Abstract:

The spectral model of soil phosphorous (P) has relatively poor stability, mainly owing to the insufficient understanding of its visible and near-infrared spectral characteristics. To this end, we propose a new method to explore the reflectance spectrum of total P using soil residues by sequentially extracting different P fractions. In particular, the reflectance spectra of different P fractions were measured indirectly using the standard whiteboard as the reference spectrum and measured directly using the soil residues as the reference spectrum. The spectral characteristics of these P fractions and their spectral models were analyzed.Both indirect and direct results showed that each P fraction had a specific reflectance spectrum with different spectral characteristics, spectral shapes, reflectance rates, and peak/valley positions. Therefore, they could be qualitatively and quantitatively analyzed by visible and near-infrared spectroscopy (200~1000 nm). Results suggesteed that 250~750 nm is the sensitive band of soil P. This study can provide an important theoretical basis for understanding the reflectance spectrum and predicting the concentrations of total P.

Key words: soil phosphorous fractions; visible-near-infrared spectral characteristics, Fe-P, Ca-P, O-P, spectral model