Benefits of Agroforestry for Maintaining Soil Health: Using Microbial Biomass Carbon (MBC) as an indicator

The conversion of natural forests for unsustainable agricultural land use continues, increasing the area of degraded land. Degraded lands can be reused for agriculture after reclaiming them using an agroforestry system (AF). Variation in plant species planted in an agroforestry system determines variation in canopy cover and in litter layer properties; litter is a source of energy for organisms while litter cover maintains soil moisture and supports the activity of soil microorganisms. This study evaluated the Microbial Biomass Carbon (MBC) content from various land use systems (LUS) with different levels of canopy cover, as an indicator of (top)soil health. The study was conducted in two places with volcanic soils: five land use systems (LUS) in Junggo village on the slopes of Mount Arjuno (Malang Regency, East Java) in 2023, and eight land use systems in two villages (Air Dingin and Sirukam) around Mount Talang (Solok Regency, West Sumatra) in 2024. Soil sampling at both study sites was carried out on plots measuring 20 × 20 m2 using a Tropical Soil Biology and Fertility (TSBF) protocol for sampling and laboratory analysis. On the slopes of Mount Arjuno, monolith samples were from 5 points and 3 soil depths (0-10 cm, 10-20 cm and 20-30 cm) per plot. MBC in the second and third layer were on average 52% and 40% of that in the first layer. Around Mount Talang only the 0-10 cm layer was sampled, in 12 points per plot (CSM-BGBD protocol). Measurements at each LUS were carried out in three replications (different plots). MBC in the remnant forest in Solok was 82% higher (477 mg kg-1) than that in the mature agroforestry systems (AFMT). AFMT in both sites had an MBC of 262-270 mg kg-1, double to four times the value at the non-agroforestry annual cropping systems (68-150 mg kg-1), and 33% higher than that of the Imperata grasslands in Solok. Agroforestry reclamation may lead to an initial drop in MBC, followed by recovery to the level of the grasslands. The MBC data align with canopy cover and its associated litter input as determinant of soil health.