European Journal of Agronomy 123 (2021) 126205 1161-0301/© 2020 Published by Elsevier B.V. Critical phosphorus dilution curve and the phosphorus-nitrogen relationship in potato Judith Nyiraneza a, *, Gilles B´ elanger b , Rim Benjannet a, b , Noura Ziadi b , Athyna Cambouris b , Keith Fuller c , Sheldon Hann d a Charlottetown Research and Development Centre, Agriculture and Agri-Food Canada, 440 University Avenue, Charlottetown, PE, C1A 4N6, Canada b Quebec Research and Development Centre, Agriculture and Agri-Food Canada, 2560 Hochelaga Boulevard, Qu´ ebec, QC, G1V 2J3, Canada c Kentville Research and Development Centre, Agriculture and Agri-Food Canada, 32 Main Street, Kentville, NS, B4N 1J5, Canada d Fredericton Research and Development Centre, Agriculture and Agri-Food Canada, 850 Lincoln Road, P.O. Box 20280, Fredericton, NB, E3B 4Z7, Canada A R T I C L E INFO Keywords: Phosphorus dilution curve Nitrogen Phosphorus Phosphorus nutrition index Potato Tubers Vines ABSTRACT Besides nitrogen (N), phosphorus (P) is the most limiting nutrient for potato growth and P acquisition and utilization is affected by the N supply. Estimating accurately the P nutrition status is critical from economic and environmental standpoints. Our objectives were to (i) compare a critical P (P c ) curve based on the biomass (DM) of the whole plant (vines + tubers) with those recently developed in Argentina (Zamuner et al., 2016, P c = 3.92 × DM 0.30 ) and Colombia (G´ omez et al., 2016, P c = 5.23 × DM -0.19 ); (ii) analyze P dilution in vines and tubers, and to develop P c curves for vines and tubers; and (iii) analyze the relationship between N and P concentrations in vine, tuber, and total biomass along with the changes in the N:P ratio with increasing biomass. Five P rates up to 240 kg P 2 O 5 ha -1 were applied to potatoes on soils located in four Canadian provinces from 2016 to 2018 for a total of 11 site-years. Vine, tuber, and total biomass, and N and P concentrations were measured weekly on fve dates starting 50 days after planting, and tuber yield was measured at harvest. The P c curve in total biomass (P c = 3.57 × DM -0 ⋅ 38 ) was below that developed in Argentina and Colombia. The P and N concentrations of vine, tuber, and total biomass as well as the N:P ratio declined with increasing biomass. and Pc curves were developed for vines (P c = 2.58 × DM -0.20 ) and tubers (P c = 2.06 × DM -0.14 ). The P nutrition index (PNI) measured in vines or tubers with their respective P c curves was signifcantly related to the PNI in total biomass, implying that P suffciency before tuber initiation can be estimated by analyzing vines only. Indices to assess P suffciency along with N and P imbalances in potato vine, tuber, or total biomass represent a promising alternative or a com- plement to the soil P tests traditionally used for fertilizer recommendations. 1. Introduction Potato growers tend to apply fertilizer P at rates greater than crop P requirements to compensate for P fxation to calcium in alkaline soils and to Al and Fe oxides and hydroxides in acidic soils (Parent et al., 2003; Benjannet et al., 2018). Several studies have reported that current P fertilizer recommendations for potatoes could be reduced without reducing yields (Fernandes and Soratto, 2016; Nyiraneza et al., 2017a,b; Benjannet et al., 2018, 2020). Increases in soil P availability due to excessive P fertilization is a known environmental issue with P reaching surface waters through erosion, resulting in eutrophication (Sharpley et al., 2013; Nair, 2014; Li et al., 2019). Impairment of water quality due to eutrophication has been reported in the USA (Stachelek et al., 2018), Canada (Munawar and Fitzpatrcik, 2018), and Europe (Whithers and Haygarth, 2007). Phosphorus suffciency diagnostic tools are therefore required to optimize P fertilizer management to increase the economic and environmental performance of potato production. Critical P concentration (P c ), defned as the minimum plant P con- centration needed to achieve maximum crop biomass, is a suitable analytical tool to assess the crop P nutrition status (B´ elanger et al., 2015a; Zamuner et al., 2016; Cadot et al., 2018; G´ omez et al., 2019). This concept, initially developed for N in different crops including Abbreviations: DAP, days after planting; DM, dry matter; NB, New Brunswick; N, nitrogen; NS, Nova Scotia; P, phosphorus; P c , critical P; PNI, phosphorus nutrition index; PEI, Prince Edward Island; RY, relative yield; QC, Quebec. * Corresponding author. E-mail address: Judith.nyiraneza@canada.ca (J. Nyiraneza). Contents lists available at ScienceDirect European Journal of Agronomy journal homepage: www.elsevier.com/locate/eja https://doi.org/10.1016/j.eja.2020.126205 Received 27 August 2020; Received in revised form 14 November 2020; Accepted 15 November 2020