Transforming Soil Analysis: A Rapid Method for Assessing Carbon and Nitrogen in South African Forestry Soils

By Ms Direshnee Naidoo, Mr Glen Cooper, Dr Richard Burgdorf, Dr Danvir Ramesar

As concerns about soil health and carbon sequestration grow, understanding the state of soil organic matter (SOM) in South African forestry plantations has never been more critical. Traditional methods for analysing SOM can be expensive and time-consuming, posing significant challenges for comprehensive monitoring. However, recent advancements in technology offer promising alternatives.

At the Institute for Commercial Forestry Research (ICFR), a team led by the authors has initiated a project to develop a rapid analysis method for measuring soil carbon, nitrogen, and organic matter using Near Infrared Reflectance Spectroscopy (NIRS).

The Challenge of Traditional Methods

Currently, total SOM is measured using loss-on-ignition (LOI), while total carbon and nitrogen are assessed through combustion-gas analysis. While these methods are reliable, they come at a high cost—ranging from R250 to R450 per sample—which can hinder extensive soil assessments. This is where the need for innovative solutions becomes evident.

Enter Near Infrared Reflectance Spectroscopy

NIRS is a non-destructive technique that evaluates the interaction of light with soil samples in the near-infrared range. By capturing the unique spectral signature of each sample, NIRS can predict key properties like SOM, carbon, and nitrogen content. This method is not only rapid and cost-effective but also allows for high-throughput analysis, addressing the limitations of traditional approaches.

ICFR’s Promising Findings

At the ICFR Forestry Research and Analytical Laboratory (FRAL), the team has utilised a diverse collection of soil samples to create and test predictive models for SOM analysis. These models have shown that NIRS can effectively interpret the spectral signatures of plantation soil samples, making it a viable tool for routine analysis. However, the team emphasises the importance of calibrating these models to specific sites to account for variations in soil composition, climate, and silvicultural practices.

The Take-Home Message

The successful application of NIRS for measuring SOM properties represents a significant advancement in soil analysis. By integrating NIRS with existing methods, the cost of analysis can be reduced, enabling a more extensive examination of soil health across forestry plantations. This innovative approach not only supports better site assessments but also fosters improved carbon management practices.

As the ICFR continues to refine these models, they aim to enhance their applicability for the entire forestry industry, paving the way for more sustainable and informed forest management practices.