Annals of Sri Lanka Department of Agriculture. 2007.9:59-69.
INFLUENCE OF NUTRIENT AND WATER MANAGEMENT PRACTICES OF AN ALKALINE SOIL ON METHANE EMISSION FROM LOWLAND RICE IN INDIA I.W.K. IMBULGODA1, B. SREEMANNARAYANA2, K.V. RAO3 and P. PRABHU PRASADINI4 1 Office of Deputy Director of Agriculture (Inter Provincial), Anuradhapura 2 AICRP on Agroforestry, Rajendranagar, Hyderabad, India 3 Directorate of Rice Research, Rajendranagar, Hyderabad, India 4 Department of Environmental Science and Technology, College of Agriculture, Rajendranagar, Hyderabad, India
ABSTRACT A field experiment was conducted to study the effect of nutrient and water management practices on methane emission from lowland rice, during rabi season of 2005-2006 at the Directorate of Rice Research, Rajendranagar, Hyderabad, India. The experiment consisted of three replicates of 12 treatment combinations of three levels of water regimes viz., continuous flooding, irrigation water by cumulative pan evaporation (IW/CPE) of 1.0 and 0.75 and four fertilizer levels viz., control (no application of chemical fertilizer or organic manure), recommended fertilizer dose (RFD), 50% RFD + 50% organic manure and organic manure alone. There was a reduction in methane emission of 25 and 40% in treatments of IW/CPE of 1.0 and 0.75 respectively over continuous flooding. There was a significant enhancement in CH 4 emission after irrigation (8.60 mg m-2 d-1) when compared with before irrigation (6.55 mg m-2 d-1) especially in the driest water regime (IW/CPE=0.75) at tillering stage. Seasonal flux of CH4 increased to 74, 54 and 45%, in the RFD, 50% RFD + 50% organic manure and organic manure alone treatments, respectively compared to the control. The methane emission per unit grain yield was lower when IW/CPE of 0.75 was combined with RFD (1.29kg) and hence can be recommended as a suitable mitigation option. KEYWORDS: Fertilizer, Methane, Rice, Seasonal flux, Water regimes.
INTRODUCTION The major environmental problem today is global warming due to accumulation of greenhouse gases like CO2, CH4, N2O and Chlorofluoro carbons along with water vapour in the atmosphere and depletion of ozone layer in stratosphere, affecting several aspects of humanity on the planet earth. The global increase in CO2 along with other gases such as CH4 and N2O trap outgoing thermal radiation, leading to increased temperature at the earth’s surface. Although CH4 has a relatively short atmospheric lifetime (8-12 years), one molecule of CH4 traps about 32 times more heat than a molecule of CO2 (Rodhe, 1990). Continued increase in atmospheric methane concentrations at the current rate of approximately 1% per year is likely to contribute more to future climate change than any other gas except CO 2 (Cicerone and Oremland, 1988). Of the wide variety of sources contributing for observed changes in atmospheric CH4, rice paddy fields are considered an
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important source because of the recent increase in harvest area in the world (Minami, 1994). Methane is exclusively produced by methanogenic bacteria that can metabolize only in the strict absence of free O 2 and at redox potentials of less than -150mV (Wang et al., 1993). Methane production is regulated by a number of physical and chemical factors such as soil pH, Eh, temperature, organic carbon supply, aeration and the water status. Application of chemical fertilizer improves plant growth and therefore increases methane production and emission. Intermittent drying of flooded rice fields reduces total methane production and thus emission (Sass et al., 1992). Rice is the basic food crop for nearly half the people on the earth, mostly in Asia. Intensification of rice cultivation to meet the demand for rice by increasing human population is imperative, especially in Asia where approximately 90% of the rice is grown and consumed (IRRI, 1993). Given the expected doubling in rice production in Asia, research on improving rice yield should focus on strategies that do not harm the environment. Therefore, the main objectives of the present investigation were to study the influence of nutrient and water management practices on methane emission from rice fields and to suggest mitigation options. METERIALS AND METHODS The experiment was conducted on a clay soil during rabi season of 2005-2006 at the Directorate of Rice Research, Rajendranagar, Hyderabad, India. The geographical location of the experimental field is 17°19′ North latitude and 78°23′ East longitudes with an altitude of 542.6m above mean sea level. The soil in the experimental area had pH 8.18, EC 0.69 dSm-1, organic carbon 0.90%, available N 254kg/ha, available P 2O5 133kg/ha, available K2O 654kg/ha, DTPA extractable Zn 9.87mg/kg and DTPA extractable Fe 41.87mg/kg soil. Three water regimes viz., continuous flooding (M 1), irrigation water by cumulative pan evaporation (IW/CPE)=1.0(M2) and IW/CPE= 0.75(M3) as main treatments and four fertilizer levels viz., control (no chemical fertilizer or organic manure) (S1), Recommended Fertilizer Dose (RFD) (S2), organic manure alone (S3) and 50% RFD + 50% organic manure (S4); as sub plot treatments were employed in a split plot design replicated thrice with 12 treatments. The plot size was 5m x 3.2m. Rice variety, IR 64 was used as the check variety. Four weeks old healthy seedlings were transplanted in the plots at a spacing of 15cm x 15cm with two plants per hill. The RFD used for the experiment were 60kg
METHANE EMISSION FROM RICE FIELD 61
P2O5 ha-1 applied at the time of planting, 60kg K2O ha-1 applied half at planting and the rest at panicle initiation (PI) stage, 120 kg N ha -1 applied in 3 split doses of 1/3:1/3:1/3 each at basal, early tillering and PI stage supplied through single super phosphate (SSP), muriate of potash (MOP) and urea respectively. Fourty kilograms of ZnSO4 ha-1 were applied at the time of planting. The amount of organic manure used for the experiment was 8.25t ha -1 vermicompost. The plots were irrigated according to the main plot treatments. For the continuous flooding treatment, plots were irrigated to maintain the water level between 5-10cm during the entire period of crop growth. For alternate flooding treatments of IW/CPE = 1.0 and IW/CPE = 0.75, water requirement (CPE-RF) was measured using V-notch weir. Plant protection measures were taken against pest and disease incidence by spraying agrochemicals as and when required. Weeds were manually controlled in all the plots. Methane gas collection was carried out by manual sampling which was done using the closed chamber technique as described by Hutchinson and Mosier (1981). Six hills of rice plants were covered with a locally fabricated acrylic (Perspex) box of 53cm x 33cm x 71cm (Fig. 1). The air inside the chamber was mixed by 2 battery operated small fans. The acrylic chambers were placed over the aluminum jackets preinserted into the soil to a depth of 5cm in each plot. The water seal surrounding the acrylic chamber in a channel made the system airtight. Gas samples were drawn at fixed intervals of 0, 15 and 30 minutes through a three-way stopcock after installation of chamber using an air tight syringe of 50ml capacity. The temperature inside and outside the chamber was recorded at the time of sampling. Soil and water temperatures were measured using a digital thermometer. Soil temperature was measured at a depth of 10cm. For diurnal variation of CH4 emission, flux measurements were taken at 2 hr intervals over a 10 hr period (7.00am - 5.00pm) at the tillering (12 days after transplanting - DAT) stage of the crop in IW/CPE = 1.0 treatment. For measuring treatment-wise CH4 emission, flux measurements were taken at tillering (29-32 DAT), panicle initiation (48-51 DAT), flowering (69-72 DAT) and maturity (88-91 DAT) of the crop of each treatment before and after irrigation. Methane concentrations in samples collected from field experiment were determined with a Shimadzu GC-14A gas chromatograph (GC) equipped with FID and Porapak N column. The column and detector were maintained at 70 and 150째C, respectively.
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Figure 1. Fabricated acrylic box for collecting methane samples.
The CH4 flux (F) was calculated using the following equation (Debnath et al., 1996); F= [(Ct – C0)/t] x H x 42.857 mg m-2 h-1 where t is time interval (min), H is height of headspace (m), C0 is initial concentration of CH4 at time 0 (ppmv), and Ct is final concentration of CH4 at time t (ppmv). At physiological maturity, the crop was harvested by cutting above ground parts from a net plot area of 12.15m 2 for recording grain and straw yields. The grain yield data were presented at 14 per cent moisture while straw yield was determined after oven drying at 70°C to constant weight. RESULTS AND DISCUSSION Diurnal variation in methane efflux Methane emission rates increased in the morning, and reached a maximum during early afternoon (12.30pm - 2.30pm), followed by a rapid decrease during the evening (Fig. 2). This distinct diurnal pattern was observed over a period of 10h (7.30am - 5.30pm). The diurnal variation would be a function of the methane concentration in soil solution. The diffusion coefficient is temperature dependent and changes significantly during the day. This diurnal pattern was similar to those observed by Wang et al. (1999) and Satpathy et al. (1997).
-1
1
Methane efflux (mg m
hr )
1 .2
-2
METHANE EMISSION FROM RICE FIELD 63
0 .8 0 .6 0 .4 0 .2 0 7 .3 0 am
9 .3 0 am
11.30 am
1 .3 0 pm
3.30 p m
5 .3 0 pm
Time
Figure 2. Diurnal variation in methane efflux at tillering stage.
Soil, water and air temperatures reached a maximum in the early afternoon when CH4 emission was the highest (Fig. 3). The CH4 emission was influenced by many factors such as solar radiation and atmospheric, soil and water temperatures (Sass et al., 1991). 40.0
30.0
o
Temperature ( C)
35.0
25.0 20.0 15.0 10.0 5.0 0.0 7.30 am
9.30 am
11.30 am
1.30 pm
3.30 pm
5.30 pm
Time Soil T 0C
Water T 0C
Ambient T 0C
Figure 3. Diurnal variation in soil, water and ambient temperatures at sampling time.
Seasonal methane flux Data presented in Table 1 revealed that seasonal CH 4 emission was significantly influenced by water regimes and fertilizer levels. The highest mean seasonal CH4 emission (7.69kgha-1) was observed in water regime of continuous flooding followed by IW/CPE=1.0. The lowest mean seasonal CH4 emission (4.65kgha-1) was associated with the driest water regime (IW/CPE of 0.75). Flooding the soil generally creates anaerobic condition which is favorable for CH4 production and emission. But under intermittent irrigation, it may not be possible to create anaerobic condition as observed under flooding and hence there was a minimum emission of CH 4 from the rice field.
64 IMBULGODA et al. Table 1. Influence of nutrient and water management practices on seasonal CH4 flux. Fertilizer levels CH4 flux(kg ha-1) Mean Continuous IW/CPE = IW/CPE = flooding (M1) 1.0 (M2) 0.75 (M3) Control 5.46 3.97 3.20 4.21 RFD 9.14 7.15 5.66 7.32 Organic manure alone 7.71 5.59 5.04 6.12 50% RFD + 50% OM 8.43 6.30 4.72 6.48 Mean 7.69 5.76 4.65 Water regime (M) Fertilizer level (S) M x S SEM Âą 0.12 0.06 0.21 CD (p = 0.05) 0.33 0.12 0.54
The results further showed that seasonal CH4 emission was also significantly influenced by fertilizer levels (Table 1). The RFD treatment recorded highest seasonal CH4 emission which was significantly superior to all other treatments, followed by 50% RFD + 50% organic manure and organic manure alone and both were on par with each other and were significantly higher than the control. The higher CH 4 emission is known to occur due to application of chemical fertilizers. Similarly, Lindau et al. (1991) reported that CH4 emission increased as the application rate of urea - N was increased. It can be seen that plots where water regime of IW/CPE = 1.0 and IW/CPE = 0.75 were adopted, there was a reduction of seasonal CH 4 flux by about 25 and 40%, respectively as compared to continuously flooded plots (Table 2). Higher production and emission of CH 4 under flooded conditions are brought out by methanogenic bacteria that can metabolize only in the strict absence of free oxygen, coupled with alkaline condition of the flooded soil which also contributes to CH4 emission (Neue, 1993; Minami 1994). A net decrease of CH4 emission to an extent of 28% was observed by Jain et al. (2000) practicing intermittent irrigation. Thus, flood water regime can have a strong influence on CH4 emission rates from rice fields (Minami, 1994, Wang et al., 2000 and Wassmann et al., 2000). Table 2. Seasonal methane emission from the rice field as affected by water regimes and fertilizer levels. Treatment Seasonal Grain yield kg CH4 t-1 % flux (t ha-1) of grain chang -1 (kg ha ) yield e Water regime Continuous flooding 7.69 4.41 1.74 IW/CPE =1.0 5.76 3.63 1.59 25 IW/CPE =0.75 4.65 3.64 1.28 40 Fertilizer levels 4.21 2.90 1.45 Control RFD 7.32 4.93 1.49 74 Organic manure alone 6.12 2.85 2.15 45 50% RFD + 50% OM 6.48 4.03 1.61 54
METHANE EMISSION FROM RICE FIELD 65
Seasonal CH4 emission was increased by 74% following application of RFD as compared to the control. It was observed that seasonal flux of CH4 increased by 45% and 54%, respectively following application of organic manure alone and 50% RFD + 50% organic manure. The least amount of CH4 t-1 grain yield was recorded in the control followed by RFD treatment. A lower amount of CH4 t-1 grain yield was recorded in 50% RFD + 50% organic manure compared to the organic manure alone. The RFD treated plots always recorded more biomass production than other treatments. The increase in CH4 emission by rice crop in response to heavy fertilization would be a function of increased biomass production. Since methane is produced in rhizosphere from organic carbon released by the plant, a higher above ground biomass would potentially release more organic carbon (Sinha, 1995). The CH4 emission from plots treated with 50% RFD + 50% organic manure was less than that of RFD treated plots. The reduction in the CH 4 emission may be due to less biomass production than RFD treated plots. When compared to plots treated with organic manure alone, plots treated with 50% RFD + 50% organic manure recorded more CH4 emission. The increase may be due to more biomass production from these plots compared to plots treated with organic manure alone. Similar results were reported by (Cicerone et al., 1983 and Sinha, 1995), wherein they clearly showed the dependence of CH 4 emission on biomass. Sole organic manure caused more CH4 emission than control plots, and may be due to the increase in readily mineralizable carbon in the soil. The mineralizable carbon in the organic amendment has been reported to be one of the principal factors affecting CH4 emission from flooded soils (Yagi and Minami, 1990). It can be seen that less amount of CH 4 t-1 grain yield was observed in combinations of M2S1, M3S1 and M3S2, but M2S1 and M3S1 recorded lower grain yield than M3S2 (Table 3). Therefore M3S2 (water regime of IW/CPE = 0.75 + RFD fertilizer level) can be recommended as a suitable mitigation practice. In this combination, CH 4 emission was reduced by 38% over M1S2 (continuous flooding + RFD) combination. These results corroborate the finding of Wang et al. (2000) and Lu et al. (2000).
66 IMBULGODA et al. Table 3.
Seasonal methane emission from the rice field as affected by interaction between water regimes and fertilizer levels. Treatment Seasonal flux Grain yield kg CH4 t-1 (kg ha-1) (t ha-1) grain yield M1S1 5.46 M1S2 9.14 M1S3 7.71 M1S4 8.43 M2S1 3.97 M2S2 7.15 M2S3 5.59 M2S4 6.30 M3S1 3.20 M3S2 5.66 M3S3 5.04 M3S4 4.72 M1- Continuous flooding M2- IW/CPE =1.0 M3- IW/CPE =0.75
2.92 1.87 5.93 1.54 2.98 2.59 5.08 1.66 3.21 1.24 4.48 1.60 2.65 2.11 3.46 1.82 2.58 1.24 4.39 1.29 2.92 1.73 3.55 1.33 S1 - Control S2 - RFD S3 - Organic manure only S4 – 50% RFD + 50% organic manure
Seasonal variations in methane efflux
Methane emission (mg m
-2
-1
d )
The data in Figures 4 and 5 revealed that the highest CH 4 emission was registered with continuous flooding throughout the rice growing season followed by water regime of IW/CPE = 1.0. The lowest CH 4 emission was observed with water regime of IW/CPE = 0. Among the fertilizer levels, the highest CH4 emission was observed in plots treated with RFD throughout the season followed by 50% RFD + 50% organic manure and organic manure alone. The lowest CH4 emission was observed in control plots. 20 18 16 14 12 10 8 6 4 2 0 B/I
A/I
T illering
B/I
A/I PI
Cont inuous floodin g
B/I
A/I
Flowering
Growth stages
IW /CP E=1.0
B/I
A/I
M at urit y IW /CP E=0.75
Figure 4. Seasonal patterns of methane emission as affected by water regimes (B/I- Before Irrigation, A/I- After Irrigation).
Methane emission (mg m
-2
-1
d )
METHANE EMISSION FROM RICE FIELD 67 18 16 14 12 10 8 6 4 2 0 B/I
A/I
T illering
B/I
A/I PI
B/I
A/I
Flowering
B/I
A/I
M at urit y
Growth stages Co nt rol
RFD
Organic manure alone
50 %RFD wit h 5 0% organic manure
Figure 5. Seasonal patterns of methane emission as affected by fertilizer levels (B/I-Before Irrigation, A/I-After Irrigation).
The CH4 emission steadily increased over the cropping season. Maximum methane emission was observed at the flowering stage. Similar seasonal pattern was observed by Holzapfe - Pschorn and Seiler (1986). The variation in methane emission during the vegetative period may be due to the gradual increase in biomass production, reaching the maximum by flowering. The higher CH4 emission between the maximum tillering and PI (ground growth period) can also be attributed to disturbance of wetland soil by cultural practices, which favours soil trapped methane to escape into the atmosphere through ebullition (Nue, 1993; Wassmann and Martius, 1997). After flowering however, the rate of CH4 emission decreases significantly. Since the rate of photosynthesis declines after the commencement of grain development, the supply of current assimilates for methane production would also decrease (Sinha, 1995), resulting in decreased CH 4 emission at maturity stage. These results suggest that it is important to evaluate the integrative effects of water management and fertilizer application for mitigating greenhouse effect caused by methane emission in order to attenuate the global warming contributed by rice paddy fields. CONCLUSIONS The results revealed a distinct diurnal pattern of methane efflux at tillering stage of rice crop. There was reduction in methane emission to an extent of 25 and 40% in treatments of IW/CPE = 1.0 and IW/CPE = 0.75 respectively over continuous flooding. The RFD treatment recorded highest seasonal CH4 emission which was significantly superior to all other treatments followed by 50% RFD + 50% organic manure and organic manure alone. The CH4 emission steadily increased over the cropping season. Maximum methane emission was observed at the flowering stage. After irrigation there was a considerable enhancement in the CH4 emission when compared with before
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irrigation, especially in intermittently flooded plots. The present investigation indicated that the combination of IW/CPE = 0.75 + RFD treatment can be recommended as a suitable mitigation option owing to its least amount of seasonal CH4 emission per 1 ton of grain yield (1.29kg CH4 t-1 of paddy). ACKNOWLEDGEMENTS The authors wish to express their gratitude to the Department of Agriculture and Sri Lanka Council for Agricultural Policy for financing this post graduate study. The valuable guidance and assistance provided by the staff of Acharya N.G. Ranga Agricultural University and Directorate of Rice Research, Rajendranagar, Hyderabad, India, are also gratefully acknowledged. REFERENCES Cicerone, R.J. and R.S. Oremland. 1988. Biogeochemical aspects of atmospheric methane. Global Biogeochemical Cycles 2: 299-327. Cicerone, R.J., J.D. Shetter and C.C. Delwiche. 1983. Seasonal variations of methane flux from a California rice paddy. Journal of Geophysical Research 88: 1102211024. Debnath, G., M.C. Jain, S. Kumar, K. Sarkar and S.K. Sinha. 1996. Methane emission from rice fields amended with biogas slurry and farm yard manure. Climate Change 33: 97-109. Holzapfel-Pschorn, A. and W. Seiler. 1986. Methane emission during a cultivation period from an Italian rice paddy. Journal of Geophysical Research 91: 1180311814. Hutchinson, G.L. and A.R. Mosier. 1981. Improved soil cover method for field measurement of nitrous oxide flux. Soil Science Society of America Journal 45: 311-316. IRRI窶的nternational Rice Research Institute. 1993. Rice Research in a time of change. Manila, Philippines, p 79. Jain, M.C., S. Kumar, R. Wassmann, S. Mitra, S.D. Singh, J.P. Singh, R. Singh, A.K. Yadav and S. Gupta. 2000. Methane emission from irrigated rice fields in Northern India (New Delhi). Nutrient Cycling in Agroecosystems 58 (1-3): 75-83. Lindau, C.W., P.K. Bollich, R.D. DeLaune, W.H. Patrick Jr. and V.J. Law. 1991. Effect of Urea fertilizer and environmental factors on CH 4 emission from a Louisiana USA rice field. Plant and Soil 136: 195-203. Lu, W.F., W. Chen, B.W. Duan, W.M. Guo, Y. Lu, R.S. Lantin, R. Wassmann and H.U. Neue. 2000. Methane emissions and mitigation options in irrigated rice fields in Southeast China. Nutrient Cycling in Agroecosystems 58(1-3): 6573. Minami, K. 1994. Methane from rice production. Fertilizer Research 37: 167-179.
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