Abstract
The content of total nitrogen, phosphorus and potassium in the soil is an important basis for calculating the best fertilization amount and realizing the reasonable fertilization of the orange planting soil in time and accurately. In this research, hyper-spectral technology is applied to detect the three soil nutrient elements in the cultivated soil of citrus trees. Four spectral bands with central wavelengths of 660, 780, 870 and 970 nm and width of 20 nm are selected to measure the spectral reflectance of the potted kumquats canopy by hand-held spectrometer. At the same time, the content of total nitrogen, phosphorus and potassium in the cultivated soil of kumquat is determined using traditional methods. The correlation between the spectral information of kumquat canopy and the content of soil nutrient elements is analyzed by correlation coefficient method. The prediction model of soil nutrient element content based on the spectral information is established by multiple linear regression method. The results showed that the total potassium content of soil is significantly correlated with the spectral reflectance at 660 nm wave band and significantly correlated with the spectral indexes of R660/R780, R660/R870 and R660/R970. R2 of the prediction model of total potassium content established on the basis of spectral reflectance and ratio spectral index of the selected band is 0.756 and 0.857 respectively, which shows good prediction effect of the model. There is no significant correlation between the spectral reflectance and ratio spectral index of the selected band towards the total soil nitrogen and phosphorus content and it cannot be used for the rapid measurement of total nitrogen and phosphorus content. Further study is needed to select suitable spectral band and spectral index.
Highlights
China is a big country of citrus production, with the largest planting area and output in the world (Li, 2011)
The purpose of this study is to investigate the correlation between the canopy spectra of citrus and the contents of total nitrogen (TN), total phosphorus (TP) and total potassium (TK) in soil
Two kinds of prediction models of soil nutrient element content based on the spectral reflectance and ratio spectral indexes of citrus canopy are established
Summary
China is a big country of citrus production, with the largest planting area and output in the world (Li, 2011). Nitrogen (N), phosphorus (P) and potassium (K) in the soil of citrus cultivation area are the main nutrient elements for the growth and development of citrus. The content of total nitrogen, phosphorus and potassium is the key index to evaluate soil quality and calculate the amount of fertilizer. The results of traditional chemical analysis methods of soil total nitrogen, phosphorus and potassium content are relatively accurate (Song et al, 2012), the long measurement cycle and high cost cannot achieve rapid, large-scale and real-time monitoring. Ding et al (2011) found that 570 nm, 600 nm and 610 nm spectral bands have good indicators for soil organic matter and fertility. Chen et al (2008) showed that the near-infrared spectroscopy technology can accurately detect the total nitrogen content and roughly estimate the total P in soil. Musadji et al (2012) found that the spectra near 700 nm and 1050 nm were closely related to the content of soil organic matter and clay minerals. Chen et al (2008) showed that the near-infrared spectroscopy technology can accurately detect the total nitrogen content and roughly estimate the total P in soil. Yi et al (2011) found that near-infrared spectroscopy can be used to predict the
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