Development of fast-determination instrument for rice leaf nitrogen content based on spectroscopy

An instrument used to measure the SPAD values and nitrogen content for rice leaf was developed based on the spectral technique. The instrument consists of optical unit, conditioning unit and control and data acquisition unit. The optical unit includes light source, detection point and photoelectric sensor. Its primary role is to control the light on or off, collect the light permeating through the leaves, and convert the optical signal to electrical signal. Conditioning unit mainly converts the weak signal to current or voltage, and enlarges it to suitable range. Control and data acquisition unit includes the AD conversion circuit, liquid crystal display circuit and SD card storage circuit. In this study, the performance of the instrument was tested through two steps: 1) Set up the prediction model between AD sampling voltage value and the SPAD value; 2) Set up the prediction model between SPAD value and the nitrogen content. After several tests, the voltage value had a high correlation with the SPAD value, and the decision coefficient (R2) was 0.956. The decision coefficient (R2) between SPAD value and nitrogen content reached 0.802. Combining the results of two models, the decision coefficient (R2) was 0.766 for nitrogen content prediction. It show that the instrument can successfully used to quick measurement for rice leaf nitrogen content in field.