Soil carbon estimation from &lt;i&gt;eucalyptus grandis&lt;/i&gt; using canopy spectra

Thamsanqa Mzinyane,Jan Van Aardt,Michael T Gebreslasie

doi:10.4314/sajg.v4i4.12

Abstract

Mapping soil fertility parameters, such as soil carbon (C), is fundamentally important for forest management and research related to forest growth and climate change. This study seeks to establish the link between Eucalyptus grandis canopy spectra and soil carbon using raw and continuum-removed spectra. Canopy-level spectra were collected using a hand-held 350-2500nm spectroradiometer and soil samples obtained at depths from 0-1.2m and analysed for carbon content. Partial least squares (PLS) selection was used to selected optimal bands for soil carbon assessment and further bootstrapped to select 35 Variable Importance in Projection (VIP) parameters, based on correlation (r) and standard error (SE). Results indicated that continuum-removed spectra and soil C yielded stronger significant correlations, when compared to soil C and raw spectra. The predictive models developed for future soil C estimation showed that continuum-removed spectra exhibited improved adjusted R 2 values in both instances, i.e., when using all significant bands and the most significant 35 VIP bands. The results indicate a distinct potential for forest managers to monitor the status of soil C in commercial forestry compartments using canopy-level spectra and determine how much fertilizer is required to optimize tree growth. Keywords : Soil carbon, Canopy spectra

Highlights

Soil represents a fundamental resource when it comes to the provision of a range of even general ecological functions, such as fibre production, food security, biodiversity, and environmental services (Biazin et al 2012)
This study demonstrated that canopy spectra can be used as proxy for soil carbon content, based on the causal relationship that exist between soil nutrients and plant growth, i.e., leaf nutrient content
The continuum-removed model performed better than the raw spectra model. Since this is first study to explore this foliage-soil approach according to our knowledge, there is a need to test the applicability of using airborne imaging spectroscopy remote sensing data such as HyMap, to acquire large spatial area coverage and to better understand the landscape variability of soil C and other soil fertility parameters at air or space platform

Summary

Introduction

Soil represents a fundamental resource when it comes to the provision of a range of even general ecological functions, such as fibre production, food security, biodiversity, and environmental services (Biazin et al 2012). Soil fertilityrelated chemical parameters, such as carbon (C), nitrogen, soil organic matter, soil salinity content, soil pH, calcium, magnesium, sodium, potassium, and phosphorus contents, previously have been assessed using conventional field-based methods (Viscarra Rossel et al 2006). The major disadvantages of field-based methods are the generation of toxic wastes, e.g., chromate oxidation (Walkley and Black, 1934), which require careful and proper disposal, combustion products (Allison et al, 1965), their expensive and time-consuming nature (Watson et al 2000, McCarty et al 2002). Soil carbon serves as a primary source of energy and nutrients for many soil organisms (Aïchi et al 2009) and is inconstant in both space and time (Batchily et al 2003). Spectroscopy datasets, including laboratory based and air borne or space borne imaging spectroscopy, have been used in the past to assess soil C content (Brunet et al 2007, Gomez et al 2008)

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