Chlorophyll meter readings in winter wheat: Cultivar differences and prediction of grain protein content

Leaves of winter wheat (Triticum aestivum L.) were measured with a Hydro N-Tester (HNT), a portable chlorophyll meter, to obtain a relative estimate of leaf chlorophyll content, which gives an indication of plant N-status. The aim was to find if there were differences in HNT values between the winter wheat cultivars investigated, and to assess whether these values could be used for prediction of grain protein content (GPC). In Experiment 1, chlorophyll meter readings were taken at growth stages (GS) Zadoks 31 and 55 in five winter wheat (Triticum aestivum L.) cultivars in 17 annual field trials located in southeast Norway in 1996, 1997, and 1998. There were significant differences in HNT values between cultivars at both GS 31 and 55, but no differences were found between the three most commonly used cultivars in Norway at present, cvs. Bjorke, Mjolner and Rudolf. Because of the variation between years the HNT values at GS 55 were found to be unsuitable for direct prediction of the GPC. In Experiment 2, HNT was used in 21 annual N-fertilizer trials with winter wheat, performed in 1996 and 1997 and located in southeast Norway. A delay in the measurements from GS 55 to GS 65 generally improved the GPC prediction in 1996. Nitrogen applied at GS 55 increased GPC by approximately 1 unit of percent in cv. Folke, regardless of HNT value, while in cv. Portal nitrogen applied at this stage gave no increase in GPC at HNT values beyond 700.