Optimal Leaf Positions for SPAD Meter Measurement in Rice

Area of Science:

• Agronomy
• Plant Physiology
• Remote Sensing

Background:

• The Soil Plant Analysis Development (SPAD) chlorophyll meter is crucial for assessing crop nitrogen status.
• Inaccurate SPAD meter measurements can arise from variations in methodology.
• Optimizing SPAD measurement techniques is essential for reliable crop nitrogen assessment.

Purpose of the Study:

• To develop an optimized methodology for SPAD meter measurements in rice (Oryza sativa L.).
• To enhance the accuracy of estimating crop nitrogen status using SPAD chlorophyll meter readings.

Main Methods:

• Utilized a flatbed color scanner to map chlorophyll distribution and leaf morphology.
• Applied calculus algorithms to determine optimal SPAD measurement points on rice leaves.
• Simultaneously analyzed data from the scanner and SPAD meter.

Main Results:

• A measurement position 2/3 from the leaf base to the apex (2/3 position) showed low variance, representing whole-leaf chlorophyll content.
• The 2/3 position on lower leaves demonstrated higher sensitivity to chlorophyll variations.
• The 2/3 position on the fourth fully expanded leaf from the top proved most effective for predicting rice nitrogen status.

Conclusions:

• Recommends SPAD measurements at the 2/3 position on the fourth fully expanded leaf from the top for accurate rice nitrogen status prediction.
• Integrating chlorophyll distribution and leaf shape data offers a promising approach for SPAD meter calibration.
• This optimized method can significantly improve in situ nitrogen management through reliable crop nutrition assessment.