N‐Tester Use in Soft Winter Wheat: Evaluation of Nitrogen Status and Grain Yield Prediction

Chlorophyll meters can be an alternative to traditional tissue analysis as plant N nutritional diagnostic tools. In the present study, the relationships among chlorophyll meter N‐Tester measurements, plant N concentration, N uptake at different growth stages (GS‐32, GS‐37), and grain yield were studied to evaluate the N‐Tester as a tool to diagnose the N status of soft red winter wheat ( Triticum aestivum L. cv. Soissons) and predict yield. Ten experiments were conducted in the years 2001, 2002, and 2003 where 0, 100, 140, 180, and 220 kg N ha −1 were applied. N‐Tester values ranged between average values of 382 and 608 at GS‐32 for 0 and 220 kg N ha −1 , respectively, and between 408 and 649 at GS‐37 for 0 and 220 kg N ha −1 correspondingly. The normalization of N‐Tester values in relation to a non‐N‐limited plot (i.e., ≥220 kg N ha −1 ) enabled the prediction of plant N concentration ( R 2 = 0.64) of Soissons soft red winter wheat at GS‐32 and N uptake at both at GS‐32 and GS‐37 ( R 2 > 0.6) in contrast to absolute N‐Tester values ( R 2 < 0.4). However, when excluding the N‐Tester values corresponding to control treatments (0 kg N ha −1 ), the robust correlations diminished as to invalidate comparison of normalized N‐Tester readings for N concentration and N uptake across different sites and years for rates in the 100 to 220 kg N ha −1 range. Normalized N‐Tester values could discriminate between grain yields from non‐N‐fertilized and fertilized plots but could not distinguish grain yields among plots fertilized in the 100 to 220 kg N ha −1 range.