文献类型： 外文期刊

作者： Xie Kai-yun;Li Xiang-lin;He Feng;Wan Li-qiang;Wang Dong;Qin Yen;Fadull, Gamal M. A.;Xie Kai-yun;Zhang Ying-jun;Hannaway, David B.

作者机构：

关键词： alfalfa (Medicago sativa);smooth bromegrass (Bromus inermis);nitrogen (N-2) fixation;nitrogen partitioning;N-15;mixture;monoculture

期刊名称： JOURNAL OF INTEGRATIVE AGRICULTURE

ISSN： 2095-3119

年卷期： 2015 年 14 卷 9 期

页码：

收录情况： SCI

摘要： Planting grass and legume mixtures on improved grasslands has the potential advantage of realizing both higher yields and lower environmental pollution by optimizing the balance between applied N fertilizer and the natural process of legume biological nitrogen fixation. However, the optimal level of N fertilization for grass-legume mixtures, to obtain the highest yield, quality, and contribution of N-2 fixation, varies with species. A greenhouse pot experiment was conducted to study the temporal dynamics of N-2 fixation of alfalfa (Medicago sativa L.) grown alone and in mixture with smooth bromegrass (Bromus inermis Leyss.) in response to the addition of fertilizer N. Three levels of N (0, 75, and 150 kg ha(-1)) were examined using N-15-labeled urea to evaluate N-2 fixation via the N-15 isotope dilution method. Treatments were designated N0 (0.001 g per pot), N75 (1.07 g per pot) and N150 (2.14 g per pot). Alfalfa grown alone did not benefit from the addition of fertilizer N; dry matter was not significantly increased. In contrast, dry weight and N content of smooth bromegrass grown alone was increased significantly by N application. When grown as a mixture, smooth bromegrass biomass was increased significantly by N application, resulted in a decrease in alfalfa biomass. In addition, individual alfalfa plant dry weight (shoots+roots) was significantly lower in the mixture than when grown alone at all N levels. Smooth bromegrass shoot and root dry weight were significantly higher when grown with alfalfa than when grown alone, regardless of N application level. When grown alone, alfalfa's N-2 fixation was reduced with N fertilization (R-2=0.9376, P=0.0057). When grown in a mixture with smooth bromegrass, with 75 kg ha(-1) of N fertilizer, the percentage of atmospheric N-2 fixation contribution to total N in alfalfa (%Ndfa) had a maximum of 84.07 and 83.05% in the 2nd and 3rd harvests, respectively. Total 3-harvest %Ndfa was higher when alfalfa was grown in a mixture than when grown alone (shoots: vertical bar t vertical bar=3.39, P=0.0096; root: vertical bar t vertical bar=3.57, P=0.0073). We believe this was due to smooth bromegrass being better able to absorb available soil N (due to its fibrous root system), resulting in lower soil N availability and allowing alfalfa to develop an effective N-2 fixing symbiosis prior to the 1st harvest. Once soil N levels were depleted, alfalfa was able to fix N-2, resulting in the majority of its tissue N being derived from biological nitrogen fixation (BNF) in the 2nd and 3rd harvests. When grown in a mixture, with added N, alfalfa established an effective symbiosis earlier than when grown alone; in monoculture BNF did not contribute a significant portion of plant N in the N75 and N150 treatments, whereas in the mixture, BNF contributed 17.90 and 16.28% for these treatments respectively. Alfalfa has a higher BNF efficiency when grown in a mixture, initiating BNF earlier, and having higher N-2 fixation due to less inhibition by soil-available N. For the greatest N-use-efficiency and sustainable production, grass-legume mixtures are recommended for improving grasslands, using a moderate amount of N fertilizer (75 kg N ha(-1)) to provide optimum benefits.

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