Issue 10, 2023

Large-scale measurement of soil organic carbon using compact near-infrared spectrophotometers: effect of soil sample preparation and the use of local modelling

Abstract

Compact near-infrared (NIR) spectrophotometers are low-cost instruments that enable rapid, non-destructive and environmentally friendly measurement of soil organic carbon (SOC). However, several aspects, such as soil sample preparation modes or modelling strategies, related to the use of these instruments in large and heterogeneous data sets are yet to be addressed extensively. This work aimed to evaluate the performance of two compact NIR spectrophotometers (NeoSpectra and NanoNIR) to determine SOC content in a large-scale application. Also, it is important to understand the implications of soil sample preparation (soil grinding and drying) and the use of local partial least squares regression (LOCAL-PLSR) on the accuracy of the models built using these instruments. The soil samples of the calibration (n = 320, selected using the Kennard–Stone algorithm) and validation sets (n = 160) were collected from Minas Gerais state (approximately 589 000 km2), Brazil. Three soil sample preparation modes were considered: air-dried and 2 mm sieved samples, air-dried and finely ground samples, and oven-dried and ground samples. Models to determine SOC were developed using the traditional PLSR (GLOBAL-PLSR) and a new approach based on LOCAL-PLSR, and their performance was evaluated using the root mean square error of prediction (RMSEP). The accuracy of the models built using the compact instruments was compared with the accuracy achieved using a bench Vis-NIR spectrophotometer. The NeoSpectra was the best-performing spectrophotometer, showing values of RMSEP, R2 and bias, respectively, between 5.2 and 6.3 g kg−1, 0.522 and 0.645 and −0.08 and −0.594. Significant enhancements in SOC estimation of up to 13% were found when models were calibrated using LOCAL-PLSR and oven-dried and ground soil samples. Our results showed that compact NIR spectrophotometers are a cost-effective alternative to the Vis-NIR spectrophotometers for large-scale SOC measurement. Models built using these instruments were accurate, mainly when LOCAL-PLSR calibration was used together with oven-dried and ground soil samples.

Graphical abstract: Large-scale measurement of soil organic carbon using compact near-infrared spectrophotometers: effect of soil sample preparation and the use of local modelling

Supplementary files

Article information

Article type
Paper
Submitted
27 feb 2023
Accepted
30 jul 2023
First published
31 jul 2023
This article is Open Access
Creative Commons BY-NC license

Environ. Sci.: Adv., 2023,2, 1372-1381

Large-scale measurement of soil organic carbon using compact near-infrared spectrophotometers: effect of soil sample preparation and the use of local modelling

A. A. Fonseca, C. Pasquini and Emanuelle. M. B. Soares, Environ. Sci.: Adv., 2023, 2, 1372 DOI: 10.1039/D3VA00046J

This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence. You can use material from this article in other publications, without requesting further permission from the RSC, provided that the correct acknowledgement is given and it is not used for commercial purposes.

To request permission to reproduce material from this article in a commercial publication, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party commercial publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements