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Knowledge about the impacts of the application of organic amendments such as straw and biochar to dryland agricultural soils with respect to soil properties, crop production, soil carbon sequestration and greenhouse gases emissions is limited. The objective of this study was to compare the effects of straw and straw-derived biochar amendments on soil properties, net global warming potential (NGWP) and net greenhouse gas intensity (NGHGI). A field experiment extending over two years was conducted involving simultaneous measurement of carbon dioxide (CO 2 ), methane (CH 4 ) and nitrous oxide (N 2 O) emissions and soil organic carbon (SOC) content in a wheat–maize crop rotation on the Loess Plateau of China. There were five treatments: control with no amendment (CK); conventional chemical fertilizer only (F); 8 t ha −1 wheat straw plus fertilizer (FS); 8 t ha −1 straw−derived biochar plus fertilizer (FBlow); and 16 t ha −1 straw−derived biochar plus fertilizer (FBhigh). SOC, C:N ratio and high active organic carbon (HAC) increased by 26.4%, 30.8% and 17.1%, respectively in the FBhigh treatment relative to the FS treatment. As compared to the F treatment, addition of straw significantly increased the total soil organic carbon sequestration rate (TSOCSR) in the soil depth of 0–100 cm and CO 2 emissions, but had no significant effect on soil N 2 O and CH 4 emissions or crop yield. However, straw–derived biochar amendment significantly decreased N 2 O emissions while significantly increasing (p < 0.05) crop yield and TSOCSR, but there was no effect on soil CO 2 emissions. Over all, our result showed an overall reduction in NGWP of 37.8% and 31.5% and in NGHGI of 28.1% and 21.2% under straw−derived biochar amendment at 8 t ha −1 and 16 t ha −1 , respectively as compared to the straw amendment. Thus, amending the soil with straw–derived biochar could provide a mechanism to lower the greenhouse gas intensity while increasing the productivity of wheat and maize cropping system in the Loess Plateau of China. [ABSTRACT FROM AUTHOR]

Summary: An empirical power function model of V = kQm has been used worldwide to describe the relationship between flow velocity (V, ms−1) and discharge rate (Q, m3 s−1) for rill and open channel flows. However, it has seldom been applied to watershed outlet channels taking into account the impacts of watershed size. In this study, observed data from four experimental watersheds of different sizes, ranging from about 1 to 100km2, were used to verify the stability of the power function model for use at a watershed level on the Loess Plateau. An alternative logarithmic function model of was also tested. Results showed that the constant parameters in both model types were impacted by watershed size, which are inherently directly related to the size of the outlet channels. The constants k and d, which represent flow velocity for unit discharge rate, were negatively correlated with watershed size. However, the exponential constants m and e, which determine the rate of change in flow velocity with respect to discharge rate, were shown to be independent of watershed size. Furthermore, soil and water conservation land use management on the Loess Plateau was also shown to indirectly affect the flow velocity–discharge rate relationship in the smallest watersheds (1km2). The study indicated that, although the performance of the logarithmic function model was acceptable, the power function model generally performed better over a larger range of flow velocity values and was better able to represent the flow velocity–discharge rate relationship in the unique context of the Loess Plateau. [Copyright &y& Elsevier]