GREENHOUSE GASES EMISSION DYNAMICS IN THE INDIAN AGRICULTURAL LANDSCAPES

Abstract

Rapid development and globalization affect agricultural production and trade. Over recent decades, there has been a notable increase in agricultural production and yields, accompanied by a global surge in fertilizer and pesticide usage. Cereal yields in developed and developing countries have experienced significant growth, ranging from 2-fold to 4.5-fold since 1961. This upward trend has led to improvements in food security, diversifying food diets towards a higher consumption of meat and dairy products. In India, agriculture plays a pivotal role in the economy, contributing significantly to food production through crop cultivation and livestock farming. Despite these positive aspects, it's crucial to acknowledge that the agricultural sector significantly contributes to greenhouse gas (GHG) emissions. These emissions primarily originate from livestock enteric fermentation and manure management, agricultural soil (via combined nitrification and denitrification processes), rice cultivation, and crop residue burning after harvesting. The intricate relationship between climate change and agriculture is gaining importance as the global population expands and the food production gap widens. The global agricultural sector contributes 24% to total greenhouse gas emissions, mainly comprised of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), contributing 60%, 15%, and 5% to global warming. CO2 emissions, constituting about 11% of the global total, arise from fossil fuel use in machinery, transportation, and land conversion. Livestock contributes to methane emissions through enteric fermentation and manure management associated with flooded rice cultivation, contributing 44% of global methane emissions. Nitrogen-based fertilizers and burning agricultural residues contribute to N2O emissions, representing 53% of global nitrous oxide emissions. Globally, India ranks 5th in total greenhouse gas emissions, with the agricultural sector contributing 14% to the overall total. Reducing agricultural GHG emissions to combat climate change is challenging due to the necessity of intensive farming for food security. Emissions from enteric fermentation, rice cultivation, synthetic fertilizer application, and crop residue burning are critical concerns for mitigation. Understanding the dynamics of CO2, CH4, and N2O emissions is crucial for tracking and quantifying their contribution to the agricultural sector. However, discrepancies in emission factors (EFs) and methodologies hinder accurate estimation. Challenges include the lack of crop-specific EFs, insufficient long-term trend analysis, and outdated EFs for Indian crop cultivation. Inconsistent calculation approaches for CH4 and N2O emissions from livestock also contribute to uncertainties. Addressing these gaps is essential for improving India's agricultural GHG emissions dynamics and implementing effective mitigation measures. This study aims to address the limitations of previous research by employing a data synthesis approach to estimate Greenhouse Gas (GHG) emissions at the district level in Indian agricultural landscapes from 1996 to 2017. The main objective is to understand and estimate the long-term, district-scale, crop-specific GHG emissions from the Indian agricultural landscapes and activities and facilitate appropriate mitigation measures in response to the dynamics of GHG emissions and their contribution to climate change and global warming. Previous studies utilized diverse methods for short-term district-level GHG estimation. In this research, the IPCC Tier 1 and Tier 2 methodology was used to synthesize data and estimate GHG (CO2, CH4, and N2O) emissions from five major sources at the district-scale: (i) N2O emissions from cropland (direct and indirect), (ii) CH4 emissions from rice cultivation in different ecosystems, (iii) CO2, N2O, and CH4 emissions from Crop Residue Burning (CRB) in situ, (iv) CH4 emissions from enteric fermentation of ruminant animals, and (v) CH4 and N2O emissions from livestock manure management. Over the last five decades, nitrous oxide (N2O) emissions from agricultural landscapes in India have significantly increased, positioning India as the fifth-largest global emitter of N2O, accounting for (~4.8%) of the total emissions. Existing studies that examined N2O emissions in India using a bottom-up approach were limited to brief periods and relied on country-level emission factors (EFs) despite the availability of long-term inventory data and spatially varying EFs. This study developed district- and crop-specific N2O EFs based on 82 field plot studies comprising 861 observations across 13 locations. The improved EFs were utilized to calculate district-level emissions from 1966 to 2017, employing a modified IPCC Tier I-Tier II approach highlighting significant spatio-temporal drivers. The findings revealed a substantial increase in total N2O emissions from Indian agricultural soils, rising from 73.7 ± 3.3 Gg in 1966 to 279.3 ± 15.8 Gg in 2017. This growth of 3.9 Gg yr−1 in total N2O emissions was closely linked to the increase in crop production (4.1 Tg yr−1), primarily driven by the escalation in fertilization (0.3 Tg yr−1). On a national scale, synthetic fertilization emerged as the primary contributor, accounting for 57% of N2O emissions in 2017, followed by animal manure (15%) and soil organic matter (9%). While synthetic fertilizer application dominated nationally, district-level analyses revealed that 18% of the districts exhibited the potential for the highest contributions from sources such as animal manure, crop residue return, and soil organic matter. The overall uncertainty stemming from this modified method and refined EFs was estimated at 5.1%. On the other hand, India is one of the largest rice producers, standing first in rice cultivated area and second in rice production, after China, contributing 21.5% to global rice production. Rice cultivation produces methane (CH4) due to anaerobic conditions induced by flood irrigation, significantly contributing to global warming. While most studies use national emission factors (EFs), our study synthesized 726 published measurements across India to develop district-level water regime-specific EFs for estimating district-scale emissions and warming potential. CH4 emissions from Indian rice fields increased from 3.7 (3.4 – 4.1) Tg to 4.8 (4.4 – 5.3) Tg during 1966-2017, driven by rice area and water-regime variations. Meanwhile, district-level emissions increased by ~ 930%, influenced by management practices like animal manure, fertilizer application, and water input, accurately reflecting regional variations compared to previous estimates. Employing a novel muti-output random forest mitigation model (R2 ~ 0.9), we found that a 25% warming reduction at the district level requires curtailing animal manure, nitrogen fertilizer, and water input by 8.5%, 12.9%, and 10.9%, respectively. These curtailments nearly double for a 50% mitigation scenario. The agricultural wastes from the intensive cultivation landscapes of India plays a major role in GHG contributions. Crop residue, a valuable resource for enhancing soil stability and fertility, is often unsustainably used and burned in developing nations, contributing to environmental challenges and greenhouse gas (GHG) emissions. Following IPCC guidelines, this study analyzed emissions from crop residue burning (CRB) in India from 1966 to 2017. Results indicate that 20.5% of the 563.6 million tonnes of crop residue produced in 2017 was burned, emitting 196.6 Tg CO2, 1.0 Tg CH4, and 0.08 Tg N2O. Rice straw burning dominated emissions, followed by wheat, maize, sugarcane, and cotton. Comprehensive estimates covering 20 major crops revealed discrepancies with previous studies and emphasized the need for integrated, sustainable crop residue management. The study, in addition to understanding India's long term GHG emission dynamics, recommended alternative approaches such as mulching, composting, and bioenergy utilization, emphasizing a comprehensive SWOT analysis for informed decision-making. In India, livestock is a major contributor to agricultural greenhouse gas emissions (GHGEs). Methane emissions (CH4es) from livestock (ruminant) digestive fermentation is the primary source. This study, utilizing a combination of IPCC Tier 1 and Tier 2 methodologies, precisely estimates methane and nitrous oxide emissions from enteric fermentation and manure management in different age groups and livestock categories, which remain poorly understood in India. By referencing government literature for country-specific emissions factors, the research improves the accuracy of estimations, aiding in reducing uncertainty in national GHG emissions. In 1966 and 2017, total net methane emissions from livestock enteric fermentation were 7.9 Tg and 11.3 Tg, while manure management resulted in 0.026 Tg and 0.039 Tg of nitrous oxide emissions. Livestock contributes around 54% of methane emissions in the agricultural sector, surpassing other subsectors like rice cultivation and crop residue burning. Cattle and dairy buffalo contribute significantly, accounting for 90% of methane emissions from livestock. The study emphasizes the importance of accurate EFs for livestock categories in reducing uncertainty in India's total GHG emissions from the livestock sector. Management practices, soil properties, precipitation, and temperature profoundly influence the amount of GHG emissions. The relationships between the occurrence of GHGs and the factors regulating them are important for devising mitigation strategies. Then, we assessed different agricultural management practices in the existing literature and discovered that GHG emissions could be effectively decreased by implementing timely interventions and adopting appropriate management practices, such as using efficient energy use in machinery, changing the ruminant's feed diets, and avoiding their products (meat and milk), livestock manure conversion to biogas, reduce tillage, change the irrigation methods, employing amendments like biochar and lime, utilizing slow-release fertilizers and nitrification inhibitors, treating plants with arbuscular mycorrhizal fungi, implementing suitable crop rotations, maintaining soil fertility and restoring degraded land and practicing integrated nutrient management. As we navigate the challenges posed by a burgeoning global population and the imperative to bridge the food production gap, understanding and addressing the complex dynamics between climate change and agriculture becomes pivotal for ensuring food security, environmental sustainability, and the overall well-being of our planet. However, the way emission reduction scenarios are commonly communicated tends to obscure the specific roles of different sectors responsible for emitting different types of GHGs. We argue for revised reporting of agricultural GHG emissions and better consideration of distinct GHG emission roles in mitigation strategies. This improves the identification and prioritization of effective emission reduction approaches. In summary, the most straightforward approach to significantly reduce GHG emissions without affecting agricultural production is to change the feed quality of ruminants, wetting and drying irrigation patterns in rice cultivation, the modifying N supply (including fertilizer type, dose, time, method, etc.), and the alternative approach of crop residue burning to a resource recovery product. Consequently, this study guides the creation of databases and the development of district-level GHG emissions from the Indian agricultural landscape, informing policymakers on climate impacts and mitigation measures towards sustainable agriculture.