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Acta Prataculturae Sinica ›› 2020, Vol. 29 ›› Issue (3): 130-136.DOI: 10.11686/cyxb2019268

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Effects of nitrogen application on nitrogen accumulation and root nitrogenase activity in Medicago sativa at different soil water contents

GAO Li-min, SU Jing, TIAN Qian, SHEN Yi-xin*   

  1. College of Agro-Grassland Science, Nanjing Agricultural University, Nanjing 210095, China
  • Received:2019-05-14 Online:2020-03-20 Published:2020-03-20

Abstract: The underlying mechanisms related to the impact of nitrogen fertilizer on alfalfa (Medicago sativa) growth at different soil water contents remain unclear. A pot experiment with three soil water levels (30%, 50% and 70% of the field water-holding capacity; W1, W2 and W3), and four nitrogen application rates (0, 0.02, 0.04 and 0.06 g N·kg-1; N1, N2, N3 and N4) was conducted to study the utilization of nitrogen fertilizer by alfalfa under different soil water regimes, and the relationships with nitrogen accumulation and root nitrogenase activity. The results indicated that: 1) for W1, alfalfa biomass increased significantly with increase in nitrogen application rate, while for W2 and W3, the highest biomass values were observed in N3 treatment; 2) for W1 and W2, the highest nitrogen accumulation was obtained in the N4 treatment, while for W3, the N3 treatment had the highest nitrogen accumulation. A positive relationship between the amount of nitrogen applied and alfalfa biomass was therefore concluded; 3) the root nitrogenase activity was increased with increase in soil water availability, but decreased with increase in nitrogen rate. No significant difference in root nitrogenase activity was observed between W3 and W4 with N4 application. Therefore, it was concluded from these results that under lower soil water content, nitrogen application was essential for meeting nitrogen demand and would promote alfalfa growth, and under higher soil water content, moderate nitrogen fertilizer application was advantageous for alfalfa growth, while higher rates of nitrogen fertilizer application inhibited root nitrogenase activity, and therefore no significant differences in nitrogen accumulation and biomass were found. The results of the present study provide a theoretical basis for determining water and nitrogen management in alfalfa production systems.

Key words: alfalfa, nitrogen application, soil water, nitrogenase activity, nitrogen accumulation