Carbon budget of diversified cropping systems in southwestern China: Revealing key crop categories and influencing factors under different classifications

Cropping systems are considered the largest source of agricultural GHG emissions. Identifying key categories and factors affecting cropping systems is essential for reducing these emissions. Most studies have focused on the carbon budget of cropping systems from the perspective of a single crop or crop category. Comprehensive studies quantifying the carbon budget of diversified cropping systems, including farmland and garden crops, are still limited. This study aims to fill this gap by quantifying the carbon budget of diversified cropping systems, clarifying their carbon attributes, and identifying key crop categories and influencing factors within different classifications of the system. This study analyzed the carbon budget of a diversified cropping system consisting of 19 crops in Yunnan Province, southwestern China, using a crop-based net greenhouse gas balance methodology based on the "cradle-to-farm" life cycle idea. Crops were categorized into three levels of categories to assess the potential impact of categorization within the cropping system on its carbon balance. Results showed that Yunnan's diversified cropping system is a significant carbon sink, with net sequestration of 33.1 Mt CO2 eq, total emissions of 37.4 Mt CO2 eq, and total sequestration of 70.5 Mt CO2 eq. Cereals, vegetables, and hobby crops were the main contributors to carbon emissions, accounting for 41.61%, 21.87%, and 15.37%, respectively. Cereal crops also made the largest contribution to carbon sequestration at 53.18%. Bananas had the highest emissions per unit area (11.45 t CO2 eq ha-1), while walnuts had the highest sequestration (20.64 t CO2 eq ha-1). In addition, this study highlights effective strategies to reduce greenhouse gas emissions, such as reducing nitrogen fertilizer use, minimizing reactive nitrogen losses, and controlling methane emissions from rice fields. By elucidating the impact of carbon dynamics and crop categories, this study provides insights for sustainable agricultural practices and policies.