Monitoring Uptake of Legume N by Apple Trees Using Nitrogen Isotope Discrimination

Intercropped legumes can supply nitrogen to fruit trees and reduce the need for purchased nitrogen fertilizer, potentially reducing costs and environmental footprint. The project evaluated nitrogen isotope techniques (comparing the 15N and 14N signal from the legume N versus other sources) to monitor the degree of uptake by apple trees of legume N grown in the orchard. The project involved two components:  1) a greenhouse study using 15N-labeled clover residue added to potted apple trees to quantify legume-N uptake and a comparison to values using nitrogen isotope natural abundance; 2) a field study in an existing orchard legume cover crop trial using natural abundance for a qualitative evaluation of legume N and the ability to detect this signal in an ambient field environment.  The 15N enrichment technique is known to be more sensitive than the natural isotope abundance technique, but is not suitable for routine field use by growers or consultants.  The objective of the project was to determine the uptake of legume-derived N in a quantitative manner and compare it with a more qualitative method to assess its utility on farms. Lower tree leaf 15N atom% with legume alleys versus grass was detected in several instances in both trials, indicating that the natural isotope abundance method does have potential use for monitoring the timing of legume uptake by trees.

Grant Information

  • Project ID: 138
  • Project Status: Complete


  • Principal Investigator(s): Granatstein, D.
  • Investigator(s): Desta, K., Pavek, P.
  • Grant Amount: $31,801


  • Principal Investigator(s): Granatstein, D.
  • Investigator(s): Davenport, J., Pavek, P.



A journal article is in preparation in collaboration with Dr. Lee Kalcsits.