This study assessed and classified the phytoremediation potentials of selected plant species around gold mining areas in restoring the environments contaminated by heavy metals. The geographic focuses of the study were the Golden Pride Gold Mine (GPGM) and Geita Gold Mine (GGM) in Tanzania. The shoots and roots of plant species surrounding the mining areas and the samples of associated soils were collected and analysed for total concentrations of lead (Pb), chromium (Cr), cadmium (Cd), copper (Cu), arsenic (As), manganese (Mn) and nickel (Ni) using Atomic Absorption Spectrophotometer (AAS) and UV-VIS spectrophotometry. Results indicated that the soils from study areas were loamy textured and slightly acid (pH 6.1–6.5), soil organic carbon and organic matter were low (0.6–2.0%), total nitrogen was very low (<0.10%), phosphorous ranged from low (6–12 mg kg⁻¹ soil) to high (13–25 mg kg⁻¹ soil), and cation exchange capacity ranged from low (6.0–12.0 cmol₍₊₎ kg⁻¹ soil) to medium (12.1–25.0 cmol₍₊₎ kg⁻¹ soil). In assessing heavy metals using plant parts, the roots of giant rats-tail grass (Sporobolus pyramidalis) accumulated highest Pb (757.78 μg g⁻¹), Creeping Blepharis (Blepharis maderaspatensis) the Cd (158.11 μg g⁻¹), lantana (Lantana camara) the As (68.61 μg g⁻¹), and leuceana (Leucaena leucocephala) accumulated higher Mn (2734.61 μg g⁻¹) and Ni (4464.33 μg g⁻¹). In shoots, L. leucocephala accumulated higher Cr (1276.67 μg g⁻¹) and higher Cu (2744.44 μg g⁻¹) in L. camara. Although S. pyramidalis, M. repens, L. camara, B. maderaspatensis and L. leucocephala are likely to pose hazards to herbivores (grazing animals) while entering the food chain, they are still potential hyperaccumulators thus can be used to decontaminate metalliferous affected soils. Blepharis maderaspatensis has never been reported anywhere as Pb, Cd, Cu, Mn and Ni uptake plant hence this can be regarded as a new finding.

A field experiment was conducted to understand whether non-formalized monocultures of maize could be substituted by the rotations with common bean on smallholder farms. This study was installed in the northern highlands of Tanzania along the slopes of the highest African peak of Mt. Kilimanjaro with the predominance of smallholder farmers. Cropping seasons (S), cropping systems (C), bean varieties (V), and their interactions were evaluated. Data collected were plant height, ground coverage, total biomass, number of pods per bean and seeds per pod, 100-seed weight, and grain yield. Results indicated that bean in long rainy seasons produced significantly larger grain yields as an effect of S (3.3 t ha−1) in 2015, C (3.4 t ha−1) in intercrop, V (2.7 t ha−1) in local bean, S × C (4.4 t ha−1) in 2015 in intercrop, S × V (3.4 t ha−1) in improved bean in 2015, C × V (4.6 t ha−1) in intercropped local bean, and S × C × V (5.0 t ha−1) in intercropped local bean in 2017. In a short rainy season, significantly larger bean grain yield (1.8 t ha−1) was recorded as an effect of C when sown subsquent to maize. The effects of V and/or C × V were not significant on bean grain yield during short rainy season. Maize in long rainy seasons produced significantly larger grain yields as an effect of C (2.9 t ha−1) but not for S and S × C in rotation with the local bean. In short rainy seasons, significantly larger maize grain yield was produced in 2015 (2.6 t ha−1) but the effects of C and S × C were not significant in 2015 and 2016. This study concluded that inclusion of intercrops (of maize and common bean) as part of a rotation with one of these crops significantly improved grain yields and hence provided promising grounds of the options for sustainable food production on smallholder farms.

Common bean (Phaseolus vulgaris L.) is an important grain legume for food and cash of the smallholder farmers worldwide. However, the total potential benefits to be derived from the common bean as a source of food and income, its complementarities with non-legume food crops, and significance to the environment are underexploited. Intensification of common bean could provide approaches that offer new techniques to better manage and monitor globally complex systems of sustainable food production. Therefore, this study tried to assess the productivity of common bean bushy varieties when are involved as part of an intercrop with maize (Zea mays L.) in varying agro-ecological zones. The factors evaluated were the cropping seasons/years (S) (2015 and 2016), agro-ecological zones (A) above sea level (lower 843 m, middle 1051 m, upper 1743 m), and cropping systems (C) (sole, intercrop). The data collected were the total biomass, number of pods per plant and seeds per pod, 100-seed weight as yield components, and grain yield. Bean and maize grain yields were used to calculate the partial (P) and total land equivalent ratio (LER). Results indicated that the main effects of S, A, C, and the interaction effects of S × A, S × C, S × A × C were significant on bean grain yields. Interactions of S × A × C were also significant on all measured variables. Results also indicated that continuous intercropping of bean with maize over two cropping seasons resulted in the increase of bean grain yields from 1.5 to 2.3 t ha⁻¹ in the lower altitude, 2.0 to 2.3 t ha⁻¹ in the middle altitude, and 1.8 to 2.9 t ha⁻¹ in the upper altitude. Land utilization advantage of intercrops over monocultures yielded a total LER of 1.58, whereas the average partial land equivalent ratio (PLER) of individual beans was 1.53.