WFL Publisher Science and Technology Rapid assessing of water and nitrogen status in wheat flag leaves

In semiarid regions, moisture supply is the most important uncontrollable factor influencing the effects of nitrogen (N) applications on wheat yields, protein content and test weight. The major effect of increasing N is to increase protein, but excessive N encourages the crop to outgrow its moisture supply, resulting in depressed crop yields and test weights. In contrast, yield may respond to N applications under abundant moisture, but protein increases occur only at very high rates. This study tested the use of near infrared transmittance (NIRt) and near infrared reflectance (NIRr) spectrometry for monitoring water and N contents in flag leaves at heading of spring wheat growing in a semi-arid region during three growing seasons (2000 to 2002). Four optical devices were compared: Minolta’s SPAD-502 that measures transmittance at two wavelengths (650 and 940 nm); Ocean Optics ’ S2000 that measures transmittance spectra (530-1100 nm); Licor’s Li-1800 spectroradiometer equipped with an external integrating sphere, that measures reflectance within the range of 400-1100 nm; and Foss NIR System’s model 5000 that measures reflectance within the NIR region (1100-2498 nm). Each set of measurements was analyzed with the Foss WinISI ® II software. Leaf water and nitrogen contents were calibrated wit