Abstract
Near-infrared (NIR) spectroscopy is widely used to predict soil organic carbon (SOC) because it is rapid and accurate under proper calibration. However, the prediction accuracy of the calibration model may be greatly reduced if the soil characteristics of some new target areas are different from the existing soil spectral library (SSL), which greatly limits the application potential of the technology. We attempted to solve the problem by building a large-scale SSL or using the spiking method. A total of 983 soil samples were collected from Zhejiang Province, and three SSLs were built according to geographic scope, representing the provincial, municipal, and district scales. The partial least squares (PLS) algorithm was applied to establish the calibration models based on the three SSLs, and the models were used to predict the SOC of two target areas in Zhejiang Province. The results show that the prediction accuracy of each model was relatively poor regardless of the scale of the SSL (residual predictive deviation (RPD) < 2.5). Then, the Kennard-Stone (KS) algorithm was applied to select 5 or 10 spiking samples from each target area. According to different SSLs and numbers of spiking samples, different spiked models were established by the PLS. The results show that the predictive ability of each model was improved by the spiking method, and the improvement effect was inversely proportional to the scale of the SSL. The spiked models built by combining the district scale SSL and a few spiking samples achieved good prediction of the SOC of two target areas (RPD = 2.72 and 3.13). Therefore, it is possible to accurately measure the SOC of new target areas by building a small-scale SSL with a few spiking samples.
Highlights
Soil is a natural resource that humans depend on for survival
Spectral data, and prediction models were established through the partial least squares (PLS) algorithm to predict the soil organic carbon (SOC) of two target areas
Since SOC is affected by regional climatic conditions, vegetation, land use, and other factors, the feasibility of the spiking method was further studied in order to improve the universality of the prediction model
Summary
Soil is a natural resource that humans depend on for survival. Soil organic carbon (SOC) content is an important indicator to evaluate soil fertility, which directly reflects the soil quality and affects crop growth [1]. The measurement of SOC content is of great significance for accurate fertilization [2]. As a part of the global carbon cycle, studying the content and distribution of SOC helps human society understand the problem of global warming [3]. As a rapid, nondestructive, and accurate technique, near-infrared (NIR). Spectroscopy has been widely used to predict soil nutrient information [4].
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