Carbon sequestration and nutrient cycling in agroforestry systems on degraded soils of Eastern Amazon, Brazil

Abstract

Land degradation and rural poverty are widespread in the Eastern Brazilian Amazon. Slash-and-burn agriculture is the main source of livelihood in small farms but also a driver of degradation. In this context, Agroforestry Systems (AFS) are an alternative for climate change mitigation and land restoration, allying food security and ecosystem services reestablishment. We evaluated the increment of carbon stock (aboveground biomass, necromass, and soil) and standing litter nutrients in AFS and compared with natural succession. Treatments were established in 30 × 30 m plots with six repetitions (randomized block design) on a very degraded soil at UEMA School farm, in Eastern Amazon. In AFS, the 17 planted tree species of local interest (for fruit, timber, N-fixing) were associated with agricultural species and fertilized according to local standards. Carbon stock was measured in 2012 before the experiment setup (baseline) and in 2018. Aboveground carbon increment (Mg ha−1) was higher in AFS (26.79 ± 23.41) than in natural succession (1.13 ± 1.5), because of tree and shrub cover as a result of planting efforts. We found very high variability in plant development and carbon sequestration between plots. Soil organic carbon did not present increment between 2012 and 2018, and no differences between treatments were found in 2018. Species choice plays a keyhole for carbon sequestration and nutrient cycling reestablishment. Areas under natural succession presented very low resilience, evidencing the need for active restoration. Diverse agroforestry systems are an efficient strategy to restore forest cover on degraded soils of Amazon allying ecosystem services reestablishment and production.