Soil Quality from Nigerian Alfisol Under Different Agricultural Land Use Types

This study focuses on the evaluation of different chemical characteristics of humic acids (HA) from Nigeria Alfisol as surrogates of soil agroecological quality under different cultivation regimes in proximity. Conventional cassava farm, oil palm plantation, agroforestry, and undisturbed sites were studied at two soil depths of 0–15 cm and 15–30 cm using elemental analysis and Fourier transform infrared spectroscopy (FTIR). The highest yield of HAs was recorded at the undisturbed site at the two soil depths (topsoil, 25%, and subsoil, 15%). The percent carbon of the humic acid extracted from the topsoil and subsoil clustered around 56%. Strong peaks attributed to structural vibrations of aromatic C = C and antisymmetrical stretching of COO– groups around 1630 cm–1 region was common to all the spectra. The topsoil of the oil palm plantation showed band peak at 1230 cm−1 which were attributed to C–O stretching and OH bending of COOH functional group. Cultivation type and soil depth had a great influence on the humic acid yield. Crops planted on the farms do not significantly influence the characteristics of humic acids, which suggest high stability and resilience as shown in the FTIR spectra of HAs. However, notable differences in the intensity of some bands were observed depending on site characteristics and soil depth. A steady supply of plant residues in the tree-based agricultural systems significantly improved OM accumulation and quantity of humic acid.