Sheep manure and sewage sludge boost biofortification of barley and restricts heavy metal accumulation in plant tissues

In recent centuries, micronutrient deficiencies are considered a major challenge for human health. Biofortification of principal crops has been broadly accepted as a sustainable scenario to overcome this limitation. The experiment was carried out in a completely randomized factorial design with three replications during the 2007-2008 and 2008-2009 growing seasons. Four fertilizers and two doses of humic acid were used in the experiment. Analysis of variance indicated that humic acid, fertilizer type, and growing season caused statistically significant differences in macro and micronutrient content and heavy metal concentrations of shoot and seed in plants. Results also denoted that organic material amendment improved macro and micronutrient content of barley plants compared with IF in which SS treatment increased Ca, Mg, Mn, Fe, Zn, and Ni concentrations in shoot/seed while SM treatment enhanced N, P, and K concentration of plants. Moreover, IF-treated plants increased heavy metal accumulation in shoot and seed tissues whereas organic amendments reduced heavy metal uptake such that the lowest Pb and Cd were determined in SM-treated plants, and the lowest Ni content was measured in W-treated samples. HA application promoted Zn, Mg, and Cu accumulation in plants, however, individual or combined with fertilizers reduced other micro and macronutrient uptake. In conclusion, the amendment of 40 tons ha-1 of sheep manure and sewage sludge is an improving and beneficial practice in barley cultivation for the biofortification of crops. However, HA treatment did not form a meaningful whole in the experiment but promoted Zn, Mg, and Cu concentrations in plant tissues.