Optimum plastic mulching application to reduce greenhouse gas emissions without compromising on crop yield and farmers' income.

With the rapid socio-economic development in China, poverty alleviation and the reduction of the environmental footprint in the plastic film mulching (PM) planting system have become key to sustainable agricultural production. Although many studies have evaluated the maize yield, agricultural economic benefits, and greenhouse gas (GHG) emissions associated with PM through small-scale field experiments, identifying suitable PM regions in combination with their demographic characteristics and the future development of such systems has received little attention. This study combines a Denitrification-Decomposition (DNDC) model and demographic characteristics to determine the optimum PM region in rainfed areas of the Loess Plateau in northwest China. The results demonstrated that PM produced a higher maize yield, agricultural net profit (ANP), and cost-benefit ratio compared to a control treatment (CK) without PM. An agricultural income far above the poverty level would assist in meeting the goals of alleviating poverty and building a prosperous society. In addition, the PM system produced more GHG emissions, but had a lower greenhouse gas intensity (GHGI) than CK under both low (200 kg N ha-1) and high (300 kg N ha-1) nitrogen (N) fertilizer rates. This study developed a framework to evaluate maize yield alongside economic and environmental indicators. We concluded that PM should be adopted in areas with precipitation less than 500 mm, and concentrated in the region with rainfall of 200-400 mm. The results provide a theoretical basis for the sustainable development of the PM maize planting system, and will contribute to the desired goal of environmentally sustainable agricultural production.

Effect of plastic film mulching and film residues on phthalate esters concentrations in soil and plants, and its risk assessment.

The application of plastic film mulching can greatly improve dryland productivity, while the release of toxic phthalate esters (PAEs) from the plastic film has generated concern. This study investigated the effects of mulched plastic film and residual plastic film on the PAE concentrations in the soil-crop system and assessed the risks to people eating crop products. The PAEs concentration in the 0-25 cm soil layer of plastic mulched farmland was 0.45-0.81 mg/kg, while the average PAEs concentration of 0.37-0.73 mg/kg in non-mulched farmland decreased by 19%. The PAEs concentration in mulched soil reached the highest in July, being 0.80-0.84 mg/kg, while in the non-mulched soil, the PAEs also appeared and gradually decreased from May at 0.62-0.74 mg/kg to October, and the PAEs concentrations were almost the same in the mulched and non-mulched soils at the harvest time in October at 0.37-0.44 mg/kg. With the amounts of residual film in farmland increasing from 0 kg/ha to 2700 kg/ha (equivalent to the total amount of residual film after 60 years of continuous plastic film mulching), the PAEs concentrations were no significant changes, being 0.54-0.93 mg/kg. Maize (Zea mays L.) roots could absorb and accumulate PAEs, and the bio-concentration factor (BCF) was 1.6-2.3, and the average PAEs concentrations in stems, leaves, and grains were 79%-80% of those in roots at 0.77-1.47 mg/kg. For the ingestion of maize grains or potato (Solanum tuberosum L.) tubers grown in plastic film mulched farmland or farmland containing residual film of 450-2700 kg/ha, the hazard index (HI) were less than 1, the carcinogenic risks (CRs) were 2.5 × 10-7-2.2 × 10-6, and the estrogenic equivalences were 6.17-17.73 ng E2/kg. This study provides important data for the risk management of PAEs in farmlands.

[Effect of Pyrolytic Temperature and Time on Characteristics of Typha angustifolia Derived Biochar and Preliminary Assessment of the Ecological Risk].

A batch of biochar was produced from pyrolysis of Typha angustifolia (TBCs) at 200-500℃ for 2 h and 6 h to investigate the effects of pyrolytic temperature and heating retention time on the physico-chemical properties. Moreover, Escherichia coli (E. coli) HB101 and the seeds of Helianthus annuus were used to preliminarily test the ecological risk of the TBCs. Results showed that the heating retention time (i.e., 2 and 6 h) had no significant effect on the properties of TBCs, while pyrolytic temperature significantly affected TBCs' characteristics. As the pyrolysis temperature increased from 200 to 500℃, the mass yield and contents of hydrogen (H) and oxygen (O) decreased, while the contents of carbon (C) and ash increased. The pH and surface pores also increased with increasing pyrolytic temperature, whereas the O-containing functional group (e.g., -COOH and -OH) decreased. These results indicated the increased carbonization and aromatization of the TBCs. For the inherent nutrients of TBCs, the total phosphorus (TP) and available potassium (K) contents significantly increased as temperature increased. The main components of dissolved organic matter (DOM) of TBCs were humic acid-like and fulvic acid-like organic compounds. As the pyrolysis temperature increased, the content of humic acid-like organic compounds decreased, while the content of fulvic acid-like organic compounds increased. All the TBCs had no significant effect on the growth of E. coli HB101 and the seed germination of Helianthus annuus, indicating the little ecological risk of TBCs under the experimental conditions. These findings provide an alternative way for resource utilization of waste wetland biomass and provide important theoretical data for screening biochar in soil reclamation.

[Pollution Characteristics and Ecological Risk Assessment of Phthalate Esters (PAEs) in the Surface Water of Jiaozhou Bay].

In order to better understand phthalate esters (PAEs) pollution in Jiaozhou Bay, surface water samples were collected for content analysis in August and November 2015 and January 2016. Fifteen kinds of PAEs were detected by stir bar sorptive extraction and gas chromatography-mass spectrometry. The content, composition, spatial distribution, seasonal variation, and ecological risk assessment of the PAEs in the surface waters were examined and analyzed. The results showed that:① The total concentrations of PAEs in the surface seawater in August and November 2015 and January 2016 were 3.63-21.20 µg·L-1, 2.24-12.60 µg·L-1, and 0.01-4.15 µg·L-1, respectively, and the average concentrations were 11.10 µg·L-1, 5.26 µg·L-1, and 0.80 µg·L-1, respectively. ② Influenced by runoff and ocean currents, the concentration of PAEs in the surface water of Jiaozhou Bay is higher near the shore and lower in the middle, and the total concentration of the east coast is higher than that of the west coast. Compared with surveys of other rivers and oceans, the PAEs content in the surface water of Jiaozhou Bay is moderate, but it is heavily polluted compared with other oceans. ③ Considering the rainfall and other factors, the distribution of PAEs in the three seasons followed the order summer > autumn > winter. The main PAEs detected were DBP, BBP, and DEHP. ④ The results of the ecological risk assessment showed that the risk quotient (RQ) of DBP at each station in Jiaozhou Bay was greater than 1; that is, the ecological risk was relatively large, while the risk of the other PAEs (RQ<1) was small. PAEs have become a potentially threatening organic pollutant in Jiaozhou Bay. Their behavior and the ecological hazards that they present to the environment still require further study.

Yield-phenology relations and water use efficiency of maize (Zea mays L.) in ridge-furrow mulching system in semiarid east African Plateau.

Yield-phenology relation is a critical issue affecting rainfed maize field productivity in semiarid east African Plateau (EAP). We first introduced Chinese ridge-furrow mulching (RFM) system to EAP, using three maize cultivars with early-, mid- and late-maturing traits as test materials. A two-year field experiment was conducted in a semiarid farm of Kenya from 2012 to 2013. Three treatments were designed: alternative ridge and furrow with transparent plastic mulching (FT), with black plastic mulching (FB) and without mulching (CK). We found that FT and FB significantly increased soil moisture and accelerated crop maturity across two growing seasons. Leaf area and shoot biomass were increased by 30.2% and 67.5% in FT, 35.2% and 73.5% in FB, respectively, compared with CK. Grain yield, water use efficiency and economic output were increased by 55.6%, 57.5% and 26.7% in FT, and 50.8%, 53.3% and 19.8% in FB, respectively. Optimal yield and economic benefit were observed in late-maturing cultivar due to increased topsoil temperature in FT in 2012 (cool), and in early-maturing cultivar owing to cooling effect in FB in 2013 (warm). Our study suggested RFM system, combined with crop phenology selection, be a promising strategy to boost maize productivity and profitability in semiarid EAP.

Integrated water resources management and water users' associations in the arid region of northwest China: a case study of farmers' perceptions.

Water scarcity is a critical policy issue in the arid regions of northwest China. The local government has widely adopted integrated water resources management (IWRM), but lacks support from farmers and farm communities. We undertook a case study in the Minqin oasis of northwest China to examine farmers' responses to IWRM and understand why farmer water users' associations (WUAs) are not functioning effectively at the community level. Results of quantitative and qualitative surveys of 392 farmers in 27 administrative villages showed that over 70% of farmers disapprove of the IWRM market-based reforms. In particular, the failure of farmer WUAs can be attributed to overlapping organizational structures between the WUAs and the villagers' committees; mismatches between the organizational scale of the WUAs and practical irrigation management by the farmers themselves; marginalization of rural women in water decision-making processes; and the inflexibility of IWRM implementation. An important policy implication from this study is that rebuilding farmer WUAs is key to overcoming the difficulties of IWRM. The current water governance structure, which is dominated by administrative systems, must be thoroughly reviewed to break the vicious cycle of tension and distrust between farmers and the government.

[Preliminary assessment of the potential of biochar technology in mitigating the greenhouse effect in China].

The production of biochar by pyrolysis and its application to soil can sequester the CO2 which was absorbed by plants from atmosphere into soil, in addition it can also bring multiple benefits for agriculture production. On the basis of the available potential survey of the biomass residues from agriculture and forestry section, life cycle assessment was employed to quantify the potential of biochar technology in mitigation of greenhouse gases in our country. The results showed: In China, the amount of available biomass resource was 6.04 x 10(8) t every year and its net greenhouse effect potential was 5.32 x 10(8) t CO(2e) (CO(2e): CO2 equivalent), which was equivalent to 0.88 t CO(2e) for every ton biomass. The greatest of contributor to the total potential was plant carbon sequestration in soil as the form of biochar which accounts for 73.94%, followed by production of renewable energy and its percentage was 23.85%. In summary, production of biochar from agriculture and forestry biomass residues had a significant potential for our country to struggle with the pressure of greenhouse gas emission.