice Intensification Objective To determine the best plant spacing in terms of phyllochron length, yield, and yield components of two rice varieties in two cropping seasons.

42.
<ul><li>Experimental design and treatments: </li></ul><ul><li>Split-plot design with three replications in both seasons. </li></ul><ul><li>The two varieties (Elon-Elon and PSBRc-82) were assigned in the main plots. </li></ul><ul><li>The three planting distances (20 x 20, 30 x 30, 45 x 45 cm) were the sub-plots. </li></ul>

43.
<ul><li>The sub-plot size was 4 m x 4 m (16 m 2 ). </li></ul><ul><li>Seedlings of Elon-Elon and PSBRc-82 were raised in well-aerated and fertile seedbeds. </li></ul><ul><li>Fifteen-day old seedlings of the two varieties were carefully transplanted in moist soil condition in a grid pattern on each prescribed spaces with only one seedling per hill. </li></ul>

44.
Table 13. Phyllochron length of rice as affected by spacing in the dry and wet seasons 2003 Phyllochron Length (days/leaf) Spacing Dry Season Wet Season 20 x 20 cm 6.1 a 5.6 a 30 x 30 cm 5.5 b 4.9 b 45 x 45 cm 5.4 b 4.8 b CV 1.5% 2.1%

45.
<ul><li>A longer phyllochron is observed at closer spacing compared to wider spacing because with closer spacing, there is competition among plants for nutrients, space, solar radiation and other growth factors that hinder the subsequent growth and development rate of the rice plants. </li></ul><ul><li>Phyllochron length is increased with planting density (Nemoto, 1995). </li></ul>

46.
Table 14. Number of productive tillers per hill of rice as affected by interaction of spacing and variety in the dry season 2003 Number of Productive Tillers per Hill Variety Spacing (cm) 20 x 20 30 x 30 45 x 45 Elon–Elon 16.2 c 28.6 a 29.7 a PSBRc-82 16.0 c 21.8 b 23.3 b

47.
Table 15. Number of productive tillers per hill of rice as affected by interaction of spacing and variety in the wet season 2003 Number of Productive Tillers per Hill Variety Spacing (cm) 20 x 20 30 x 30 45 x 45 Elon–Elon 20.4 d 37.9 c 63.9 a PSBRc-82 25.1 d 37.7 c 54.8 b

48.
Table 16. Number of filled spikelets per panicle of rice as affected by spacing in the dry and wet seasons 2003 Number of Filled Spikelets per Panicle Spacing Dry Season Wet Season 20 x 20 cm 146.6 b 178.7 b 30 x 30 cm 174.5 a 217.0 45 x 45 cm 176.7 a 234.1 a

49.
Table 17. Grain weight per panicle of rice as affected by spacing in the dry and wet seasons 2003 Weight of Grain per Panicle (gm) Spacing Dry Season Wet Season 20 x 20 cm 3.0 b 3.6 b 30 x 30 cm 3.4 a 4.6 a 45 x 45 cm 3.6 a 4.8 a CV 4.1% 9.9%

50.
Table 18. Grain yield (t ha -1 ) of rice as affected by spacing in the dry and wet seasons 2003. Grain Weight (t ha -1 ) Spacing Dry Season Wet Season 20 x 20 cm 2.8 b 4.5 c 30 x 30 cm 3.9 a 6.1 b 45 x 45 cm 4.4 a 7.3 a CV 14.5% 5.6%

51.
Yield difference due to spacing was mainly attributed to the number of productive tillers per hill, number of filled spikelets per panicle, and grain weight per panicle. The regression model for the dry season was: Yield = 1.014776 + 0.13 (number of productive tillers/hill) + 0.06 (filled spikelets/panicle) + 0.45 (grain weight/panicle).

52.
<ul><li>Regression model for the wet season yield was: </li></ul><ul><li>Yield = 16.11+ 0.17 (number of productive tillers/hill) + 0.02 (filled spikelets/panicle) + 0.72 (grain weight/panicle). </li></ul>

53.
The full set of SRI practices: transplanting younger seedling singly per hill at 45 x 45 cm spacing under minimum water management during the vegetative growth stage, mechanical weeding with rotary-hoe and using compost increased rice yield to 7–8 t ha -1 in the wet season, when relatively optimum growing conditions were prevailed. In the same season, older seedlings with similar management practices produced only 5-6 t ha -1 . This result suggests that the synergetic effect of all combinations of SRI practices used together.

54.
Table 1. Phyllochron (day/leaf) of each leaf of rice as affected by variety and seedling age in the dry season 2003 Seedling Age (Days) Leaf Number on the Main Stem 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Total Leaves Elon-Elon 8 - - 4 3 3 3 3 3 4 6 7 8 9 9 7 13 15 - - 3 3 3 3 3 3 4 5 7 8 9 8 7 13 20 - - - 7 6 4 4 5 7 8 9 9 8 - - 10 25 - - - - 8 6 4 4 6 8 8 9 7 - - 9 PSBRc-82 8 - - 3 3 3 3 3 3 4 5 7 8 8 7 - 12 15 - - 3 3 3 3 3 3 4 6 7 7 7 7 - 12 20 - - - 7 4 3 3 4 4 5 7 7 7 - - 10 25 - - - - 8 6 4 3 4 7 8 8 7 - - 9

55.
Table 2. The phyllochron (days/leaf) of each leaf of rice as affected by variety and seedling age in the wet season 2003 Seedling Age (Days) Leaf Numbers on the Main Stem 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Tot.Leaves Elon-Elon 8 - - 4 3 3 3 4 3 3 3 4 6 7 7 8 10 7 - 15 15 - - 4 3 3 3 4 3 3 3 4 5 6 7 8 10 7 - 15 20 - - - 6 4 4 4 4 5 6 7 7 8 10 7 - - - 12 25 - - - - 7 6 5 5 4 5 6 7 8 10 8 - - - 11 PSBRc-82 8 - - 3 3 3 3 3 3 3 3 4 6 6 7 7 8 - - 14 15 - - 3 3 3 3 3 3 3 3 4 5 6 7 6 7 - - 14 20 - - - 6 5 3 3 4 4 5 6 7 6 7 7 - - - 12 25 - - - - 6 5 4 4 4 5 5 6 6 8 7 - - - 11

56.
<ul><ul><li>The variation of phyllochron among each leaf across the growing period observed in this experiment had similarity with the findings of Nemato et al. (1995), which showed that the phyllochron varies between 4 and 7 days in the early growth stage, and then gradually increases to 10 to 15 days during the initiation of the inflorescence. </li></ul></ul><ul><ul><li>Nemato (1995) suggested that the retardation of phyllochron length in the later growth stages is due to internodal elongation. </li></ul></ul>

57.
<ul><li>Technical discussion on leaf counts and phyllochron calculation: </li></ul><ul><ul><li>The appearance of the new leaves and the length of time between them amounted to the phyllochron of each leaf. </li></ul></ul><ul><ul><li>Total number of leaves on the main culm was monitored and measured every 2 to 3 days after transplanting, up to the complete appearance of the flag leaf. </li></ul></ul>

58.
<ul><li>Five representative plants at the center of the rows of each plot were randomly marked with bamboo sticks. </li></ul><ul><li>The leaf growth stage( Huan leaf number) was determined by </li></ul><ul><li>1) Counting all fully exerted leaves on the main stem, plus </li></ul><ul><li>2) The percentage length of the exerted portion of the top-most leaf (youngest leaf). </li></ul>

59.
<ul><li>Huan leaf number was calculated using the following formula (Wilhelm and McMaster, 1995): Lm / L(n-1) + n-1 </li></ul><ul><li>Where </li></ul><ul><li>Lm = the length of the youngest leaf blade, </li></ul><ul><li>L (n-1) = the length of the leaf blade that emerges before the youngest leaf, and </li></ul><ul><li>n = the total number of leaves that are visible on the main culm. </li></ul>

60.
<ul><li>Phyllochron </li></ul><ul><li>The phyllochron (day/leaf) of each successive leaf on the main stem of each sample plants was determined at each measurement day. </li></ul><ul><li>It was determined by dividing the number of elapsed days between the appearance of two consecutive Huan leaf numbers by the difference of the two consecutive Huan leaf number measurements (Wilhelm and McMaster, 1995). </li></ul>

61.
<ul><li>Example how to calculate the phyllochron </li></ul><ul><li>April 1, 2003: the number leaves on the main stem of a single plant = 2.9 leaves </li></ul><ul><li>April 4, 2003: the number of leaves on the main stem = 3.8 leaves </li></ul><ul><li>The number of elapsed days between the appearances of the two leaves was = 3 days </li></ul><ul><li>The measurement difference between the two Huan leaves 3.8 - 2.9 = 0.9 leaves </li></ul><ul><li>Phyllochron = 3 days = 3 days/ leaf </li></ul><ul><li> 0.9 leaves </li></ul>