Predicting post-anthesis N requirements of bread wheat with a Minolta SPAD meter

Winter wheat (Triticum aestivum L., cv. Hereward, a bread-making variety) was grown on different fields at Rothamsted (England) in eight seasons (1993-2001). Each crop received a range of N fertiliser (0-300 kg N/ha as granular ammonium nitrate) applied as soil top-dressings in March-April. The aim was to see if N concentrations in shoots and leaves at anthesis could be used to predict %N in grain at maturity, and therefore, the need for post-anthesis fertiliser to boost grain protein. The Minolta SPAD meter which estimates chlorophyll concentration in single leaves was also investigated as a potential indicator method. Grain yield ranged from 3 to 11 t/ha (85% DM), and grain N from 1.43 to 2.46% in response to N rate. A 13% protein target for milling quality (0% moisture), equivalent to a grain N concentration of 2.3% (assuming a conversion factor of 5.7), was associated with a yield of 11 t/ha (85% DM), and required N concentrations at anthesis of 2% in whole shoots and 4% in flag leaves. A yield of 11 t/ha (85% DM) combined with 2.3% N in grain equates to a grain N requirement of 215 kg/ha. SPAD readings in flag leaves at anthesis could also be used to predict %N in grain at maturity. The critical SPAD value was 52.4 for 2.3% grain N. The SPAD meter has potential for predicting grain N requirements, but further work is needed to establish SPAD calibrations for other wheat varieties under UK conditions. (C) 2003 Elsevier B.V. All rights reserved.