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    农业生态环境-氮素合辑Agro-ecosystem & Environment—Nitrogen

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    Nitrogen release and re-adsorption dynamics on crop straw residue during straw decomposition in an Alfisol
    LI Ji-fu, ZHONG Fang-fang
    2021, 20(1): 248-259.   DOI: 10.1016/S2095-3119(20)63238-5
    Returning crop straw to the field not only improves the nitrogen (N) supplying capacity and N retention of soil but also decreases the amount of rural organic waste and prevents air pollution.  Therefore, understanding the mechanisms of the N release and re-adsorption dynamics on crop straw residue during straw decomposition in agricultural soil is important, and this understanding can help us strengthen N fertilizer management during the crop growth period.  An on-farm incubation experiment was conducted in the Jianghan Plain in Central China under flooded conditions using the nylon mesh bag method.  Results showed that the decomposition rate of crop straw was much faster at the beginning of the incubation stage, whereas it was steady during the later stage with no observed differences among the three types of crop straw.  After 120 d of incubation, the cumulative decomposition proportion of rice straw, wheat straw and rape straw was 72.9, 56.2, and 66.9%, respectively.  The proportion of N that released from the three crop straws was 52.0, 54.4 and 54.9%, respectively.  The zeta potentials and Brunauer, Emmett and Teller (BET) surface area of the rice, wheat and rape straw residues increased gradually as the decomposition period progressed.  The water adsorption capacity of the rice straw was significantly affected during the decomposition period.  The saturated water adsorption capacity of rice straw was the highest at 30 d of decomposition (4.17 g g–1) and then decreased slightly.  The saturated water adsorption of wheat and rape straws reached the lowest value at 30 d and then gradually increased and became stable.  All the results demonstrated that crop straw and straw residue can re-adsorb NH4+ ions from the surrounding solution.  The re-adsorption was affected by the decomposition period and concentration of exogenous NH4+ and was independent of the crop species via the combined efforts of physical and chemical adsorption, ion exchange and water retention on residue surfaces.  Future studies will focus on straw returning and N fertilizer application at different levels of moisture content of the soil reduce potential negative effects such as water-logging and excess N caused by the straw substrate.
     
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    Nitrogen acquisition, fixation and transfer in maize/alfalfa intercrops are increased through root contact and morphological responses to interspecies competition
    SHAO Ze-qiang, ZHENG Cong-cong, Johannes A. POSTMA, LU Wen-long, GAO Qiang, GAO Ying-zhi, ZHANG Jin-jing
    2021, 20(8): 2240-2254.   DOI: 10.1016/S2095-3119(20)63330-5
    Nitrogen (N) fixation by legumes and nitrogen transfer to cereals have been considered as important pathways for overyielding and higher N use efficiency in cereal/legume intercropping systems.  However, the extent to which root morphology contributes to N fixation and transfer is unclear.  A two-factorial greenhouse experiment was conducted to quantify the N fixation, transfer and root morphology characteristics of the maize/alfalfa intercropping system in two consecutive years using the 15N-urea leaf labeling method, and combining two N levels with three root separation techniques.  N application could inhibit N fixation and transfer in a maize/alfalfa intercropping system.  Irrespective of the N application level, compared with plastic sheet separation (PSS), no separation (NS) and nylon mesh separation (NNS) significantly increased the total biomass (36%) and total N content (28%), while the N fixation rate also sharply increased by 75 to 134%, and the amount of N transferred with no root barrier was 1.24–1.42 times greater than that with a mesh barrier.  Redundancy analysis (RDA) showed that the crown root dry weight (CRDW) of maize and lateral root number (LRN) of alfalfa showed the strongest associations with N fixation and transfer.  Our results highlight the importance of root contact for the enhancement of N fixation and transfer via changes in root morphology in maize/alfalfa intercropping systems, and the overyielding system was achieved via increases in maize growth, at the cost of smaller decreases in alfalfa biomass production.
     
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    Effects of nitrogen application rates and irrigation regimes on grain yield and water use efficiency of maize under alternate partial rootzone irrigation
    QI Dong-liang, HU Tian-tian, SONG Xue
    2020, 19(11): 2792-2806.   DOI: 10.1016/S2095-3119(20)63205-1
    Faced with the scarcity of water resources and irrational fertilizer use, it is critical to supply plants with water and fertilizer in a coordinated pattern to improve yield with high water use efficiency (WUE).  One such method, alternate partial root-zone irrigation (APRI), has been practiced worldwide, but there is limited information on the performance of different irrigation regimes and nitrogen (N) rates under APRI.  The objectives of this study were to investigate the effects of varying irrigation regimes and N rates on shoot growth, grain yield and WUE of maize (Zea mays L.) grown under APRI in the Hexi Corridor area of Northwest China in 2014 and 2015.  The three N rates were 100, 200 and 300 kg N ha–1, designated N1, N2 and N3, respectively.  The three irrigation regimes of 45–50%, 60–65% and 75–80% field capacity (FC) throughout the maize growing season, designated W1, W2 and W3, respectively, were applied in combination with each N rate.  The results showed that W2 and W3 significantly increased the plant height, stem diameter, crop growth rate, chlorophyll SPAD value, net photosynthetic rate (Pn), biomass, grain yield, ears per ha, kernels per cob, 1 000-kernel weight, harvest index, evapotranspiration and leaf area index (LAI) compared to W1 at each N rate.  The N2 and N3 treatments increased those parameters compared to N1 in each irrigation treatment.  Increasing the N rate from the N2 to N3 resulted in increased biomass and grain yield under W3 while it had no impact on those under the W1 and W2 treatments.  The W3N3 and W2N2 and W2N3 treatments achieved the greatest and the second-greatest biomass and grain yield, respectively.  Increasing the N rate significantly enhanced the maximum LAI (LAI at the silking stage ) and Pn under W3, suggesting that the interaction of irrigation and fertilizer N management can effectively improve leaf growth and development, and consequently provide high biomass and grain yield of maize.  The W2N2, W2N3 and W3N3 treatments attained the greatest WUE among all the treatments.  Thus, either 60–65% FC coupled with 200–300 kg N ha–1 or 75–80% FC coupled with 300 kg N ha–1 is proposed as a better pattern of irrigation and nitrogen application with positive regulative effects on grain yield and WUE of maize under APRI in the Hexi Corridor area of Northwest China and other regions with similar environments.  These results can provide a basis for in-depth understanding of the mechanisms of grain yield and WUE to supply levels of water and nitrogen.
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    Food safety inspection and the adoption of traceability in aquatic wholesale markets: A game-theoretic model and empirical evidence
    JIN Cang-yu, Retsef LEVI, LIANG Qiao, Nicholas RENEGAR, ZHOU Jie-hong
    2021, 20(10): 2807-2819.   DOI: 10.1016/S2095-3119(21)63624-9
    Supply chain traceability is key to reduce food safety risks, since it allows problems to be traced to their sources.  Moreover, it allows regulatory agencies to understand where risk is introduced into the supply chain, and offers a major disincentive for upstream agricultural businesses engaging in economically motivated adulteration.  This paper focuses on the aquatic supply chain in China, and seeks to understand the adoption of traceability both through an analytical model, and empirical analysis based on data collected through an extensive (largest ever) field survey of Chinese aquatic wholesale markets.  The field survey includes 76 managers and 753 vendors, covering all aquatic wholesale markets in Zhejiang and Hunan provinces.  The analytical and empirical results suggest that the adoption of traceability among wholesale market vendors is significantly associated with inspection intensity, their individual history of food safety problems, and their risk awareness.  The effect of inspection intensity on traceability adoption is stronger in markets which are privately owned than in markets with state/collective ownership.  The analysis offers insights into the current state of traceability in China.  More importantly, it suggests several hypothesized factors that might affect the adoption of traceability and could be leveraged by regulatory organizations to improve it.
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    Closing the nitrogen use efficiency gap and reducing the environmental impact of wheat-maize cropping on smallholder farms in the Guanzhong Plain, Northwest China
    LÜ Feng-lian, HOU Miao-miao, ZHANG Hong-tao, Asif Khan, Muhammad Ayaz, QIANGJIU Ciren, HU Chang-lu, YANG Xue-yun, SUN Ben-hua, ZHANG Shu-lan
    2019, 18(1): 169-178.   DOI: 10.1016/S2095-3119(18)61948-3
    A high crop yield with the minimum possible cost to the environment is generally desirable.  However, the complicated relationships among crop production, nitrogen (N) use efficiency and environmental impacts must be clearly assessed.  We conducted a series of on-farm N application rate experiments to establish the linkage between crop yield and N2O emissions in the Guanzhong Plain in Northwest China.  We also examined crop yield, partial factor productivity of applied N (PFPN) and reactive N (Nr) losses through a survey of 1 529 and 1 497 smallholder farms that grow wheat and maize, respectively, in the region.  The optimum N rates were 175 and 214 kg ha−1 for winter wheat and summer maize, respectively, thereby achieving the yields of 6 799 and 7 518 kg ha−1, correspondingly, with low N2O emissions based on on-farm N rate experiments.  Among the smallholder farms, the average N application rates were 215 and 294 kg ha−1 season−1, thus producing 6 490 and 6 220 kg ha−1 of wheat and maize, respectively.  The corresponding PFPN values for the two crops were 36.8 and 21.2 kg N kg−1, and the total N2O emissions were 1.50 and 3.88 kg ha−1, respectively.  High N balance, large Nr losses and elevated N2O emissions could be explained by the overdoses of N application and low grain yields under the current farming practice.  The crop yields, N application rates, PFPN and total N2O for wheat and maize were 18 and 24% higher, 42 and 37% less, 75 and 116% higher, and 42 and 47% less, correspondingly, in the high-yield and high-PFPN group than in the average smallholder farms.  In conclusion, closing the PFPN gap between the current average and the value for the high-yield and high-PFPN group would increase crop production and reduce Nr losses or the total N2O emissions for the investigated cropping system in Northwest China.
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    The effects of water and nitrogen on the roots and yield of upland and paddy rice
    ZHANG Ya-jie, XU Jing-nan, CHENG Ya-dan, WANG Chen, LIU Gao-sheng, YANG Jian-chang
    2020, 19(5): 1363-1374.   DOI: 10.1016/S2095-3119(19)62811-X
    It is of great significance to study the root characteristics of rice to improve water and nitrogen (N) use efficiency and reduce environmental pollution.  This study investigated whether root traits and architecture of rice influence grain yield, as well as water and N utilization efficiency.  An experiment was conducted using the upland rice cultivar Zhonghan 3 (a japonica cultivar) and paddy rice cultivar Huaidao 5 (also a japonica cultivar) using three N levels, namely, 2 g urea/pot (low amount, LN), 3 g urea/pot (normal amount, NN), and 4 g urea/pot (high amount, HN), and three soil water potentials (SWPs, namely, well-watered (0 kPa), mildly dried (–20 kPa) and severely dried (–40 kPa).  The results showed that with decreasing SWP, the percentage of upland rice roots increased in the 0–5 cm tillage layer, and decreased in the 5–10 and 10–20 cm tillage layers, whereas paddy rice roots showed the opposite trend.  With increasing amounts of N, the yield of upland and paddy rice increased, and the percentage of root volume ratios of the two rice cultivars in the 0–5 and 5–10 cm tillage layers increased, whereas that in the 10–20 cm tillage layer decreased.  The roots of upland rice are mainly distributed in the 10–20 cm tillage layer, whereas most paddy rice roots are in the 0–5 cm tillage layer.  These results indicate that the combination of −20 kPa SWP and NN in upland rice and 0 kPa SWP and LN in paddy rice promotes the growth of the root system during the middle and late stages, which in turn may decrease the requirements for water and N fertilizer and increase rice yield. 
     
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    Strategies for timing nitrogen fertilization of pear trees based on the distribution, storage, and remobilization of 15N from seasonal application of (15N H4)2SO4
    JIANG Hai-bo, LI Hong-xu, ZHAO Ming-xin, MEI Xin-lan, KANG Ya-long, DONG Cai-xia, XU Yang-chun
    2020, 19(5): 1340-1353.   DOI: 10.1016/S2095-3119(19)62758-9
    In order to improve the management of nitrogen (N) fertilization in pear orchards, we investigated the effects of application timing on the distribution, storage, and remobilization of N in mature pear trees in a field experiment at Jingtai County, Gansu Province, China.  Nine trees were selected for the experiment and each received equal aliquots of 83.33 g N in the autumn, spring, and summer, with 15N-labeled (NH4)2SO4 used in one of the aliquots each season.  Results showed that the (15NH4)2SO4 applied in the autumn remained in the soil during the winter.  In the following spring this N was absorbed and rapidly remobilized into each organ, especially new organs (leaves, fruit and new shoots).  The 15N supplied in spring was rapidly transported to developing fruit between the young fruit and fruit enlargement stages.  15N from the summer application of fertilizer was mainly stored in the coarse roots over the winter, then was mobilized to support growth of new organs in spring.  In conclusion, for pear trees we recommend that the autumn application of N-fertilizer be soon after fruit harvest in order to increase N stores in fine roots.  Spring application should be between full bloom and the young fruit stages to meet the high N demands of developing fruit.  Summer application of fertilizer at the fruit enlargement stage does not contemporaneously affect the growth of pears, but increases the N stored in coarse roots, and in turn the amount available for remobilization in spring.
     
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