Humic acid structural characteristics in soils under different land uses in Ilesa, Nigeria

Numerous studies have examined the spectroscopic and elemental properties of soil humic acids (HA) from different soil orders, but little is known about how land usage affects the features of humic acids from Nigerian alfisol. The aim of the study is to ascertain how land use affects HA properties, which have a significant impact on the quality of organic matter. It was predicted that HA characteristics are dependent on the agricultural use of the soil and its years of existence. The study was conducted on six different types of land uses in Nigeria: a maize farm (MF), a citrus grove (CT), an oil palm plantation (OP), an abandoned alley crop farm (AC), an agroforestry site (AG), and an area with solely natural vegetation (NC). Soil HAs were analysed by Fourier transform infrared (FTIR) and UV-Vis spectroscopies. The percent humic acid yield of 100 g of soil was highest at the uncultivated site. The HA samples appeared to be highly aromatic, condensed, and hydrophobic for all land use types, according to FTIR spectroscopy. The spectra also showed a low E4/E6 absorbance coefficient, indicating a tendency for increased condensation of aromatic structures, higher molecular weight, and greater humification. No significant effect due to land use was observed between the two techniques. However, further in-depth investigation is required on the impacts of factors such as particle size and the potential of HAs from these soils.