Submitted to: Crop Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/19/2013
Publication Date: 2/27/2014
Citation: Wang, G., Bronson, K.F., Thorp, K.R., Mon, J., Badaruddin, M. 2014. Multiple leaf measurements improve effectiveness of the cholorophyll meter in drum wheat nitrogen management. Crop Science. 54:817-826. Interpretive Summary: After water, nitrogen is the most important resource required for crop production. Excessive use of nitrogen fertilizer contributes to environmental degradation because fossil fuels are burned to produce the fertilizer and because nitrates from agricultural fields leach to surface water and groundwater. Therefore, research efforts are needed to find better ways to manage nitrogen resources. The purpose of this study was to evaluate alternative indies from a SPAD meter, a commercial device that measures the level of chlorophyll in plant leaves. Experiments were conducted to grow different durum wheat cultivars with varying levels of nitrogen fertilizer in central Arizona. A SPAD meter was used to measure leaf chlorophyll at different leaf positions on the plant, and various SPAD indices were calculated. The results demonstrated a new SPAD index, SPAD21, that improved the effectiveness of using a SPAD meter for durum wheat N management, as compared to previous SPAD indices. The results are useful for N fertility research in durum wheat, and the results are also being extended to durum wheat growers in central Arizona.
Technical Abstract: Simple 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 make 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 1) SPAD readings on the most recent fully expanded leaves (SPAD1), 2) Sufficiency Index or normalized SPAD index (SI), 3) Normalized difference SPAD index (NDSPAD), and 4) 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, Feekes 10, and Feekes 10.5) performed better than the other three indices in predicting crop yield due to the use of reference plots. This study suggests that using SPAD21 can improve the effectiveness of the SPAD meter in durum wheat N management as compared to SPAD1