Monitoring Uptake of Legume N by Apple Trees Using Nitrogen Isotope Discrimination
CSANR Project 138
Intercropped legumes can supply nitrogen to fruit trees and reduce the need for purchased nitrogen fertilizer, potentially reducing costs and environmental footprint. The proposed research project will address the biologically-intensive and organic approaches to sustainable management of soil quality priority. The project will evaluate the nitrogen isotope abundance technique (comparing the 15N and 14N signal from the legume N versus other sources) as a method to monitor the degree of uptake by apple trees of legume N grown in the orchard. The project involves two components: 1) a greenhouse study using 15N-labeled clover residue added to potted apple trees for a quantitative evaluation of legume-N uptake and a comparison to values using nitrogen isotope 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 discriminate this signal in an ambient field environment. The 15N enrichment technique is known to be more sensitive than the nitrogen isotope abundance technique, but is not suitable for routine field use by growers or consultants. The objective of the proposed project is 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.