Journal
AGRICULTURE ECOSYSTEMS & ENVIRONMENT
Volume 298, Issue -, Pages -Publisher
ELSEVIER
DOI: 10.1016/j.agee.2020.106968
Keywords
Rice-cropping system; Net ecosystem carbon budget; N fertilization; Straw incorporation; Net primary production; Ecosystem respiration
Funding
- National Key R&D Program of China [2017YFD0200100]
- National Science Foundation of China [41425005, 41471238]
- Humboldt Postdoctoral Research Fellowship
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Nitrogen fertilization (NF) is an important agricultural management practice that greatly affects soil carbon (C) storage through regulating the balance of soil C input (straw biomass) and output (ecosystem respiration), especially for agroecosystems with simultaneous straw incorporation (SI). However, little is known about how different NF rates affect soil C balance (net ecosystem carbon budget, NECB) in flooded paddy ecosystems with SI. We conducted a two-year field experiment in a typical rice-wheat cropping system in southern China to investigate the response of soil C input (net primary production (NPP) and SI), output (ecosystem respiration and methane emissions), and NECB and N losses under five different NF rates (0/0, 120/90, 180/135, 240/180 and 300/225 kg N ha(-1) for the rice/wheat season). Straw harvested from previous cropping season was chopped and fully incorporated into the soil prior to the next season. Our results showed that all treatments had a positive NECB value ranged between 4057-14380 kg C ha(-1) yr(-1). Compared with the no NF, NF treatments clearly increased the annual NECB by 17.2 %-185 % depending on NF rate. A 20 % reduction relative to the local NF rate (525 kg N ha(-1)) increased annual crop yield by 4.1 %-6.7 % and NECB by 9.6 %-16.8 %, which was attributed to the increase in NPP (2.6 %-6.2 %) and straw C input (3.8 %-6.1 %), and the decrease in ecosystem respiration (1.8 %-2.1 %) and methane emissions (8.4 %-10.4 %). Moreover, total reactive N losses were significantly decreased by 21 %. However, further reducing the rate by 40 % from local NF rate significantly decreased crop yield by 12.7 %-14.9 % and NECB by 16.7 %-19 %, mainly due to the significant decrease in soil C input through NPP by 14 %-18 % and straw C input by 7.4 %-15.8 % as the inadequate N supply impaired crop growth. Our results suggest that optimizing NF rate is effective in further enhancing soil C storage, decreasing N pollution and sustaining food security in paddy ecosystems with simultaneous SI.
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