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Silicate fertilization in no-tillage rice farming for mitigation of methane emission and increasing rice productivity
Agriculture, Ecosystems and Environment 132 (2009) 16–22
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Silicate fertilization in no-tillage rice farming for mitigation of methane emission and increasing rice productivity Muhammad Aslam Ali a,*, Chang Hoon Lee b, Yong Bok Lee c, Pil Joo Kim d a
Crop Science, Graduate Training Institute, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh Functional Cereal Crop Research Division, National Institute of Crop Science, RDA, 1085 Naey-dong, Milyang, South Korea c Division of Plant Nutrition, National Institute of Agricultural Science and Technology, Suwon 441-701, South Korea d Institute of Agriculture and Life Sciences, Gyeongsang National University, Jinju 660-701, South Korea b
A R T I C L E I N F O
A B S T R A C T
Article history: Received 20 August 2008 Received in revised form 15 February 2009 Accepted 17 February 2009 Available online 23 April 2009
Agricultural practices mostly influence methane (CH4) emissions from rice field, which must be controlled for maintaining the ecosystem balance. No-tillage farming with chemical amendments having electron acceptors could be an effective mitigation strategy in CH4 emissions from irrigated rice (Oryza sativa L.) field. An experiment was conducted in Korean paddy field under tillage and notillage farming practices with silicate iron slag amendments (1–4 Mg ha1) for suppressing CH4 emissions and maintaining rice productivity. It was found that CH4 emissions from the no-tillage rice field significantly decreased as compared to that of tilled field, irrespective of silicate amendments. The total seasonal CH4 flux from the control tillage and control no-tillage plots were recorded 38.1 and 27.9 g m2, respectively, which were decreased by 20% and 36% with 4 Mg ha1 silicate amendment. Silicate fertilization (4 Mg ha1) with no-tillage system decreased total seasonal CH4 flux by 54% as compared to that of control tillage plot. This is most likely due to the higher concentrations of active iron and free iron oxides in the no-tilled rice field as compared to that of tilled field under silicate fertilization, which acted as electron acceptors and contributed to decrease CH4 emission. In addition, the improved soil porosity and redox potential, rice plant growth parameters such as active tillering rate, root volume and porosity, etc. in combination increased the rhizosphere oxygen concentrations and eventually suppressed CH4 emission during the rice growing season. The leaf photosynthetic rate was significantly increased with 4 Mg ha1 silicate amendment, which ultimately increased grain yield by 18% and 13% in the tilled and no-tilled rice field, respectively. CH4 flux showed a strong positive correlation with the availability of soil organic carbon, while there were negative correlations with soil porosity, soil pH, soil Eh, and the content of active iron and free iron oxides in soil. ß 2009 Elsevier B.V. All rights reserved.
Keywords: Methane flux Silicon Iron oxides No-tillage Photosynthesis Rice
1. Introduction Agriculture represents a significant source of the world’s total anthropogenic greenhouse gas emissions. Among the greenhouse gases, methane is the most important due to its radiative effects as well as global warming (Cicerone and Oremland, 1988; IPCC, 2001). Wetland rice agriculture has been identified as one of the major sources of anthropogenic CH4 emissions to the atmosphere (IPCC, 1995), which accounts for as much as 26% of the global anthropogenic CH4 budget (Neue and Roger, 1993). The intensification of agricultural practices to meet the food demand of the
* Corresponding author. Tel.: +88 91 65082; fax: +88 91 55810. E-mail address: [email protected] (M.A. Ali). 0167-8809/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.agee.2009.02.014
expanding world population has raised the risk of long-term sustainability of agro-ecosystems (Lal, 1997; Liebig et al., 2004). It has already been reported that rice production must increase from a 1990 value of 473 million tons to at least 781 million tons by 2020 (IRRI, 1989); which may increase the associated CH4 emissions by 40–50% (Anastasic et al., 1992) and may accelerate the global warming effects. Agricultural field management practices such as tillage and notillage farming mainly control the rate of soil carbon losses through CO2, CH4, etc. gases and the content of soil carbon. It has been reported that tillage accelerates the decomposition of organic matter by soil microorganisms and stimulates the emission of global warming gases (Doran and Smith, 1987; Balesdent et al., 2000). CH4 production and oxidation in flooded rice soils are regulated by various microorganisms, which are controlled by
M.A. Ali et al. / Agriculture, Ecosystems and Environment 132 (2009) 16–22
physical, chemical and biological factors of the soil environment. Among the factors, the content of soil oxidants (electron acceptors) and reductants (electron donors) play a vital role in controlling CH4 emissions from wetland rice agriculture (Watanabe and Kimura, 1999). Iron reduction is a dominant process within the redox sequence in anaerobic system (Reddy et al., 1980), which may suppress methane emission by stimulating the activity of iron reducing bacteria and suppressing the activity of methanogens for the common electron donors (Lovely and Phillips, 1987; Achtnich et al., 1995; Jackel and Schnell, 2000). It was found that silicate fertilization in rice farming, being potential source of electron acceptors as active iron and free iron oxides, decreased total CH4 flux by 16–20%, while increased rice productivity by 13–18% under conventional tillage system (Ali et al., 2008). Recently, it has been recognized that no-till farming could be an effective mitigation strategy in global warming gas emissions as well as to sustain crop productivity maintaining long-term soil quality (Batjes and Sombroek, 1997; Lal, 1997). In addition, silicate amendments in no-tillage rice paddy soil may significantly control the emission of methane by regulating the activitiy of methanogens and improving the soil physico-chemical properties. However, there are no specific research findings available so far in regards to silicate fertilization in no-tillage rice field and controlling methane emissions from the irrigated rice ecosystem. Therefore, this research experiment was conducted to evaluate the effects of silicate fertilization in no-tillage rice farming for mitigating methane emissions as well as sustaining rice productivity. 2. Materials and methods 2.1. Experimental field preparation and rice cultivation The experiment was carried out in Agronomy field, Gyeongsang National University, Jinju, South Korea, in 2007. The soil in the experimental site was moist, poorly drained, silt loam, andiaquands type. The organic matter content of the soil before experimentation was 39.6 4.8 g kg1 and other chemical properties were: soil pH (1:5 with H2O) 6.2 0.19; available P2O5: 68.9 2.9 mg kg1; available SiO2 82.6 3.15 mg kg1. The experimental field had two side-by-side blocks (tillage and no-tillage), and each plot (100 m2) was laid down in a randomized block design with triple replication. No-tillage plot was controlled with the same fertilization and plantation background as the conventional tillage for the last 2 years. The selected silicate fertilizer was granular form, slag type with pH 9.5 and was composed mainly of CaO (41.8%), SiO2 (33.5%) and Fe2O3 (5.4%). Average active and free iron concentrations were 3078 and 1571 mg Fe kg1, respectively. Silicate fertilizer was applied in the rice paddy field with 0, 1, 2 and 4 Mg ha1 2 days before rice transplanting. Dried rice straw was added into soils at the rate of 5 Mg ha1 1-week prior to flooding in all plot. Chemical fertilizers were applied 1 day before transplanting as basal doze: 55 kg N ha1 (urea), 90 kg P2O5 ha1 (super phosphate) and 40.6 kg K2O ha1 (potassium chloride). Second split of urea fertilizer (22 kg N ha1) was applied at tiller initiation stage (3 weeks after rice transplanting) and the third split of fertilizer (33 kg N ha1, 17.4 kg K2O ha1) was applied at 6 weeks of rice transplanting. Applied fertilizers and rice straw were mixed mechanically within 15 cm depth of the surface soil in conventional tillage plots, but just broadcasted on the surface in no-tillage plots. Rice seedlings (14 days old, cultivar, Dongjinbyeo, Japonica type) were transplanted into field on 2nd June in 2007 at a spacing 30 cm 15 cm and harvested by 10th October in the same year. Water level was maintained at 5 cm depth during the cropping season.
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2.2. CH4 gas sampling and analysis A closed-chamber method (Rolston, 1986; Ali et al., 2008) was used to estimate methane emissions during rice cultivation. The air gas samples from the transparent glass chamber (Length of square shaped chamber base 62 cm, and height 112 cm) were collected by using 50 ml gas-tight syringes at 0, 15 and 30 min after chamber placement over the rice planted plots. Gas samplings were carried out at 3 times (8.00–12.00–16.00) in a day to get the average CH4 emissions during the cropping season. The surface area of each chamber was 62 cm 62 cm, and the chamber was placed permanently on the flooded soil. Eight rice hills were covered by each chamber. There were 4 holes at the bottom of each chamber through which water movement was controlled. CH4 concentrations in the collected air samples were measured by Gas Chromatography (Shimadzu, GC-2010, Japan) packed with Porapak NQ column (Q 80–100 mesh) and a flame ionization detector (FID). The temperatures of column, injector and detector were adjusted at 100, 200, and 200 8C respectively. Helium and H2 gases were used as carrier and burning gases, respectively. 2.3. Estimation of methane emission Methane emission from the paddy field was calculated from the increase in CH4 concentrations per unit surface area of the chamber for a specific time intervals. A closed-chamber equation (Rolston, 1986) was used to estimate methane fluxes from each treatment. F ¼ r V=A Dc=Dt 273=T where F = methane flux (mg CH4 m2 h1), r = gas density (0.714 mg cm3), V = volume of chamber(A h; m3), A = surface area of chamber (length width of base; m2), h = height of the chamber (m), Dc/Dt = rate of increase of methane gas concentration in the chamber (mg m3 h1), T (absolute temperature) = 273 + mean temperature in chamber (8C). Total methane flux for the entire cropping period were computed by the formula (Singh et al., 1999): Total CH4 P flux ¼ ni¼1 ðRi Di Þ, where Ri is the rate of methane flux 2 1 (g m d ) in the ith sampling interval, Di is the number of days in the ith sampling interval, and n the number of sampling intervals. 2.4. Investigation of rice plant growth and yield characteristics Rice plant growth parameters such as plant height, tiller number, leaf area, leaf area index, shoot biomass, root volume and porosity were investigated during the growing period. Yield components such as panicle number per plant, number of grains per panicle, ripened grains, 1000 grain weight and harvest index were determined at the harvesting stage. Leaf area was measured by Leaf area meter (Li-3100, Li-COR, USA), root volume and porosity were measured by water displacement method and Pycnometer method (Jensen et al., 1969), respectively, during rice cultivation. Root oxidase activity was measured by a-Naphthylamine oxidation method (Ota, 1970). 2.5. Investigation of photosynthetic rate Leaf photosynthetic rates, i.e., CO2 assimilation rates at different growth stages such as active tillering to maximum tillering stage (45–57 DAT), panicle initiation to flowering stage (71–77 DAT), anthesis period (87–95) and grain filling to maturation (105–120 DAT) stages were measured by an infra-red gas analyzer (IRGA, LICOR, LI-6400; Portable Photosynthesis System, USA) under ambient environmental conditions. The middle portion of a fully expanded healthy-green 2nd leaf from the top was used for
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M.A. Ali et al. / Agriculture, Ecosystems and Environment 132 (2009) 16–22
Fig. 1. Trends of CH4 emission rates from tillage and no-tillage cultivation practices with silicate fertilizer amendments during rice cultivation (Note: error bars indicate standard deviation among the mean values).
measurement up to the panicle initiation stage and the flag leaf was used for photosynthesis measurement from panicle initiation stage of the crop. Leaves were held in the chamber (1–3 min) until constant values (steady state) of photosynthesis were obtained. The net photosynthesis (Pn) measurements were conducted under the photosynthetically active photon flux density (PPFD) 1500– 1700 mmol m2 s1, which were sufficiently higher than the light saturation point. The average relative humidity (%RH) recorded during the sampling periods were within the range 85–95%; ambient air temperature 28–33 8C, inside chamber air temperature 30–37 8C and soil temperature 29–32 8C.
2.7. Statistical analysis Statistical analyses were conducted using SAS software (SAS Institute, 1990). Rice growth, yield, soil properties and methane emission data were subjected to the analysis of variance and
2.6. Investigation of soil properties Soil redox potential (Eh) and soil pH were measured by Eh meter (PRN-41, DKK-TOA Corporation) and pH meter (Orion 3 star, Thermo electron corporation), respectively, during rice cultivation. At the harvesting stage, soil bulk density was analyzed using cores (volume 100 cm3, inner diameter 5 cm), filled with fresh moisture soils. The collected soil core samples were oven dried at 105 8C for 24 h and then measured the weight of dried core samples. Soil porosity was calculated using the bulk density (BD) and particle density (PD, 2.65 Mg m3) according to the equation: Porosity (%) = (1 BD/PD) 100. At harvesting stage, the chemical properties of the collected soil samples were analyzed for pH (1:5 with H2O), organic matter content (Wakley and Black method; Allison, 1965), exchangeable Ca2+, Mg2+, and K+ (1 M NH4–acetate pH 7.0, AA, Shimazu 660), and available silicate content (1 M Na–acetate pH 4.0, UV spectrometer). The content of soil organic carbon after rice harvesting in the dried soil samples were determined by standard chromic acid wet oxidation method (Jackson, 1973). The available phosphate content was determined using Lancaster method (RDA, 1988). Ferrous and water soluble iron concentrations in fresh soil samples were determined by 2 M Na–acetate extraction method (Modified from Kumada and Asami, 1958) and distilled water method (Loeppert and Inskeep, 1996) respectively. In the dried soil, the total soil iron, active iron and free iron concentrations were determined by modified acid digestion (12 M HCl), acid ammonium oxalate in darkness and citrate dithionite bicarbonate dissolution procedures, respectively (Loeppert and Inskeep, 1996).
Fig. 2. Rice leaf CO2 assimilation rates with silicate amendments cultivated under tillage and no-tillage systems (Note: error bars indicate standard deviation among the mean values).
M.A. Ali et al. / Agriculture, Ecosystems and Environment 132 (2009) 16–22
regression. Fisher’s protected least significant difference (LSD) was calculated at the 0.05 probability level for making treatment mean comparisons. 3. Results Measurement of CH4 fluxes showed significant differences (p < 0.01) in CH4 emission rates among the treatments both in tillage and no-tillage rice cultivation systems (Fig. 1). CH4 emissions from the silicate iron amended treatments significantly (p < 0.01) decreased as compared to that of control treatment. The most important phenomenon observed in this study is that CH4 emission rates from the no-tilled rice field significantly (p < 0.001) decreased as compared to that of tilled rice field. Two distinct CH4 emission peaks were detected during the rice growing period, one at active tillering stage (35–42 DAT) and the other at panicle initiation to flowering stage (76–83 DAT). In tillage system, the highest CH4 peak was observed at 76 DAT, while the CH4 emission peak delayed by 1 week (at 83 DAT) in no-till system (Fig. 1). The CH4 emission rates finally dropped at grain maturation stage in both cultivation systems. Silicate amendments significantly stimulated rice plant growth, photosynthesis (Fig. 2) and yield parameters in both cultivation systems (Table 1), although the responses were more pronounced in tillage system as compared to those of no-tillage system. It was found that the leaf photosynthetic rates were increased with plant phenological growth stages such as maximum tillering stage (57 DAT), panicle initiation to flowering stage (77 DAT) and anthesis period (95 DAT), while decreased at
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ripening to grain maturation stage (116–120 DAT). The maximum photosynthetic rate was recorded at flowering to heading stage in both cultivation systems (Fig. 2). Tiller number, leaf area index and total biomass were significantly (p < 0.01) increased by silicate amendments in both cultivation systems. The yield components such as panicle number, number of grains per panicle, 1000 grain weight, ripened grains and harvest index were also increased significantly (p < 0.01) by silicate amendments (Table 1). The most interesting phenomenon in this study is that rice root growth characteristics such as root biomass, root volume, root porosity, and root oxidase activities significantly increased by silicate fertilization in both cultivation systems (Table 1), which were negatively correlated with total seasonal CH4 flux (Table 3). The total seasonal CH4 flux from the control tillage and control no-tillage plots were 38.1 and 27.9 g m2, which were decreased by 20% and 36%, respectively, with 4 Mg ha1 silicate fertilizer application (Fig. 3). The interaction of silicate fertilizer (4 Mg ha1) and no-tillage system significantly decreased total CH4 flux by 54% and 36% as compared to that of control tillage and control notillage treatments, respectively. On the other hand, rice grain yield was significantly (p < 0.01) increased by silicate amendments in both cultivation systems. Using quadratic equation model (Fig. 3), the maximum increase in grain yield was estimated 7518 kg (18% yield increased over the control tillage system) and 6944 kg ha1 (13% yield increased over the control no-tillage system) with 4 Mg ha1 silicate fertilizer application (Fig. 3). The soil pH, available P2O5 and SiO2, exchangeable cations such as Ca, Mg and K, etc., and the concentrations of active iron, free iron
Table 1 Rice growth and yield characteristics with silicate fertilization in the conventional tillage and no-tillage cultivation systems at ripening stage. Silicate fertilization (t ha1)
Tillage systems
Plant parameters
0
1
2
4
Conventional tillage
Plant height (cm) Tiller number per hill Leaf area indexb Shoot biomass (g hill1) Root biomass (g hill1) Total dried matter (g hill1) Root length (cm) Root volume (cm3 hill1) Root porosity (%) Root oxidase activity (mg N g1dry root h1)a Panicle number per hill Number of grains per panicle Ripened grains (%) 1000 grain weight (g) Grain yield (g m2) Harvest indexc
101.0 15.0 2.0 40.5 8.3 84.7 26.7 42.6 24.5 586 15.0 107 84.7 25.7 678.3 0.48
103.0 16.0 2.1 41.8 8.5 88.3 28.3 45.0 27.1 641 16.0 112 89.1 26.0 822.0 0.49
106.0 16.6 2.2 44.3 8.9 93.6 29.0 49.0 29.8 676 16.3 117 91.6 26.5 911.0 0.49
110.0 17.7 2.3 47.8 9.5 101 31.0 54.5 32.4 739 17.0 121 93.9 26.9 961.2 0.51
12.5 1.33 0.20 1.62 0.43 2.40 3.35 4.86 1.50 83.9 2.92 3.56 2.63 0.25 153.0 0.02
No-Tillage
Plant height (cm) Tiller number per hill Leaf area indexb Shoot biomass (g hill1) Root biomass (g hill1) Total dried matter (g hill1) Root length (cm) Root volume (cm3 hill1) Root porosity (%) Root oxidase activity (mg N g1dry root h1)a Panicle number per hill Number of grains per panicle Ripened grains (%) 1000 grain weight (g) Grain yield (g m2) Harvest indexc
100.0 14.3 1.9 40.2 8.2 84.2 25.3 39.6 22.8 492.0 15.0 102 83.9 24.8 642.2 0.47
102.0 15.6 2.0 41.0 8.3 87.2 27.6 43.0 25.4 585.0 15.6 106 86.9 25.6 784.6 0.48
105.0 16.0 2.2 44.3 8.4 92.2 28.3 45.7 27.5 620.0 16.3 110 88.3 25.9 881.8 0.48
108.0 16.7 2.2 45.1 8.6 94.9 29.0 48.7 30.4 689.0 16.7 115 90.8 26.5 945.5 0.49
10.13 1.21 0.10 2.19 0.17 2.2 2.3 6.31 1.35 64.5 2.66 8.13 2.54 0.46 164.0 0.01
Note: LSD0.05, Least significant difference at 5% level. a N denotes a-Naphthylamine oxidized (Root oxidation power, Ota, 1970). b (LAI) is the ratio of total leaf area to ground area covered by the plant. c Refers to the ratio of grain yield to total biological yield.
LSD0.05
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There were negative correlations between total seasonal CH4 flux and the rice growth (except tiller numbers) and yield parameters (Table 3). On the other side, CH4 flux showed a strong positive correlation with the availability of soil organic carbon, while there were negative correlations with soil porosity, soil pH, soil Eh, and the content of active iron, free iron, and ferrous iron oxides in soil at rice harvesting stage (Table 3). 4. Discussion
Fig. 3. Total seasonal CH4 flux and rice grain yield with silicate fertilizer applications under tillage and no-tillage systems (Note: error bars indicate standard deviation among the mean values).
and ferrous iron oxides in soil significantly increased with silicate amendments in both cultivation systems (Table 2). In addition, notillage system significantly improved the soil physical properties such as soil porosity and the content of soil organic matter (Table 2). Soil redox potential (Eh) was also increased with silicate amendments and no-tillage system. The interaction of no-tillage system and silicate amendments significantly improved the soil physico-chemical properties, which significantly decreased CH4 emissions during the entire rice cultivation period.
The seasonal patterns of CH4 emissions were more or less similar in both cultivation systems, i.e., CH4 flux remained high during the maximum tillering and flowering stages, which decreased at ripening stage. However, CH4 emission rates were significantly higher in all treatments under the tillage system as compared to that of no-tillage system. This is likely due to the increased availability of labile organic carbon and root exudates (Schutz et al., 1989; Wassmann et al., 1993; Inubushi et al., 2003) around the rice rhizosphere under tillage system. The higher root volume and porosity in the rice plant grown in tilled plot as compared to that of no tillage plot might have stimulated the conductivity of CH4 gas from the root rhizosphere to the atmosphere, which was consistent with the findings of Mariko et al. (1991) and Kludze et al. (1993). The sharp fall in CH4 emission rates at grain maturation stage in both cultivation systems may be due to the aging of rice plant, decreased photosynthetic capacity and less conductivity of CH4 gas through the rice plant as supported by Nouchi (1994) and Aulakh et al. (2000). Silicate amendments stimulated the rice growth and yield components (Table 1), most probably due to the increased availability of nutrients such as silicon, phosphate, exchangeable Ca, Mg and K, soluble Fe, etc. to rice plant by increasing soil pH
Table 2 Physical and chemical properties of paddy soil amended with silicate fertilization in conventional tillage and no-tillage cultivation systems at rice harvesting. Cultivation systems
Conventional Tillage
No-Tillage
Soil parameters
Silicate fertilization (t ha1)
LSD0.05
0
1
2
4
Bulk density (g cm3) Soil porosity Soil pH (1:5 with H2O) Soil Eh Organic matter (g kg1) Available P2O5 (mg kg1) Available SiO2 (mg kg1) Ex. Cations (cmol+ kg1) Ca Mg K Active iron (g Fe kg1)a Free iron (g Fe kg1)b Ferrous iron (mg Fe2+ kg1)c
1.25 0.52 6.6 163.3 24.9 69.6 68.0
1.24 0.53 7.08 143.6 26.3 81.1 92.3
1.17 0.55 7.20 135.3 27.7 95.4 117.7
1.14 0.57 7.3 123.6 28.9 115.4 137.3
0.03 0.01 0.13 23.5 2.79 7.78 4.0
3.7 1.2 0.24 8.63 4.51 81.7
5.3 1.3 0.30 9.15 5.0 157.5
6.1 1.4 0.33 9.55 5.30 191.0
6.8 1.6 0.38 9.95 5.90 249.6
0.56 0.11 0.02 0.36 0.30 21.84
Bulk density (g cm3) Soil porosity Soil pH (1:5 with H2O) Soil Eh Organic matter (g kg1) Available P2O5 (mg kg1) Available SiO2 (mg kg1) Ex. Cations (cmol+ kg1) Ca Mg K Active iron (g Fe kg1)a Free iron (g Fe kg1)b Ferrous iron (mg Fe2+ kg1)c
1.21 0.54 6.62 148.6 25.0 61.2 66.8
1.17 0.55 6.85 133.3 27.2 70.2 79.9
1.14 0.57 7.0 121.6 28.6 81.4 98.4
1.10 0.58 7.17 108.6 29.6 98.7 113.5
0.04 0.01 0.11 17.9 2.30 8.21 6.14
3.0 0.80 0.17 8.63 4.53 73.5
3.5 1.2 0.26 9.25 5.1 140.5
4.2 1.3 0.33 9.63 5.41 183.5
5.1 1.5 0.35 10.22 6.15 232.8
0.55 0.57 0.04 0.36 0.30 16.53
Note: LSD0.05, Least significant difference at 5% level. a Acid ammonium oxalate in darkness. b Citrate dithionate extractable (Loeppert and Inskeep, 1996). c 2 M Na–acetate extractble (modified from Kumada and Asami, 1958; Loeppert and Inskeep, 1996).
M.A. Ali et al. / Agriculture, Ecosystems and Environment 132 (2009) 16–22 Table 3 Correlations of CH4 emissions with selected rice plant growth, yield and soil parameters in conventional tillage and no-tillage systems at harvesting stage. Parameters
Correlation coefficient (r) (n = 12) Tillage
No Tillage
Growth and yield components Tiller number Leaf area index Aboveground biomass Total dry matter Root dry weight Root volume Root porosity Root oxidase activity Panicle number Grain yield Harvest index
0.520* 0.780** 0.766** 0.765** 0.653** 0.828*** 0.891*** 0.842*** 0.709** 0.745** 0.480
0.239 0.721** 0.729** 0.787** 0.745** 0.784** 0.890*** 0.889*** 0.610* 0.741** 0.445
Soil properties Organic carbon Bulk density Soil porosity Soil pH Soil Eh Available P2O5 Available SiO2 Active Fe Free Fe Ferrous Fe
0.556* 0.756** 0.763** 0.732** 0.835*** 0.643** 0.635* 0.865*** 0.854*** 0.841***
0.527* 0.743** 0.843*** 0.701** 0.811*** 0.623* 0.715** 0.843*** 0.833*** 0.815***
Note: Asterisks (*, ** and ***) denote significant at 5%, 1% and 0.1% levels, respectively.
around the neutral point. This was supported by Bohn et al. (1979) and Lee et al. (2004). The leaf photosynthetic rates were increased with plant phenological growth stages (Fig. 2). In addition, silicate amendments significantly stimulated the photosynthetic rates through improving canopy architecture, leaf erectness and increasing leaf chlorophyll content, as supported by Fuji et al. (1999) and Saigusa et al. (2003). The maximum photosynthetic rate recorded at flowering to heading stage in both cultivation systems could be due to their strong sink capacity for carbohydrate utilization in terms of grain formation. Silicate amendments stimulated rice root growth characteristics such as root biomass, root volume, root porosity, and root oxidase activities, which were negatively correlated with total seasonal CH4 flux (Table 3). This implies the significance of silicate iron slag which acted as oxidizing agent as well as electron acceptor, thereby, enhanced the oxidation potential in rice root rhizosphere (Ali et al., 2008). Ponnamperuma (1965b) also reported that adequate silicon supply increased oxygen transport from the plants’ top to the roots through enlargement of aerenchyma gas channels, thereby, enhanced root rhizospheric oxidation. This might have accelerated CH4 oxidation in the root rhizosphere, which eventually reduced CH4 emission (Hanson, 1980). The concentration of active iron, free iron and ferrous iron oxides in soil at harvesting stage significantly (p < 0.001) increased with the increasing levels of silicate amendments in both cultivation systems (Table 2). The applied ferric oxide through silicate fertilization acted as an oxidizing agent as well as electron acceptor, probably the ferric oxide reacted with free electrons formed under anaerobic soil conditions and leached as reduced ferrous oxide. Therefore, the methanogens’ activity might have suppressed by the electron accepting effects of iron oxides (Jackel and Schnell, 2000). In our experiment, silicate amendment with 4 Mg ha1 under no-tillage rice farming caused 54% reduction in total CH4 flux as compared to that of control tillage, which is mostly due to the higher content of active iron and free iron oxides in soil, improved
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soil redox potential and porosity in no-tilled rice field at harvesting stage. Hanaki et al. (2002) also reported more than 50% reduction in the cumulative seasonal CH4 flux from the no-tillage rice field in Japan as compared to that of tilled field. Furukawa and Inubushi (2004) also reported 30% reduction in total CH4 flux from paddy soil by the application of 20 Mg ha1 revolving furnace slag (RFS), which acted as potential source of electron acceptors. Total seasonal CH4 flux showed strong negative correlation with the active iron, free iron and ferrous iron concentrations in soil at harvesting stage (Table 3). This implies the released iron materials from the applied silicate fertilizer acted as electron acceptor and ultimately suppressed CH4 emissions. Rice grain yield was increased by 18% over the control tillage system and 13% over the control no-tillage system with 4 Mg ha1 silicate fertilizer application (Fig. 3). It has also reported that the application of silicate slag at 1.5–2.0 Mg ha1 in lowland rice soils of Japan increased rice yield by 5–15% and sustained rice productivity in the range 6–9 Mg ha1 (Takahashi et al., 1990). In this experiment, rice grain yield and harvest index were negatively correlated with seasonal CH4 flux, which was supported by Denier van Der Gon et al. (2002). 5. Conclusion It was found that no-tillage system with 4 Mg ha1 silicate fertilization decreased total seasonal CH4 flux by 53% and 36%, while maximized grain yield by 18% and 13% over the control tillage and control no-tillage systems, respectively. This reduction in CH4 flux is due to the improved soil physico-chemical properties such as soil porosity, soil redox potential, increased concentrations of active iron and free iron oxides in soil being acted as electron acceptors. Conclusively, no-tillage rice farming with silicate amendment was found an effective strategy for significant reduction in CH4 emissions, while increasing rice productivity under irrigated paddy soil conditions. References Achtnich, C., Bak, F., Conrad, R., 1995. Competition for electron donors among nitrate reducers, ferric iron reducers, sulfate reducers and methanogens in anoxic paddy soil. Biol. Fertil. Soils 19, 65–72. Ali, M.A., Lee, C.H., Kim, P.J., 2008. Effect of silicate fertilizer on reducing methane emission during rice cultivation. Biol. Fertil. Soils 44, 597–604. Allison, L.E., 1965. Organic carbon. In: Black, C.A., Evans, D.D., White, J.L., Ensminger, L.E., Clark, F.E. (Eds.), Methods of Soil Analysis, Part 2. American Soc. of Agron., Madison, WI, USA, pp. 1367–1376. Anastasic, C., Dowding, M., Simpson, V.J., 1992. Future CH4 emissions from rice production. J. Geophys. Res. 97, 7521–7525. Aulakh, M.S., Bodenbender, J., Wassmann, R., Rennenberg, H., 2000. Methane transport capacity of rice plants: influence of methane concentration and growth stage analyzed with an automated measuring system. Nutr. Cycl. Agroecosyst. 58, 357–366. Balesdent, J., Chenu, C., Balabane, M., 2000. Relationship of soil organic matter dynamics to physical protection and tillage. Soil Till. Res. 53, 215–230. Batjes, N.H., Sombroek, W.G., 1997. Possibilities for carbon sequestration in tropical and subtropical soils. Global Change Biol. 3, 161–173. Bohn, M., McNeal, G., Connor, G.O., 1979. Soil Chemistry. Chichester Brisane Toronto: A Wiley-Interscience Publication, New York. Cicerone, R.J., Oremland, R.S., 1988. Biogeochemical aspects of atmospheric methane. Global Biogeochem. Cycl. 299–327. Denier van Der Gon, H.A.C., Kropff, M.J., van Breemen, N., Wassmann, R., Lantin, R.S., Aduna, E., Corton, T.M., 2002. Optimizing grain yields reduces CH4 emissions from rice paddy fields. Proc. Natl. Acad. Sci. U.S.A. 99, 12021– 12024. Doran, J.W., Smith, M.S., 1987. Organic matter management and utilisation of soil and fertilizer nutrients. In: Follett, R.F., Stewart, J.W.B., Cole, C.V. (Eds.), Soil Fertility and Organic Matter as Critical Components of Production Systems. American Society of Agronomy, Madison, WI, pp. 53–72. Fuji, H., Hayasaka, T., Yokoyama, K., Ando, H., 1999. Effect of silica application to a nursery bed of rice on rooting ability and early growth of rice plants. Jpn. J. Soil Sci. Plant Nutr. 70, 785–790. Furukawa, Y., Inubushi, K., 2004. Evaluation of slag application to decrease methane emission from paddy soil and fate of iron. Soil Sci. Plant Nutr. 50 (7), 1029– 1036.
22
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Hanaki, M., Toyoaki, I., Saigysa, M., 2002. Effect of no-tillage rice cultivation on methane emission in three paddy field of different soil types with rice straw application. Jpn. Soc. Soil Sci. Plant Nutr. 73, 135–143. Hanson, R.S., 1980. Ecology and diversity of methylotrophic organisms. Adv. Appl. Microbiol. 26, 13–40. Intergovernmental Panel on Climate Change (IPCC), 1995. The Science of Climate Change: Climate Change, impacts, adaptations and mitigation of climate change. In: Houghton, I.T., Meira, F., Callander, L.G., Harris, B.A., Kattenberg, A., Maskell, K. (Eds.), Scientific Technical Analysis. Cambridge University Press, Cambridge, UK. Intergovernmental Panel on Climate Change, 2001. Climate Change 2001. The Scientific basis, contribution of working group I to the third assessment report of the IPCC. In: Houghton, J.T., Ding, Y., Griggs, D.J., Noguer, M., van der Linden, P.J., Xiaosa, D. (Eds.), Cambridge University Press, Cambridge. International Rice Research Institute, 1989. IRRI Toward 2000 and Beyond, IRRI, Manila, Philippines. Inubushi, K., Cheng, W.G., Aonuma, S., Hoque, M.M., Kobayashi, K., Miura, S., Kim, H.Y., Okada, M., 2003. Effects of free air CO2 enrichment on methane emission from a rice paddy field. Global Change Biol. 9, 1458–1464. Jackel, U., Schnell, S., 2000. Suppression of methane emission from rice paddies by ferric iron fertilization. Soil Biol. Biochem. 32 (11–12), 1811–1814. Jackson, M.L., 1973. Soil Chemical Analysis. Prentice Hall, Inc., Englewood Cliffs, NJ. Jensen, C.R., Luxmoore, R.J., Van Gundy, S.D., Stolzy, L.H., 1969. Root air-space measurements by a pycnometer method. Agron. J. 61, 474–475. Kludze, H.K., Delaune, R.D., Patrick Jr., W.H., 1993. Aerenchyma formation and methane and oxygen exchange in rice. Soil Sci. Soc. Am. J. 57, 382–385. Kumada, K., Asami, T., 1958. A new method for determining ferrous iron in paddy soils. Soil Plant Food 3, 187–193. Lal, R., 1997. Residue management, conservation tillage and soil restoration for mitigating greenhouse effect by CO2-enrichment. Soil Till. Res. 43, 10–81. Lee, Y.B., Lee, C.H., Hawng, J.Y., Lee, I.B., Kim, P.J., 2004. Enhancement of phosphate desorption by silicate in soils with salt accumulation. Soil Sci. Plant Nutr. 50, 43–499. Liebig, M.A., Tanaka, D.L., Wienhold, B.J., 2004. Tillage and cropping effects on quality indicators in the northern Great Plains. Soil. Till. Res. 78, 131–141. Loeppert, R.H., Inskeep, W.P., 1996. Iron. In: Sparks, D.L., Page, A.L., Loeppert, R.H., Johnston, C.T., Sumner, M.E., Bigham, J.M. (Eds.), Methods of Soil Analysis, Part 3, Chemical Methods. Soil Science Society of America and American Society of Agronomy, Madison, USA, pp. 639–664.
Lovely, D.R., Phillips, E.P., 1987. Competitive mechanisms for inhibition of sulfate reduction and methane production in the zone of ferric iron reduction in sediments. Appl. Environ. Microbiol. 53, 2636–2641. Mariko, S., Harazano, Y., Owa, N., Nouchi, I., 1991. Methane in flooded soil water and the emission through rice plants to atmosphere. Environ. Exp. Bot. 31, 343–350. Neue, H.U., Roger, P.A., 1993. Rice agriculture: factors affecting methane emissions. In: Khalil, M.A.K. (Ed.), Atmospheric Methane: Sources, Sinks and Role in Global Change. Springer-Verlag, Berlin, pp. 254–298. Nouchi, I., 1994. Mechanisms of methane transport through rice plants. In: Minami, K., Mosier, A., Sass, R.L. (Eds.), CH4 and N2O: Global emissions and controls from rice fields and other agricultural and industrial sources. NIAES Series 2, Tsukuba, Japan, pp. 87–104. Ota, Y., 1970. Diagnostic method for measurement of root activity in rice plant. Japan Agric. Res. Quart. 5, 1–6. Ponnamperuma, F.N., 1965b. Review of the symposium on the mineral nutrition of the rice plant. In: The Mineral Nutrition of Rice Plant, John Hopkins Press, Baltimore, MD, pp. 461–482. RDA, Rural Development Administration, 1988. Method of soil chemical analysis, National Institute of Agricultural Science and Technology, Suwon, Korea. Reddy, K.R., Overcash, M.R., Khaleel, R., Westerman, P.W., 1980. Phosphorus adsorption-desorption characteristics of two soils utilized for disposal of animal wastes. J. Environ. Qual. 9, 86–92. Rolston, D.E., 1986. Gas flux. In: Klute, A. (Ed.), Methods of Soil Analysis, Part 1. 2nd ed. Agron. Monogr. 9. ASA and SSSA, Madison, WI, pp. 1103–1119. Saigusa, M., Heinai, H., Shibuya, K., Yoshida, K., Okazaki, H., 2003. Effect of acidified porous hydrate calcium silicate applied in a nursery bed soil on growth and nutrient uptake of rice seedling. Jpn. J. Soil Sci. Plant Nutr. 74, 333–337. SAS/STAT User’s Guide, vol. 1, 1990. ACECLUS-FREQ, Version 6, 4th edition, SAS Institute, Inc., Cary, NC. Schutz, H., Seiler, W., Conrad, R., 1989. Processes involved in formation and emission of methane in rice paddies. Biogeochemistry 7, 33–53. Singh, S., Singh, J.S., Kashyap, A.K., 1999. Methane flux from irrigated rice fields in relation to crop growth and N-fertilization. Soil Biol. Biochem. 31, 1219–1228. Takahashi, E., Ma, J.F., Miyake, Y., 1990. The possibility of silicon as an essential element for higher plants. Comments Agril. Food Chem. 2, 99–122. Wassmann, R., Papen, H., Rennenberg, H., 1993. Methane emission from rice paddies and possible mitigation strategies. Chemosphere 26, 201–217. Watanabe, A., Kimura, M., 1999. Influence of chemical properties of soils on methane emissions from rice paddies. Commun. Soil Sci. Plant Anal. 30, 2449–2463.
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Agriculture, Ecosystems and Environment journal homepage: www.elsevier.com/locate/agee
Silicate fertilization in no-tillage rice farming for mitigation of methane emission and increasing rice productivity Muhammad Aslam Ali a,*, Chang Hoon Lee b, Yong Bok Lee c, Pil Joo Kim d a
Crop Science, Graduate Training Institute, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh Functional Cereal Crop Research Division, National Institute of Crop Science, RDA, 1085 Naey-dong, Milyang, South Korea c Division of Plant Nutrition, National Institute of Agricultural Science and Technology, Suwon 441-701, South Korea d Institute of Agriculture and Life Sciences, Gyeongsang National University, Jinju 660-701, South Korea b
A R T I C L E I N F O
A B S T R A C T
Article history: Received 20 August 2008 Received in revised form 15 February 2009 Accepted 17 February 2009 Available online 23 April 2009
Agricultural practices mostly influence methane (CH4) emissions from rice field, which must be controlled for maintaining the ecosystem balance. No-tillage farming with chemical amendments having electron acceptors could be an effective mitigation strategy in CH4 emissions from irrigated rice (Oryza sativa L.) field. An experiment was conducted in Korean paddy field under tillage and notillage farming practices with silicate iron slag amendments (1–4 Mg ha1) for suppressing CH4 emissions and maintaining rice productivity. It was found that CH4 emissions from the no-tillage rice field significantly decreased as compared to that of tilled field, irrespective of silicate amendments. The total seasonal CH4 flux from the control tillage and control no-tillage plots were recorded 38.1 and 27.9 g m2, respectively, which were decreased by 20% and 36% with 4 Mg ha1 silicate amendment. Silicate fertilization (4 Mg ha1) with no-tillage system decreased total seasonal CH4 flux by 54% as compared to that of control tillage plot. This is most likely due to the higher concentrations of active iron and free iron oxides in the no-tilled rice field as compared to that of tilled field under silicate fertilization, which acted as electron acceptors and contributed to decrease CH4 emission. In addition, the improved soil porosity and redox potential, rice plant growth parameters such as active tillering rate, root volume and porosity, etc. in combination increased the rhizosphere oxygen concentrations and eventually suppressed CH4 emission during the rice growing season. The leaf photosynthetic rate was significantly increased with 4 Mg ha1 silicate amendment, which ultimately increased grain yield by 18% and 13% in the tilled and no-tilled rice field, respectively. CH4 flux showed a strong positive correlation with the availability of soil organic carbon, while there were negative correlations with soil porosity, soil pH, soil Eh, and the content of active iron and free iron oxides in soil. ß 2009 Elsevier B.V. All rights reserved.
Keywords: Methane flux Silicon Iron oxides No-tillage Photosynthesis Rice
1. Introduction Agriculture represents a significant source of the world’s total anthropogenic greenhouse gas emissions. Among the greenhouse gases, methane is the most important due to its radiative effects as well as global warming (Cicerone and Oremland, 1988; IPCC, 2001). Wetland rice agriculture has been identified as one of the major sources of anthropogenic CH4 emissions to the atmosphere (IPCC, 1995), which accounts for as much as 26% of the global anthropogenic CH4 budget (Neue and Roger, 1993). The intensification of agricultural practices to meet the food demand of the
* Corresponding author. Tel.: +88 91 65082; fax: +88 91 55810. E-mail address: [email protected] (M.A. Ali). 0167-8809/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.agee.2009.02.014
expanding world population has raised the risk of long-term sustainability of agro-ecosystems (Lal, 1997; Liebig et al., 2004). It has already been reported that rice production must increase from a 1990 value of 473 million tons to at least 781 million tons by 2020 (IRRI, 1989); which may increase the associated CH4 emissions by 40–50% (Anastasic et al., 1992) and may accelerate the global warming effects. Agricultural field management practices such as tillage and notillage farming mainly control the rate of soil carbon losses through CO2, CH4, etc. gases and the content of soil carbon. It has been reported that tillage accelerates the decomposition of organic matter by soil microorganisms and stimulates the emission of global warming gases (Doran and Smith, 1987; Balesdent et al., 2000). CH4 production and oxidation in flooded rice soils are regulated by various microorganisms, which are controlled by
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physical, chemical and biological factors of the soil environment. Among the factors, the content of soil oxidants (electron acceptors) and reductants (electron donors) play a vital role in controlling CH4 emissions from wetland rice agriculture (Watanabe and Kimura, 1999). Iron reduction is a dominant process within the redox sequence in anaerobic system (Reddy et al., 1980), which may suppress methane emission by stimulating the activity of iron reducing bacteria and suppressing the activity of methanogens for the common electron donors (Lovely and Phillips, 1987; Achtnich et al., 1995; Jackel and Schnell, 2000). It was found that silicate fertilization in rice farming, being potential source of electron acceptors as active iron and free iron oxides, decreased total CH4 flux by 16–20%, while increased rice productivity by 13–18% under conventional tillage system (Ali et al., 2008). Recently, it has been recognized that no-till farming could be an effective mitigation strategy in global warming gas emissions as well as to sustain crop productivity maintaining long-term soil quality (Batjes and Sombroek, 1997; Lal, 1997). In addition, silicate amendments in no-tillage rice paddy soil may significantly control the emission of methane by regulating the activitiy of methanogens and improving the soil physico-chemical properties. However, there are no specific research findings available so far in regards to silicate fertilization in no-tillage rice field and controlling methane emissions from the irrigated rice ecosystem. Therefore, this research experiment was conducted to evaluate the effects of silicate fertilization in no-tillage rice farming for mitigating methane emissions as well as sustaining rice productivity. 2. Materials and methods 2.1. Experimental field preparation and rice cultivation The experiment was carried out in Agronomy field, Gyeongsang National University, Jinju, South Korea, in 2007. The soil in the experimental site was moist, poorly drained, silt loam, andiaquands type. The organic matter content of the soil before experimentation was 39.6 4.8 g kg1 and other chemical properties were: soil pH (1:5 with H2O) 6.2 0.19; available P2O5: 68.9 2.9 mg kg1; available SiO2 82.6 3.15 mg kg1. The experimental field had two side-by-side blocks (tillage and no-tillage), and each plot (100 m2) was laid down in a randomized block design with triple replication. No-tillage plot was controlled with the same fertilization and plantation background as the conventional tillage for the last 2 years. The selected silicate fertilizer was granular form, slag type with pH 9.5 and was composed mainly of CaO (41.8%), SiO2 (33.5%) and Fe2O3 (5.4%). Average active and free iron concentrations were 3078 and 1571 mg Fe kg1, respectively. Silicate fertilizer was applied in the rice paddy field with 0, 1, 2 and 4 Mg ha1 2 days before rice transplanting. Dried rice straw was added into soils at the rate of 5 Mg ha1 1-week prior to flooding in all plot. Chemical fertilizers were applied 1 day before transplanting as basal doze: 55 kg N ha1 (urea), 90 kg P2O5 ha1 (super phosphate) and 40.6 kg K2O ha1 (potassium chloride). Second split of urea fertilizer (22 kg N ha1) was applied at tiller initiation stage (3 weeks after rice transplanting) and the third split of fertilizer (33 kg N ha1, 17.4 kg K2O ha1) was applied at 6 weeks of rice transplanting. Applied fertilizers and rice straw were mixed mechanically within 15 cm depth of the surface soil in conventional tillage plots, but just broadcasted on the surface in no-tillage plots. Rice seedlings (14 days old, cultivar, Dongjinbyeo, Japonica type) were transplanted into field on 2nd June in 2007 at a spacing 30 cm 15 cm and harvested by 10th October in the same year. Water level was maintained at 5 cm depth during the cropping season.
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2.2. CH4 gas sampling and analysis A closed-chamber method (Rolston, 1986; Ali et al., 2008) was used to estimate methane emissions during rice cultivation. The air gas samples from the transparent glass chamber (Length of square shaped chamber base 62 cm, and height 112 cm) were collected by using 50 ml gas-tight syringes at 0, 15 and 30 min after chamber placement over the rice planted plots. Gas samplings were carried out at 3 times (8.00–12.00–16.00) in a day to get the average CH4 emissions during the cropping season. The surface area of each chamber was 62 cm 62 cm, and the chamber was placed permanently on the flooded soil. Eight rice hills were covered by each chamber. There were 4 holes at the bottom of each chamber through which water movement was controlled. CH4 concentrations in the collected air samples were measured by Gas Chromatography (Shimadzu, GC-2010, Japan) packed with Porapak NQ column (Q 80–100 mesh) and a flame ionization detector (FID). The temperatures of column, injector and detector were adjusted at 100, 200, and 200 8C respectively. Helium and H2 gases were used as carrier and burning gases, respectively. 2.3. Estimation of methane emission Methane emission from the paddy field was calculated from the increase in CH4 concentrations per unit surface area of the chamber for a specific time intervals. A closed-chamber equation (Rolston, 1986) was used to estimate methane fluxes from each treatment. F ¼ r V=A Dc=Dt 273=T where F = methane flux (mg CH4 m2 h1), r = gas density (0.714 mg cm3), V = volume of chamber(A h; m3), A = surface area of chamber (length width of base; m2), h = height of the chamber (m), Dc/Dt = rate of increase of methane gas concentration in the chamber (mg m3 h1), T (absolute temperature) = 273 + mean temperature in chamber (8C). Total methane flux for the entire cropping period were computed by the formula (Singh et al., 1999): Total CH4 P flux ¼ ni¼1 ðRi Di Þ, where Ri is the rate of methane flux 2 1 (g m d ) in the ith sampling interval, Di is the number of days in the ith sampling interval, and n the number of sampling intervals. 2.4. Investigation of rice plant growth and yield characteristics Rice plant growth parameters such as plant height, tiller number, leaf area, leaf area index, shoot biomass, root volume and porosity were investigated during the growing period. Yield components such as panicle number per plant, number of grains per panicle, ripened grains, 1000 grain weight and harvest index were determined at the harvesting stage. Leaf area was measured by Leaf area meter (Li-3100, Li-COR, USA), root volume and porosity were measured by water displacement method and Pycnometer method (Jensen et al., 1969), respectively, during rice cultivation. Root oxidase activity was measured by a-Naphthylamine oxidation method (Ota, 1970). 2.5. Investigation of photosynthetic rate Leaf photosynthetic rates, i.e., CO2 assimilation rates at different growth stages such as active tillering to maximum tillering stage (45–57 DAT), panicle initiation to flowering stage (71–77 DAT), anthesis period (87–95) and grain filling to maturation (105–120 DAT) stages were measured by an infra-red gas analyzer (IRGA, LICOR, LI-6400; Portable Photosynthesis System, USA) under ambient environmental conditions. The middle portion of a fully expanded healthy-green 2nd leaf from the top was used for
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M.A. Ali et al. / Agriculture, Ecosystems and Environment 132 (2009) 16–22
Fig. 1. Trends of CH4 emission rates from tillage and no-tillage cultivation practices with silicate fertilizer amendments during rice cultivation (Note: error bars indicate standard deviation among the mean values).
measurement up to the panicle initiation stage and the flag leaf was used for photosynthesis measurement from panicle initiation stage of the crop. Leaves were held in the chamber (1–3 min) until constant values (steady state) of photosynthesis were obtained. The net photosynthesis (Pn) measurements were conducted under the photosynthetically active photon flux density (PPFD) 1500– 1700 mmol m2 s1, which were sufficiently higher than the light saturation point. The average relative humidity (%RH) recorded during the sampling periods were within the range 85–95%; ambient air temperature 28–33 8C, inside chamber air temperature 30–37 8C and soil temperature 29–32 8C.
2.7. Statistical analysis Statistical analyses were conducted using SAS software (SAS Institute, 1990). Rice growth, yield, soil properties and methane emission data were subjected to the analysis of variance and
2.6. Investigation of soil properties Soil redox potential (Eh) and soil pH were measured by Eh meter (PRN-41, DKK-TOA Corporation) and pH meter (Orion 3 star, Thermo electron corporation), respectively, during rice cultivation. At the harvesting stage, soil bulk density was analyzed using cores (volume 100 cm3, inner diameter 5 cm), filled with fresh moisture soils. The collected soil core samples were oven dried at 105 8C for 24 h and then measured the weight of dried core samples. Soil porosity was calculated using the bulk density (BD) and particle density (PD, 2.65 Mg m3) according to the equation: Porosity (%) = (1 BD/PD) 100. At harvesting stage, the chemical properties of the collected soil samples were analyzed for pH (1:5 with H2O), organic matter content (Wakley and Black method; Allison, 1965), exchangeable Ca2+, Mg2+, and K+ (1 M NH4–acetate pH 7.0, AA, Shimazu 660), and available silicate content (1 M Na–acetate pH 4.0, UV spectrometer). The content of soil organic carbon after rice harvesting in the dried soil samples were determined by standard chromic acid wet oxidation method (Jackson, 1973). The available phosphate content was determined using Lancaster method (RDA, 1988). Ferrous and water soluble iron concentrations in fresh soil samples were determined by 2 M Na–acetate extraction method (Modified from Kumada and Asami, 1958) and distilled water method (Loeppert and Inskeep, 1996) respectively. In the dried soil, the total soil iron, active iron and free iron concentrations were determined by modified acid digestion (12 M HCl), acid ammonium oxalate in darkness and citrate dithionite bicarbonate dissolution procedures, respectively (Loeppert and Inskeep, 1996).
Fig. 2. Rice leaf CO2 assimilation rates with silicate amendments cultivated under tillage and no-tillage systems (Note: error bars indicate standard deviation among the mean values).
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regression. Fisher’s protected least significant difference (LSD) was calculated at the 0.05 probability level for making treatment mean comparisons. 3. Results Measurement of CH4 fluxes showed significant differences (p < 0.01) in CH4 emission rates among the treatments both in tillage and no-tillage rice cultivation systems (Fig. 1). CH4 emissions from the silicate iron amended treatments significantly (p < 0.01) decreased as compared to that of control treatment. The most important phenomenon observed in this study is that CH4 emission rates from the no-tilled rice field significantly (p < 0.001) decreased as compared to that of tilled rice field. Two distinct CH4 emission peaks were detected during the rice growing period, one at active tillering stage (35–42 DAT) and the other at panicle initiation to flowering stage (76–83 DAT). In tillage system, the highest CH4 peak was observed at 76 DAT, while the CH4 emission peak delayed by 1 week (at 83 DAT) in no-till system (Fig. 1). The CH4 emission rates finally dropped at grain maturation stage in both cultivation systems. Silicate amendments significantly stimulated rice plant growth, photosynthesis (Fig. 2) and yield parameters in both cultivation systems (Table 1), although the responses were more pronounced in tillage system as compared to those of no-tillage system. It was found that the leaf photosynthetic rates were increased with plant phenological growth stages such as maximum tillering stage (57 DAT), panicle initiation to flowering stage (77 DAT) and anthesis period (95 DAT), while decreased at
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ripening to grain maturation stage (116–120 DAT). The maximum photosynthetic rate was recorded at flowering to heading stage in both cultivation systems (Fig. 2). Tiller number, leaf area index and total biomass were significantly (p < 0.01) increased by silicate amendments in both cultivation systems. The yield components such as panicle number, number of grains per panicle, 1000 grain weight, ripened grains and harvest index were also increased significantly (p < 0.01) by silicate amendments (Table 1). The most interesting phenomenon in this study is that rice root growth characteristics such as root biomass, root volume, root porosity, and root oxidase activities significantly increased by silicate fertilization in both cultivation systems (Table 1), which were negatively correlated with total seasonal CH4 flux (Table 3). The total seasonal CH4 flux from the control tillage and control no-tillage plots were 38.1 and 27.9 g m2, which were decreased by 20% and 36%, respectively, with 4 Mg ha1 silicate fertilizer application (Fig. 3). The interaction of silicate fertilizer (4 Mg ha1) and no-tillage system significantly decreased total CH4 flux by 54% and 36% as compared to that of control tillage and control notillage treatments, respectively. On the other hand, rice grain yield was significantly (p < 0.01) increased by silicate amendments in both cultivation systems. Using quadratic equation model (Fig. 3), the maximum increase in grain yield was estimated 7518 kg (18% yield increased over the control tillage system) and 6944 kg ha1 (13% yield increased over the control no-tillage system) with 4 Mg ha1 silicate fertilizer application (Fig. 3). The soil pH, available P2O5 and SiO2, exchangeable cations such as Ca, Mg and K, etc., and the concentrations of active iron, free iron
Table 1 Rice growth and yield characteristics with silicate fertilization in the conventional tillage and no-tillage cultivation systems at ripening stage. Silicate fertilization (t ha1)
Tillage systems
Plant parameters
0
1
2
4
Conventional tillage
Plant height (cm) Tiller number per hill Leaf area indexb Shoot biomass (g hill1) Root biomass (g hill1) Total dried matter (g hill1) Root length (cm) Root volume (cm3 hill1) Root porosity (%) Root oxidase activity (mg N g1dry root h1)a Panicle number per hill Number of grains per panicle Ripened grains (%) 1000 grain weight (g) Grain yield (g m2) Harvest indexc
101.0 15.0 2.0 40.5 8.3 84.7 26.7 42.6 24.5 586 15.0 107 84.7 25.7 678.3 0.48
103.0 16.0 2.1 41.8 8.5 88.3 28.3 45.0 27.1 641 16.0 112 89.1 26.0 822.0 0.49
106.0 16.6 2.2 44.3 8.9 93.6 29.0 49.0 29.8 676 16.3 117 91.6 26.5 911.0 0.49
110.0 17.7 2.3 47.8 9.5 101 31.0 54.5 32.4 739 17.0 121 93.9 26.9 961.2 0.51
12.5 1.33 0.20 1.62 0.43 2.40 3.35 4.86 1.50 83.9 2.92 3.56 2.63 0.25 153.0 0.02
No-Tillage
Plant height (cm) Tiller number per hill Leaf area indexb Shoot biomass (g hill1) Root biomass (g hill1) Total dried matter (g hill1) Root length (cm) Root volume (cm3 hill1) Root porosity (%) Root oxidase activity (mg N g1dry root h1)a Panicle number per hill Number of grains per panicle Ripened grains (%) 1000 grain weight (g) Grain yield (g m2) Harvest indexc
100.0 14.3 1.9 40.2 8.2 84.2 25.3 39.6 22.8 492.0 15.0 102 83.9 24.8 642.2 0.47
102.0 15.6 2.0 41.0 8.3 87.2 27.6 43.0 25.4 585.0 15.6 106 86.9 25.6 784.6 0.48
105.0 16.0 2.2 44.3 8.4 92.2 28.3 45.7 27.5 620.0 16.3 110 88.3 25.9 881.8 0.48
108.0 16.7 2.2 45.1 8.6 94.9 29.0 48.7 30.4 689.0 16.7 115 90.8 26.5 945.5 0.49
10.13 1.21 0.10 2.19 0.17 2.2 2.3 6.31 1.35 64.5 2.66 8.13 2.54 0.46 164.0 0.01
Note: LSD0.05, Least significant difference at 5% level. a N denotes a-Naphthylamine oxidized (Root oxidation power, Ota, 1970). b (LAI) is the ratio of total leaf area to ground area covered by the plant. c Refers to the ratio of grain yield to total biological yield.
LSD0.05
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M.A. Ali et al. / Agriculture, Ecosystems and Environment 132 (2009) 16–22
There were negative correlations between total seasonal CH4 flux and the rice growth (except tiller numbers) and yield parameters (Table 3). On the other side, CH4 flux showed a strong positive correlation with the availability of soil organic carbon, while there were negative correlations with soil porosity, soil pH, soil Eh, and the content of active iron, free iron, and ferrous iron oxides in soil at rice harvesting stage (Table 3). 4. Discussion
Fig. 3. Total seasonal CH4 flux and rice grain yield with silicate fertilizer applications under tillage and no-tillage systems (Note: error bars indicate standard deviation among the mean values).
and ferrous iron oxides in soil significantly increased with silicate amendments in both cultivation systems (Table 2). In addition, notillage system significantly improved the soil physical properties such as soil porosity and the content of soil organic matter (Table 2). Soil redox potential (Eh) was also increased with silicate amendments and no-tillage system. The interaction of no-tillage system and silicate amendments significantly improved the soil physico-chemical properties, which significantly decreased CH4 emissions during the entire rice cultivation period.
The seasonal patterns of CH4 emissions were more or less similar in both cultivation systems, i.e., CH4 flux remained high during the maximum tillering and flowering stages, which decreased at ripening stage. However, CH4 emission rates were significantly higher in all treatments under the tillage system as compared to that of no-tillage system. This is likely due to the increased availability of labile organic carbon and root exudates (Schutz et al., 1989; Wassmann et al., 1993; Inubushi et al., 2003) around the rice rhizosphere under tillage system. The higher root volume and porosity in the rice plant grown in tilled plot as compared to that of no tillage plot might have stimulated the conductivity of CH4 gas from the root rhizosphere to the atmosphere, which was consistent with the findings of Mariko et al. (1991) and Kludze et al. (1993). The sharp fall in CH4 emission rates at grain maturation stage in both cultivation systems may be due to the aging of rice plant, decreased photosynthetic capacity and less conductivity of CH4 gas through the rice plant as supported by Nouchi (1994) and Aulakh et al. (2000). Silicate amendments stimulated the rice growth and yield components (Table 1), most probably due to the increased availability of nutrients such as silicon, phosphate, exchangeable Ca, Mg and K, soluble Fe, etc. to rice plant by increasing soil pH
Table 2 Physical and chemical properties of paddy soil amended with silicate fertilization in conventional tillage and no-tillage cultivation systems at rice harvesting. Cultivation systems
Conventional Tillage
No-Tillage
Soil parameters
Silicate fertilization (t ha1)
LSD0.05
0
1
2
4
Bulk density (g cm3) Soil porosity Soil pH (1:5 with H2O) Soil Eh Organic matter (g kg1) Available P2O5 (mg kg1) Available SiO2 (mg kg1) Ex. Cations (cmol+ kg1) Ca Mg K Active iron (g Fe kg1)a Free iron (g Fe kg1)b Ferrous iron (mg Fe2+ kg1)c
1.25 0.52 6.6 163.3 24.9 69.6 68.0
1.24 0.53 7.08 143.6 26.3 81.1 92.3
1.17 0.55 7.20 135.3 27.7 95.4 117.7
1.14 0.57 7.3 123.6 28.9 115.4 137.3
0.03 0.01 0.13 23.5 2.79 7.78 4.0
3.7 1.2 0.24 8.63 4.51 81.7
5.3 1.3 0.30 9.15 5.0 157.5
6.1 1.4 0.33 9.55 5.30 191.0
6.8 1.6 0.38 9.95 5.90 249.6
0.56 0.11 0.02 0.36 0.30 21.84
Bulk density (g cm3) Soil porosity Soil pH (1:5 with H2O) Soil Eh Organic matter (g kg1) Available P2O5 (mg kg1) Available SiO2 (mg kg1) Ex. Cations (cmol+ kg1) Ca Mg K Active iron (g Fe kg1)a Free iron (g Fe kg1)b Ferrous iron (mg Fe2+ kg1)c
1.21 0.54 6.62 148.6 25.0 61.2 66.8
1.17 0.55 6.85 133.3 27.2 70.2 79.9
1.14 0.57 7.0 121.6 28.6 81.4 98.4
1.10 0.58 7.17 108.6 29.6 98.7 113.5
0.04 0.01 0.11 17.9 2.30 8.21 6.14
3.0 0.80 0.17 8.63 4.53 73.5
3.5 1.2 0.26 9.25 5.1 140.5
4.2 1.3 0.33 9.63 5.41 183.5
5.1 1.5 0.35 10.22 6.15 232.8
0.55 0.57 0.04 0.36 0.30 16.53
Note: LSD0.05, Least significant difference at 5% level. a Acid ammonium oxalate in darkness. b Citrate dithionate extractable (Loeppert and Inskeep, 1996). c 2 M Na–acetate extractble (modified from Kumada and Asami, 1958; Loeppert and Inskeep, 1996).
M.A. Ali et al. / Agriculture, Ecosystems and Environment 132 (2009) 16–22 Table 3 Correlations of CH4 emissions with selected rice plant growth, yield and soil parameters in conventional tillage and no-tillage systems at harvesting stage. Parameters
Correlation coefficient (r) (n = 12) Tillage
No Tillage
Growth and yield components Tiller number Leaf area index Aboveground biomass Total dry matter Root dry weight Root volume Root porosity Root oxidase activity Panicle number Grain yield Harvest index
0.520* 0.780** 0.766** 0.765** 0.653** 0.828*** 0.891*** 0.842*** 0.709** 0.745** 0.480
0.239 0.721** 0.729** 0.787** 0.745** 0.784** 0.890*** 0.889*** 0.610* 0.741** 0.445
Soil properties Organic carbon Bulk density Soil porosity Soil pH Soil Eh Available P2O5 Available SiO2 Active Fe Free Fe Ferrous Fe
0.556* 0.756** 0.763** 0.732** 0.835*** 0.643** 0.635* 0.865*** 0.854*** 0.841***
0.527* 0.743** 0.843*** 0.701** 0.811*** 0.623* 0.715** 0.843*** 0.833*** 0.815***
Note: Asterisks (*, ** and ***) denote significant at 5%, 1% and 0.1% levels, respectively.
around the neutral point. This was supported by Bohn et al. (1979) and Lee et al. (2004). The leaf photosynthetic rates were increased with plant phenological growth stages (Fig. 2). In addition, silicate amendments significantly stimulated the photosynthetic rates through improving canopy architecture, leaf erectness and increasing leaf chlorophyll content, as supported by Fuji et al. (1999) and Saigusa et al. (2003). The maximum photosynthetic rate recorded at flowering to heading stage in both cultivation systems could be due to their strong sink capacity for carbohydrate utilization in terms of grain formation. Silicate amendments stimulated rice root growth characteristics such as root biomass, root volume, root porosity, and root oxidase activities, which were negatively correlated with total seasonal CH4 flux (Table 3). This implies the significance of silicate iron slag which acted as oxidizing agent as well as electron acceptor, thereby, enhanced the oxidation potential in rice root rhizosphere (Ali et al., 2008). Ponnamperuma (1965b) also reported that adequate silicon supply increased oxygen transport from the plants’ top to the roots through enlargement of aerenchyma gas channels, thereby, enhanced root rhizospheric oxidation. This might have accelerated CH4 oxidation in the root rhizosphere, which eventually reduced CH4 emission (Hanson, 1980). The concentration of active iron, free iron and ferrous iron oxides in soil at harvesting stage significantly (p < 0.001) increased with the increasing levels of silicate amendments in both cultivation systems (Table 2). The applied ferric oxide through silicate fertilization acted as an oxidizing agent as well as electron acceptor, probably the ferric oxide reacted with free electrons formed under anaerobic soil conditions and leached as reduced ferrous oxide. Therefore, the methanogens’ activity might have suppressed by the electron accepting effects of iron oxides (Jackel and Schnell, 2000). In our experiment, silicate amendment with 4 Mg ha1 under no-tillage rice farming caused 54% reduction in total CH4 flux as compared to that of control tillage, which is mostly due to the higher content of active iron and free iron oxides in soil, improved
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soil redox potential and porosity in no-tilled rice field at harvesting stage. Hanaki et al. (2002) also reported more than 50% reduction in the cumulative seasonal CH4 flux from the no-tillage rice field in Japan as compared to that of tilled field. Furukawa and Inubushi (2004) also reported 30% reduction in total CH4 flux from paddy soil by the application of 20 Mg ha1 revolving furnace slag (RFS), which acted as potential source of electron acceptors. Total seasonal CH4 flux showed strong negative correlation with the active iron, free iron and ferrous iron concentrations in soil at harvesting stage (Table 3). This implies the released iron materials from the applied silicate fertilizer acted as electron acceptor and ultimately suppressed CH4 emissions. Rice grain yield was increased by 18% over the control tillage system and 13% over the control no-tillage system with 4 Mg ha1 silicate fertilizer application (Fig. 3). It has also reported that the application of silicate slag at 1.5–2.0 Mg ha1 in lowland rice soils of Japan increased rice yield by 5–15% and sustained rice productivity in the range 6–9 Mg ha1 (Takahashi et al., 1990). In this experiment, rice grain yield and harvest index were negatively correlated with seasonal CH4 flux, which was supported by Denier van Der Gon et al. (2002). 5. Conclusion It was found that no-tillage system with 4 Mg ha1 silicate fertilization decreased total seasonal CH4 flux by 53% and 36%, while maximized grain yield by 18% and 13% over the control tillage and control no-tillage systems, respectively. This reduction in CH4 flux is due to the improved soil physico-chemical properties such as soil porosity, soil redox potential, increased concentrations of active iron and free iron oxides in soil being acted as electron acceptors. Conclusively, no-tillage rice farming with silicate amendment was found an effective strategy for significant reduction in CH4 emissions, while increasing rice productivity under irrigated paddy soil conditions. References Achtnich, C., Bak, F., Conrad, R., 1995. Competition for electron donors among nitrate reducers, ferric iron reducers, sulfate reducers and methanogens in anoxic paddy soil. Biol. Fertil. Soils 19, 65–72. Ali, M.A., Lee, C.H., Kim, P.J., 2008. Effect of silicate fertilizer on reducing methane emission during rice cultivation. Biol. Fertil. Soils 44, 597–604. Allison, L.E., 1965. Organic carbon. In: Black, C.A., Evans, D.D., White, J.L., Ensminger, L.E., Clark, F.E. (Eds.), Methods of Soil Analysis, Part 2. American Soc. of Agron., Madison, WI, USA, pp. 1367–1376. Anastasic, C., Dowding, M., Simpson, V.J., 1992. Future CH4 emissions from rice production. J. Geophys. Res. 97, 7521–7525. Aulakh, M.S., Bodenbender, J., Wassmann, R., Rennenberg, H., 2000. Methane transport capacity of rice plants: influence of methane concentration and growth stage analyzed with an automated measuring system. Nutr. Cycl. Agroecosyst. 58, 357–366. Balesdent, J., Chenu, C., Balabane, M., 2000. Relationship of soil organic matter dynamics to physical protection and tillage. Soil Till. Res. 53, 215–230. Batjes, N.H., Sombroek, W.G., 1997. Possibilities for carbon sequestration in tropical and subtropical soils. Global Change Biol. 3, 161–173. Bohn, M., McNeal, G., Connor, G.O., 1979. Soil Chemistry. Chichester Brisane Toronto: A Wiley-Interscience Publication, New York. Cicerone, R.J., Oremland, R.S., 1988. Biogeochemical aspects of atmospheric methane. Global Biogeochem. Cycl. 299–327. Denier van Der Gon, H.A.C., Kropff, M.J., van Breemen, N., Wassmann, R., Lantin, R.S., Aduna, E., Corton, T.M., 2002. Optimizing grain yields reduces CH4 emissions from rice paddy fields. Proc. Natl. Acad. Sci. U.S.A. 99, 12021– 12024. Doran, J.W., Smith, M.S., 1987. Organic matter management and utilisation of soil and fertilizer nutrients. In: Follett, R.F., Stewart, J.W.B., Cole, C.V. (Eds.), Soil Fertility and Organic Matter as Critical Components of Production Systems. American Society of Agronomy, Madison, WI, pp. 53–72. Fuji, H., Hayasaka, T., Yokoyama, K., Ando, H., 1999. Effect of silica application to a nursery bed of rice on rooting ability and early growth of rice plants. Jpn. J. Soil Sci. Plant Nutr. 70, 785–790. Furukawa, Y., Inubushi, K., 2004. Evaluation of slag application to decrease methane emission from paddy soil and fate of iron. Soil Sci. Plant Nutr. 50 (7), 1029– 1036.
22
M.A. Ali et al. / Agriculture, Ecosystems and Environment 132 (2009) 16–22
Hanaki, M., Toyoaki, I., Saigysa, M., 2002. Effect of no-tillage rice cultivation on methane emission in three paddy field of different soil types with rice straw application. Jpn. Soc. Soil Sci. Plant Nutr. 73, 135–143. Hanson, R.S., 1980. Ecology and diversity of methylotrophic organisms. Adv. Appl. Microbiol. 26, 13–40. Intergovernmental Panel on Climate Change (IPCC), 1995. The Science of Climate Change: Climate Change, impacts, adaptations and mitigation of climate change. In: Houghton, I.T., Meira, F., Callander, L.G., Harris, B.A., Kattenberg, A., Maskell, K. (Eds.), Scientific Technical Analysis. Cambridge University Press, Cambridge, UK. Intergovernmental Panel on Climate Change, 2001. Climate Change 2001. The Scientific basis, contribution of working group I to the third assessment report of the IPCC. In: Houghton, J.T., Ding, Y., Griggs, D.J., Noguer, M., van der Linden, P.J., Xiaosa, D. (Eds.), Cambridge University Press, Cambridge. International Rice Research Institute, 1989. IRRI Toward 2000 and Beyond, IRRI, Manila, Philippines. Inubushi, K., Cheng, W.G., Aonuma, S., Hoque, M.M., Kobayashi, K., Miura, S., Kim, H.Y., Okada, M., 2003. Effects of free air CO2 enrichment on methane emission from a rice paddy field. Global Change Biol. 9, 1458–1464. Jackel, U., Schnell, S., 2000. Suppression of methane emission from rice paddies by ferric iron fertilization. Soil Biol. Biochem. 32 (11–12), 1811–1814. Jackson, M.L., 1973. Soil Chemical Analysis. Prentice Hall, Inc., Englewood Cliffs, NJ. Jensen, C.R., Luxmoore, R.J., Van Gundy, S.D., Stolzy, L.H., 1969. Root air-space measurements by a pycnometer method. Agron. J. 61, 474–475. Kludze, H.K., Delaune, R.D., Patrick Jr., W.H., 1993. Aerenchyma formation and methane and oxygen exchange in rice. Soil Sci. Soc. Am. J. 57, 382–385. Kumada, K., Asami, T., 1958. A new method for determining ferrous iron in paddy soils. Soil Plant Food 3, 187–193. Lal, R., 1997. Residue management, conservation tillage and soil restoration for mitigating greenhouse effect by CO2-enrichment. Soil Till. Res. 43, 10–81. Lee, Y.B., Lee, C.H., Hawng, J.Y., Lee, I.B., Kim, P.J., 2004. Enhancement of phosphate desorption by silicate in soils with salt accumulation. Soil Sci. Plant Nutr. 50, 43–499. Liebig, M.A., Tanaka, D.L., Wienhold, B.J., 2004. Tillage and cropping effects on quality indicators in the northern Great Plains. Soil. Till. Res. 78, 131–141. Loeppert, R.H., Inskeep, W.P., 1996. Iron. In: Sparks, D.L., Page, A.L., Loeppert, R.H., Johnston, C.T., Sumner, M.E., Bigham, J.M. (Eds.), Methods of Soil Analysis, Part 3, Chemical Methods. Soil Science Society of America and American Society of Agronomy, Madison, USA, pp. 639–664.
Lovely, D.R., Phillips, E.P., 1987. Competitive mechanisms for inhibition of sulfate reduction and methane production in the zone of ferric iron reduction in sediments. Appl. Environ. Microbiol. 53, 2636–2641. Mariko, S., Harazano, Y., Owa, N., Nouchi, I., 1991. Methane in flooded soil water and the emission through rice plants to atmosphere. Environ. Exp. Bot. 31, 343–350. Neue, H.U., Roger, P.A., 1993. Rice agriculture: factors affecting methane emissions. In: Khalil, M.A.K. (Ed.), Atmospheric Methane: Sources, Sinks and Role in Global Change. Springer-Verlag, Berlin, pp. 254–298. Nouchi, I., 1994. Mechanisms of methane transport through rice plants. In: Minami, K., Mosier, A., Sass, R.L. (Eds.), CH4 and N2O: Global emissions and controls from rice fields and other agricultural and industrial sources. NIAES Series 2, Tsukuba, Japan, pp. 87–104. Ota, Y., 1970. Diagnostic method for measurement of root activity in rice plant. Japan Agric. Res. Quart. 5, 1–6. Ponnamperuma, F.N., 1965b. Review of the symposium on the mineral nutrition of the rice plant. In: The Mineral Nutrition of Rice Plant, John Hopkins Press, Baltimore, MD, pp. 461–482. RDA, Rural Development Administration, 1988. Method of soil chemical analysis, National Institute of Agricultural Science and Technology, Suwon, Korea. Reddy, K.R., Overcash, M.R., Khaleel, R., Westerman, P.W., 1980. Phosphorus adsorption-desorption characteristics of two soils utilized for disposal of animal wastes. J. Environ. Qual. 9, 86–92. Rolston, D.E., 1986. Gas flux. In: Klute, A. (Ed.), Methods of Soil Analysis, Part 1. 2nd ed. Agron. Monogr. 9. ASA and SSSA, Madison, WI, pp. 1103–1119. Saigusa, M., Heinai, H., Shibuya, K., Yoshida, K., Okazaki, H., 2003. Effect of acidified porous hydrate calcium silicate applied in a nursery bed soil on growth and nutrient uptake of rice seedling. Jpn. J. Soil Sci. Plant Nutr. 74, 333–337. SAS/STAT User’s Guide, vol. 1, 1990. ACECLUS-FREQ, Version 6, 4th edition, SAS Institute, Inc., Cary, NC. Schutz, H., Seiler, W., Conrad, R., 1989. Processes involved in formation and emission of methane in rice paddies. Biogeochemistry 7, 33–53. Singh, S., Singh, J.S., Kashyap, A.K., 1999. Methane flux from irrigated rice fields in relation to crop growth and N-fertilization. Soil Biol. Biochem. 31, 1219–1228. Takahashi, E., Ma, J.F., Miyake, Y., 1990. The possibility of silicon as an essential element for higher plants. Comments Agril. Food Chem. 2, 99–122. Wassmann, R., Papen, H., Rennenberg, H., 1993. Methane emission from rice paddies and possible mitigation strategies. Chemosphere 26, 201–217. Watanabe, A., Kimura, M., 1999. Influence of chemical properties of soils on methane emissions from rice paddies. Commun. Soil Sci. Plant Anal. 30, 2449–2463.