Quantifying of soil organic carbon and total nitrogen through near infrared spectroscopy on forest plantations in Sabah, Malaysia

Understanding the physiochemical properties of soil is critical in ensuring the optimal growth of crops and trees in forest plantation. The utility of near infrared (NIR) spectroscopy has proven as an effective and inexpensive method for soil properties evaluation. Nevertheless, it requires a calibrated technique that must be developed to account for the heterogeneity of specific regions. Thus, this study aimed to develop NIR spectral calibrations for quantitation of soil total organic carbon (TOC) and total nitrogen (TN). Soil samples were collected from three sites in Sabah, Malaysia, namely Pitas, Kota Marudu, and Tawau districts. Soil TOC and TN were obtained from 143 soil samples that were collected, scanned, and analysed using standard chemical method and NIR spectroscopy. Partial least squares regression (PLSR) analysis using cross validation was performed and then validated using independent sample set. Calibrations were generated utilising only the A-horizon samples due to inadequate sampling size to be used as an independent validation set. The predictions of TOC and TN concentrations by the PLSR method were statistically sound, with high coefficients of determination for the validation set (R2 pred TOC =0.77 and R2 pred TN =0.53) and low root mean square error of prediction (RMSEPTOC =0.44 and RMSEPTN =0.051). The implementation of these calibrations to offer spatial evaluation of two contrasting micro-sites within a same area (AFI site) was also demonstrated. The study also demonstrates the potential utility of NIR spectroscopy predictions in swiftly and non-invasively characterizing site-soil attributes, thereby presenting it as an important decision support tool in managing forest plantations, particularly when combined with NIR spectroscopic measurement of foliar nutrient levels.

Text 116964.pdf Download (1MB) Official URL or Download Paper: http://ethesis.upm.edu.my/id/eprint/18303

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