Abstract
Nitrous oxide (N2O) and methane (CH4) emissions were monitored from an intensive vegetable production region with four typical consecutive rotations and a bare fallow in Nanjing, China, from 2009 to 2010. The four consecutive rotations were established as follows: Celery (Apium graveolens dulce L.)–Tung choy (Ipomoea aquatica Forsk L.)–Baby bok choy (Brassica rapa Chinensis L.)–Amaranth (Amaranthus mangostanus L.) (C-T-Bb-A), Choy sum (Brassica rapa Chinensis L.)–Celery–Tung choy–Bok choy (Brassica rapa Chinensis L.) (Cs-C-T-Bc), Garland chrysanthemum (Chrysanthemum coronarium L.)–Tung choy–Bok choy (G-T-Bc), and Celery–Choy sum–Lettuce (Lactuca sativa L.)–Bok choy (C-Cs-L-Bc). Annual cumulative N2O emissions were 237.7 ± 18.3, 137.2 ± 8.5, 100.9 ± 7.5, 56.4 ± 10.6 and 29.2 ± 3.7 kg N ha−1 from the G-T-Bc, C-T-Bb-A, Cs-C-T-Bc, C-Cs-L-Bc rotation fields and the bare fallow, respectively. Cumulative N2O emissions from the rotation fields, except the C-Cs-L-Bc rotation, were significantly higher than that from the bare fallow. Annual cumulative CH4 emissions were 9.0 ± 3.5, 13.9 ± 1.5, 18.8 ± 1.2, 12.1 ± 3.8 and 16.1 ± 3.5 kg C ha−1 from the bare fallow, C-T-Bb-A, Cs-C-T-Bc, G-T-Bc and C-Cs-L-Bc, respectively, and they did not show significant differences among systems. The annual N2O emission factor averaged 2.6%, ranging from 1.2% to 5.0%, and was higher than the current IPCC default value (1.0%). Total N fertilizer application rate explained 35.5% of annual N2O emissions. N2O emissions from intensively managed vegetable fields were characterized by high fluxes and emission factors that varied with cropping systems. Frequent year-round monitoring of N2O fluxes from intensively managed vegetable fields is essential for better constraint of the national N2O budget.
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