Assessing leaf nitrogen content and leaf mass per unit area of wheat in the field throughout plant cycle with a portable spectrometer

Leaf nitrogen content (LNC) and leaf mass per unit area (LMA) were assessed by near-infrared spectroscopy (NIRS) on fresh and dried plants of durum wheat (Triticum turgidum ssp). Individual leaves were scanned with a portable spectrometer and reference analyses of LNC and LMA were then carried out. Partial least squares (PLS) regression was used for calibration and cross-validation. LNC was accurately predicted for both fresh and dry leaves whatever the phenologic stage (correlation coefficient of calibration R2cal ranging from 0.932 to 0.958, standard error of cross-validation SECV ranging from 0.215 to 0.320% (dry matter)). LMA was predicted with R2cal = 0.942 and SECV = 4.84 g m−2. The combination of these two calibrations made it possible to predict leaf nitrogen per unit area (R2cross-validation = 0.94, SECV = 0.248 gN m−2) and provides a relevant and non-destructive tool for following the dynamics of three major leaf parameters.

► Accurate calibrations (R2 > 0.93) predict wheat leaf nitrogen content and leaf mass per area. ► One calibration is valid during all wheat plant cycle. ► Calibrations are robust because a wide range of genotypes and conditions were included. ► Assessed foliar parameters could be integrated in ecophysiology functional modeling. ► Calibrations are valid both on fresh or dried leaves.