A Portable Method for Determining Nitrogen Efficiency of Woody Plants in the Field

A portable method for determining nitrogen efficiency of woody plants in the field, which belongs to the technical field of determining nitrogen efficiency of woody plants. The method includes the following steps: 1) Setting of nitrogen concentration gradient and blank control, 15N isotope labeled urea with 50% abundance; 3) Each plant is slowly watered along the base with 500-1000 mL of 15N labeled urea and blank control pure water with the above five concentration gradients; 4) After one week, the mature leaves at the top of each plant are collected; 5) The leaves are washed with pure water respectively, which are ground with a pulverizer after freeze-drying, and stored in a drying dish for determining; 6) The 15N abundance and total nitrogen content of the sample are determined by C / N element analyzer; 7) Calculating of the plant nitrogen efficiency; 8) Nonlinear fitting.