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

Aims 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. Methods 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. Results 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. Conclusions 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.