Green Manure Addition to Soil Increases Grain Zinc Concentration in Bread Wheat

Zinc (Zn) deficiency is a major problem for many people living on wheat-based diets. Here, we explored whether addition of green manure of red clover and sunflower to a calcareous soil or inoculating a non-indigenous arbuscular mycorrhizal fungal (AMF) strain may increase grain Zn concentration in bread wheat. For this purpose we performed a multifactorial pot experiment, in which the effects of two green manures (red clover, sunflower), ZnSO4 application, soil gamma-irradiation (elimination of naturally occurring AMF), and AMF inoculation were tested. Both green manures were labeled with Zn-65 radiotracer to record the Zn recoveries in the aboveground plant biomass. Application of ZnSO4 fertilizer increased grain Zn concentration from 20 to 39 mg Zn kg(-1) and sole addition of green manure of sunflower to soil raised grain Zn concentration to 31 mg Zn kg(-1). Adding the two together to soil increased grain Zn concentration even further to 54 mg Zn kg(-1). Mixing green manure of sunflower to soil mobilized additional 48 mu g Zn (kg soil)(-1) for transfer to the aboveground plant biomass, compared to the total of 132 mu g Zn (kg soil)(-1) taken up from plain soil when neither green manure nor ZnSO4 were applied. Green manure amendments to soil also raised the DTPA-extractable Zn in soil. Inoculating a non-indigenous AMF did not increase plant Zn uptake. The study thus showed that organic matter amendments to soil can contribute to a better utilization of naturally stocked soil micronutrients, and thereby reduce any need for major external inputs.