Relationship between the normalized SPAD index and the nitrogen nutrition index: application to durum wheat
Debaeke, P. | Rouet, P. | Justes, E.
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 nondestructive 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.
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