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Global warming potential of manure amended soils under rice–wheat system in the Indo-Gangetic plains
ARTICLE IN PRESS
Atmospheric Environment 39 (2005) 6976–6984 www.elsevier.com/locate/atmosenv
Global warming potential of manure amended soils under rice–wheat system in the Indo-Gangetic plains A. Bhatiaa, H. Pathakb,, N. Jaina, P.K. Singha, A.K. Singhc a
Division of Environmental Sciences, Indian Agricultural Research Institute, New Delhi 110 012, India Unit of Simulation and Informatics, Indian Agricultural Research Institute, New Delhi 110 012, India c Water Technology Center, Indian Agricultural Research Institute, New Delhi 110 012, India
b
Received 29 October 2004; received in revised form 12 July 2005; accepted 18 July 2005
Abstract Use of organic amendments such as farmyard manure (FYM), green manure (GM) and crop residues is important to improve soil health and reduce the dependence on synthetic chemical fertilizer. However, these organic amendments also effect the emissions of greenhouse gas (GHG) from soil. Influence of different organic amendments on emissions of GHG from soil and their global warming potential (GWP) was studied in a field experiment in rice–wheat cropping system of Indo-Gangetic plains (IGP). There was 28% increase in CH4 emissions on addition of 25% N through Sesbania GM along with urea compared to urea alone. Substitution of 100% inorganic N by organic sources lead to a 60% increase in CH4 emissions. The carbon equivalent emission from rice–wheat systems varied between 3816 and 4886 kg C equivalent ha1 depending upon fertilizer and organic amendment. GWP of rice–wheat system increased by 28% on full substitution of organic N by chemical N. However, the C efficiency ratios of the GM and crop residue treatments were at par with the recommended inorganic fertilizer treatment. Thus use of organic amendments along with inorganic fertilizer increases the GWP of the rice–wheat system but may improve the soil fertility status without adversely affecting the C efficiency ratio. However, the trade-off between improved yield and soil health versus GHG emissions should be taken into account while promoting the practice of farming with organic residues substitution for mineral fertilizer. r 2005 Elsevier Ltd. All rights reserved. Keywords: Carbon equivalent emission; Carbon dioxide; Methane; Nitrous oxide; Greenhouse gas
1. Introduction The rice–wheat cropping system occupying 24 million hectares of some of the productive areas in the IndoGangetic plains (IGP) of south Asia and China is Corresponding author. Institut fur Meteorology und Klimaforschung, Kreuzeckbahnstr. 19, 82467 Garmisch-Partenkirchen, Germany. Tel.: +49 8821 183141; fax: +49 8821 183296. E-mail address: [email protected] (H. Pathak).
important for the food security of the region (Ladha et al., 2003). Recent analysis of some of the long-term experiments of the region showed a decline/stagnation in the productivity of this cropping system raising concern about its sustainability (Ladha et al., 2003; Yadav et al., 2000). Depletion of soil organic carbon (SOC) and nitrogen, and deterioration of soil physical properties are suggested to be the major causes of such yield decline (Ladha et al., 2003; Sharma et al., 2003). Improvement of SOC status through use of organic amendments such as manures and crop residues is, therefore, urgently
1352-2310/$ - see front matter r 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2005.07.052
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needed for sustaining and increasing the productivity of the rice–wheat system in the IGP. Carbon dioxide (CO2) methane (CH4) and nitrous oxide (N2O) are important greenhouse gases (GHG) contributing 60%, 15% and 5%, respectively, towards the enhanced global warming (Watson et al., 1996). The concentrations of these gases are increasing at 0.42%, 3.0% and 0.22% per year, respectively (Machida et al., 1995; Battle et al., 1996). Agricultural soil is a major contributor of these gases. The recommended fertilizer practice in the IGP is to apply 120 kg N ha1 through inorganic fertilizer (urea) in rice and wheat each. The farmers also apply different kinds of organic manure such as farmyard manure (FYM), green manure (GM), biofertilizer and crop residues for the partial substitution of the inorganic fertilizer. Although, the use of organic amendments in rice–wheat systems of IGP may lead to higher SOC and crop productivity, it may also increase the GHG emission and global warming potential (GWP) of the system. However, the magnitude of the emission will vary depending upon the composition of the manure and indigenous fertility status of soil. The objectives of the study were to: (1) estimate the emission of CO2, CH4, and N2O from organic manure amended soils under rice–wheat cropping systems and (2) evaluate the GWP of rice–wheat cropping system in the IGP.
2. Materials and methods 2.1. Experimental site and soil A field experiment was conducted in rice–wheat system during 2001–02 in a Typic Ustochrept at the experimental farm of the Indian Agricultural Research Institute, New Delhi, India. The site is located in the Indo-Gangetic alluvial tract at 281400 N and 771120 E, at an altitude of 228 m above mean sea level. The climate of the region is subtropical, semi-arid. The area receives an annual rainfall of 750 mm, about 80% of which occurs from June to September. The mean maximum and minimum temperatures from July to October (rice season) are 35 and 18 1C; while from November to March (wheat season) 22.6 and 6.7 1C, respectively. The alluvial soil of experimental site was loam in texture and had an organic carbon, Olsen P, and KMnO4, extractable N contents of 5.9, 0.014, 0.11 g kg1, respectively. The physico-chemical properties of the soil are given in Table 1. 2.2. Treatments and crop management The experiment included six treatments with three replicates in plots of 10 m long and 5 m wide (Table 2). All the organic amendments (FYM, GM and residues) were incorporated into the soil 2 weeks before transplanting of rice and sowing of wheat. Composition of
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Table 1 Some physico-chemical properties of soil (0–0.15 m depth) at the start of the experiment Soil property
Values
Sand (%) Silt (%) Clay (%) EC (dS m1) pH (1:2Hsoil:water) CEC (cmol kg1) Organic C (%) Bulk density (Mg m3) Hydraulic conductivity (cm d1) Ammo. acetate ex. K (kg ha1) Olsen P (kg ha1) KMnO4 extractable N (kg ha1) 1 NH+ 4 -N (kg ha ) 1 NO 3 -N (kg ha ) Moisture content at field capacity (%) Moisture content at permanent wilting point (%)
40 32 28 0.78 8.0 7.3 0.59 1.4 4.8 361 31.8 251 24.9 33.4 20.5 6.5
Table 2 Treatments Treatment Details T1 T2 T3 T4 T5 T6
Unfertilized 100% NPKa 100% NPK (25% N by FYM)b 100% NPK (25% N by GM)c 100% NPK+residue of the previous crop (2 t ha1) 100% N by organic source (50% FYM+25% biofertilizer+25% residue of the previous crop)
a 100% NPK is N, P, and K at 120, 26 and 50 kg ha1, respectively. b 25% of inorganic N was substituted by N in FYM. c 25% of inorganic N was substituted by N in GM.
various amendments has been given in Table 3. Inorganic N was applied through surface broadcast of urea in three splits of 60, 30 and 30 kg N ha1 at 17, 37 and 62 days after transplanting (DAT) of rice; while in wheat it was applied at 11, 32, and 84 days after sowing (DAS). Phosphorus (26.2 kg ha1) and K (50 kg ha1) were incorporated into the soil at the time of transplanting/sowing using single super phosphate (SSP) and muriate of potash (KCl), respectively, in all plots. In rice, blue green algae (BGA) was applied as biofertilizer in the treatment with 100% organic source (T6). Azospirillum brasilense (strain CD) was used as biofertilizer for wheat and was applied as seed coating using a carrier based inoculants. For rice the field was flooded with water and then puddled. Subsequently 2–3 seedlings (called as 1 hill) of rice (cultivar Pusa 44) of 30 days age were transplanted
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A. Bhatia et al. / Atmospheric Environment 39 (2005) 6976–6984
Table 3 Composition of different organic amendments (dry weight basis) Organic amendments
C (g kg1)
N (g kg1)
C:N
P (g kg1)
K (g kg1)
FYM GM (Sesbania rostrata) Wheat straw Rice straw
318 410 420 434
9.6 20.7 4.6 5.3
33 20 91 82
2.9 1.9 0.4 1.6
4.8 18.5 10.4 21.2
in the field. The distance between each hill in a row was 15 cm and between two rows was 20 cm. Wheat (cultivar HD 2687, 100 kg seed ha1) was sown in rows 22.5 cm apart. Irrigation water of 572 cm each was applied on surface through check-basin method. Irrigation in rice was given in 3–4 days interval while in wheat 5 irrigations were given. Weeds, pests, and diseases were controlled as required. 2.3. Gas sample collection and analysis Collection of gas samples for CH4 and N2O was carried out by the closed-chamber technique using the chambers of 50 cm 30 cm 100 cm (length width height) (Pathak et al., 2002). Collection of gas samples for CO2 was done using the chambers of 15 cm 15 cm 50 cm (length width height) placed between the rows of the plants. Gas samples were drawn with 50 mL syringe with the help of a hypodermic needle (24 gauge) at 0, 15, and 30 min for CH4 and 0, 30, and 60 min for N2O and CO2. The samples of gases were collected and brought to the laboratory where they were analysed within 2 h. Concentration of CH4 in the gas samples was estimated by Gas Chromatograph fitted with a flame ionization detector (FID) and N2O samples were analysed using electron capture detector (ECD). For CO2, the gas samples were converted to CH4 using a methanizer (Ni catalyst, 320 1C) and then analysed using a FID (Kotsyurbenko et al., 2004). Estimation of total CO2, CH4 and N2O emissions during the crop season was done by successive linear interpolation of average emission on the sampling days assuming that emission followed a linear trend during the periods when no sample was taken (Pathak et al., 2003a).
2.5. Soil sample analysis Soil samples from the 0–15 cm soil layer in three locations in each plot were collected using a core sampler. The entire volume of soil was weighed and mixed thoroughly and a subsample was taken to determine dry weight. The fresh soil was air-dried for 7 days, sieved through a 2 mm screen, mixed, and stored in sealed plastic jars for analyses. Representative subsamples were drawn to determine physico-chemical properties using standard procedures (Page et al., 1982). 2.6. GWP and carbon equivalent emission GWP is an index defined as the cumulative radiative forcing between the present and some chosen later time ‘horizon’ caused by a unit mass of gas emitted now. It is used to compare the effectiveness of each GHG to trap heat in the atmosphere relative to some standard gas, by convention CO2. The GWP for CH4 (based on a 100year time horizon) is 21 and N2O 310 when for CO2 the value is taken as 1. The GWP of different treatments were calculated using the following equation (Watson et al., 1996): GWP ¼ CO2 þ CH4 n21 þ N2 On310:
(1)
The carbon equivalent emissions (CEE) and carbon efficiency ratio (CER) of the treatments were calculated using the following equations: CEE ¼ GWPn12=44;
(2)
CER ¼ grain yield ðin terms of CÞ of the rice2wheat system=CEE:
(3)
2.4. Estimation of yields of rice and wheat 3. Results and discussion Rice and wheat yields were determined from the total plot area by harvesting all the hills excluding the hills bordering the plot. The grains were separated from the straw, dried, and weighed. Grain moisture was determined immediately after weighing and subsamples were dried in an oven at 65 1C for 48 h.
3.1. Methane flux in rice Fluxes of CH4 fluctuated between 0.04 and 1.09 kg ha1 d1 during the rice season and no specific pattern was observed in any of the treatments (Fig. 1).
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Relatively low rates of CH4 emission were due to partially aerobic soil conditions because of intermittent drying and wetting due to porous and highly percolating nature of the soil. On many days there was no standing water in the field and the redox potential (Eh) was above 100 mV as observed in our earlier experiment conducted in the same field (Jain et al., 2000). The anaerobic condition, required for the formation of CH4, thus was not prevailing during the entire rice crop period. The highest flux of 1.09 kg ha1 CH4 was observed in the FYM treatment (T3) on 12 DAT. In the 100% organic treatment (T6) on most days higher CH4 emissions were observed as compared to the other treatments. The
No fertilizer (T1) 100% NPK (T2) 100% NPK (25% N by FYM) (T3) 100% NPK (25% N by GM) (T4) 100% NPK + crop residue (T5) 100% organic source (T6)
1.4
CH4 (kg ha-1 d-1)
1.2 1 0.8 0.6 0.4 0.2 0
1 3 7 12 18 23 30 38 45 50 61 68 70 79 85 93 97 112
Days after transplanting rice Fig. 1. Emission of CH4 from soil with different organic amendments in rice.
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average daily flux in the 100% organic treatment was 0.54 kg ha1 as compared to 0.48 kg ha1 in the NPK+FYM treatment. Total emission of CH4 during the cropping period was lowest (35.1 kg ha1) in the control treatment (T1) and the highest (57.1 kg ha1) with application of 100% N through organic sources (Table 4). Treatment with only urea (T2) had emission similar to the control treatment. Application of FYM, GM and crop residues enhanced emission of CH4 by providing additional C substrate as compared to urea alone treatment (Lu et al., 2000). Emission of CH4 in 100% N through organic sources (T6) treatment at 57.1 kg ha1 was higher than the treatments where 25% N was added by either FYM (T3) or GM (T4). Additional amount of organic matter added through the organic amendments served as a source of electrons (Singh et al., 1998) creating more anaerobic conditions (Mishra et al., 1997) and higher CH4 formation. Higher emission in the 100% N through organics (T6) could also be due to the presence of blue green algae as biofertilizer, which provided mediation of CH4 transport from floodwater of rice soil into the atmosphere (Ying et al., 2000). Lower emissions of CH4 in crop residue treatment (T5) as compared to FYM (T3) and GM (T4) treatments could be due to higher lignin content (14.7%) in crop residue, which decomposed slowly (Berg and Matzner, 1997). The effect of organic amendments on CH4 emission also depended on their C/N ratios (Table 3). Crop residues such as wheat and rice straws with high C/N ratios had lower emission.
Table 4 Seasonal emissions of carbon dioxide, nitrous oxide and methane from organic manure amended soil and total carbon equivalent emission in rice-wheat system Treatment
CH4 emission in rice (kg ha1)
N2O-N N2O-N emission in rice emission in (g ha1) wheat (g ha1)
CO2-C CO2-C emission in rice emission in (kg ha1) wheat (kg ha1)
GWP of rice–wheat systemb (kg CO2 ha1)
C equivalent emissionc (CEE) (kg C ha1)
Unfertilized 100% NPK 100% NPK (25% N by FYM) 100% NPK (25% N by GM) 100% NPK+crop residue 100% organic source
35.1ea 35.9e 49.6b
320d 569ab 503c
359f 736d 860b
1294f 1578e 1975b
1682d 1922c 2458a
11,860e 13,992d 17,718a,b
3234e 3816d 4832a,b
46.0c
579a
922a
1853c
2493a
17,367b
4736b
42.7d
549ab
820c
1642d
2167b
15,287c
4169c
57.1a
537bc
564e
2081a
2385a
17,916a
4886a
a
In a column, values followed by the same letter are not significantly different at Po0:05 by Duncan’s multiple range test. GWP, global warming potential ¼ CO2+(CH4 in rice21)+(N2O in rice+N2O in wheat)310. c Carbon equivalent emission ¼ GWP12/44. b
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This was because of their slow decomposition owing to limited N availability caused by net immobilization (Khalil et al., 2001). There was 28% increase in CH4 emissions on addition of 25% N through Sesbania GM along with urea compared to urea alone (Table 4). Substitution of 100% inorganic N by organic sources lead to a 60% increase in CH4 emissions. Adhya et al. (2000), however, observed a much higher (212%) increase in CH4 emission on substituting 33% of urea N through Sesbania GM in eastern India as the soil was continuously submerged for the entire rice-growing period and also had a higher SOC content.
No fertilizer (T1) 100% NPK (T2) 100% NPK (25% N by FYM) (T3) 100% NPK (25% N by GM) (T4)
50
100% NPK + crop residue (T5) 100% organic source (T6)
NH4-N (kg ha-1 d-1)
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40 30 20 10 0
3.2. Nitrous oxide flux in rice
1
10
1
10
(a)
No fertilizer (T1) 100% NPK (T2) 100% NPK (25% N by FYM) (T3) 100% NPK (25% N by GM) (T4) 100% NPK + crop residue (T5) 100% organic source (T6)
N2O-N (g ha-1 d-1)
25 20 15 10 5 0
1 3 7 12 18 23 30 38 45 50 63 68 70 79 85 93 97 112
(a)
Days after transplanting rice
N2O-N (g ha-1 d-1)
25 20 15 10 5 0 1
(b)
5
9 12 17 23 33 37 46 55 62 68 80 85 88 93 107 120
Days after sowing wheat
Fig. 2. Emission of N2O from soil with different organic amendments in (a) rice and (b) wheat. k and m arrows indicate the days of fertilizer application and the days of irrigation, respectively.
64
85
64
85
25 NO3-N (kg ha-1 d-1)
Flux of N2O-N was large on 1 DAT and decreased later (Fig. 2a). Denitrification of initial indigenous NO 3N (Fig. 3b) was presumably responsible for this initial large flux. As NO 3 -N in soil decreased due to plant uptake and losses through denitrification and leaching, N2O flux declined later. The trend of reduction in N2ON flux continued till the application of urea on 17 DAT when N2O-N flux increased. Similar high peaks of N2ON flux were observed after every dose of N application, which supplied the substrate for nitrification (NH+ 4 -N) (Fig. 3a) and subsequently for denitrification (NO 3 -N). In the soil both the processes might have occurred
18 30 38 50 Days after transplanting rice
20 15 10 5 0
(b)
18
30
38
50
Days after transplanting rice
Fig. 3. Temporal status of NH4-N (a) and NO3-N (b) in soil with different treatments in rice.
simultaneously, because the soil was not fully anaerobic as submergence was not maintained in this highly percolating soil and frequent irrigation carried dissolved O2 in water making the soil partially aerobic (Majumdar et al., 2000). Total emission of N2O-N during rice ranged from 320 g ha1 in the unfertilized treatment (T1) to 579 g ha1 with urea plus GM treatment (T4) (Table 4). There was no statistically significant difference in the N2O-N emissions in GM (T4), crop residue (T5), and urea (T2) treatments while the treatments with FYM (T3 and T6) had lower emissions than these treatments. Presence of N in readily available form in treatments T2, T4 and T5 was responsible for greater N2O-N emission as compared to the FYM treatments. Lower emissions in the FYM treatments were due to slow decomposition of N from FYM compared to GM because of higher C/N ratio of the former (Table 3). Lower emission in the FYM treatment compared to the crop residue treatment was because of addition of 25% more inorganic N in the residue treatment (Table 2). Pathak et al. (2002) observed that use of FYM and urea in combination reduced emission of N2O-N in rice compared to application of urea alone.
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3.3. Nitrous oxide flux in wheat Fluxes of N2O-N in wheat on 1 DAS ranged from 7.2 to 10.5 g ha1 d1, which decreased on day 5 except in the GM treatment (T3) in which the flux of N2O-N increased (Fig. 2b). Application of water in the dry soil for land preparation before sowing of wheat along with operations performed during sowing might have stimulated the activity of the nitrifying microbes resulting in greater fluxes of N2O-N on 1 DAS. Subsequently, when NH+ 4 -N content in soil (Fig. 4a) decreased as a result of nitrification, N2O-N emission declined. A peak in N2ON emission was observed after application of N fertilizer on 11 DAS in all the treatments. After every dose of N fertilizer application N2O-N flux increased due to availability of substrate (NH+ 4 -N) for nitrification. Increase in N2O-N flux was observed after each irrigation due to enhanced nitrification and also denitrification of NO 3 in anaerobic microsites in the soil (Arah and Smith, 1989). The N2O-N emission observed in wheat was primarily a result of nitrification except during short periods after each irrigation event when anoxic soil condition was created resulting in denitrification of NO 3 -N (Bremner and Blackmer, 1978).
No fertilizer (T1) 100% NPK (T2) 100% NPK (25% N by FYM) (T3) 100% NPK (25% N by GM) (T4) 100% NPK + crop residue (T5) 100% organic source (T6)
30
NH4-N (kg ha-1d-1)
25 20 15 10 5 0 1
(a)
9
17
33
55
68
85
107
NO3-N (kg ha-1d-1)
25 20
Total emission of N2O-N during 120 days of wheat cropping ranged from 359 g ha1 in the unfertilized treatment to 922 g ha1 in the GM treatment (Table 3). Compared to rice, the emission of N2O-N in various treatments was more in wheat due to faster decomposition of organic residues in soils under aerobic condition than in anaerobic condition (Neue and Scharpenseel, 1987). Higher emission of N2O-N was observed in GM treatment with lower C/N ratio compared to the FYM treatment. Substitution of 25% of inorganic fertilizer by FYM and GM increased N2O-N emission by 17% and 25%, respectively, compared to urea alone. Addition of rice residue along with 100% NPK fertilizer (T5) also led to an increase in N2O-N emission by 11%. Aulakh et al. (2001) observed an increase in gaseous N losses on incorporation of rice straw residue and GM alongwith inorganic N. Substitution of the entire chemical N by organic sources, however, decreased the emission of N2O-N by 24%. 3.4. Carbon dioxide flux in rice Fluxes of CO2-C on 1 DAT of rice were in the range of 13–18 kg ha1 d1 (Fig. 5a), which then increased. The highest peak was observed in the GM (T4) treatment on 12 DAT followed by 100% organic (T6) and FYM (T3) treatments on 17 DAT. Within a treatment temporal variation in CO2-C flux were observed due to alternate drying and wetting of soil releasing the CO2 stored in the soil pores. Cumulative seasonal emission of CO2-C ranged from 1294 kg ha1 in the unfertilized treatment (T1) to 2081 kg ha1 in the 100% organic (T6) treatment (Table 4). Addition of 100% N through organic sources (T6) increased CO2-C emission by 32% over the 100% inorganic NPK treatment (T2). Substitution of 25% inorganic N by FYM (T3) and GM (T4) led to increased emission of CO2-C by 25% and 17%, respectively. Higher CO2-C fluxes in the GM, FYM and 100% organic treatments were due to higher availability of organic C resulting in increased soil respiration (Scott et al., 2000). Lower C/N ratio in GM and FYM compared to crop residues resulted in higher fluxes of CO2 due to faster C decomposition. 3.5. Carbon dioxide flux in wheat
15 10 5 0 1
(b)
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9
17
33
55
68
85
107
Days after sowing wheat
Fig. 4. Temporal status of NH4-N (a) and NO3-N (b) in soil with different treatments in wheat.
Fluxes of CO2-C (15–18 kg ha1 d1) were higher on day 1 after sowing of wheat (Fig. 5b). On application of first dose of fertilizer N on 11 DAS, the fluxes increased due to increased availability of N, which accelerated the mineralization of organic C and soil respiration (Pathak and Rao, 1998). The peaks of CO2C fluxes at 34.0 and 40.4 kg CO2-C d1 were observed on 12 DAS in T3 and T4 treatments, respectively. Subsequently there was a decline in the flux till the next dose
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No fertilizer (T1) 100% NPK (T2) 100% NPK (25% N by FYM) (T3) 100% NPK (25% N by GM) (T4) 100% NPK + crop residue (T5) 100% organic source (T6)
40
CO2-C (kg ha-1d-1)
35 30 25 20 15 10 5 0
1 3 7 12 17 23 30 38 45 50 63 68 70 79 85 93 97 112
CO2-C (kg ha-1d-1)
(a)
Days after transplanting rice 45 40 35 30 25 20 15 10 5 0 1
(b)
5
9 12 17 23 33 37 46 55 62 68 80 85 88 93 107120
Days after sowing wheat
Fig. 5. Emission of CO2 from soil with different organic amendments in (a) rice and (b) wheat.
of N was applied when a small increase in CO2-C emission was observed. Smaller peaks were observed after every irrigation event indicating that soil moisture played a crucial role in the emission of CO2. The increase in soil moisture after irrigation stimulated the microbial activity and also more diffusion of CO2 trapped in soil (Pathak et al., 2003b). The highest average CO2-C flux (21.0 kg ha1 d1) was observed in the GM treated plots (T4), while the lowest flux was observed in the unfertilized plots (13.7 kg ha1 d1). In wheat seasonal emissions varied from 1682 kg CO2C ha1 in the unfertilized plots to 2493 kg CO2-C ha1 in GM treated plots (Table 4). Substitution of 100% inorganic N with 100% organic N led to 21% increase in the emission of CO2-C. Substitution of 25% N through FYM (T3) and GM (T4) increased emission by 27% and 30%, respectively, over the 100% inorganic NPK (T2) treatment. Addition of rice residues along with urea (T5) in wheat increased emissions by 12% over the urea alone treatment (T2). 3.6. GWP and carbon equivalent emission The GWP of various treatments in rice–wheat system varied between 11860 kg CO2 equivalent ha1 in the unfertilized to 17916 kg CO2 ha1 with 100% organic treatment (Table 4). Increase in GWP with the application of organic amendments ranged from 9% with urea
plus crop residue treatment (T5) to 28% with 100% organic treatment (T6) compared to 100% inorganic NPK treatment (T2). There was no significant difference between the FYM and 100% organic treatment in terms of GWP. Research on GWP of rice–wheat system is very limited. Earlier Grace et al. (2003) estimated annual GWP of 3496–7137 kg C ha1 of irrigated rice–wheat system in the IGP depending on crop management practices. However, they used the Inter-Governmental Panel of Climate Change (IPCC) default GHG emission coefficients and included only CH4 and N2O emissions and not CO2 emission in their estimation. In our study for computation of GWP, CO2 emission were only based on the flux measured between rows of plants and emission or consumption CO2 due to plant respiration and photosynthesis, respectively, were not considered. This is because in a conventional crop growing condition, the emission and consumption of CO2 due to plant respiration and photosynthesis, respectively, are balanced, and therefore, plant emission of CO2 during respiration is not taken into account while computing GWP from agriculture. Robertson et al. (2000) and Six et al. (2004) observed that the change in SOC or soil respiration should be measured for accounting of GWP of soils. Six et al. (2004) and Yu and Patrick (2004) computed the GWP of different soils by measuring the changes in SOC storage. The IPCC (2001) also suggest calculating GWP using the same approach. The CEE was smallest (3234 kg C ha1) in the unfertilized treatment (Table 4). The 100% inorganic treatment also had smaller CEE compared to the treatments with organic amendments. Among the organic amended treatments the lowest CEE was observed in the 100% NPK plus crop residue treatment (Table 4).
3.7. Yields of rice and wheat and CER Yields of rice ranged from 3.43 to 6.40 Mg ha1, while that of wheat ranged from 2.54 to 4.62 Mg ha1 (Table 5). Treatments with GM plus urea gave highest yields of rice and wheat probably because of higher nutrient availability as compared to the inorganic fertilizer treatment (Singh et al., 1999). Goyal et al. (1997) observed higher crop yields and N uptake with the addition of Sesbania GM. Application of 100% N through organic sources (T6) reduced rice yield by 19% over application of 100% inorganic fertilizer (T2). In wheat, however, yields were similar in both these treatments. Similarly, substitution of 25% N by FYM decreased rice yield but had no significant effect on wheat yield. Lower yields in the FYM (T3) and 100% organic treatment (T6) as compared to 100% inorganic NPK (T2) treatment was due to lower N availability
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Table 5 Yield of rice and wheat as affected by various nutrient sources Treatment
Rice Yield (Mg ha1)
Wheat Yield (Mg ha1)
Total C fixeda (Mg ha1)
Carbon efficiency ratio
Unfertilized 100% NPK 100% NPK (25% N by FYM) 100% NPK (25% N by GM) 100% NPK+crop residue 100% organic source
3.43e 5.70b 5.09c 6.40a 5.72b 4.59d
2.54c 3.71b 3.46b 4.62a 3.52b 3.60b
2.87 4.52 4.11 5.29 4.53 3.93
0.89 1.19 0.85 1.12 1.09 0.80
a
Carbon contents in rice and wheat are 48% and 47% of total biomass, respectively.
because of slow mineralization of organic N from these sources. The CER, i.e., C fixed in grain by rice and wheat per unit of C emitted, was the largest (1.19) in the 100% inorganic treatment (T2) followed by the GM and crop residue treatments (Table 5). Lowest CER (0.80) was in 100% organic treatment as this had the largest CO2 emissions and the smaller amount of C fixed (crop yield) in rice and wheat.
4. Conclusions Rice–wheat cropping system in the IGP could be a major source of atmospheric CO2, CH4 and N2O because of its large area and high use of agricultural inputs. The carbon equivalent emission from rice–wheat systems in IGP varied between 3816 and 4886 kg CE ha1 depending upon fertilizer and organic amendments. Though addition of organic sources such as GM, FYM and crop residues has potential to improve soil health and increase crop productivity, it also results in increased GHG emissions. The application of GM along with NPK led to an increase in C equivalent emissions and also increased the C fixed significantly. However, the C efficiency ratio was at par with the 100% inorganic fertilizer treatment. Thus use of GM along with inorganic fertilizer increases the GWP of the rice–wheat system but may improve the soil fertility status without adversely affecting the C efficiency ratio.
References Adhya, T.K., Bharti, K., Mohanty, S.R., Ramakrishnan, B., Rao, V.R., Sethunathan, N., Wassmann, R., 2000. Methane emission from rice fields at Cuttak, India. Nutrient Cycling in Agroecosystem 58, 95–106. Arah, J.R.M., Smith, K.A., 1989. Steady state denitrification in aggregated soils: a mathematical model. Journal of Soil Science 40, 139–149.
Aulakh, M.S., Khera, T.S., Doran, J.W., Bronson, K.F., 2001. Denitrification, N2O and CO2 fluxes in rice–wheat cropping system as affected by crop residues, fertilizer N and legume green manure. Biology and Fertility of Soils 34, 375–389. Battle, M., Bender, M., Sowers, T., Tans, P.P., Butler, J.H., Elkins, J.W., Ellis, J.T., Conway, T., Zhang, N., Lang, P., Clarke, A.D., 1996. Atmospheric gas concentrations over the past century measured in air from firn at the south pole. Nature 383, 231–235. Berg, B., Matzner, E., 1997. Effect of N deposition on decomposition of plant litter and soil organic matter in forest systems. Environmental Reviews 5, 1–25. Bremner, J.M., Blackmer, A.M., 1978. Nitrous oxide: emission from soils during nitrification of fertilizer nitrogen. Science 199, 295–297. Goyal, S., Mishra, M.M., Hooda, I.S., Singh, R., 1997. Organic matter–microbial biomass relationships in field experiments under tropical conditions: effects of inorganic fertilization and organic amendments. Soil Biology and Biochemistry 24, 1081–1084. Grace, P.R., Harrington, L., Jain, M.C., Robertson, G.P., 2003. Long term sustainability of tropical and subtropical rice–wheat system: an environmental perspective. In: Ladha, J.K. (Ed.), Improving the Productivity and Sustainability of Rice–wheat Systems: Issues and Impacts. ASA Special Publication 65. CSSA and SSSA, Madison, WI, pp. 27–41. IPCC—Intergovernmental Panel on Climate Change, 2001. Emissions Scenarios, Special Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, UK available at: http://www.ipcc.ch/pub/pub.htm Jain, M.C., Kumar, S., Wassmann, R., Mitra, S., Singh, S.D., Singh, J.P., Singh, R., Yadav, A.K., Gupta, S., 2000. Methane emissions from irrigated rice fields in northern India (New Delhi). Nutrient Cycling in Agroecosystems 58, 75–83. Khalil, M.I., Boeckx, P., Rosenani, A.B., Cleemput, O.V., 2001. Nitrogen transformations and emission of greenhouse gases from three acid soils of humid tropics amended with N sources and moisture regime. II. Nitrous oxide and methane fluxes. Communications in Soil Science and Plant Analysis 32, 2909–2924. Kotsyurbenko, O.R., Chin, K.J., Glagolev, M.V., Stubner, S., Simankova, M.V., Nozhevnikova, A.N., Conrad, R., 2004. Acetoclastic and hydrogenotrophic methane production
ARTICLE IN PRESS 6984
A. Bhatia et al. / Atmospheric Environment 39 (2005) 6976–6984
and methanogenic populations in an acidic West-Siberian peat bog. Environmental Microbiology Online Early. Ladha, J.K., Dawe, D., Pathak, H., Padre, A.T., Yadav, R.L., Bijay-Singh, Yadvinder-Singh, Singh, P., Kundu, A.L., Sakal, R., Ram, N., Regmi, A.P., Gami, S.K., Bhandari, A.L., Amin, K., Yadav, C.R., Bhattarai, E.M., Gupta, R.K., Hobbs, P.R., 2003. How extensive are yield declines in long-term rice–wheat experiments in Asia? Field Crops Research 81, 159–180. Lu, W.F., Chen, W., Duan, B.W., Guo, W.M., Lu, Y., Lantin, R.S., Wassmann, R., Neue, H.U., 2000. Methane emission and mitigation options in irrigated rice fields in southeast China. Nutrient Cycling in Agroecosystems 58, 65–74. Machida, T., Nakazawa, T., Fujii Yaola, S., Watanabe, O., 1995. Increase in the atmospheric nitrous oxide concentration during the last 250 years. Geophysical Research Letters 22, 2921–2924. Majumdar, D., Kumar, S., Pathak, H., Jain, M.C., Kumar, U., 2000. Reducing nitrous oxide emission from rice field with nitrification inhibitors. Agriculture Ecosystem and Environment 81, 163–169. Mishra, S., Rath, A.K., Adhya, T.K., Rao, V.R., Sethunathan, N., 1997. Effect of continuous flooding and alternate water regimes on methane efflux from rice under greenhouse conditions. Biology and Fertility of Soils 24, 399–407. Neue, H.U., Scharpenseel, H.W., 1987. Decomposition pattern of 14C-labeled rice straw in anaerobic and submerged rice soils of the Philippines. Science of the Total Environment 62, 431–434. Page, A.L., Miller, R.H., Keeney, D.R., 1982. Methods of Soil Analysis. Part 2, Chemical and Microbiological Properties. Agronomy No. 9, second ed. ASA-SSSA, Madison, WI, USA, p. 1159. Pathak, H., Rao, D.L.N., 1998. Carbon and nitrogen mineralization from added organic matter in saline and alkali soils. Soil Biology and Biochemistry 30, 695–702. Pathak, H., Bhatia, A., Prasad, S., Jain, M.C., Kumar, S., Singh, S., Kumar, U., 2002. Emission of nitrous oxide from soil in rice-wheat systems of Indo-Gangetic plains of India. Environmental Monitoring and Assessment 77, 163–178. Pathak, H., Prasad, S., Bhatia, A., Singh, S., Kumar, S., Singh, J., Jain, M.C., 2003a. Methane emission from rice-wheat cropping system of India in relation to irrigation, farmyard manure and dicyandiamide application. Agriculture Ecosystem and Environment 97, 309–316. Pathak, H., Rastogi, M., Rai, H.K., Sharma, A., 2003b. Carbon dioxide emission from soil. In: Pathak, H., Kumar, S. (Eds.),
Soil and Greenhouse Effect, Monitoring and Mitigation. CBS Publishers and Distributors, New Delhi, p. 47. Robertson, G.P., Paul, E.A., Harwood, R.R., 2000. Greenhouse gases in intensive agriculture: contributions of individual gases to the radiative forcing of the atmosphere. Science 289, 1922–1925. Scott, A., Ball, B.C., Crichton, I.J., Aitken, M.N., 2000. Nitrous oxide and carbon dioxide emissions from grassland amended with sewage sludge. Soil Use Management 16, 36–41. Sharma, P.K., Ladha, J.K., Bhushan, L., 2003. Soil physical effects of puddling in rice–wheat cropping systems. In: Ladha, J.K., Hill, J.E., Duxbury, J.M., Gupta, R.K., Buresh, R.J. (Eds.), Improving the Productivity and Sustainability of Rice–wheat Systems: Issues and Impacts. ASA Special Publication 65. CSSA and SSSA, Madison, USA, pp. 97–113. Singh, J.S., Raghubanshi, A.S., Reddy, V.S., Singh, S., Kashyap, A.K., 1998. Methane flux from irrigated paddy and dryland rice fields, and from seasonally dry tropical forest and savanna soils of India. Soil Biology and Biochemistry 30, 135–139. Singh, G.R., Parihar, S.S., Chaure, N.K., 1999. Response of organic manures in a rice (Oryza sativa)–chickpea (Cicer arietinum) crop sequence. IRRN 24 (3), 25. Six, J., Ogle, S.M., Breidt, F.J., Conant, R.T., Mosier, A.R., Paustian, K., 2004. The potential to mitigate global warming with no-tillage management is only realized when practised in the long term. Global Change Biology 10, 155–160. Watson, R.T., Zinyowera, M.C., Moss, R. H., Dokken, D.J., 1996. Climate change (1995), impacts, adaptations and mitigation of climate change. Scientific Technical Report Analyses. In: Watson, R.T., Zinyowera, M.C., Ross, R.H. (Eds.), Contribution of Working Group II to the Second Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge, New York, p. 880. Yadav, R.L., Dwivedi, B.S., Pandey, P.S., 2000. Rice–wheat cropping system: assessment of sustainability under green manuring and chemical fertilizer inputs. Field Crops Research 65, 15–30. Ying, Z., Boecky, P., Chen, G.X., Van Cleemput, O., 2000. Influence of Azolla on methane emission from rice fields. Nutrient Cycling in Agroecosystem 58, 321–326. Yu, K., Patrick Jr., W.H., 2004. Redox window with minimum global warming potential contribution from rice soils. Soil Science Society America Journal 68, 2086–2091.
Atmospheric Environment 39 (2005) 6976–6984 www.elsevier.com/locate/atmosenv
Global warming potential of manure amended soils under rice–wheat system in the Indo-Gangetic plains A. Bhatiaa, H. Pathakb,, N. Jaina, P.K. Singha, A.K. Singhc a
Division of Environmental Sciences, Indian Agricultural Research Institute, New Delhi 110 012, India Unit of Simulation and Informatics, Indian Agricultural Research Institute, New Delhi 110 012, India c Water Technology Center, Indian Agricultural Research Institute, New Delhi 110 012, India
b
Received 29 October 2004; received in revised form 12 July 2005; accepted 18 July 2005
Abstract Use of organic amendments such as farmyard manure (FYM), green manure (GM) and crop residues is important to improve soil health and reduce the dependence on synthetic chemical fertilizer. However, these organic amendments also effect the emissions of greenhouse gas (GHG) from soil. Influence of different organic amendments on emissions of GHG from soil and their global warming potential (GWP) was studied in a field experiment in rice–wheat cropping system of Indo-Gangetic plains (IGP). There was 28% increase in CH4 emissions on addition of 25% N through Sesbania GM along with urea compared to urea alone. Substitution of 100% inorganic N by organic sources lead to a 60% increase in CH4 emissions. The carbon equivalent emission from rice–wheat systems varied between 3816 and 4886 kg C equivalent ha1 depending upon fertilizer and organic amendment. GWP of rice–wheat system increased by 28% on full substitution of organic N by chemical N. However, the C efficiency ratios of the GM and crop residue treatments were at par with the recommended inorganic fertilizer treatment. Thus use of organic amendments along with inorganic fertilizer increases the GWP of the rice–wheat system but may improve the soil fertility status without adversely affecting the C efficiency ratio. However, the trade-off between improved yield and soil health versus GHG emissions should be taken into account while promoting the practice of farming with organic residues substitution for mineral fertilizer. r 2005 Elsevier Ltd. All rights reserved. Keywords: Carbon equivalent emission; Carbon dioxide; Methane; Nitrous oxide; Greenhouse gas
1. Introduction The rice–wheat cropping system occupying 24 million hectares of some of the productive areas in the IndoGangetic plains (IGP) of south Asia and China is Corresponding author. Institut fur Meteorology und Klimaforschung, Kreuzeckbahnstr. 19, 82467 Garmisch-Partenkirchen, Germany. Tel.: +49 8821 183141; fax: +49 8821 183296. E-mail address: [email protected] (H. Pathak).
important for the food security of the region (Ladha et al., 2003). Recent analysis of some of the long-term experiments of the region showed a decline/stagnation in the productivity of this cropping system raising concern about its sustainability (Ladha et al., 2003; Yadav et al., 2000). Depletion of soil organic carbon (SOC) and nitrogen, and deterioration of soil physical properties are suggested to be the major causes of such yield decline (Ladha et al., 2003; Sharma et al., 2003). Improvement of SOC status through use of organic amendments such as manures and crop residues is, therefore, urgently
1352-2310/$ - see front matter r 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2005.07.052
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needed for sustaining and increasing the productivity of the rice–wheat system in the IGP. Carbon dioxide (CO2) methane (CH4) and nitrous oxide (N2O) are important greenhouse gases (GHG) contributing 60%, 15% and 5%, respectively, towards the enhanced global warming (Watson et al., 1996). The concentrations of these gases are increasing at 0.42%, 3.0% and 0.22% per year, respectively (Machida et al., 1995; Battle et al., 1996). Agricultural soil is a major contributor of these gases. The recommended fertilizer practice in the IGP is to apply 120 kg N ha1 through inorganic fertilizer (urea) in rice and wheat each. The farmers also apply different kinds of organic manure such as farmyard manure (FYM), green manure (GM), biofertilizer and crop residues for the partial substitution of the inorganic fertilizer. Although, the use of organic amendments in rice–wheat systems of IGP may lead to higher SOC and crop productivity, it may also increase the GHG emission and global warming potential (GWP) of the system. However, the magnitude of the emission will vary depending upon the composition of the manure and indigenous fertility status of soil. The objectives of the study were to: (1) estimate the emission of CO2, CH4, and N2O from organic manure amended soils under rice–wheat cropping systems and (2) evaluate the GWP of rice–wheat cropping system in the IGP.
2. Materials and methods 2.1. Experimental site and soil A field experiment was conducted in rice–wheat system during 2001–02 in a Typic Ustochrept at the experimental farm of the Indian Agricultural Research Institute, New Delhi, India. The site is located in the Indo-Gangetic alluvial tract at 281400 N and 771120 E, at an altitude of 228 m above mean sea level. The climate of the region is subtropical, semi-arid. The area receives an annual rainfall of 750 mm, about 80% of which occurs from June to September. The mean maximum and minimum temperatures from July to October (rice season) are 35 and 18 1C; while from November to March (wheat season) 22.6 and 6.7 1C, respectively. The alluvial soil of experimental site was loam in texture and had an organic carbon, Olsen P, and KMnO4, extractable N contents of 5.9, 0.014, 0.11 g kg1, respectively. The physico-chemical properties of the soil are given in Table 1. 2.2. Treatments and crop management The experiment included six treatments with three replicates in plots of 10 m long and 5 m wide (Table 2). All the organic amendments (FYM, GM and residues) were incorporated into the soil 2 weeks before transplanting of rice and sowing of wheat. Composition of
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Table 1 Some physico-chemical properties of soil (0–0.15 m depth) at the start of the experiment Soil property
Values
Sand (%) Silt (%) Clay (%) EC (dS m1) pH (1:2Hsoil:water) CEC (cmol kg1) Organic C (%) Bulk density (Mg m3) Hydraulic conductivity (cm d1) Ammo. acetate ex. K (kg ha1) Olsen P (kg ha1) KMnO4 extractable N (kg ha1) 1 NH+ 4 -N (kg ha ) 1 NO 3 -N (kg ha ) Moisture content at field capacity (%) Moisture content at permanent wilting point (%)
40 32 28 0.78 8.0 7.3 0.59 1.4 4.8 361 31.8 251 24.9 33.4 20.5 6.5
Table 2 Treatments Treatment Details T1 T2 T3 T4 T5 T6
Unfertilized 100% NPKa 100% NPK (25% N by FYM)b 100% NPK (25% N by GM)c 100% NPK+residue of the previous crop (2 t ha1) 100% N by organic source (50% FYM+25% biofertilizer+25% residue of the previous crop)
a 100% NPK is N, P, and K at 120, 26 and 50 kg ha1, respectively. b 25% of inorganic N was substituted by N in FYM. c 25% of inorganic N was substituted by N in GM.
various amendments has been given in Table 3. Inorganic N was applied through surface broadcast of urea in three splits of 60, 30 and 30 kg N ha1 at 17, 37 and 62 days after transplanting (DAT) of rice; while in wheat it was applied at 11, 32, and 84 days after sowing (DAS). Phosphorus (26.2 kg ha1) and K (50 kg ha1) were incorporated into the soil at the time of transplanting/sowing using single super phosphate (SSP) and muriate of potash (KCl), respectively, in all plots. In rice, blue green algae (BGA) was applied as biofertilizer in the treatment with 100% organic source (T6). Azospirillum brasilense (strain CD) was used as biofertilizer for wheat and was applied as seed coating using a carrier based inoculants. For rice the field was flooded with water and then puddled. Subsequently 2–3 seedlings (called as 1 hill) of rice (cultivar Pusa 44) of 30 days age were transplanted
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Table 3 Composition of different organic amendments (dry weight basis) Organic amendments
C (g kg1)
N (g kg1)
C:N
P (g kg1)
K (g kg1)
FYM GM (Sesbania rostrata) Wheat straw Rice straw
318 410 420 434
9.6 20.7 4.6 5.3
33 20 91 82
2.9 1.9 0.4 1.6
4.8 18.5 10.4 21.2
in the field. The distance between each hill in a row was 15 cm and between two rows was 20 cm. Wheat (cultivar HD 2687, 100 kg seed ha1) was sown in rows 22.5 cm apart. Irrigation water of 572 cm each was applied on surface through check-basin method. Irrigation in rice was given in 3–4 days interval while in wheat 5 irrigations were given. Weeds, pests, and diseases were controlled as required. 2.3. Gas sample collection and analysis Collection of gas samples for CH4 and N2O was carried out by the closed-chamber technique using the chambers of 50 cm 30 cm 100 cm (length width height) (Pathak et al., 2002). Collection of gas samples for CO2 was done using the chambers of 15 cm 15 cm 50 cm (length width height) placed between the rows of the plants. Gas samples were drawn with 50 mL syringe with the help of a hypodermic needle (24 gauge) at 0, 15, and 30 min for CH4 and 0, 30, and 60 min for N2O and CO2. The samples of gases were collected and brought to the laboratory where they were analysed within 2 h. Concentration of CH4 in the gas samples was estimated by Gas Chromatograph fitted with a flame ionization detector (FID) and N2O samples were analysed using electron capture detector (ECD). For CO2, the gas samples were converted to CH4 using a methanizer (Ni catalyst, 320 1C) and then analysed using a FID (Kotsyurbenko et al., 2004). Estimation of total CO2, CH4 and N2O emissions during the crop season was done by successive linear interpolation of average emission on the sampling days assuming that emission followed a linear trend during the periods when no sample was taken (Pathak et al., 2003a).
2.5. Soil sample analysis Soil samples from the 0–15 cm soil layer in three locations in each plot were collected using a core sampler. The entire volume of soil was weighed and mixed thoroughly and a subsample was taken to determine dry weight. The fresh soil was air-dried for 7 days, sieved through a 2 mm screen, mixed, and stored in sealed plastic jars for analyses. Representative subsamples were drawn to determine physico-chemical properties using standard procedures (Page et al., 1982). 2.6. GWP and carbon equivalent emission GWP is an index defined as the cumulative radiative forcing between the present and some chosen later time ‘horizon’ caused by a unit mass of gas emitted now. It is used to compare the effectiveness of each GHG to trap heat in the atmosphere relative to some standard gas, by convention CO2. The GWP for CH4 (based on a 100year time horizon) is 21 and N2O 310 when for CO2 the value is taken as 1. The GWP of different treatments were calculated using the following equation (Watson et al., 1996): GWP ¼ CO2 þ CH4 n21 þ N2 On310:
(1)
The carbon equivalent emissions (CEE) and carbon efficiency ratio (CER) of the treatments were calculated using the following equations: CEE ¼ GWPn12=44;
(2)
CER ¼ grain yield ðin terms of CÞ of the rice2wheat system=CEE:
(3)
2.4. Estimation of yields of rice and wheat 3. Results and discussion Rice and wheat yields were determined from the total plot area by harvesting all the hills excluding the hills bordering the plot. The grains were separated from the straw, dried, and weighed. Grain moisture was determined immediately after weighing and subsamples were dried in an oven at 65 1C for 48 h.
3.1. Methane flux in rice Fluxes of CH4 fluctuated between 0.04 and 1.09 kg ha1 d1 during the rice season and no specific pattern was observed in any of the treatments (Fig. 1).
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Relatively low rates of CH4 emission were due to partially aerobic soil conditions because of intermittent drying and wetting due to porous and highly percolating nature of the soil. On many days there was no standing water in the field and the redox potential (Eh) was above 100 mV as observed in our earlier experiment conducted in the same field (Jain et al., 2000). The anaerobic condition, required for the formation of CH4, thus was not prevailing during the entire rice crop period. The highest flux of 1.09 kg ha1 CH4 was observed in the FYM treatment (T3) on 12 DAT. In the 100% organic treatment (T6) on most days higher CH4 emissions were observed as compared to the other treatments. The
No fertilizer (T1) 100% NPK (T2) 100% NPK (25% N by FYM) (T3) 100% NPK (25% N by GM) (T4) 100% NPK + crop residue (T5) 100% organic source (T6)
1.4
CH4 (kg ha-1 d-1)
1.2 1 0.8 0.6 0.4 0.2 0
1 3 7 12 18 23 30 38 45 50 61 68 70 79 85 93 97 112
Days after transplanting rice Fig. 1. Emission of CH4 from soil with different organic amendments in rice.
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average daily flux in the 100% organic treatment was 0.54 kg ha1 as compared to 0.48 kg ha1 in the NPK+FYM treatment. Total emission of CH4 during the cropping period was lowest (35.1 kg ha1) in the control treatment (T1) and the highest (57.1 kg ha1) with application of 100% N through organic sources (Table 4). Treatment with only urea (T2) had emission similar to the control treatment. Application of FYM, GM and crop residues enhanced emission of CH4 by providing additional C substrate as compared to urea alone treatment (Lu et al., 2000). Emission of CH4 in 100% N through organic sources (T6) treatment at 57.1 kg ha1 was higher than the treatments where 25% N was added by either FYM (T3) or GM (T4). Additional amount of organic matter added through the organic amendments served as a source of electrons (Singh et al., 1998) creating more anaerobic conditions (Mishra et al., 1997) and higher CH4 formation. Higher emission in the 100% N through organics (T6) could also be due to the presence of blue green algae as biofertilizer, which provided mediation of CH4 transport from floodwater of rice soil into the atmosphere (Ying et al., 2000). Lower emissions of CH4 in crop residue treatment (T5) as compared to FYM (T3) and GM (T4) treatments could be due to higher lignin content (14.7%) in crop residue, which decomposed slowly (Berg and Matzner, 1997). The effect of organic amendments on CH4 emission also depended on their C/N ratios (Table 3). Crop residues such as wheat and rice straws with high C/N ratios had lower emission.
Table 4 Seasonal emissions of carbon dioxide, nitrous oxide and methane from organic manure amended soil and total carbon equivalent emission in rice-wheat system Treatment
CH4 emission in rice (kg ha1)
N2O-N N2O-N emission in rice emission in (g ha1) wheat (g ha1)
CO2-C CO2-C emission in rice emission in (kg ha1) wheat (kg ha1)
GWP of rice–wheat systemb (kg CO2 ha1)
C equivalent emissionc (CEE) (kg C ha1)
Unfertilized 100% NPK 100% NPK (25% N by FYM) 100% NPK (25% N by GM) 100% NPK+crop residue 100% organic source
35.1ea 35.9e 49.6b
320d 569ab 503c
359f 736d 860b
1294f 1578e 1975b
1682d 1922c 2458a
11,860e 13,992d 17,718a,b
3234e 3816d 4832a,b
46.0c
579a
922a
1853c
2493a
17,367b
4736b
42.7d
549ab
820c
1642d
2167b
15,287c
4169c
57.1a
537bc
564e
2081a
2385a
17,916a
4886a
a
In a column, values followed by the same letter are not significantly different at Po0:05 by Duncan’s multiple range test. GWP, global warming potential ¼ CO2+(CH4 in rice21)+(N2O in rice+N2O in wheat)310. c Carbon equivalent emission ¼ GWP12/44. b
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This was because of their slow decomposition owing to limited N availability caused by net immobilization (Khalil et al., 2001). There was 28% increase in CH4 emissions on addition of 25% N through Sesbania GM along with urea compared to urea alone (Table 4). Substitution of 100% inorganic N by organic sources lead to a 60% increase in CH4 emissions. Adhya et al. (2000), however, observed a much higher (212%) increase in CH4 emission on substituting 33% of urea N through Sesbania GM in eastern India as the soil was continuously submerged for the entire rice-growing period and also had a higher SOC content.
No fertilizer (T1) 100% NPK (T2) 100% NPK (25% N by FYM) (T3) 100% NPK (25% N by GM) (T4)
50
100% NPK + crop residue (T5) 100% organic source (T6)
NH4-N (kg ha-1 d-1)
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40 30 20 10 0
3.2. Nitrous oxide flux in rice
1
10
1
10
(a)
No fertilizer (T1) 100% NPK (T2) 100% NPK (25% N by FYM) (T3) 100% NPK (25% N by GM) (T4) 100% NPK + crop residue (T5) 100% organic source (T6)
N2O-N (g ha-1 d-1)
25 20 15 10 5 0
1 3 7 12 18 23 30 38 45 50 63 68 70 79 85 93 97 112
(a)
Days after transplanting rice
N2O-N (g ha-1 d-1)
25 20 15 10 5 0 1
(b)
5
9 12 17 23 33 37 46 55 62 68 80 85 88 93 107 120
Days after sowing wheat
Fig. 2. Emission of N2O from soil with different organic amendments in (a) rice and (b) wheat. k and m arrows indicate the days of fertilizer application and the days of irrigation, respectively.
64
85
64
85
25 NO3-N (kg ha-1 d-1)
Flux of N2O-N was large on 1 DAT and decreased later (Fig. 2a). Denitrification of initial indigenous NO 3N (Fig. 3b) was presumably responsible for this initial large flux. As NO 3 -N in soil decreased due to plant uptake and losses through denitrification and leaching, N2O flux declined later. The trend of reduction in N2ON flux continued till the application of urea on 17 DAT when N2O-N flux increased. Similar high peaks of N2ON flux were observed after every dose of N application, which supplied the substrate for nitrification (NH+ 4 -N) (Fig. 3a) and subsequently for denitrification (NO 3 -N). In the soil both the processes might have occurred
18 30 38 50 Days after transplanting rice
20 15 10 5 0
(b)
18
30
38
50
Days after transplanting rice
Fig. 3. Temporal status of NH4-N (a) and NO3-N (b) in soil with different treatments in rice.
simultaneously, because the soil was not fully anaerobic as submergence was not maintained in this highly percolating soil and frequent irrigation carried dissolved O2 in water making the soil partially aerobic (Majumdar et al., 2000). Total emission of N2O-N during rice ranged from 320 g ha1 in the unfertilized treatment (T1) to 579 g ha1 with urea plus GM treatment (T4) (Table 4). There was no statistically significant difference in the N2O-N emissions in GM (T4), crop residue (T5), and urea (T2) treatments while the treatments with FYM (T3 and T6) had lower emissions than these treatments. Presence of N in readily available form in treatments T2, T4 and T5 was responsible for greater N2O-N emission as compared to the FYM treatments. Lower emissions in the FYM treatments were due to slow decomposition of N from FYM compared to GM because of higher C/N ratio of the former (Table 3). Lower emission in the FYM treatment compared to the crop residue treatment was because of addition of 25% more inorganic N in the residue treatment (Table 2). Pathak et al. (2002) observed that use of FYM and urea in combination reduced emission of N2O-N in rice compared to application of urea alone.
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3.3. Nitrous oxide flux in wheat Fluxes of N2O-N in wheat on 1 DAS ranged from 7.2 to 10.5 g ha1 d1, which decreased on day 5 except in the GM treatment (T3) in which the flux of N2O-N increased (Fig. 2b). Application of water in the dry soil for land preparation before sowing of wheat along with operations performed during sowing might have stimulated the activity of the nitrifying microbes resulting in greater fluxes of N2O-N on 1 DAS. Subsequently, when NH+ 4 -N content in soil (Fig. 4a) decreased as a result of nitrification, N2O-N emission declined. A peak in N2ON emission was observed after application of N fertilizer on 11 DAS in all the treatments. After every dose of N fertilizer application N2O-N flux increased due to availability of substrate (NH+ 4 -N) for nitrification. Increase in N2O-N flux was observed after each irrigation due to enhanced nitrification and also denitrification of NO 3 in anaerobic microsites in the soil (Arah and Smith, 1989). The N2O-N emission observed in wheat was primarily a result of nitrification except during short periods after each irrigation event when anoxic soil condition was created resulting in denitrification of NO 3 -N (Bremner and Blackmer, 1978).
No fertilizer (T1) 100% NPK (T2) 100% NPK (25% N by FYM) (T3) 100% NPK (25% N by GM) (T4) 100% NPK + crop residue (T5) 100% organic source (T6)
30
NH4-N (kg ha-1d-1)
25 20 15 10 5 0 1
(a)
9
17
33
55
68
85
107
NO3-N (kg ha-1d-1)
25 20
Total emission of N2O-N during 120 days of wheat cropping ranged from 359 g ha1 in the unfertilized treatment to 922 g ha1 in the GM treatment (Table 3). Compared to rice, the emission of N2O-N in various treatments was more in wheat due to faster decomposition of organic residues in soils under aerobic condition than in anaerobic condition (Neue and Scharpenseel, 1987). Higher emission of N2O-N was observed in GM treatment with lower C/N ratio compared to the FYM treatment. Substitution of 25% of inorganic fertilizer by FYM and GM increased N2O-N emission by 17% and 25%, respectively, compared to urea alone. Addition of rice residue along with 100% NPK fertilizer (T5) also led to an increase in N2O-N emission by 11%. Aulakh et al. (2001) observed an increase in gaseous N losses on incorporation of rice straw residue and GM alongwith inorganic N. Substitution of the entire chemical N by organic sources, however, decreased the emission of N2O-N by 24%. 3.4. Carbon dioxide flux in rice Fluxes of CO2-C on 1 DAT of rice were in the range of 13–18 kg ha1 d1 (Fig. 5a), which then increased. The highest peak was observed in the GM (T4) treatment on 12 DAT followed by 100% organic (T6) and FYM (T3) treatments on 17 DAT. Within a treatment temporal variation in CO2-C flux were observed due to alternate drying and wetting of soil releasing the CO2 stored in the soil pores. Cumulative seasonal emission of CO2-C ranged from 1294 kg ha1 in the unfertilized treatment (T1) to 2081 kg ha1 in the 100% organic (T6) treatment (Table 4). Addition of 100% N through organic sources (T6) increased CO2-C emission by 32% over the 100% inorganic NPK treatment (T2). Substitution of 25% inorganic N by FYM (T3) and GM (T4) led to increased emission of CO2-C by 25% and 17%, respectively. Higher CO2-C fluxes in the GM, FYM and 100% organic treatments were due to higher availability of organic C resulting in increased soil respiration (Scott et al., 2000). Lower C/N ratio in GM and FYM compared to crop residues resulted in higher fluxes of CO2 due to faster C decomposition. 3.5. Carbon dioxide flux in wheat
15 10 5 0 1
(b)
6981
9
17
33
55
68
85
107
Days after sowing wheat
Fig. 4. Temporal status of NH4-N (a) and NO3-N (b) in soil with different treatments in wheat.
Fluxes of CO2-C (15–18 kg ha1 d1) were higher on day 1 after sowing of wheat (Fig. 5b). On application of first dose of fertilizer N on 11 DAS, the fluxes increased due to increased availability of N, which accelerated the mineralization of organic C and soil respiration (Pathak and Rao, 1998). The peaks of CO2C fluxes at 34.0 and 40.4 kg CO2-C d1 were observed on 12 DAS in T3 and T4 treatments, respectively. Subsequently there was a decline in the flux till the next dose
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No fertilizer (T1) 100% NPK (T2) 100% NPK (25% N by FYM) (T3) 100% NPK (25% N by GM) (T4) 100% NPK + crop residue (T5) 100% organic source (T6)
40
CO2-C (kg ha-1d-1)
35 30 25 20 15 10 5 0
1 3 7 12 17 23 30 38 45 50 63 68 70 79 85 93 97 112
CO2-C (kg ha-1d-1)
(a)
Days after transplanting rice 45 40 35 30 25 20 15 10 5 0 1
(b)
5
9 12 17 23 33 37 46 55 62 68 80 85 88 93 107120
Days after sowing wheat
Fig. 5. Emission of CO2 from soil with different organic amendments in (a) rice and (b) wheat.
of N was applied when a small increase in CO2-C emission was observed. Smaller peaks were observed after every irrigation event indicating that soil moisture played a crucial role in the emission of CO2. The increase in soil moisture after irrigation stimulated the microbial activity and also more diffusion of CO2 trapped in soil (Pathak et al., 2003b). The highest average CO2-C flux (21.0 kg ha1 d1) was observed in the GM treated plots (T4), while the lowest flux was observed in the unfertilized plots (13.7 kg ha1 d1). In wheat seasonal emissions varied from 1682 kg CO2C ha1 in the unfertilized plots to 2493 kg CO2-C ha1 in GM treated plots (Table 4). Substitution of 100% inorganic N with 100% organic N led to 21% increase in the emission of CO2-C. Substitution of 25% N through FYM (T3) and GM (T4) increased emission by 27% and 30%, respectively, over the 100% inorganic NPK (T2) treatment. Addition of rice residues along with urea (T5) in wheat increased emissions by 12% over the urea alone treatment (T2). 3.6. GWP and carbon equivalent emission The GWP of various treatments in rice–wheat system varied between 11860 kg CO2 equivalent ha1 in the unfertilized to 17916 kg CO2 ha1 with 100% organic treatment (Table 4). Increase in GWP with the application of organic amendments ranged from 9% with urea
plus crop residue treatment (T5) to 28% with 100% organic treatment (T6) compared to 100% inorganic NPK treatment (T2). There was no significant difference between the FYM and 100% organic treatment in terms of GWP. Research on GWP of rice–wheat system is very limited. Earlier Grace et al. (2003) estimated annual GWP of 3496–7137 kg C ha1 of irrigated rice–wheat system in the IGP depending on crop management practices. However, they used the Inter-Governmental Panel of Climate Change (IPCC) default GHG emission coefficients and included only CH4 and N2O emissions and not CO2 emission in their estimation. In our study for computation of GWP, CO2 emission were only based on the flux measured between rows of plants and emission or consumption CO2 due to plant respiration and photosynthesis, respectively, were not considered. This is because in a conventional crop growing condition, the emission and consumption of CO2 due to plant respiration and photosynthesis, respectively, are balanced, and therefore, plant emission of CO2 during respiration is not taken into account while computing GWP from agriculture. Robertson et al. (2000) and Six et al. (2004) observed that the change in SOC or soil respiration should be measured for accounting of GWP of soils. Six et al. (2004) and Yu and Patrick (2004) computed the GWP of different soils by measuring the changes in SOC storage. The IPCC (2001) also suggest calculating GWP using the same approach. The CEE was smallest (3234 kg C ha1) in the unfertilized treatment (Table 4). The 100% inorganic treatment also had smaller CEE compared to the treatments with organic amendments. Among the organic amended treatments the lowest CEE was observed in the 100% NPK plus crop residue treatment (Table 4).
3.7. Yields of rice and wheat and CER Yields of rice ranged from 3.43 to 6.40 Mg ha1, while that of wheat ranged from 2.54 to 4.62 Mg ha1 (Table 5). Treatments with GM plus urea gave highest yields of rice and wheat probably because of higher nutrient availability as compared to the inorganic fertilizer treatment (Singh et al., 1999). Goyal et al. (1997) observed higher crop yields and N uptake with the addition of Sesbania GM. Application of 100% N through organic sources (T6) reduced rice yield by 19% over application of 100% inorganic fertilizer (T2). In wheat, however, yields were similar in both these treatments. Similarly, substitution of 25% N by FYM decreased rice yield but had no significant effect on wheat yield. Lower yields in the FYM (T3) and 100% organic treatment (T6) as compared to 100% inorganic NPK (T2) treatment was due to lower N availability
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Table 5 Yield of rice and wheat as affected by various nutrient sources Treatment
Rice Yield (Mg ha1)
Wheat Yield (Mg ha1)
Total C fixeda (Mg ha1)
Carbon efficiency ratio
Unfertilized 100% NPK 100% NPK (25% N by FYM) 100% NPK (25% N by GM) 100% NPK+crop residue 100% organic source
3.43e 5.70b 5.09c 6.40a 5.72b 4.59d
2.54c 3.71b 3.46b 4.62a 3.52b 3.60b
2.87 4.52 4.11 5.29 4.53 3.93
0.89 1.19 0.85 1.12 1.09 0.80
a
Carbon contents in rice and wheat are 48% and 47% of total biomass, respectively.
because of slow mineralization of organic N from these sources. The CER, i.e., C fixed in grain by rice and wheat per unit of C emitted, was the largest (1.19) in the 100% inorganic treatment (T2) followed by the GM and crop residue treatments (Table 5). Lowest CER (0.80) was in 100% organic treatment as this had the largest CO2 emissions and the smaller amount of C fixed (crop yield) in rice and wheat.
4. Conclusions Rice–wheat cropping system in the IGP could be a major source of atmospheric CO2, CH4 and N2O because of its large area and high use of agricultural inputs. The carbon equivalent emission from rice–wheat systems in IGP varied between 3816 and 4886 kg CE ha1 depending upon fertilizer and organic amendments. Though addition of organic sources such as GM, FYM and crop residues has potential to improve soil health and increase crop productivity, it also results in increased GHG emissions. The application of GM along with NPK led to an increase in C equivalent emissions and also increased the C fixed significantly. However, the C efficiency ratio was at par with the 100% inorganic fertilizer treatment. Thus use of GM along with inorganic fertilizer increases the GWP of the rice–wheat system but may improve the soil fertility status without adversely affecting the C efficiency ratio.
References Adhya, T.K., Bharti, K., Mohanty, S.R., Ramakrishnan, B., Rao, V.R., Sethunathan, N., Wassmann, R., 2000. Methane emission from rice fields at Cuttak, India. Nutrient Cycling in Agroecosystem 58, 95–106. Arah, J.R.M., Smith, K.A., 1989. Steady state denitrification in aggregated soils: a mathematical model. Journal of Soil Science 40, 139–149.
Aulakh, M.S., Khera, T.S., Doran, J.W., Bronson, K.F., 2001. Denitrification, N2O and CO2 fluxes in rice–wheat cropping system as affected by crop residues, fertilizer N and legume green manure. Biology and Fertility of Soils 34, 375–389. Battle, M., Bender, M., Sowers, T., Tans, P.P., Butler, J.H., Elkins, J.W., Ellis, J.T., Conway, T., Zhang, N., Lang, P., Clarke, A.D., 1996. Atmospheric gas concentrations over the past century measured in air from firn at the south pole. Nature 383, 231–235. Berg, B., Matzner, E., 1997. Effect of N deposition on decomposition of plant litter and soil organic matter in forest systems. Environmental Reviews 5, 1–25. Bremner, J.M., Blackmer, A.M., 1978. Nitrous oxide: emission from soils during nitrification of fertilizer nitrogen. Science 199, 295–297. Goyal, S., Mishra, M.M., Hooda, I.S., Singh, R., 1997. Organic matter–microbial biomass relationships in field experiments under tropical conditions: effects of inorganic fertilization and organic amendments. Soil Biology and Biochemistry 24, 1081–1084. Grace, P.R., Harrington, L., Jain, M.C., Robertson, G.P., 2003. Long term sustainability of tropical and subtropical rice–wheat system: an environmental perspective. In: Ladha, J.K. (Ed.), Improving the Productivity and Sustainability of Rice–wheat Systems: Issues and Impacts. ASA Special Publication 65. CSSA and SSSA, Madison, WI, pp. 27–41. IPCC—Intergovernmental Panel on Climate Change, 2001. Emissions Scenarios, Special Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, UK available at: http://www.ipcc.ch/pub/pub.htm Jain, M.C., Kumar, S., Wassmann, R., Mitra, S., Singh, S.D., Singh, J.P., Singh, R., Yadav, A.K., Gupta, S., 2000. Methane emissions from irrigated rice fields in northern India (New Delhi). Nutrient Cycling in Agroecosystems 58, 75–83. Khalil, M.I., Boeckx, P., Rosenani, A.B., Cleemput, O.V., 2001. Nitrogen transformations and emission of greenhouse gases from three acid soils of humid tropics amended with N sources and moisture regime. II. Nitrous oxide and methane fluxes. Communications in Soil Science and Plant Analysis 32, 2909–2924. Kotsyurbenko, O.R., Chin, K.J., Glagolev, M.V., Stubner, S., Simankova, M.V., Nozhevnikova, A.N., Conrad, R., 2004. Acetoclastic and hydrogenotrophic methane production
ARTICLE IN PRESS 6984
A. Bhatia et al. / Atmospheric Environment 39 (2005) 6976–6984
and methanogenic populations in an acidic West-Siberian peat bog. Environmental Microbiology Online Early. Ladha, J.K., Dawe, D., Pathak, H., Padre, A.T., Yadav, R.L., Bijay-Singh, Yadvinder-Singh, Singh, P., Kundu, A.L., Sakal, R., Ram, N., Regmi, A.P., Gami, S.K., Bhandari, A.L., Amin, K., Yadav, C.R., Bhattarai, E.M., Gupta, R.K., Hobbs, P.R., 2003. How extensive are yield declines in long-term rice–wheat experiments in Asia? Field Crops Research 81, 159–180. Lu, W.F., Chen, W., Duan, B.W., Guo, W.M., Lu, Y., Lantin, R.S., Wassmann, R., Neue, H.U., 2000. Methane emission and mitigation options in irrigated rice fields in southeast China. Nutrient Cycling in Agroecosystems 58, 65–74. Machida, T., Nakazawa, T., Fujii Yaola, S., Watanabe, O., 1995. Increase in the atmospheric nitrous oxide concentration during the last 250 years. Geophysical Research Letters 22, 2921–2924. Majumdar, D., Kumar, S., Pathak, H., Jain, M.C., Kumar, U., 2000. Reducing nitrous oxide emission from rice field with nitrification inhibitors. Agriculture Ecosystem and Environment 81, 163–169. Mishra, S., Rath, A.K., Adhya, T.K., Rao, V.R., Sethunathan, N., 1997. Effect of continuous flooding and alternate water regimes on methane efflux from rice under greenhouse conditions. Biology and Fertility of Soils 24, 399–407. Neue, H.U., Scharpenseel, H.W., 1987. Decomposition pattern of 14C-labeled rice straw in anaerobic and submerged rice soils of the Philippines. Science of the Total Environment 62, 431–434. Page, A.L., Miller, R.H., Keeney, D.R., 1982. Methods of Soil Analysis. Part 2, Chemical and Microbiological Properties. Agronomy No. 9, second ed. ASA-SSSA, Madison, WI, USA, p. 1159. Pathak, H., Rao, D.L.N., 1998. Carbon and nitrogen mineralization from added organic matter in saline and alkali soils. Soil Biology and Biochemistry 30, 695–702. Pathak, H., Bhatia, A., Prasad, S., Jain, M.C., Kumar, S., Singh, S., Kumar, U., 2002. Emission of nitrous oxide from soil in rice-wheat systems of Indo-Gangetic plains of India. Environmental Monitoring and Assessment 77, 163–178. Pathak, H., Prasad, S., Bhatia, A., Singh, S., Kumar, S., Singh, J., Jain, M.C., 2003a. Methane emission from rice-wheat cropping system of India in relation to irrigation, farmyard manure and dicyandiamide application. Agriculture Ecosystem and Environment 97, 309–316. Pathak, H., Rastogi, M., Rai, H.K., Sharma, A., 2003b. Carbon dioxide emission from soil. In: Pathak, H., Kumar, S. (Eds.),
Soil and Greenhouse Effect, Monitoring and Mitigation. CBS Publishers and Distributors, New Delhi, p. 47. Robertson, G.P., Paul, E.A., Harwood, R.R., 2000. Greenhouse gases in intensive agriculture: contributions of individual gases to the radiative forcing of the atmosphere. Science 289, 1922–1925. Scott, A., Ball, B.C., Crichton, I.J., Aitken, M.N., 2000. Nitrous oxide and carbon dioxide emissions from grassland amended with sewage sludge. Soil Use Management 16, 36–41. Sharma, P.K., Ladha, J.K., Bhushan, L., 2003. Soil physical effects of puddling in rice–wheat cropping systems. In: Ladha, J.K., Hill, J.E., Duxbury, J.M., Gupta, R.K., Buresh, R.J. (Eds.), Improving the Productivity and Sustainability of Rice–wheat Systems: Issues and Impacts. ASA Special Publication 65. CSSA and SSSA, Madison, USA, pp. 97–113. Singh, J.S., Raghubanshi, A.S., Reddy, V.S., Singh, S., Kashyap, A.K., 1998. Methane flux from irrigated paddy and dryland rice fields, and from seasonally dry tropical forest and savanna soils of India. Soil Biology and Biochemistry 30, 135–139. Singh, G.R., Parihar, S.S., Chaure, N.K., 1999. Response of organic manures in a rice (Oryza sativa)–chickpea (Cicer arietinum) crop sequence. IRRN 24 (3), 25. Six, J., Ogle, S.M., Breidt, F.J., Conant, R.T., Mosier, A.R., Paustian, K., 2004. The potential to mitigate global warming with no-tillage management is only realized when practised in the long term. Global Change Biology 10, 155–160. Watson, R.T., Zinyowera, M.C., Moss, R. H., Dokken, D.J., 1996. Climate change (1995), impacts, adaptations and mitigation of climate change. Scientific Technical Report Analyses. In: Watson, R.T., Zinyowera, M.C., Ross, R.H. (Eds.), Contribution of Working Group II to the Second Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge, New York, p. 880. Yadav, R.L., Dwivedi, B.S., Pandey, P.S., 2000. Rice–wheat cropping system: assessment of sustainability under green manuring and chemical fertilizer inputs. Field Crops Research 65, 15–30. Ying, Z., Boecky, P., Chen, G.X., Van Cleemput, O., 2000. Influence of Azolla on methane emission from rice fields. Nutrient Cycling in Agroecosystem 58, 321–326. Yu, K., Patrick Jr., W.H., 2004. Redox window with minimum global warming potential contribution from rice soils. Soil Science Society America Journal 68, 2086–2091.