Nutrient Cycling in Agroecosystems

, Volume 80, Issue 1, pp 49–60 | Cite as

Crop responses to 15N-labelled organic and inorganic nitrogen sources

  • Ahmed El-Naggar
  • Ahmed El-Araby
  • Andreas de Neergaard
  • Henning Høgh-Jensen
Research Article


A major challenge for low-external-input farming systems is to secure the N supply. Lack of synchrony between mineralization of organic N sources and plant N requirements is causing many growers to use different techniques to overcome this problem. One of these techniques is the application of soluble water extracts of different farm residues and plants. A field study was conducted to study the crop uptake of applied 15N-labeled alfalfa and clover extracts as compared to the N uptake from15N-glycine and three levels of 15N-(NH4)2SO4. The results show that total N accumulation in the field crops, squash and lettuce was primarily affected by the amount of added N (P ≤ 0.05) and not by the form in which the N was applied (P ≤ 0.05). The utilization efficiencies of N (pNdff) from plant extracts and glycine increased (P ≤ 0.05) gradually from 10, 20, to 30 days after application in contrast to (NH4)2SO4 which peaked in utilization efficiencies of 56% around 20 days after application. The pNdff reached 60%, 40% and 36% of the applied glycine, alfalfa and clover extracts, respectively in lettuce. Squash showed the same pattern during at 10, 20 and 30 days; however, the proportion of N derived from most of the treatments was higher in squash than in lettuce (P ≤ 0.05). These results indicate that plant extracts of clover and alfalfa can be used as efficient N fertilisers in low-external-input agroecosystems.


Organic N Plant extracts Amino acids uptake Fertiliser efficiency 



The authors would like to thank the Danish Research Council for funding the project, Dr Yahia Galal from the Egyptian Atomic Energy Authority for facilitating the 15N analysis and Mr Jim Rasmussen for useful comments preparing the manuscript. Thanks are due to agronomist Mr Abd El-Galil and others for their help during the field work.


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Copyright information

© Springer Science+Business Media B.V. 2007

Authors and Affiliations

  • Ahmed El-Naggar
    • 1
    • 2
  • Ahmed El-Araby
    • 2
  • Andreas de Neergaard
    • 1
  • Henning Høgh-Jensen
    • 1
  1. 1.Department of Agricultural Sciences, Faculty of Life SciencesCopenhagen UniversityTaastrupDenmark
  2. 2.Department of Soil Science, Faculty of AgricultureAin Shams UniversityCairoEgypt

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