Net ecosystem carbon budget, net global warming potential and greenhouse gas intensity in intensive vegetable ecosystems in China

The net ecosystem carbon budget (NECB), global warming potential (GWP) and greenhouse gas intensity (GHGI) of vegetable ecosystems are not well documented. The net GWP and GHGI either including the carbon emissions from agricultural management (net mGWP/mGHGI) or not were estimated from an intensive vegetable production system in Nanjing, China between 2009 and 2010. The four typical consecutive rotations included celery–tung choy–baby bok choy–amaranth (C–T–Bb–A), choy sum–celery–tung choy–bok choy (Cs–C–T–Bc), garland chrysanthemum–tung choy–bok choy (G–T–Bc), and celery–choy sum–lettuce–bok choy (C–Cs–L–Bc). A net sink was observed and estimated at crop seasonal time scale for both the NECB and the soil organic carbon change (δSOC) from the four vegetable rotation fields. The mGWP, net GWP, net mGWP, GHGI and mGHGI all showed nearly consistent changes among the rotations and among the vegetables within each rotation. The global warming potential ranged from 26 Mg CO2 equiv. ha−1 to 109 Mg CO2 equiv. ha−1 for net GWP and 36 Mg CO2 equiv. ha−1 to 131 Mg CO2 equiv. ha−1 for mGWP. The GHGI and mGHGI ranged from 0.17 kg CO2 equiv. kg−1vegetable to 0.41 kg CO2 equiv. kg−1 vegetable and from 0.22 kg CO2 equiv. kg−1vegetable to 0.49 kg CO2 equiv. kg−1 vegetable, respectively. The mGWP, net GWP, net mGWP, GHGI and mGHGI were dominated by the GWP resulting from N2O emissions. Annual cumulative direct N2O emissions were 374 kg N2O ha−1 for G–T–Bc, 216 kg N2O ha−1 for C–T–Bb–A, 159 kg N2O ha−1 for Cs–C–T–Bc and 89 kg N2O ha−1 for C–Cs–L–Bc, respectively. High N fertilizer input was likely responsible for the high N2O emissions. Increasing fertilizer use efficiency and adoption of best practices are effective measures for sustainable intensive vegetable production.