Design Of OSAVI Measuring Instrument Facing To Variable Nitrogen Application

Application of nitrogen fertilizer is an important method in crop production. Adequate nitrogen fertilizer can increase crop yield and protein content, but excessive nitrogen fertilizer can not achieve the objective of high yield and high quality. What's worse, it will reduce nitrogen fertilizer use efficiency, increase nitrogen fertilizer loss, and cause pollution of the environment.There is correlation between spectral index (such as NDVI and OSAVI) and vegetation physiological indicators. The researchers at home and abroad found that OSAVI could be applied to the growth of crops and nitrogen monitoring, so we can use variable fertilizer according to the growth of crop (OSAVI values). So finding a cheap and convenient method for measuring the OSAVI will bring significance for using nitrogen fertilizer rationally and reducing environment pollution.For the problem of excessive nitrogen application, variable nitrogen application algorithm based on spectral index is introduced, and a novel instrument for measuring optimization soil-adjusted vegetation index (OSAVI) is introduced. The optical design, hardware design and software design are introduced in the paper. The light intensity is converted to the current by the sensor, and then the current will be converted to the voltage by the conversion circuit. The voltage will connect to the ADC which integrates in the MSP430. OSAVI measuring instrument which uses the MSP430 as the core has LCD, keyboard, flash memory, serial port and can easily communicate with the upper computer. Modular design method and structured design method were used in the software design of OSAVI measuring instrument. The software of OSAVI measuring instrument includes initialization routine, main circulation routine and interrupt service routine. The reflectivity value of OSAVI measuring instrument is a relative value, so instrument calibration should be carried on with ASD spectrometer. Least square estimation can be used in the calibration and improve the accuracy of the instrument.OSAVI measuring instrument has the characteristic of simple structure, low cost and convenient application. The test shows that OSAVI measuring instrument can measure spectral index precisely and has low power. Upper computer software can use the OSAVI values to calculate the amount of nitrogen fertilizer, so the system can direct the variable nitrogen application accordind to the algorithm.