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

Ahmed El-Naggar, Ahmed El-Araby, Andreas de Neergaard, Henning Høgh Jensen

Research output: Contribution to journalJournal articleResearchpeer-review


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.

Original languageEnglish
JournalNutrient Cycling in Agroecosystems
Issue number1
Pages (from-to)49-60
Publication statusPublished - 2008
Externally publishedYes


  • Organic N
  • Plant extracts
  • Amino acids uptake
  • Fertiliser efficiency


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