Field testing of a handy near-infrared reflectance meter for on-site measurement on leaf nitrogen
1999
Adachi, S. | Ito, O. | Kubota, S. (International Rice Research Inst., P.O. Box 3127, 1271 Makati City (Philippines))
On-site estimation of leaf N is very useful not only for practical purposes such as deciding when to apply N fertilizers but also for physiological studies on leaf N status. This has been done extensively using a SPAD meter and a leaf color chart. These estimations are based on the close relationship between chlorophyll content and N content in leaves. The relationship can be generallly applied, but not in all cases, especially during leaf senescence. Estimation of total N by a near-infrared reflectance (NIR) is based on signals emitted by the N molecules and does not require any wet chemistry procedure unlike the conventional Kjeldahl digestion method. A handy type of NIR meter has recently been developed for field use. The objective of this study is to test the applicability of the meter in estimating leaf N in rice plants. Leaf N was estimated by SPAD (Minolta, Model SPAD-502), NIR (Satake, Model CCN-05A), and kjeldahl digestion. The measurements were taken from the long-term continuous cropping experiment at IRRI [Philippines], which had four levels of N treatments (0, 45, 90 and 135 kg/ha). The experiment was repeated two times (early and late wet season). In general, a significant correlation was obtained between SPAD and NIR measurements regardless of leaf position (flag leaf, 2nd and 3rd from the top). A high correlation (r square=0.89) was obtained among 45 cultivars tested in separate experiments. The total N analysis by wet chemistry is now on going. A difference between two meter readings was observed in N distribution along the leaf vein. The SPAD reading showed a tendency to increase with distance from the leaf tip, but the NIR reading tended to decrease. It is suggested that the handy NIR can become a powerful tool for the field N estimation
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