| Large amounts of fresh straws are produced with increasing crop yield. Returning straw to the field is an important measure for comprehensive utilization and recycling of the resources in the agricultural ecosystem. Straw management can improve soil quality and increase crop production. However, conventional straw incorporation has some disadvantages, i.e., lower tilling quality, negative effects on seed emergence and increase of greenhouse gas emissions. The new approaches and modes of straw returning are required in agricultural production, to deal with the global warming and reduce the greenhouse gas (GHG) emission.The effects of concentrated-ditch-buried straw returning mode and straw biochar on soil carbon sequestration and GHG emission were studied. Three experiments were conducted:(1) A field experiment was carried out from the wheat growing season in 2008 in Nantong, Jiangsu on the long-term effects of concentrated-ditch-buried straw returning on soil carbon sequestration. The straw residue was collected and buried in several ditches with a given space and covered with soil. The straw of wheat or rice was returned for four consecutive years, with different depth (20,30 and 40 cm); (2) A field experiment was conducted in Chongming island, Shanghai, from the wheat growing season in 2010 and the rice growing season in 2011, respectively to test the effects of concentrated-ditch-buried straw returning mode. Here, the treatments of normal returning and the concentrated-ditch-buried straw returning with 20,40 and 60 cm in depth were set, the emissions of CO2, CH4 and N2O during the two growing seasons after returning were investigated, and the soil bulk density, soil organic carbon and nitrogen content were measured; (3) A field experiment was conducted in the cotton growing season in 2011 in Shihezi, Xinjiang to study the effects of fertilization and irrigation on CH4 and N2O emissions in the cotton filed. The main results are as follows:1. Concentrated-ditch-buried straw returning improved the soil physical properties.Compared with no straw returning, concentrated-ditch-buried straw returning treatments decreased the soil density and increased the soil noncapillary porosity, capillary porosity, and total porosity in the straw layer and layers nearby. This result suggested that straw concentrated burying could benefit soil physical properties. Compared with no straw returning, concentrated-ditch-buried straw returning treatments decreased the soil density by 3.40%-21.10%, and increased the soil total porosity by 3.05%-22.15% in the straw layer and layers nearby.2. Concentrated-ditch-buried straw returning increased the carbon pool management index (CPMI) in a certain time after straw returning.The soil organic carbon (SOC), oxidizable organic carbon (ROC), and CPMI with conventional straw incorporation were significantly higher than those with the other four treatments in one-and-a-half years after straw returning, however, the difference in SOC, ROC, and CPMI showed a decreasing trend as time progressed. In two years after wheat straw returning, compared with no straw returning and buried with the depth of 60 cm, buried 20 cm increased CPMI by 4.27% and 3.88%, respectivily.3. Concentrated-ditch-buried straw returning decreased the GHG emission.Compared with normal straw returning, concentrated-ditch-buried straw returning decreased the GHG emission, and led to a lower global warming potential (GWP). Under the rice straw returning with 40 and 60 cm, GWP per unit yield gain decreased by 13.33% and 14.04%.4. Concentrated-ditch-buried straw returning improved the soil carbon sequestration and benefited the ecological economic value.Concentrated-ditch-buried straw returning increased the SOC and fixed carbon content significantly in all soil layers, especially in the layers around straw, decreased the straw decomposition rate and increased the straw carbon sequestration. The straw carbon sequestration was increased by 40.43%,32.54% and 33.35% in 0-30 cm,0-40 cm and 0-50 cm under the concentrated-ditch-buried straw returning with the depth of 20 cm,30 cm and 40 cm, respecitively. In addition, the concentrated-ditch-buried straw returning mode improved the ecological economic value, due to additional gain of 15,000 to 16,800 RMB by decreased carbon production.5. Straw biochar application decreased N2O emission while increased CH4 emission in the cotton filed.Application of straw biochar decreased the accumulated emission amount of N2O, especially under the furrow irrigation, while increased CH4 emission. GWP per unit yield gain was not affected significantly by straw biochar, while GWP per unit yield gain under drip irrigation was significantly lower than that under furrow irrigation.In conclusion, concentrated-ditch-buried straw returning improved the soil carbon sequestration, decreased the GHG emission, and benefited the ecological economic value, In addition, GWP per unit yield gain was not affected significantly by straw biochar, while GWP per unit yield gain under drip irrigation was significantly lower than that under furrow irrigation. |
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