Changes in Soil Zinc Chemical Fractions and Improvements in Wheat Grain Quality in Response to Zinc Solubilising Bacteria

This study was performed to investigate the impacts of two indigenous strains of zinc (Zn) solubilising bacteria on Zn fractionation in soil, Zn uptake and the molar ratio of phytic acid to Zn (PA/Zn) in wheat grain cv. Chamran. The experiment was implemented in a completely randomised factorial design that included the treatment of bacterial inoculation consisting of B0 (control), B1 (Bacillus megaterium), B2 (Enterobacter cloacae), B3 (a mixed inoculation of both bacteria), and ZnSO4 fertiliser at three application levels: Zn0 (control), Zn1 (5.1mgkg-1), and Zn2 (10.1mgkg-1). Bacillus megaterium was isolated from the rhizosphere of Zea mays, which can solubilise Zn and phosphate and produce auxin. Enterobacter cloacae, which had been isolated from sugarcane root, was screened qualitatively and determined to be the best isolate to solubilise Zn. The results indicated the maximum values of organically bound (2.08 mg kg-1) and exchangeable Zn (0.89 mg kg-1) in the Zn2B3 treatment. Also, the highest amounts of carbonate bound (9.25 mg kg-1), FeMn-oxides (10.70 mg kg-1), and residual fractions (16.17 mg kg-1) were recorded for the Zn2B0 treatment. The relative proportions of residual, FeMn-oxides, carbonate, organic, and exchangeable Zn fractions in Zn0B0 were 40.48, 29.2, 27.1, 2.18, and 0.84%, respectively. These proportions changed to 37.24, 29.51, 26.9, 4.3, and 1.75%, in the Zn0B3 treatment. Maximum values of Zn uptake and grain yield were associated with the Zn2B3 treatment, showing increases (compared to the control) of 214 and 46%, respectively. The lowest ratio of PA/Zn was obtained in the Zn2B3 and Zn2B2 treatments, which exhibited reductions of 31.38 and 30.86%, respectively, when compared to the control.

Potential phytoremediation of soil cadmium and zinc by diverse ornamental and energy grasses

The potential of 32 frequently studied ornamental and/or energy grasses and two cadmium/zinc hyperaccumulators for phytoextraction and phytostabilization was compared by their growth in a historically contaminated soil over a three-month pot experiment. Shoot and root biomasses varied by factors of 14.2 and 62.7, respectively. Mainly due to their large biomass, Napier grass (Pennisetum purpureum ‘Purple’) and variegated giant reed (Arundo donax var. versicolor) accumulated cadmium and zinc contents in shoots up to 109.3% and 55.4% higher, respectively, than those in the cadmium/zinc hyperaccumulators, despite their lower metal concentrations. Pennisetum purpureum ‘Purple’ accumulated the most zinc and the third highest cadmium in roots. Bioconcentration factors of cadmium in roots were greater than 1 for 19 grasses. The present study demonstrated that many of these grasses may be suitable for phytostabilization of soil cadmium. Arundo donax var. versicolor exhibited the most potential for phytoextraction of soil zinc, whereas Pennisetum purpureum ‘Purple’ was best for phytoextraction and phytostabilization of cadmium and phytostabilization of zinc. Ornamental/energy grasses may have greater potentials for soil remediation than hyperaccumulators, especially given their utility and eco-economic benefits. The considerable variation in their performance emphases the value of screening to select the most effective candidates.

Soil Zinc Is Associated with Serum Zinc But Not with Linear Growth of Children in Ethiopia

To our knowledge, the relationships among soil zinc, serum zinc and children’s linear growth have not been studied geographically or at a national level in any country. We use data from the cross-sectional, nationally representative Ethiopian National Micronutrient Survey (ENMS) (n = 1776), which provided anthropometric and serum zinc (n = 1171) data on children aged 6–59 months. Soil zinc levels were extracted for each child from the digital soil map of Ethiopia, developed by the Africa Soil Information Service. Children’s linear growth was computed using length/height and age converted into Z-scores for height-for-age. Multi-level mixed linear regression models were used for the analysis. Nationally, 28% of children aged 6–59 months were zinc deficient (24% when adjusted for inflammation) and 38% were stunted. Twenty percent of households in the ENMS were located on zinc-deficient soils. Soil zinc (in mg/kg) was positively associated with serum zinc (in µg/dL) (b = 0.9, p = 0.020) and weight-for-height-Z-score (b = 0.05, p = 0.045) but linear growth was not associated with soil zinc (p = 0.604) or serum zinc (p = 0.506) among Ethiopian preschool children. Intervention studies are needed to determine whether there are causal links between soil and human zinc status.