Shea (Vitellaria paradoxa) tree and soil parent material effects on soil properties and intercropped sorghum grain-Zn in southern Mali, West Africa

Abstract

Agroforestry parklands are an important agricultural practice in southern Mali where trees such as the Shea (Vitellaria paradoxa C.F. Gaertn) improve soil fertility and crop growth. However, it is not known whether Shea trees can ameliorate Zn-deficient soils or improve Zn uptake from soils of high-Zn, mafic origin. A total of 22 Shea trees preserved in traditional parklands with sorghum (Sorghum bicolor L. Moench) were selected from two soil parent material (PM) types (mafic and non-mafic). Sorghum grain and soil samples were taken along a transect from the bole to 12 m beyond the canopy and analyzed for soil and grain parameters including diethylenetriaminepentaacetic acid (DTPA)-extractable soil-Zn and grain-Zn concentration. Zn-deficient soils were observed with most occurring at non-mafic PM. Mean DTPA-extractable Zn concentrations ranged from 0.55-2.98 μg g−1 in mafic soils and 0.34-1.02 μg g−1 in non-mafic soils. PM influenced soil available-Zn, but not grain-Zn concentration. Both soil available-Zn and grain-Zn concentrations decreased away from trees with grain-Zn concentration not consistently decreasing across all soils. These results suggest that Shea trees grown in soils derived from mafic PM can improve soil-Zn availability, but that other growth factors are more important in determining grain-Zn content.