Multiple Leaf Measurements Improve Effectiveness of Chlorophyll Meter for Durum Wheat Nitrogen Management

Abstract

ABSTRACTSimple and rapid methods are needed to measure durum wheat (Triticum durum L.) nitrogen (N) status and make on‐site N application decisions for increased crop yield and grain quality. Although chlorophyll meters (SPAD meters) have been widely tested for cereal crop N management, significant variation in SPAD meter readings among growing seasons, locations, and crop cultivars makes them challenging. Experiments with six durum wheat cultivars and six N fertilizer rates were conducted in Arizona in the 2010–2011 and 2011–2012 growing seasons to test whether multiple leaf SPAD readings on the same plants can improve estimation of crop N status by SPAD meters. The relationships between N nutrition index (NNI) and SPAD readings on the most recent fully expanded leaves (SPAD1), Sufficiency Index or normalized SPAD index (SI), Normalized difference SPAD index (NDSPAD), and the differences in SPAD readings between the second most recent and most recent fully expanded leaves (SPAD21) were compared. The results showed SPAD1 varied with growing season, growth stage, and durum wheat cultivar. All three indices, SI, NDSPAD, and SPAD21, improved the prediction of durum wheat N status compared to SPAD1. The SI measured at Feekes 10.5 or mean SI over growth stages (Feekes 5, 10, and 10.5) performed better than the other three indices in predicting crop yield. This study suggests that using SPAD21 can improve the effectiveness of the SPAD meter compared to SPAD1 and that SPAD21 can be as effective as SI without requirement of reference plots in durum wheat N management.