Petiole Nitrate Analysis: A Diagnostic Method for Optimizing Nitrogen Management in Potato

Abstract

Petiole nitrate-N (NO₃⁻-N) concentration can serve as a diagnostic method to adjust in-season nitrogen (N) application rates. However, its utility in determining the economic optimum N rate (EONR) has not been evaluated for the potato crop. This study aimed to (i) assess petiole NO₃⁻-N as a predictor of N nutritional status, potato tuber yield response to N, and the EONR; (ii) define critical NO₃⁻-N concentrations in petioles throughout the growing season; and (iii) develop a model to estimate the EONR based on petiole NO₃⁻-N. Sixteen field experiments were conducted evaluating four N rates. Petiole NO₃⁻-N concentration, shoot N concentration (Nsh), and shoot N nutrition index (NNIsh) were measured from 40 to 80 days after planting (DAP), while total tuber yield was recorded at maturity. Petiole NO₃⁻-N concentration was significantly and positively related with Nsh and NNIsh and was associated with tuber yield response to N and the EONR. A model to define the critical NO₃⁻-N concentration during the growing season was developed (Critical NO₃⁻-N = −0.36 × DAP + 32.6), identifying a high probability of N deficiency below the calculated critical threshold. Additionally, models were created to estimate the EONR when a deficiency is detected. These findings confirm that petiole NO₃⁻-N concentration is a reliable and low-labour method for monitoring N status during the potato growing season. The proposed models can help potato growers optimize N application rates, promoting sustainable N management practices.