Abstract
There exists serious heavy metal contamination of agricultural soils in China. It is not only time- and labor-intensive to monitor soil contamination, but it also has limited scope when using conventional chemical methods. However, the method of the heavy metal monitoring of soil based on vegetation hyperspectral technology can break through the vegetation barrier and obtain the heavy metal content quickly over large areas. This paper discusses a highly accurate method for predicting the soil heavy metal content using hyperspectral techniques. We collected leaf hyperspectral data outdoors, and also collected soil samples to obtain heavy metal content data using chemical analysis. The prediction model for heavy metal content was developed using a difference spectral index, which was not highly satisfactory. Subsequently, the five factors that have a strong influence on the content of heavy metals were analyzed to determine multiple regression models for the elements As, Pb, and Cd. The results showed that the multiple regression model could better estimate the heavy metal content with stable fitting that has high prediction accuracy compared with the linear model. The results of this research provide a scientific basis and technical support for the hyperspectral inversion of the soil heavy metal content.
Highlights
Soil is the basis for plant growth and development, supplying the water, air, and mineral elements on which plants depend
Zhao et al selected two Cd gradient sample plots in Guixi to study the effect of rice Cd pollution on the spectral characteristics, and the results showed that with an increased Cd content in the soil, the depth of the blue and red valleys became shallow, the slope of the red pass became smaller, the NDVI705 (Normalized Difference Vegetation Index) value decreased, and the reflectance decreased in the near-infrared waveband (R750–1250 ) [25]
In order to analyze the relationship between spectral indices and soil heavy metal elements, we explored the correlation between four spectral indices with different wave combinations and six soil heavy metal elements, by which we determined the sensitive wave combinations of each heavy metal element
Summary
Soil is the basis for plant growth and development, supplying the water, air, and mineral elements on which plants depend. In 2014, China conducted a national survey on soil pollution, which showed an alarming overall soil environment, especially for heavy metal pollution on farmland and industrial and mining wasteland [1,2]. Excessive heavy metals in soil will cause stress to crops and affect their growth and development [6,7,8], and accumulate in crops through the food chain and in the human body, which makes them a major safety hazard to human health and the environment [9,10,11].
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