The nitrogen nutrition index as a tool to assess nitrogen use efficiency in potato genotypes

Enhancing nitrogen (N) use efficiency (NUE) is crucial for the sustainable production of potatoes (Solanum tuberosum L.). The aims of this study were to assess i) the genotypic variation of the main components of NUE (N utilization efficiency (NUTE) and N recovery efficiency (NRE)), ii) the association between these components, related traits, and cultivars, and iii) the usefulness of N nutrition index (NNI) to assess NUTE and NRE of potato genotypes grown under different levels of N availability. Two field experiments were carried out in Chile during the season 2021–2022. Treatments were the combination of 15 potato cultivars and three rates of N (0, 200, and 400 kg N ha⁻¹). High variations were observed in total dry matter biomass (DM) (5.9–22.1 Mg ha⁻¹), tuber DM biomass (5.1–18.3 Mg ha⁻¹), total N concentration (1.01–2.24 %), total N uptake (98–323 kg ha⁻¹), NUTE (35–91 kg tuber DM kg⁻¹ N), and NRE (−14–54 %). Total N uptake was significantly related to total DM biomass and traits related to N concentration and N uptake. In both experiments, strong negative correlations were observed between total N concentration and NUTE (r = −0.95 – −0.98). Also, NUTE and N harvest index were positively correlated. The relationship between NUTEtub and NNI was well described (p < 0.01; R² = 0.55–0.87) by a negative power function. The predicted average of NUTEtub for a NNI = 1 (optimal N status) showed a narrow range (49.5–56.9 kg DM kg⁻¹ N). Both relative tuber yield and relative total biomass were significantly related to NNI (R² = 0.56 and 0.66). The cultivar Desiree, Karu-INIA, and Shepody were among the cultivars with the highest NNI. A significant positive relationship (p < 0.01; R² = 0.42) was observed between NRE and NNI. This study demonstrates the effectiveness of the NNI in evaluating and interpreting NUTE and NRE based on genotype and nitrogen supply, ultimately enhancing decision support for improving NUE in potato production systems.