Assessing the effects of bio-organic and chemical fertilizers application on absorption of macronutrients and heavy metals in vegetables (Case study: Lepidium sativum)

Long-term used of sewage sludge and fertilizer causes accumulation of heavy metals in the soil, which may lead to excessive absorption of these elements by plants and consequently entering these toxic metals into the human and animal food chain. Therefore, this study was conducted to investigate the effects of bio-organic and chemical fertilizers application on the absorption of macronutrients and heavy metals in Lepidium sativum.

In this descriptive study, the experiment was carried out in a completely randomized design with three replications in the environment and greenhouse conditions. Fertilizer treatments included chemical fertilizer treatment (diammonium phosphate), anaerobically digested sludge compost, sludge compost without digestion and raw sludge at the weight of 28, 57 and 115 g and control treatment. Finally, the concentrations of heavy metals Pb, Cd, Hg and As and macronutrients including phosphorus, nitrogen and carbon in the leaf of L. sativum were measured using ICP-OES. All statistical analysis was performed using SPSS version 21.

The results showed that the maximum mean concentrations of As and nitrogen in L. sativum vegetables were 0.592 and 10.2 mg/kg in 115 g raw sludge treatment, the maximum mean concentration of Cd, Hg, Pb, carbon and phosphorus elements in L. sativum were 0.956, 0.701, 1.25, 98.5 and 10.3 mg/kg, respectively in 115 g treatment raw diammonium phosphate fertilizer. The results of variance analysis showed that there was a significant difference between fertilizer, sludge and control treatment and there was a significant difference between amounts 28, 57 and 115 g from fertilizer treatment in L. sativum in terms of concentration of heavy metals and macronutrients (p < 0.050).

In conclusion, it was concluded that increasing the amount of fertilizer and sludge in the soil leads to an increase in the concentration of heavy metals and macro nutrients in L. sativum. Therefore, in the use of fertilizers and sludge for agricultural lands, it is necessary to pay attention to this issue. It was also found that the highest uptake of heavy metals and macronutrients in L. sativum was related to raw sludge treatment and diammonium phosphate fertilizer, which is indicating better quality of compost with respect to chemical fertilizer and raw sludge.