Relationship Between the Normalized SPAD Index and the Nitrogen Nutrition Index: Application to Durum Wheat

ABSTRACT

In a three-year field experiment in Toulouse (in Southwest France), two indicators of plant nitrogen (N) status were compared on five durum wheat cultivars: the normalized SPAD index and the nitrogen nutrition index (NNI). SPAD value is a non-destructive measurement of chlorophyll content from the last expanded leaf. The normalized SPAD index is expressed relative to SPAD reading on a fully fertilized crop. The NNI is calculated from the crop biomass and total plant N content using a universal N-dilution curve for wheat. The normalized SPAD index and NNI were closely related irrespective of year, cultivar, and growth stage. When N was a limiting factor, the SPAD index measured at anthesis predicted grain yield and protein content accurately. Unlike NNI, SPAD index cannot be used to predict these variables when wheat is over-fertilized.

Keywords:

• SPAD
• nitrogen nutrition index
• durum wheat
• plant N status
• grain protein content
• chlorophyll meter

ACKNOWLEDGMENTS

The experiments were conducted on the INRA Experimental Station of Toulouse-Auzeville by J. M. Nolot and his technical staff. J. P. Hardouin (C. C. Benoist) provided the D95-223 line for this study. NIRS determinations were made by INRA-Montpellier (UMR DGPC). This work was supported by GIE Blé Dur and the French Ministry of Agriculture (2000–2002). We are grateful to all of them for their help.

Notes

*Including an extra 60 kg N ha applied on April 13.