Developing An Instrument To Measure The Nutrient Of Crop Canopy Using Machine Vision Technology

Excessive application of fertilizer not only caused a lot of waste,increase the cost of agriculture production,but also caused a lot of environmental pollution and soil erosion.It is not conducive to the sustainable development of agriculture.To solve this problem,we need to enter the thinking of precision agriculture.We should to treated crops in fields differently.To achieve this goal we must know the nitrogen levels of crop in a rapid non-destructive testing way first.Based on this demand,this study developed an instrument using machine vision technology,which can measure the SPAD of crop in a rapid and non-destructive way.Specific research contents and conclusions are as follows:(1)In the near-infrared the reflectance of crop canopy is much higher than the soil background.Using this feature,we made a reference plate whose reflectance in near-infrared is between crop canopy and soil background.In the picture of crop canopy in the near-infrared using the gray value of the panel as a threshold value can separate crop canopy and soil background well.(2)The gray value is determined by the ambient light and the reflectance.We made four different colors on the reference panel.And there is a gradient of reflectance in the four colors.Using this we can make a model between gray value and reflectance.In this way we can eliminate the influence of ambient light on the crop canopy reflectance calculation successfully.(3)Determine the gray value of crop canopy first.Than using the model between gray value and reflectance wen can know the crop canopy reflectance in the green and near-infrared bands,and then obtain the GNDVI of crop canopy.We also use SPAD-502 to measure the SPAD of crop canopy.In this study we make a line fitting between GNDVI and SPAD for pepper and tea respectively.The equation of papper is SPAD= 116.72 GNDVI-29.066 and coefficient of determination(R2)is 0.8768.The equation of tea is SPAD=88.81GNDVI-11.32 and coefficient of determination(R2)is 0.7396.Both validation experiments also achieve good results.It shows that the measurement can meet the needs of the actual agricultural production.In addition,the instrument is applicable not only with one crop,and has a potential to measure a variety of crops.(4)In this study we make a line fetting between GNDVI and SPAD of papper and tea,whith were mixed.The result is SPAD=104.17GNDVI-20.896 and coefficient of determination(R2)is 0.7945.It is a good result.The verification experimental also shows the error is within the allowable range.It indicates that the instrument has the potential to measure a variety of crops with a same model(5)I write the corresponding image processing software for this system using VB language and develop the corresponding hardware,making the system works good.