تخمین کربن آلی خاک با استفاده از مدل‌های شبکه عصبی مصنوعی و رگرسیون خطی چندگانه بر اساس پردازش تصاویر رنگی

کربن آلی خاک منبع عظیمی از مواد مغذی برای گیاه بوده و به‌عنوان عاملی فعال در گسترش ساختمان خاک، نقش مهمی در بهبود حاصل‌خیزی خاک‌های کشاورزی دارد. هدف اصلی از این پژوهش، تخمین میزان کربن آلی خاک در زمین‌های کشاورزی با استفاده از یک روش ساده، سریع و کم هزینه می‌باشد. 80 نمونه خاک از مزارع کشاورزی شمال آذربایجان غربی تا جنوب استان به‌صورت انتخابی جمع‌آوری شد و پس از تعیین مقدار کربن آلی نمونه‌ها در آزمایشگاه، نمونه‌ها در شرایط کنترل شده مورد تصویربرداری قرار گرفتند. تصاویر رنگی در چندین فضای رنگی مختلف تحلیل شدند و در هر فضای رنگی، مدل‌های شبکه عصبی و رگرسیون چندگانه برای برآورد میزان کربن آلی خاک توسعه یافت. نتایج مدل‌سازی خطی نشان داد که بالاترین ضریب همبستگی در فضاهای رنگی lab و luv به‌ترتیب 0/91 و 0/92 برای مدل‌های استخراج شده از مولفه‌های این فضاها و کربن آلی خاک به‌دست آمد. نتایج حاصل از طبقه‌بندی به‌وسیله شبکه عصبی نشان داد که ضریب همبستگی در فضای rgb‌ بالاترین مقدار را داشته و برابر با 0/94 بوده است. نتایج نشان داد که در تمامی فضاها مدل‌سازی شبکه عصبی دقت مدل را افزایش داده است.

Estimation of Soil Organic Carbon using Artificial Neural Network and Multiple Linear Regression Models based on Color Image Processing

<strong > Introduction </strong >The color of soil depends on its composition and this feature is easily available and rather stable. Fast and accurate determination of soil organic matter distribution in the agricultural fields is required, especially in precision farming. General laboratory methods for determining the soil organic carbon are expensive, timeconsuming with many repetitions, and high consumption of chemicals. Soil scientists use the Munsell soil color diagrams to define the soil color. Due to the nature of Munsell color diagrams; this system is less suitable for recognizing exact color of the soil because of weak relationship and limited number of chips. Fast methods like image processing, colorimetric and spectroscopy provide a description of most physical characteristics of the soil color. Some of the advantages of using digital cameras was used in this study, are simple sampling of screened soil, being free from chemicals and toxic materials and being fast, inexpensive and precise. <strong >Materials and Methods </strong >In this research, 80 Ahorizon (010 cm) soil samples were collected from various agricultural soils in west Azerbaijan, in the North West of Iran. Soil texture of these fields was loam clay and clay. The amount of organic carbon in samples was determined. The camera was installed at the distance of 0.5 m from the Petri dish on the lighting compartment. Captured images with the digital camera were saved in RGB color space. Processing operations were done by MATLAB 2012 software. The features extracted from the color images are used to model the soil organic carbon including the color features in different spaces. Fourcolor spaces including RGB, HSI, LAB and LUV were studied to find the relation between the color and the soil organic carbon. <strong >Results and Discussion </strong >The correlation of R component in the RGB model shows a strong singleparameter relation with the organic carbon as R2=0.83. This good relationship can be due to the compound information of the red color component on both brightness and chromaticity dimension. The results also show that the organic carbon has a relatively strong correlation with the light parameters, intensity and lightness in the HSI, Lab and LUV color spaces respectively. It also has a weak correlation with other parameters, since they cannot have a proper linear correlation with organic carbon due to their structural nature. Results show that the highest correlation is obtained when the R and G components participate in modeling and the component B is omitted. One explanation of this high correlation could be the high sensitivity of component B to the intensity and the angle of light. Even a small change in light changes this component. Thus, in order to reduce the effect of this component, it is better to omit it from the models and make models independent of it. In next section, 51 data were used to train neural network, 14 data were used to test the network and 12 data for network validating. The amount of soil organic carbon was output of the neural networks that was estimated after training using the color component values of each segment. To assess the accuracy of the network, estimated values and actual values of each sample were plotted in a graph. The minimum MSE values were 7.28e6 with 16 neurons, 3.77e6 with 14 neurons, 4.8e3 with 10 neurons and 3.77e6 with 12 neurons for RGB, HSI, Lab and LUV color spaces respectively. <strong >Conclusions </strong >The availability of digital cameras, possibility to use it in different situations, being inexpensive and providing many samples are the advantages of this method to estimate the soil organic carbon amount. Therefore, digital photography can be used as an analytical method to evaluate the soil fertility. It also requires a low cost of sample testing, and can provide a good possibility of time and place classification for studying a vast area. However to develop more reliable models, more effort is needed, such as collecting more soil samples of different areas that include a wide range of soil features.