title: Nondestructive diagnostic test for nitrogen nutrition of grapevine (Vitis vinifera L.) based on dualex leaf-clip measurements in the field.
abstract: Crop nitrogen status is a major issue for crop yield and quality. It is usually assessed by destructive leaf or petiole tissue analysis. A quantitative nondestructive optical estimation of N sufficiency would be a great leap forward toward precision crop management. We therefore calibrated three optical indices against leaf nitrogen content: chlorophyll (Chl), epidermal flavonols, and the nitrogen balance index (NBI), which is the ratio of the former two indices. NBI was the best estimator of leaf N content measured by the Dumas or Kjeldahl method with a root-mean-square error smaller than 2 mg of N g(-1) dry weight, followed by Chl (3 mg g(-1)) and flavonols (4 mg g(-1)). This allowed us to propose the threshold values for the Dualex optical indices that characterize nitrogen supply to grapevines: the first is the threshold below which N supply to the vine can be considered deficient, and the second is the threshold above which N supply is excessive. For a putative optimal N content of 30 mg g(-1) < x < 40 mg g(-1), these thresholds are 30 μg cm(-2) < x < 40 μg cm(-2) for Chl and 11 < x < 18 for NBI at flowering. At bunch closure, for N thresholds of 22 < x < 32, Chl is 29 < x < 37 and NBI is 8 < x < 11, in respective units. These values should be verified and refined in the future for various growth regions and cultivars using the specified protocol. The sample size should be 36-60 leaves from a fixed node position, preferably node no. 5 from the tip of the shoot. An alternative to the use of the NBI would be to discard leaves that are not light exposed by checking their flavonol content and to deduce the N sufficiency directly from the Chl values.
authors: †Laboratoire Écologie Systématique et Évolution, Université Paris-Sud, UMR 8079 CNRS, Bâtiment 362, F-91405 Orsay, France.|‡AgroParisTech, F-75231 Paris, France.
authors: Zoran G
authors: ZG
authors: Cerovic
authors: §FORCE-A, Université Paris-Sud, Bâtiment 503, F-91405 Orsay, France.
authors: Naïma Ben
authors: NB
authors: Ghozlen
authors: §FORCE-A, Université Paris-Sud, Bâtiment 503, F-91405 Orsay, France.
authors: Charlotte
authors: C
authors: Milhade
authors: ∥Château Gazin, Chemin de Chantecaille, F-33500 Pomerol, France.
authors: Mickaël
authors: M
authors: Obert
authors: ⊥Comité Interprofessionnel du Vin de Champagne (CIVC), 5 rue Henri-Martin, boîte postale 135, F-51200 Epernay, France.
authors: Sébastien
authors: S
authors: Debuisson
authors: §FORCE-A, Université Paris-Sud, Bâtiment 503, F-91405 Orsay, France.
authors: Marine
authors: M
authors: Le Moigne
mesh_terms: D002623:Chemistry Techniques, Analytical / Q000295:instrumentation / Q000379:methods*; D009584:Nitrogen / Q000032:analysis*; D018515:Plant Leaves / Q000737:chemistry*; D027843:Vitis / Q000737:chemistry*
chemical_list: D009584:Nitrogen
keywords: Dualex; chlorophyll; flavonols; nitrogen balance index; nitrogen fertilization; optical sensors; precision farming