Evaluation of the ¹⁵Nitrogen Isotope Dilution Technique for Estimating Crop Nitrogen Uptake from Organic Residues

Abstract

A field experiment was conducted to test the new approach for estimating crop nitrogen (N) uptake from organic inputs. The soil was prelabeled with ¹⁵N by applying ¹⁵N fertilizer to sunflower crop (Helianthus annuus L. var. Viki). The ¹⁴N plots, which received unlabelled fertilizer, were also set up. At harvest, ¹⁵N labeled residues were added to the unlabeled soils at a rate of 73 kg N ha⁻¹ (direct technique) and unlabeled residues were added to the ¹⁵N‐labeled soils at the same rate (indirect technique). Control plots without residues were also established. All plots were sown with the wheat (Triticum aestivum L. var merchouch)–fababean (Vicia faba L.)–wheat (Triticum aestivum L. var merchouch) cropping sequence.

In the cropping sequence, the first, second and third crop derived respectively 12.01, 2.4, and 1.93 kg N ha⁻¹ from crop residues estimated by the direct method and 14.77, 3.3, and 1.85 kg N ha⁻¹ estimated by the indirect method. The results showed no significant difference between the two techniques, which suggests that the new soil prelabeling technique compares well with the direct technique.

Keywords:

• Crop residues
• isotope techniques
• ¹⁵N
• nitrogen recovery

Acknowledgments

We gratefully acknowledge the financial support of the International Atomic Energy Agency (IAEA) and the Food and Agricultural Organization of the United Nations (FAO). We thank Felipe Zapata and K. S. Kumarasinghe for their help with all aspects of this work. We also to thank the Siebersdorf Laboratories for ¹⁵N analysis.