The potential of the marula tree, Sclerocarya birrea, (A. Rich.) Horchst subspecies litterfall in enhancing soil fertility and carbon storage in drylands

The potential of Sclerocarya birrea subspecies as native trees to improve agricultural productivity and combat global warming through carbon storage has not been fully explored, despite their extensive distribution across global drylands. The objective of this study was to determine the potential of litterfall from Sclerocarya birrea subspecies to improve soil organic carbon (OC) and fertility, and carbon storage in drylands. Leaf and fruit litterfall samples, comprising 18 samples for each subspecies, from nine trees of subspecies birrea, caffra, and multifoliata were collected in Tanzania. Soil samples were collected under and away from the canopies of the selected trees. The soil pH and the concentrations of organic carbon (OC) and nutrients (total Nitrogen - TN, P, K, Ca, Mg, Na, Cu, Zn, Fe, Mn, S) in the soil, fruit, and leaf litterfall were determined using standard laboratory methods of analysis. The results showed that leaf OC in S. birrea subspecies ranged from 41.16% to 43.49%, and TN from 1.01% to 1.19%. The C:N ratio ranged from 34.58% to 41.66% in leaf, and from 52.73% to 75.12% in fruit litterfall. Phosphorus was significantly higher in fruit (0.17-0.20%) than in leaf (0.02-0.04%) for all subspecies. Ca and Mg were higher in leaf litterfall (0.54-0.89% Ca and 0.19-0.27% Mg), than in fruit litterfall (0.08-0.11% Ca and 0.10% Mg). Cu, Fe, and Mn concentrations were significantly higher in fruit, ranging from 11.71 to 31.42 mg kg-1, 214.13 to 400.59 mg kg-1, and 31.42 to 54.77 mg kg-1, respectively, than in leaf with 3.32 to 4.39 mg kg-1, 64.10 to 107.70 mg kg-1, and 16.08 to 18.97 mg kg-1, respectively. Contrastingly, Zn in leaf ranged from 412.97 in multifoliata to 499.78 mg kg-1 in caffra, which was 33 to 46 times higher than in fruit litterfall. Soils under the canopies of subsp. birrea, caffra, and multifoliata had significantly higher OC and K, Na, and S (p < 0.05), and numerically higher concentrations of most nutrients than soils away from the canopies. We concluded that leaf and fruit litterfall of the Sclerocarya birrea subspecies can improve soil fertility and carbon storage in drylands if managed properly.