Assessment of carbon footprint reduction through organic rice cultivation practices

Paddy fields emit roughly 11% of global agricultural methane, yet switching to organic management may alter this balance in ways that aren’t fully mapped. This research compared the carbon footprint of organic, integrated, and conventional rice cultivation over six consecutive seasons (Kharif 2020 to Rabi 2023) on a permanent trial at Shivamogga, Karnataka. Greenhouse gas fluxes (CH4, N2O, soil CO2) were measured fortnightly using closed chamber techniques. The organic system reduced the carbon footprint from 5.14 to 2.11 t CO2-eq ha-1 season-1 over the six seasons, a 59% decline relative to the conventional baseline. Methane accounted for 54-62% of total emissions across all systems. Soil organic carbon rose by 0.18 percentage points under organic management versus 0.03 under conventional. Grain yield in the organic system stabilised at 4.31 t ha-1 by the fifth season, only 9.7% below the conventional yield. These results suggest that organic rice, once the transition period passes, can sharply lower greenhouse gas intensity without large yield trade-offs.

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Comparison of Rice Management SystemsClose ×

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Kh 2020 and Ra 2021 and more: Organic vs Integrated vs ConventionalClose ×

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SOC final (%): Organic vs Integrated vs ConventionalClose ×

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Introduction

When the Green Revolution brought high-yielding rice varieties and synthetic fertilisers to South Asia in the 1960s, methane emissions from paddy fields were barely on anyone's radar. Half a century later, rice paddies are recognised as one of the largest anthropogenic sources of CH 4 , contributing 1.5% of total global greenhouse gas output [1] . Conventional flooded rice management keeps soils anaerobic for weeks, creating ideal conditions for methanogenic archaea to convert organic matter into methane [2] . Organic rice cultivation replaces synthetic N fertilisers with farmyard manure, compost, and green manures. While this removes the direct N 2 O spike associated with urea hydrolysis, it may initially raise CH 4 emissions by adding labile carbon to waterlogged soil [3] . Over several seasons, however, the carbon inputs build soil organic matter, improve aggregate stability, and may shift microbial communities toward methanotrophs that oxidise CH 4 before it escapes to the atmosphere [4] . Whether the net effect is positive or negative for the carbon footprint depends on the balance between these opposing fluxes, and long-term field data from tropical India are scarce [5] . This research aimed to (i) track season-by-season changes in CH 4 , N 2 O, and soil CO 2 emissions under organic, integrated, and conventional rice over six consecutive seasons, (ii) estimate the total carbon footprint per unit area and per unit grain produced, and (iii) assess whether soil organic carbon accumulation under organic management partly offsets field emissions.

Materials and Methods

Materials and Methods

Materials

The trial occupied a 0.6 ha permanent experimental block at the University of Agricultural and Horticultural Sciences, Shivamogga (13°57′ N, 75°34′ E, 590 m a.s.l.). Three management systems were compared: organic (farmyard manure at 10 t ha -1 + green manure Sesbania + biofertilisers), integrated (50% organic + 50% RDF), and conventional (full RDF: 100:50:50 kg N:P 2 O 5 :K 2 O ha -1 ). Each system was replicated four times in a randomised block design with plot size 10 m × 8 m. Rice variety 'Jyothi' was transplanted at 20 cm × 15 cm spacing. The research ran from Kharif 2020 through Rabi 2023 [7] .

Methods

Gas samples were collected fortnightly using static closed chambers (50 cm × 50 cm × 50 cm acrylic boxes) fitted with a sampling port. Syringes drew 20 mL at 0, 15, and 30 minutes after closure; samples were analysed by gas chromatography (Shimadzu GC-2014) for CH 4 and N 2 O. Soil CO 2 efflux was measured with an infrared gas analyser (LI-COR 8100A). Fluxes were integrated over the season using the trapezoidal method. Global warming potential was expressed as CO 2 -equivalents using IPCC AR5 factors (CH 4 = 28, N 2 O = 265) [8] . Soil organic carbon was determined by the Walkley-Black method at the end of each Rabi season. Data were analysed by repeated-measures ANOVA in R.

Carbon and Greenhouse Gas Accounting

The carbon footprint for each system was calculated as the sum of (i) direct field emissions (CH 4 + N 2 O + soil CO 2 ), (ii) embodied emissions from input manufacture (fertilisers, pesticides), and (iii) farm operations (tillage, pumping). Emission factors for input manufacture followed national inventory guidelines [9] . Carbon sequestration in soil was estimated from the change in soil organic carbon stock (0-15 cm) using measured bulk density. Net carbon footprint = total emissions-soil C gain.

Results

The organic system's carbon footprint fell steadily from 3.82 t CO 2 -eq ha -1 in Kharif 2020 to 2.11 t in Rabi 2023, a 45% within-system decline (Table 1). The conventional system, by contrast, remained near 5 t CO 2 -eq ha -1 throughout. By the final season, organic management cut the footprint by 56% relative to conventional. Methane was the dominant gas, contributing 54-62% of emissions across systems.

System	Kh 2020	Ra 2021	Kh 2022	Ra 2023	Δ (%)
Organic	3.82	3.41	2.38	2.11	-44.8
Integrated	4.37	4.02	3.19	2.93	-33.0
Conventional	5.14	5.08	4.81	4.76	-7.4
CD (p = 0.05)	0.41	0.38	0.33	0.29	-

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Season-wise carbon footprint (t CO₂-eq ha⁻¹) under three rice management systems

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Comprehensive Interpretation

The declining trend in organic emissions appears driven by two parallel processes: rising methanotroph activity as soil structure improved, and lower labile C availability as farmyard manure matured in the soil [4] . Soil organic carbon increased by 0.18 percentage points under organic management, equivalent to roughly 3.6 t C ha -1 sequestered over three years, which offset about 22% of cumulative field emissions.

Discussion

The 56% reduction in carbon footprint under organic rice by the sixth season is at the upper end of values reported in the literature. A meta-analysis covering 63 comparisons worldwide found organic systems reduced emission intensity by 20-40% on average [10] . The larger reduction here may reflect the warm, humid conditions in Karnataka that favour rapid organic matter decomposition and methanotroph proliferation once continuous flooding is avoided [11] . Methane dominated all systems (54-62% of total GWP), consistent with flooded rice everywhere [2] . The organic system's CH 4 share dropped from 62% in the first season to 54% by the sixth, suggesting a gradual shift in the soil microbial balance toward methane oxidation. N 2 O contributed less than 12% in every system because standing water suppresses nitrification, the main pathway for N 2 O production [12] . Grain yield under organic management stabilised at 4.31 t ha -1 (mean of last two seasons), only 9.7% below the conventional check. This yield gap is smaller than the 15-25% typically cited for organic cereals in temperate regions [13] and aligns with tropical data suggesting the gap narrows as soil biology recovers [14] . From an economic standpoint, the premium that organic-certified paddy commands in Indian markets (20-40% above conventional) more than compensates for the modest yield shortfall [15] .

Conclusion

Organic rice cultivation reduced the per-hectare carbon footprint by 56% relative to conventional management over six seasons, driven mainly by declining methane emissions and rising soil organic carbon stocks. The yield gap narrowed to under 10% once the transition period passed, making the trade-off economically acceptable, especially where organic price premiums apply. Soil carbon gains offset roughly 22% of cumulative field emissions, providing a tangible co-benefit. For rice growers in the humid tropics of southern India, these data support a realistic pathway to lower-emission production without abandoning yield targets. But the transition takes time: the first two seasons showed higher CH 4 under organic inputs, and farmers will need bridging incentives during that window. Future work should extend monitoring beyond six seasons and incorporate life-cycle costs of organic certification.

Figures and tables from the paper

System	SOC initial (%)	SOC final (%)	Mean yield (t/ha)
Organic	0.58	0.76	4.31
Integrated	0.58	0.67	4.58
Conventional	0.58	0.61	4.77

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Soil organic carbon (%) and grain yield (t ha⁻¹) at the end of six seasons

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Trend in carbon footprint across six cropping seasons under organic, integrated, and conventional rice management.

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Cumulative greenhouse gas emission sources (CH₄, N₂O, soil CO₂) under organic rice during Kharif 2022.

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