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, GS37), 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-Nfertilized and fertilized plots but could not distinguish grain yields among plots fertilized in the 100 to 220 kg N ha^-1 range.