Soil Fertility Assessment of the Rehabilitated Riparian Areas in Mt. Kitanglad, Lirongan, Talakag, Bukidnon, Philippines

Soil resource degradation is one of the recurring problems in the Philippines, mainly driven by deforestation and poor agricultural practices, leading to decreased fertility and soil erosion. In Mt. Kitanglad, Lirongan, Talakag, Bukidnon, a restoration method is introduced using Calliandra calothyrsus to eradicate the dense Imperata cylindrica spreading in the area and causing impairment to the landscape ecosystem. This study determines the soil’s available nutrients and quality in areas rehabilitated with Calliandra calothyrsus, compared to a control site dominated by Imperata cylindrica. Soil samples from six rehabilitated sites and one control site were analyzed for physical and chemical content. Composite samples were collected from six to ten soil subsamples from each site to analyze the physical and chemical properties of the soil. The temperature and moisture of the soil were measured on-site using soil test kits. The hydrometer and core methods assessed soil texture and bulk density, respectively. The findings suggest that the control site had higher soil fertility indicators – including organic carbon, organic matter, and nitrogen (N). The rehabilitated sites with Calliandra calothyrsus had an optimum N content of 0.49 ± 0.18% and bulk density of 1.08 ± 0.11 g cm3 but showed deficiencies in the soil pH (5.30 ± 0.39), phosphorus (0.50 ± 0.16 mg kg–1), and potassium [0.17 ± 0.16 cmol (+) kg–1]. Thus, a revision of the management approach such as increased fertilizer application and agricultural lime is recommended to improve the soil fertility and neutralize the soil pH in the rehabilitated areas. Periodic physicochemical monitoring, soil micronutrient assessment, and microbial analysis will further aid in assessing the effects of Calliandra calothyrsus on soil fertility at the study site.