[Soil organic and inorganic carbon pools as affected by straw return modes under a wheat-maize rotation system in the Guanzhong Plain, Northwest China]. / å ³ä¸­å¹³åŽŸéº¦çŽ‰è½®ä½œä½“ç³»ä½œç‰©ç§¸ç§†ä¸åŒè¿˜ç”°æ¨¡å¼ä¸‹åœŸå£¤æœ‰æœºç¢³å’Œæ— æœºç¢³åº“å˜åŒ–ç‰¹å¾.

To understand the effects of straw return modes on soil carbon pools, we investigated total soil organic carbon (SOC), labile organic carbon fractions, and inorganic carbon (SIC) in different straw return modes at a depth of 0-40 cm under a maize-wheat cropping system in the Guanzhong Plain, Shaanxi, based on an 11-year field experiment. There were five straw return modes, i.e., no return of straw of both wheat and maize (CK), the retention of high wheat stubble plus the return of chopped maize straw (WH-MC), the return of both chopped wheat and maize straw (WC-MC), the retention of high wheat stubble and no return of maize straw (WH-MN), and the return of chopped wheat straw and no return of maize straw (WC-MN). The proportions of SOC storage were significantly higher under the WH-MC and WC-MC treatments than that under the CK by 28.1% and 22.2%, respectively. The proportions of SIC storage were increased by 20.4% and 17.3%, respectively. Compared with the initial value, the increases of sequestered SOC and SIC ranged from -0.84 t·hm-2 to 6.55 t·hm-2, respectively, and from -0.26 t·hm-2 to 8.61 t·hm-2, respectively. The efficiency of sequestration of SOC was 7.5%. To maintain the basic SOC level, the minimum carbon input from straw was 4.65 t·hm-2·a-1. The contents of labile carbon fractions at the 0-20 cm layer increased significantly under the WH-MC and WC-MC treatments compared with those of the control. Results of principal component analysis showed that the changes in soil carbon pools were primarily affected by the amount of straw return. Additionally, the increases in SIC storage could be ascribed to the Ca2+ and Mg2+ ions derived from irrigation water and plant residues that could coprecipitate with the CO2 from SOC mineralization to form CaCO3. In conclusion, our results indicated that the straw return mode that utilized the retention of high wheat stubble and chopped maize straw was sufficient to maintain soil carbon storage and would be the optimal straw-returning strategy for the region.

Integrated wheat-maize straw and tillage management strategies influence economic profit and carbon footprint in the Guanzhong Plain of China.

Appropriate straw and tillage management strategies increase grain yields, and promote atmospheric carbon dioxide (CO2) mitigation through soil organic carbon (SOC) sequestration. However, little is known about economic parameters and carbon footprint (CF, defined as total greenhouse gases emission from the whole life cycle perspective) of intensive wheat (Triticum aestivum L.)-maize (Zea mays L.) double cropping production under different integrated strategies of straw-return and tillage. To quantify the differences of straw-return and tillage integrated strategies in economic parameters and carbon sustainability, a field experiment was established in 2008 in which six integrated strategies were evaluated: straw return of both maize and wheat (MR-WR), MR-WR with subsoiling to ~40 cm depth after maize harvest (MS-WR), single straw return of wheat (MN-WR), single straw return of maize (MR-WN), MR-WN with subsoiling to ~40 cm depth after maize harvest (MS-WN) and no straw return (MN-WN). Results showed that the MS-WR had the greatest grain yields of both wheat and maize, gross revenue and economic profit with increases of 45.5%, 35.6%, 26.5%, and 79.7% relative to the MN-WN, respectively. Compared with the initial SOC level, the SOC stock increased by 22.9% under MS-WR, following by MR-WR (16.0%), MS-WN (11.6%), MR-WN (8.0%), MN-WR (5.1%), and MN-WN (-3.8%). The MS-WR reduced the net CF and net CF per economic profit by 35.4% and 64.1% relative to the MN-WN although it elevated the CF by 25.3%. Therefore, adopting the integrated strategies of both maize and wheat straw return with subsoiling to ~40 cm depth after maize harvest represented an economically and C-friendly optimal field management practice for intensive wheat-maize double cropping production in the Guanzhong Plain or other regions with similar environmental conditions in the world.

Potassium fertilization combined with crop straw incorporation alters soil potassium fractions and availability in northwest China: An incubation study.

Potassium (K) input is essential for the improvement of soil fertility in agricultural systems. However, organic amendment may differ from mineral K fertilization with respect to modifying the soil K transformation among different fractions, affecting soil K availability. We conducted a 60-day lab incubation experiment to evaluate the response of soil K dynamics and availability in various fractions with a view to simulating crop residue return and chemical K fertilization in an Anthrosol of northwest China. The tested soil was divided into two main groups, no K fertilization (K0) and K fertilization (K1), each of which was subjected to four straw addition regimes: no straw addition (Control), wheat straw addition (WS), maize straw addition (MS), and both wheat straw and maize straw addition (WS+MS). Soil K levels in the available (AK) and non-exchangeable (NEK) fractions were both significantly increased after K addition, following the order of K>WS>MS. Fertilizer K was the most efficient K source, demonstrating a 72.9% efficiency in increasing soil AK, while wheat and maize straw exhibited efficiencies of 47.1% and 39.3%, respectively. Furthermore, K fertilization and wheat and maize straw addition increased the soil AK in a cumulative manner when used in combination. The mobility factor (MF) and reduced partition index (IR) of soil K were used to quantitate the comprehensive soil K mobility and stability, respectively. Positive relationships were observed between the MF and all relatively available fractions of soil K, whereas the IR value of soil K correlated negatively with both MF and all available fractions of soil K. In conclusion, straw amendment could be inferior to mineral K fertilization in improving soil K availability when they were almost equal in the net K input. Crop straw return coupled with K fertilization can be a promising strategy for improving both soil K availability and cycling in soil-plant systems.

Heterogeneity of influential factors across the entire air quality spectrum in Chinese cities: A spatial quantile regression analysis.

Most of the previous researches estimate influencing factors impact on air quality average without considering the heterogeneity of influential factors on different levels of air quality. In order to detect the different effects of influencing factors on air quality index (AQI) between lower-AQI and higher-AQI cities, this study applies a spatial quantile regression model (SQRM) to investigate heterogeneity of influential factors on AQI, while accounting for spatial autocorrelation of AQI. The results show that heterogeneity effects of windspeed, terrain slope, urbanization sprawl and spatial autocorrelation on AQI are large across the entire AQI spectrum, while heterogeneity effects of precipitation, temperature, relative humidity, terrain fluctuation and urbanization intensity on AQI are not obvious. The spatial positive autocorrelation of AQI in higher-AQI cities is greater than that in lower-AQI cities. Compared with higher-AQI cities, the negative impact of terrain slope on AQI is lager in lower-AQI cities. One unit increase in wind speed contributes AQI to decrease 9.31 to 5.64 then to 5.39 for lower, medium and higher-AQI cities. One unit increase in urbanization sprawl would lead AQI increase 25.6 to 15.6 then to 10.5 for lower, medium and higher-AQI cities. The heterogeneity analysis of meteorological, topographic and socioeconomic factors effects on air quality are of guiding significance for realizing the differentiation of policy measures for air pollution prevention and control.

Effects of long-term straw return on soil organic carbon storage and sequestration rate in North China upland crops: A meta-analysis.

Soil organic carbon (SOC) is essential for soil fertility and climate change mitigation, and carbon can be sequestered in soil through proper soil management, including straw return. However, results of studies of long-term straw return on SOC are contradictory and increasing SOC stocks in upland soils is challenging. This study of North China upland agricultural fields quantified the effects of several fertilizer and straw return treatments on SOC storage changes and crop yields, considering different cropping duration periods, soil types, and cropping systems to establish the relationships of SOC sequestration rates with initial SOC stocks and annual straw C inputs. Our meta-analysis using long-term field experiments showed that SOC stock responses to straw return were greater than that of mineral fertilizers alone. Black soils with higher initial SOC stocks also had lower SOC stock increases than did soils with lower initial SOC stocks (fluvo-aquic and loessial soils) following applications of nitrogen-phosphorous-potassium (NPK) fertilizer and NPK+S (straw). Soil C stocks under the NPK and NPK+S treatments increased in the more-than-20-year duration period, while significant SOC stock increases in the NP and NP+S treatment groups were limited to the 11- to 20-year period. Annual crop productivity was higher in double-cropped wheat and maize under all fertilization treatments, including control (no fertilization), than in the single-crop systems (wheat or maize). Also, the annual soil sequestration rates and annual straw C inputs of the treatments with straw return (NP+S and NPK+S) were significantly positively related. Moreover, initial SOC stocks and SOC sequestration rates of those treatments were highly negatively correlated. Thus, long-term straw return integrated with mineral fertilization in upland wheat and maize croplands leads to increased crop yields and SOC stocks. However, those effects of straw return are highly dependent on fertilizer management, cropping system, soil type, duration period, and the initial SOC content.

What Induces the Energy-Water Nexus in China's Supply Chains?

Given energy and water scarcity, it is necessary to develop an in-depth understanding of the energy-water nexus in China for its sustainable development. Previous studies have focused on nexus accounting, synergy conservation, and system optimization, but its induction mechanism along the supply chains has not been uncovered. This paper proposes a top-down structural path analysis (SPA) and combines it with an environmental input-output model (EIOM) to identify the critical final demand, consumption sectors, and supply chain paths inducing the energy-water nexus. The results show that the largest final demand of water for energy production (WFE) is capital formation, while the largest final demand of energy for water supply (EFW) is urban consumption. The distribution of WFE at different production layers shows an inverted U shape. Most WFE is indirectly consumed by other sectors, such as construction, through three-step supply chain paths. In contrast, the distribution of EFW shows a L shape, and most EFW is directly consumed by the final demand. In addition, some critical supply chain paths inducing more WFE and EFW are identified. Finally, some policies targeting the energy-water nexus management are proposed, which are conducive to resource conservation and the sustainable supply of energy and water.

Structural analysis of indirect carbon emissions embodied in intermediate input between Chinese sectors: a complex network approach.

The indirect carbon emission embodied in the intermediate input is also an important indicator of assessing a producer's carbon emissions. Structural analysis of indirect carbon emissions is helpful to understand the responsibilities between producers and pay efforts to key areas. The aim of this study is to analyze indirect carbon emissions embodied in intermediate input between sectors and explore the distribution structure of indirect carbon emissions flow network (namely, ICEFN). Based on the modified input-output model and complex network theory, this study constructed four directed and weighted ICEFNs with 28 sectors from 1997 to 2012. The results show that indirect carbon emissions between sectors are significantly higher than direct carbon emissions, accounting for nearly 70% of the total carbon emissions of China. Second, we analyzed the embodied carbon emission intensity (namely, ECI) of each sector. Although the ECI has been decreasing over time, the decrease has increasingly diminished, which indicates that the additional carbon emission reductions are more difficult. Third, we identified the key sectors which play different roles in the ICEFNs. Meanwhile, we studied the key paths which show more closed relationships between some sectors in ICEFNs. Finally, based on the above analysis, we made policy recommendations.

[Effects of different straw-returning regimes on soil organic carbon and carbon pool management index in Guanzhong Plain, Northwest China].

A four-year (2008-2012) field experiment was conducted to investigate the effects of different straw-returning regimes on soil total organic carbon (TOC), labile organic carbon (LOC) and the ratio of LOC to TOC (LOC/TOC) as well as TOC stock (SCS) and soil carbon pool management index (CPMI) in a farmland with maize-wheat double cropping system in Guanzhong Plain area, Shaanxi Province, China. The results indicated that soil TOC and LOC contents and SCS were significantly increased when wheat or maize straw was returned to field, and the increasing extent showed the rising order as follows: double straw-returning > single straw-returning > no straw-returning. Compared to no straw returning, a significant increase of TOC and LOC contents and SCS was found in the treatment of wheat straw chopping retention combined with maize straw chopping subsoiling retention (WC-MM), and CPMI of WC-MM was significantly higher than in the other treatments in 0-20 cm soil layer. Compared to no wheat straw returning, soil CPMIs in 0-10 cm and 10-20 cm soil layer increased by 19.1% and 67.9% for the wheat straw chopping returning treatment, and by 22.6% and 32.4% for the maize straw chopping subsoiling treatment, respectively. Correlation analysis showed that soil CPMI was a more effective index reflecting the sequestration of soil organic carbon in 0-30 cm soil layer than the ratio of LOC to TOC. This study thus suggested that WC-MM regime is the best straw-returning regime for soil organic carbon sequestration.

[Effect of long-term shallow tillage and straw returning on soil potassium content and stratification ratio in winter wheat/summer maize rotation system in Guanzhong Plain, Northwest China].

Soil stratified sampling method and potassium chemical fractionation analysis were used to investigate effects of long-term shallow tillage and straw returning on soil K contents and stratification ratios in winter wheat/summer maize rotation system in Guanzhong Plain of Northwest China. The results showed that after 13-year continuous shallow tillage and straw returning, surface accumulation and stratification effect obviously occurred for soil available K (SAK) and non-exchangeable K (NEK), which was particularly remarkable for SAK and its fractions. Serious depletion of SAK occurred in 15-30 cm soil layer, and the SAK value was lower than the critical value of soil potassium deficiency. Meanwhile, significant differences were found between SR1 and SR2 values of SAK and its fractions, SR was obtained by values of topsoil layer (0-5 cm) divided by corresponding values of lower soil layers (5-15 cm layer, SR1, or 15-30 cm layer, SR2). However, no significant difference was observed between SR values of NEK and mineral K. In conclusion, returning of all straw over 10 years in the winter wheat/summer maize rotation system contributed greatly to maintaining soil K pool balance, while special attention should be paid to the negative effects of surface accumulation and stratification of SAK on soil K fertility.