Methane emission from a flooded field of Eastern India as influenced by planting date and age of rice (Oryza sativa L.) seedlings

Agriculture, Ecosystems and Environment 115 (2006) 79–87 www.elsevier.com/locate/agee

Methane emission from a flooded field of Eastern India as influenced by planting date and age of rice (Oryza sativa L.) seedlings D.R. Nayak a, T.K. Adhya a,*, Y.J. Babu b, A. Datta a, B. Ramakrishnan a, V.R. Rao a a

Laboratory of Soil Microbiology, Division of Soil Science and Microbiology, Central Rice Research Institute, Cuttack 753006, Orissa, India b School of Geography and Geology, McMaster University, Hamilton, Ont., Canada L8S4K1 Received 29 June 2005; received in revised form 23 November 2005; accepted 1 December 2005 Available online 14 February 2006

Abstract Flooded paddy is considered to be one of the major anthropogenic sources of atmospheric methane (CH4), a potent greenhouse gas. Emission of CH4 from flooded rice soils is affected by a multitude of factors including crop management practices. In a field study, CH4 fluxes from a sub-humid tropical flooded field of Cuttack, eastern India, as affected by planting with 20 and 35-day old rice (Oryza sativa L.) seedlings on two sets of planting dates were measured with the closed chamber method in 2002–2003 encompassing wet (kharif) season, 2002 and dry (rabi) season, 2003. In the wet season of 2002, CH4 emission from staggered planting was measured with two varieties viz. Lalat and Gayatri, while during the dry season of 2003, the experiment was conducted with cv. Lalat. CH4 emission was low from plots planted to aged seedlings (35-day) as well as seedlings transplanted late in both sets of experiments that were transplanted to the main field with an interval of 15 days during the two growing seasons. Cumulative CH4 emission from early- and late-transplanted plots during wet season, 2002 was 408.77 and 308.58 kg ha
1 and during the dry season, 2003 was 431.35 and 328.66 kg ha
1, respectively. Early transplanted seedlings had higher number of tillers and exhibited low soil redox (Eh) potential thereby favouring higher CH4 emission. There was no statistically significant yield reduction due to transplanting of aged seedlings or planting late over that of young seedlings planted early. Our results suggest that in rainfed rice cultivation, as practiced in greater part of Asia and Africa, transplanting late with comparatively aged seedlings could lead to a considerable reduction in CH4 emission without being detrimental to the yield. # 2005 Elsevier B.V. All rights reserved. Keywords: Methane emission; Rice paddy; Planting date; Seedling age; Mitigation option

1. Introduction The current global average atmospheric concentration of CH4, a major greenhouse gas, is 1.78 ppmv, more than double of its pre-industrial value of 0.8 ppmv (Dlugokencky, 2001). About 70% of CH4 production arises from anthropogenic sources and about 30% from natural sources (Mosier et al., 1998). Flooded fields planted to rice (Oryza sativa L.) are considered as one of the major biogenic sources for atmospheric CH4, contributing approximately 10–13% to the global CH4 emission (Neue et al., 1997; * Corresponding author. Tel.: +91 671 2367777x312; fax: +91 671 2367663. E-mail address: [email protected] (T.K. Adhya). 0167-8809/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.agee.2005.12.011

Crutzen and Lelieveld, 2001). Rice cultivation contributes a large part to the tropical food production, especially in Asia covering about 154 million ha with more than 50% area located in India and China. India, with an area of about 44.5 Mha under rice cultivation, merits special attention for CH4 from this source. Projected increase in rice production during the coming decades (Maclean et al., 2002), is anticipated to result in a further increase in CH4 fluxes to the atmosphere if the prevalent cultivation practices are continued (Anastasi et al., 1992). During the past 15 years, a large number of field studies have quantified CH4 emissions from rice fields during the rice-growing season (Adhya et al., 2000; Wassmann et al., 2000). These and a host of other studies have shown that emissions are affected by a multitude of factors related to both natural conditions as

80

D.R. Nayak et al. / Agriculture, Ecosystems and Environment 115 (2006) 79–87

well as crop management practices. In order to increase the accuracy in the estimation of CH4 emission from rice paddies and to predict the future CH4 emission as well as to develop desired mitigation options, understanding the mechanism of CH4 emission from rice paddy is highly imperative. Plant age and the time of planting have significant impact on the growth and yield potential of rice plants (Slaton et al., 2003). Yield potential, as affected by seeding date is valuable to farmers because they often make decisions on which crop species or cultivar to seed while considering productivity, production costs and environmental conditions. These decisions are most frequently considered when adverse weather conditions prevent rice establishment during the optimum seeding period, or when transplanting is necessary. Transplanting seedlings of different age at different time intervals is one of the important strategies to achieve the target yields (Yoshida, 1983; Pattar et al., 2001). Further, timely transplanting with appropriate age of the seedlings is an important non-cash input for realizing higher productivity of rice. A 35-day old seedling of rice cv. Swarnamahsuri performed better in terms of plant growth and grain yield over 25-day old ones under late-planted conditions (Balasubramanian et al., 1977; Rao and Raju, 1987). As major part of the Indian paddy (60%) is grown under rainfed conditions, transplanting practices are mostly influenced by the onset of monsoon, often resulting in the use of aged seedlings planted at odd intervals. Such practices of delayed planting may also influence CH4 emission from the growing rice crop. The objectives of the present research were to (i) study the effects of planting rice seedlings of two different ages in two sets of planting on CH4 emission from a flooded alluvial field during the wet and dry seasons; (ii) ascertain the effect of related soil parameters on CH4 emission; (iii) compare the influence of plant morphological parameters on CH4 emission from rice; (iv) understand the relationship of yield attributes on CH4 emission from rice.

2. Materials and methods 2.1. Field experiment CH4 emission from paddy fields was estimated during the wet cropping season (June–December) of 2002 and dry cropping season (January–May) at the experimental farm of the Central Rice Research Institute (CRRI), Cuttack, India (858550 E, 208250 N; elevation 24 m above the MSL). Annual precipitation is about 1500 mm year
1, of which 75% occurs during June–September. The difference between mean summer soil temperature and mean winter soil temperature is more than 5 8C, thus qualifying for hyperthermic temperature class. The soil was an Aeric Endoaquept with sandy clay loam texture (25.9% clay, 21.6% silt and 52.5% sand), bulk density 1.40, percolation rate <10 mm day
1, pH (H2O) 6.16, cation exchange capacity

15 mEq 100 g
1, electrical conductivity 0.5 dS m
1, total C 0.66% and total N 0.08%, exchangeable K 120 kg ha
1. The field was ploughed, puddled thoroughly to 15 cm depth, and leveled. Rice plants were transplanted at a spacing of 15 cm  20 cm in field plots (5 m  5 m) well separated by levees. The experiment was laid out in a split-plot design with the two planting dates (first and second fortnight of July, 2002 for the wet season crop and first and second fortnight of February, 2003 for the dry season crop) as main treatments and two different aged seedlings (20 and 35-day old seedlings) as sub-treatments with four replications each. The treatments thus included (i) early transplanted 20-day old seedlings (E-20), (ii) early transplanted 35-day old seedlings (E-35), (iii) late transplanted 20-day old seedlings (L-20) and (iv) late transplanted 35-day old seedlings (L-35). In other words, 20- and 35-day old seedlings were transplanted to the main field on the same day in two sets of transplanting at 15 days intervals. For both the wet and dry season crops, seedlings of rice cv. Lalat, a daylight-insensitive rice cultivar, was used in the experiment. In an additional experiment during the wet season 2002, seedlings of rice cv. Gayatri, a photo-sensitive rice cultivar, were planted in only two combinations viz. early transplanted 35-day old seedlings and late transplanted 45-day old seedlings during the first and second fortnight of July, respectively. Field plots transplanted to rice were amended with potassium (40 kg K2O ha
1) as muriate of potash in two splits with 2/3rd of the fertilizer being applied as basal and the remaining 1/3rd at panicle initiation stage. Phosphorus (40 kg P2O5 ha
1) as single superphosphate (SSP) was applied uniformly to all the field plots as basal dressing. Nitrogen (80 kg N ha
1 as urea) was applied to all the field plots in three splits with half of the total N applied at the time of transplantation and the rest divided into two equal halves and applied at maximum tillering and panicle initiation stages, respectively. While the crop during the wet season was grown under rainfed condition with the soil remaining flooded (12  7 cm) throughout the cropping period, the crop during the dry season was grown under irrigated conditions to keep continuously flooded (10  2 cm) during the entire period of crop growth. The field plots were drained 10 days before harvest. The crop was grown without application of any pesticide and was harvested at maturity. 2.2. Weather and soil data Weather data during the experimental period were collected from the meteorological station of the institute maintained through an automatic weather station (m Metos1, Pesst Inst. GmbH, Weiz, Austria). Redox potential and pH of the soil in the immediate vicinity of the roots (5 cm deep) in the planted field plots were measured with each set of CH4 flux measurement. The redox potential of the field soil was measured by inserting a combined platinum-calomel electrode (Barnant Co., IL,

D.R. Nayak et al. / Agriculture, Ecosystems and Environment 115 (2006) 79–87

81

USA) to the root region and measuring the potential difference in mV (Bharati et al., 2000). All the values were corrected to that of a hydrogen electrode by adding +240 mV to the redox readings. The pH of soil was measured with a portable pH meter (Philips Analytical, Cambridge, UK).

patting the roots dry in a blotting paper. Both the aerial and the underground (root) biomass values were expressed as g m
2 (dry weight basis). Tiller no., grain weight and grain and straw yields from individual replicated plots were measured at maturity and the harvest index calculated (Bharati et al., 2000).

2.3. Methane emission measurement

2.6. Statistical analyses

CH4 emission from flooded fields planted to rice was monitored as described previously (Adhya et al., 1994), at regular intervals from the day of transplanting till maturity. Samplings for CH4 efflux measurement were done from all the replicated plots in the morning (09:00–09:30) and in the afternoon (15:00–15:30) and the average of morning and afternoon fluxes was used as flux for the day. For measuring CH4 emission, six rice hills were covered with a locally fabricated Perspex chamber (53 cm  37 cm  51 cm, length  width  height). A battery-operated air circulation pump with air displacement of 1.5 l min
1 (M/s Aerovironment Inc., Monrovia, CA, USA), connected to polyethylene tubing was used to mix the air inside the chamber and draw the air samples into Tedlar1 air-sampling bags (M/s Aerovironment Inc.) at fixed intervals of 0, 15 and 30 min. The air samples from the sampling bags were analyzed for CH4.

Individual character datasets were statistically analyzed and the least significant difference between treatments was established using statistical package (IRRISTAT, version 3.1, International Rice Research Institute, Philippines). Simple and multiple correlations between CH4 flux and select soil and plant parameters were analyzed using the variation at each time of observation.

2.4. Methane estimation CH4 concentration in the air samples collected from the crop canopy was analyzed by gas chromatography in a Varian 3600 gas chromatograph equipped with FID and Porapak N column (2 m length, 1/8 in. OD, 80/100 mesh, stainless steel column). The injector, column and detector were maintained at 80, 70 and 120 8C, respectively. Highpurity nitrogen gas maintained at 30 ml min
1 was used as carrier gas. A 1 ml gas sample was injected into the gas chromatograph with a gas-tight syringe. The gas chromatograph was calibrated before and after each set of measurements using 5.38, 9.03 and 10.8 ml CH4 ml
1 in N2 (Scotty1 II analyzed gases, M/s Altech associates Inc., USA) as primary standard and 2.14 ml ml
1 in air as secondary standard to provide a standard curve linear over the concentration range used. Under these conditions, the retention time of CH4 was 0.53 min and the minimum detectable limit was 0.5 ml ml
1. 2.5. Plant parameters Mean aerial biomass (fresh and dry weights) was measured by harvesting above-ground portions of rice plant, one hill from each replicated plot, on each day of CH4 sampling as well as at maturity. Root biomass (dry weight) was measured only at maturity stage of the rice plant by carefully scooping out individual hill along with soil, washing gently under tap water to dislodge the soil and

3. Results 3.1. Staggered planting and CH4 emission Planting early or late had significant influence (P < 0.05) on CH4 emission (Fig. 1). In both wet season, 2002 and dry season, 2003, CH4 emission from cv. Lalat varied significantly between early- and late-transplanted plots. CH4 emission followed almost similar pattern in both earlyand late-transplanted crops but the magnitude of emissions varied. Cumulative CH4 emission from early- and latetransplanted plots during wet season, 2002 was 408.77 and 308.58 kg ha
1 and during the dry season, 2003 was 431.35 and 328.66 kg ha
1, respectively. In experiments with cv. Gayatri, CH4 emission varied with the time of transplanting with nearly twice the amount of CH4 emission from earlytransplanted plots as compared to late-transplanted series (Fig. 2). 3.2. Influence of the age of seedlings on CH4 emission Influence of the age of seedlings on CH4 efflux from flooded alluvial field is shown in Fig. 1. A 20-day old seedlings of cv. Lalat emitted higher CH4 than 35-day old seedlings during both wet and dry seasons. Crop transplanted with 20-day old seedlings showed three emission maxima during wet season. The first peak was observed almost immediately after transplanting while the second peak was observed at panicle initiation (56 DAT) and the third peak at grain filling stage (76 DAT). On the contrary, during the dry season, only two emission peaks were observed the first emission peak being immediately after transplanting (7 DAT) followed by a second maxima at maximum tillering stage (50 DAT). The magnitude of CH4 emission was low in 35-day old seedlings and emission flux increased slowly concomitant with plant growth. An early peak was observed between 10 and 15 DAT and the second peak was recorded around 50–60 DAT. Average CH4

82

D.R. Nayak et al. / Agriculture, Ecosystems and Environment 115 (2006) 79–87

Fig. 1. Seasonal changes in CH4 efflux from a flooded field planted to rice (cv. Lalat), as affected by planting date and age of seedlings. Means of four replicate values plotted, bars/half-bars indicate the standard deviation (~: early 20 days; ^: early 35 days; : late 20 days; : late 35 days).

emission from 20-day old seedling and 35-day old seedling was 20.14 and 15.43 mg m
2 h
1 during the wet season and 24.75 and 16.98 mg m
2 h
1 during the dry season, respectively. In case of cv. Gayatri also, 45-day old seedlings exhibited lower CH4 emission (12.30 mg m
2 h
1) as compared to 35-day old seedlings (22.33 mg m
2 h
1). 3.3. Interaction of planting date and age of seedling on CH4 emission The mean effect table indicated the existence of considerable interaction between planting dates with age of seedlings and its effect on CH4 emission for both the seasons (Tables 1 and 2). CH4 emission was low from latetransplanted plots as well as plots planted with aged (35day old) seedlings. However, the effect was more pronounced when both the factors were considered together. Late transplanted plots with 35-day old seedlings emitted least amount of CH4, while plots transplanted early with 20-day old seedlings recorded the highest CH4 emission. Admittedly, CH4 emission was low from both 20 and 35-day old seedlings under late-transplanted conditions. For cv. Gayatri, early transplanted plots with 35-day old seedlings showed much higher CH4 emission than late transplanted plots with 45-day old seedlings and the difference was statistically significant throughout the cropping period. Cumulative CH4 emission was nearly double in the early-transplanted plots with 35-day old

seedlings than the late-transplanted plots with 45-day old seedlings. 3.4. Effect of soil parameters on CH4 emission Eh of the field plots under various treatments were monitored to establish the relevant effects on CH4 emission measurements. As the field remains flooded for the major part of the year, soil Eh was low and decreased further after transplantation. Soil Eh was lowest in earlytransplanted plots with 20-day old seedlings during both wet and dry seasons. Mean Eh (mV) values followed the order of E-20 (
243) < E-35 (
240) < L-20 (
224) < L35 (
213) during the wet season 2002 and E-20 (
296) < L-35 (
258) < E-35 (
244) < L-20 (
218) during the dry season 2003 with the dry season exhibiting more reduced condition than the wet season. The soil pH during the entire experimental period ranged between 6 and 8. 3.5. Influence of plant morphological parameters on CH4 emission The date of planting and the age of seedlings had significant impact on plant parameters during the crop growth period. However, depending upon the climatic condition, the effect varied over the seasons. Earlytransplanted plants (cv. Lalat) were relatively taller with more tillers in both wet and dry seasons (Table 3).

D.R. Nayak et al. / Agriculture, Ecosystems and Environment 115 (2006) 79–87

83

Fig. 2. Effect of staggered transplantation on (A) CH4 efflux from a flooded field planted to rice (cv. Gayatri) and (B) changes in soil redox potential (wet season, 2002). Means of four replicate values plotted, bars/half-bars indicate the standard deviation (^: early 35 days; &: late 45 days).

Similar type of results were also observed in cv. Gayatri (Fig. 2) where early transplanted 35-day old seedlings emitted more CH4 than late transplanted 45-day old seedlings. Among the different plant parameters, tiller number showed a positive relationship with CH4 emission but it was not significant (r = 0.369, p < 0.05, n = 6). Other parameters such as root length, root volume and dry root weight did not show any relation with CH4 emission. Dry

The age of seedlings also influenced the plant parameters. During both wet and dry seasons, the 35-day old seedlings revealed better plant height. A 20-day old seedlings of rice cv. Lalat had more tillers as compared to 35-day old seedlings in both wet season, 2002 and dry season, 2003. Aerial shoot biomass, root biomass, root volume, shoot volume and shoot length, however, did not show any correlation with CH4 emission (Table 4).

Table 1 Mean effect of seedling age and planting schedule on CH4 emission from an alluvial field planted to rice (cv. Lalat) (wet season, 2002) Parameter

CH4 emission (mg m
2) Days of sampling (D) 5

Seedling age (S)

15

30

50

60

80

90

Mean

20 days

35 days

Mean

Planting schedule (P) Early 22.35 Late 23.93 Mean 23.14

19.07 14.72 16.89

10.65 19.96 15.31

22.69 18.98 20.83

22.78 14.46 18.62

19.39 5.14 12.27

16.43 11.33 13.88

19.05 15.50 –

21.85 18.47 20.16

16.25 12.54 14.39

19.05 15.50 –

Seedling age (S) 20 days 32.01 35 days 14.28 Mean 23.14

15.91 17.88 16.89

16.19 14.42 15.31

26.71 14.96 20.83

18.36 18.87 18.62

14.16 10.37 12.27

17.78 9.98 13.88

20.16 14.39 –

Least significant difference (%)

S

P

D

SP

PD

SD

SPD

5 1

3.80 4.99

3.80 4.99

2.03 2.67

2.69 3.53

1.44 1.89

1.44 1.89

1.02 1.34

Coefficient of variation (%) = 11.2.

84

D.R. Nayak et al. / Agriculture, Ecosystems and Environment 115 (2006) 79–87

Table 2 Mean effect of planting schedule and seedling age on CH4 emission from an alluvial field planted to rice (cv. Lalat) (dry season, 2003) Parameter

CH4 emission (mg m
2) Days of sampling (D) 5

Seedling age (S)

10

35

40

50

60

70

75

Mean

20 days

35 days

Mean

Planting schedule (P) Early 39.56 Late 15.28 Mean 27.42

32.14 11.04 21.59

25.11 34.55 29.83

21.26 22.17 21.71

26.25 24.30 25.27

19.93 12.64 16.28

2.43 9.67 6.05

2.70 3.90 3.30

23.53 17.84 –

28.45 21.89 25.17

18.61 13.80 16.20

23.53 17.84 –

Seedling age (S) 20 days 37.15 35 days 17.69 Mean 27.42

19.56 23.62 21.59

35.85 23.81 29.83

23.13 20.29 21.71

28.90 21.65 25.27

15.11 17.45 16.28

6.32 5.78 6.05

3.95 2.65 3.30

25.17 16.20 –

Least significant difference (%)

S

P

D

SP

PD

SD

SPD

5 1

7.28 9.56

7.28 9.56

2.97 3.91

5.15 6.76

2.10 2.76

2.10 2.76

1.48 1.95

Coefficient of variation (%) = 18.0.

shoot weight showed a significant negative relationship with the CH4 emission (r =
0.837*, p < 0.05, n = 6) (Table 4) in experiments in the wet season 2002 with cv. Gayatri. 3.6. Yield attributes and CH4 emission Depending upon the season, grain yield of rice in the present experiment was differentially influenced by the date of planting and/or the age of seedlings. While late transplanted, 35-day old seedlings produced the highest grain yield during the wet season of 2002, grain yield was not significantly different during the dry season of 2003, irrespective of planting date or the age of the seedlings (Table 5). In both the seasons, late-transplanted plots

produced comparatively higher grain yield. During wet season, 2002, the average grain yield was 3.89 Mg ha
1 in early-transplanted plots and 4.08 Mg ha
1 in late-transplanted plots. Similarly, during the dry season of 2003, the grain yield was 4.43 and 4.53 Mg ha
1 for early- and latetransplanted plots, respectively. Cumulative CH4 emission was low in late-transplanted plots than in early-transplanted plots. When expressed in terms of CH4 emission per kg grain yield, the highest emission was from early-planted 20-day old seedlings in both wet season, 2002 and dry season, 2003 with values of 109.40 and 102.58 g CH4 kg
1 grain yield, respectively. The lowest emission was from late-planted 35-day old seedlings during both seasons and was in the range of 66.40–66.04 g

Table 3 Effect of planting schedule and age of seedling on different plant parameters of cv. Lalat over two seasons Treatments

Plant parameters Height (cm)

Tiller number (m
2)

Aerial biomass (g m
2)

Root biomass (g m
2)

Root length (cm)

Root volume (ml m
2)

Shoot volume (ml m
2)

Wet season, 2002 Planting schedule Early Late

86.41 79.52

397 361

699 810

254 257

17.34 15.52

784 845

2627 2493

Age of seedlings 20 days 35 days CV (%) LSD (5%)

82.43 83.50 0.6 0.92

405 353 1.2 9

741 768 1.5 23

254 256 4.4 22

16.17 16.68 4.4 1.45

761 868 1.7 27

2456 2663 0.9 46

Dry season, 2003 Planting schedule Early Late

70.53 69.51

381 356

653 641

256 251

16.17 16.51

686 703

2041 2075

Age of seedlings 20 days 35 days CV (%) LSD (5%)

69.26 70.78 0.6 0.87

379 358 1.0 7

670 623 4.8 24

265 242 4.8 20

16.12 16.56 2.0 0.65

710 678 3.4 47

2131 1985 3.9 159

CV: coefficient of variation; LSD: least significant difference.

D.R. Nayak et al. / Agriculture, Ecosystems and Environment 115 (2006) 79–87 Table 4 Correlation between CH4 emission and different plant parameters of rice cv. Lalat (wet season, 2002 and dry season, 2003) and cv. Gayatri (wet season, 2002) Plant parameters

Plant height Tiller number Shoot volume Dry shoot weight Root length Root volume Dry root weight *

cv. Lalat

cv. Gayatri

Wet season, 2002

Dry season, 2003

Wet season, 2002

r-value (n)

r-value (n)

r-value (n)

0.242 (12) 0.632* (12)
0.010 (12) 0.028 (12) 0.429 (12)
0.429 (12)
0.010 (12)


0.004 (15) 0.605* (15)
0.018 (15) 0.147 (15)
0.221 (15)
0.011 (15) 0.031 (15)

0.026 (6) 0.369 (6)
0.669 (6)
0.837* (6) 0.612 (6)
0.624 (6)
0.333 (6)

Significant at p < 0.05.

CH4 kg
1 grain yield. In cv. Gayatri also, CH4 (g) emitted kg
1 grain yield was double in early planted 35-day old seedlings (149.11) than late planted 45-day old seedlings (76.64).

4. Discussion There is growing evidence that plant productivity via photosynthesis is one of the master variables regulating CH4 production in wetlands including flooded paddy. Under anoxic conditions as exists in flooded rice soils, plant detritus undergoes fermentation to relatively simple compounds, such as acetate and CO2-H2 (Takai and Kamura, 1960). Perhaps the most absorbing evidence for a tight coupling between photosynthesis and methanogenesis is that elevated CO2 can stimulate CH4 emissions even in the absence of an increase in plant biomass (Megonigal and Schlesinger, 1997). Photosynthetic activity of rice plants correlates well with CH4 production and emission (Sass

85

et al., 1991). Using a 13C-labeling technique, Minoda and Kimura (1996) determined that recent photosynthates contribute 30% of the C substrates used by methanogens in rice paddy microcosms. Critical factors that affect the growth and development of rice plants are soil temperature, soil moisture content and solar radiation (Stansel, 1975). Early transplanted plants receive higher quantum of solar radiation and highest CH4 emission was recorded from early-transplanted plots (Sass and Fischer, 1994). Late transplanted seedlings received less solar radiation and emitted less CH4. Sass et al. (1991) showed that 1% reduction in solar radiation received during the critical growth period (heading  21 days) results in 1.11% reduction in grain yield and 1.70% reduction in CH4 emission. In the present experiment with cv. Lalat, cumulative sunshine hours for early transplanted plots during both wet and dry seasons were higher than the late transplanted plots (Table 6). In experiments with cv. Gayatri, cumulative sunshine hours for the early- and latetransplanted plots were 701 and 651 h, respectively. In addition, early-transplanted plots received more rainfall than late-transplanted plots for both cv. Lalat and Gayatri during the wet season experiments (Table 6). The early emission peak emanates from the decomposition of plant residues of previous season (Neue et al., 2000) and the wide difference in CH4 emission during the initial stages of crop growth could be due to the difference in CH4 transport capacity of seedlings of different age (Aulakh et al., 2000; Satpathy et al., 1998). CH4 emission from aged (35-day old) seedlings was low and could be due to the crop duration and differences in growth pattern of rice plants. Aged seedlings spent more time in the seed-bed than the field and the well-developed roots were disturbed during transplantation that required more time for recuperation. In a similar study, Ko et al. (2000) observed that transplanting of 8 and 30-day old seedlings resulted in an emission of 42

Table 5 Effect of staggered planting on grain and straw yields of rice (cv. Lalat) (wet season, 2002 and dry season, 2003) Season

CH4 (g) kg
1 grain yield

Yield parametersa Grain yield (Mg ha
1)

Straw yield (Mg ha
1)

Harvest index (%)

Wet season, 2002 E-20 E-35 L-20 L-35 CV (%) LSD (5%)

4.05 3.74 3.86 4.22 8.3 ns

8.05 8.48 7.55 8.71 5.5 0.78

33.45 30.54 33.82 33.16

116.50 97.70 94.80 66.40

Dry season, 2003 E-20 E-35 L-20 L-35 CV (%) LSD (5%)

4.53 4.31 4.65 4.40 5.7 ns

8.03 8.21 8.29 7.95 5.1 ns

36.10 34.42 35.96 35.62

102.58 92.64 79.09 66.04

CV: coefficient of variation; LSD: least significant difference. a Average of four replicate observations.

86

D.R. Nayak et al. / Agriculture, Ecosystems and Environment 115 (2006) 79–87

Table 6 Meteorological parameters during the cropping periods of wet season, 2002 and dry season, 2003 Cultivar/season

Total sunshine hour (h)

Total rainfall (mm)

Maximum temperature (8C)

Minimum temperature (8C)

E-Lalat (Wet season, 2002) L-Lalat (Wet season, 2002) E-Gayatri (Wet season, 2002) L-Gayatri (Wet season, 2002) E-Lalat (Dry season, 2003) L-Lalat (Dry season, 2003)

496.3 482.7 701.1 657.1 778.8 761.5

784.1 491.7 745.3 529.1 30.2 33.4

36.4 35.0 36.4 35.0 39.3 39.3

19.0 18.8 14.9 14.9 18.4 18.4

E: early transplanted; L: late transplanted.

and 40 g CH4 m
2 season
1. This was probably due to differences in aerenchyma formation or CH4 transport capacity of different aged seedlings (Aulakh et al., 2000; Wang et al., 1999). CH4 production is largely favoured by a soil Eh value lower than
150 mV, a pH between 6 and 8, temperature above 10 8C and supply of low molecular fatty acids derived from easily degradable organic matter (Neue et al., 2000). Rice plants can influence the soil Eh by consuming O2 from the rhizosphere (root respiration) and through enhanced supply of electron donors, i.e. readily decomposable organic substrates through root exudates, sloughed-off tissues and debris, microbially reduced Mn2+, Fe2+ ions and chelates (Sahrawat, 2004). Soil Eh was lowest in early-transplanted plots with 20-day old seedlings during both wet and dry seasons. The lowest soil redox potential in early transplanted 20-day old seedlings can be attributed to higher root biomass which might have released more root exudates that acted as electron acceptors for both aerobes and anaerobes and resulted in a lower redox potential. The soil Eh showed significant negative relationship with CH4 emision for both wet season 2002 (r =
0.356, p < 0.05, n = 34) and dry season 2003 (r =
0.350, p < 0.05, n = 48). The soil pH during the entire experimental period was within a range that is considered optimum for methanogenic activity (Masscheleyn et al., 1993). Thus lower redox potential, large quantity of root exudates and favourable pH together resulted into higher CH4 emission in early transplanted plots. With delayed transplantation, dry weights of root and shoot increased in wet season. Lack of sunlight during the early growth and development of the rice plant normally does not limit grain yield except under excessively cloudy and cool conditions (Stansel, 1975). Low yields do occur in years of low sunlight caused by cloudy conditions and rain during the wet season. These conditions also produce taller plants and severe lodging. Seasonal effects of low yield with increased plant height and biomass have been duplicated in shading experiments and in experiments in which radiation was changed by employing different planting dates during the same year (Stansel, 1975). Approximately 60% of the yield variability was caused by sunlight levels during the critical period. During the dry season, plant height, dry root weight and dry shoot weight were higher in earlytransplanted plots and could be due to comparatively sunny weather and higher cumulative radiation. However, such

differences in physiognomy did not result into wide difference in CH4 emission between wet and dry seasons. Early transplanting produced more number of tillers in 25-day old seedlings than in 35- and 45-day old seedlings (Pattar et al., 2001). CH4 emission showed a positive relation with tiller number during both the seasons (r = 0.632*, 0.605*; p < 0.05). Aulakh et al. (2000) concluded that tiller number can be considered as a major controlling factor of plant-mediated CH4 transport. This is presumably due to the proportional enhancement in channels or outlets of aerenchyma for the upward transport of CH4 from base through the sites of release to the atmosphere (Aulakh et al., 2000). Better vegetative growth in terms of aerial biomass was observed in the wet season than in the dry season. Plant height, tiller number, root volume, shoot volume, root weight and shoot weight were higher in wet season as compared to dry season. In Louisiana, Jodon and McIlrath (1971) found that April-seeded rice produced the highest grain yields and seeding after the first week of May resulted in a pronounced yield decline. Gravois and Helms (1998) also showed that rice grain yields declined as seeding date was delayed and that very short-season cultivars did not always produce higher grain yields than midseason cultivars when seeded late. In the present experiment 20-day old seedlings produced higher grain yield than the 35-day old seedlings during the dry season although the difference was statistically not significant. During the wet season, however, the results of grain yield were erratic. The results of this study emphasize the significance of cultural practices on CH4 emission. In the wet season 2002, late transplantation of 35-day old seedlings was most effective in reducing CH4 emission coupled with higher grain yield. In dry season, however, there was no significant difference in grain yield between the treatments. Early transplanted 20-day old seedlings resulted in a higher number of tillers but it was not reflected in grain yield as the number of productive tiller was less. Our results further indicate that planting late and even aged seedlings could effectively mitigate CH4 emission without reducing the yield. Such situations are encountered most often under rainfed rice production systems and practiced by the farming community. This could well be an effective cultural management practice for reducing CH4 emission without significantly affecting the crop yield and productivity, particularly under rainfed rice cultivation.

D.R. Nayak et al. / Agriculture, Ecosystems and Environment 115 (2006) 79–87

5. Conclusions Rice seeded early or during the optimum periods generally produce the highest grain yield and yields decline as seeding date is delayed. Results from the present experiment clearly demonstrate that transplanting aged seedlings and planting late, can significantly lower the rate of CH4 emission during both dry and wet seasons without significantly affecting the grain yield. Supportive evidences substantiate the observed effects through the alterations in soil redox status, number of tillers and other soil and plant parameters. Growing rice under rainfed conditions is loaded with series of uncertainties wherein farmers are forced to plant aged seedlings at odd intervals in tune with the onset of monsoon. It is evident that delayed planting can serve as an effective cultural practice for mitigation of CH4 emission, especially under rainfed rice agriculture.

Acknowledgements The work was supported, in part, by the National Agricultural Technology Project entitled, ‘‘Greenhouse Gas Emission form Rice-based Cropping Systems’’ (Grant No. 26(4)/97-NATP) by the Indian Council of Agricultural Research, New Delhi. We thank the Director, Central Rice Research Institute, Cuttack for permission to publish this study. D.R. Nayak was supported by a fellowship from Council of Scientific and Industrial Research, New Delhi.

References Adhya, T.K., Rath, A.K., Gupta, P.K., Rao, V.R., Das, S.N., Parida, K., Parashar, D.C., Sethunathan, N., 1994. Methane emission from flooded rice fields under irrigated conditions. Biol. Fertil. Soils 18, 245–248. Adhya, T.K., Bharati, K., Mohanty, S.R., Ramakrishnan, B., Rao, V.R., Sethunathan, N., Wassmann, R., 2000. Methane emission from rice fields at Cuttack. India. Nutr. Cycl. Agroecosyst. 58, 95–105. Anastasi, C., Dowding, M., Simpson, V.J., 1992. Future CH4 emissions from rice production. J. Geophys. Res. 97, 7521–7525. Aulakh, M.S., Bodenbender, J., Wassmann, R., Rennenberg, H., 2000. Methane transport capacity of rice plants. II. Variation among different rice cultivars and relationship with morphological characteristics. Nutr. Cycl. Agroecosyst. 58, 367–375. Balasubramanian, A., Venkataraman, R., Palaniappan, S.P., 1977. Studies on the time of planting and seedling age on the performance of rice. Madras Agric. J. 64, 49–50. Bharati, K., Mohanty, S.R., Singh, D.P., Rao, V.R., Adhya, T.K., 2000. Influence of incorporation or dual cropping of Azolla on methane emission from a flooded alluvial soil planted to rice in Eastern India. Agric. Ecosyst. Environ. 79, 73–83. Crutzen, P.J., Lelieveld, J., 2001. Human impacts on atmospheric chemistry. Ann. Rev. Earth Planet. Sci. 29, 17–45. Dlugokencky, E., 2001. NOAA CMDL carbon cycle greenhouse gases, global average atmospheric methane mixing ratios. NOAA CMDL cooperative air sampling network. http://www.cmdl.noaa.gov./ccg/ figures/ch4trend.global.gif.

87

Gravois, K.A., Helms, R.S., 1998. Seeding date effects on rough rice yield and head rice and selection for stability. Euphytica 102, 151–159. Jodon, N.E., McIlrath, W.O., 1971. Response of rice to time of seeding in Louisiana. Louisiana Agric. Exp. Stn. Bull. 384, Louisiana State University, Baton Rouge, LA. Ko, J.Y., Kang, H.W., Park, K.B., 2000. Effects of cultural practices on methane emission from rice paddy fields in South Korea. Nutr. Cycl. Agroecosyst. 58, 311–314. Maclean, J.L., Dawe, D.C., Hardy, B., Hettel, G.P., 2002. Rice Almanac. International Rice Research Institute, Los Banos, Philippines. Masscheleyn, P.H., DeLaune, R.D., Patrick Jr., W.H., 1993. Methane and nitrous oxide emissions from laboratory measurements of rice soils suspensions: effect of soil oxidation reduction status. Chemosphere 26, 251–260. Megonigal, J.P., Schlesinger, W.H., 1997. Enhanced CH4 emissions from a wetland soil exposed to elevated CO2. Biogeochemistry 37, 77–88. Minoda, T., Kimura, M., 1996. Photosynthates as dominant source of CH4 and CO2 in soil water and CH4 emitted to the atmosphere from paddy fields. J. Geophys. Res. 101, 21091–21097. Mosier, A.R., Duxbury, J.M., Freney, J.R., Heinemeyer, O., Minami, K., Johnson, D.E., 1998. Mitigating agricultural emissions of methane. Climatic Change 49, 39–80. Neue, H.U., Wassmann, R., Kludze, H.K., Wang, B., Lantin, R.S., 1997. Factors and processes controlling methane emission from rice fields. Nutr. Cycl. Agroecosyst. 49, 111–117. Neue, H.U., Wassmann, R., Lantin, R.S., 2000. Methane efflux from wetland rice fields. In: Yunus, M. (Ed.), Environmental Stress: Indication, Mitigation and Eco-conservation. Kluwer Academic Publishers, The Netherlands, pp. 323–333. Pattar, P.S., Reddy, B.G.M., Kuchanur, P.H., 2001. Yield and yield parameters of rice (Oryza sativa) as influenced by date of planting and age of seedlings. Indian J. Agric. Sci. 71, 521–522. Rao, C.P., Raju, M.S., 1987. Effect of age of seedlings, nitrogen and spacing on rice. Indian J. Agron. 32, 100–102. Sahrawat, K.L., 2004. Organic matter accumulation in submerged soils. Adv. Agron. 81, 169–201. Sass, R.L., Fischer, F.M., 1994. CH4 emission from paddy fields in United States gulf coast area. In: Minami, K., Mosier, A.R., Sass, R.L. (Eds.), CH4 and N2O: Global Emissions and Controls from Rice Fields and Other Agricultural and Industrial Sources. Yokendo Publishers, Tokyo, pp. 65–77. Sass, R.L., Fisher, F.M., Harcombe, P.A., Turner, F.T., 1991. Methane emission from rice fields as influenced by solar radiation, temperature and straw incorporation. Global Biogeochem. Cycl. 5, 335–350. Satpathy, S.N., Mishra, S., Adhya, T.K., Ramakrishnan, B., Rao, V.R., Sethunathan, N., 1998. Cultivar variation in methane efflux from tropical rice. Plant Soil 202, 223–229. Slaton, N.A., Linscombe, S.D., Norman, R.J., Gbur Jr., E.E., 2003. Seeding date effect on rice grain yields in Arkansas and Louisiana. Agron. J. 95, 218–223. Stansel, J.W., 1975. Six Decades of Rice Research in Texas. Texas Agricultural Experiment Station, College station, TX. Takai, Y., Kamura, T., 1960. The mechanism of reduction in waterlogged paddy soils. Folia Microbiol. 11, 304–313. Wang, B., Xu, Y., Wang, Z., Li, Z., Guo, Y., Shao, K., Chen, Z., 1999. Methane emissions from rice fields as affected by organic amendment, water regime, crop establishment, and rice cultivar. Environ. Monitor. Assess. 57, 213–228. Wassmann, R., Neue, H.U., Lantin, R.S., 2000. Characterization of methane emission from rice fields in Asia. I. Comparison among field sites in five countries. Nutr. Cycl. Agroecosyst. 58, 1–12. Yoshida, S., 1983. Growth and yield of field crop: rice. In: Potential Productivity of Field Crops Under Different Environment, International Rice Research Institute, Los Banos, Philippines, pp. 103–107.