Effect of enriched cow manure with converter sludge on Fe bio-availability in a lead polluted soil

Nowadays, different materials such as applying Fe chelates, soil acidifying materials and industrial wastes are used to correct soil Fe deficiency. Slag and convertor sludge of steel factories are useful as a reclamation material for Fe nutrition among the industrials wastes for this purpose. These materials contain considerable amount of Fe produced in large quantities every year. Application of slag and convertor sludge to soil may affect bioavailability and chemical forms of Fe in soil. On the other hand, environmental pollution caused by heavy metals such as lead (Pb) is a serious and growing problem and can affect nutrient management such as Fe. Considering interaction of Fe and Pb, this research was performed to investigate the effect of converter sludge enriched cow manure on the changes in Fe bio-availability in a Pb polluted soil.
A factorial experiment with a randomized complete block design with 3 factors in three replications was conducted in greenhouse conditions. Treatments were consisting of applying enriched cow manure (0, 15 and 30 t ha-1) with 0 and 5% pure Fe from converter sludge. In addition, the soil was polluted with Pb from Pb(NO3)2 source at the rates of 0, 200, 300 and 400 mg Pb kg-1 soil and incubated for one month. Then, the enriched cow manure was added to the Pb polluted soil and corn (Zea mays L. single grass 704) seeds were sown. After 60 days from the experiment, soil physio-chemical properties and soil and plant Fe concentration were measured.
Increasing the loading rate of cow manure from 0 to 15 and 30 t ha-1 in a Pb polluted soil (300 mg Pb soil-1) caused an increasing in DTPA extractable-Fe by 21 and 35 times, respectively. Similar to this result, root and shoot Fe concentration was also increased, as, applying 30 t ha-1 cow manure in a polluted soil (200 mg Pb soil-1) caused an increasing in root and shoot Fe concentration by 7 and 12.3 times, respectively. Enriched cow manure with converter sludge had also a positive effect on root and shoot Fe concentration, as, applying 30 t ha-1 enriched cow manure in a Pb polluted soil (200 mg Pb soil-1) caused an increasing in root and shoot Fe concentration by 2 and 7.7 times, respectively.
The greatest DTPA extractable Fe and root and shoot Fe concentration was belong to the non- polluted soil treated with 30 t ha-1 cow manure enriched with 5% Fe pure from converter sludge. Considering the interaction effect of Fe and Pb, increasing the soil Pb pollution caused the significant decreasing in soil Fe availability and root and shoot Fe concentration. The result of this study showed that applying cow manure enriched with 5% Fe pure from converter sludge can probably increase soil and plant Fe bio-availability. However, the role of applying cow manure on decreasing Pb bio-availability and thereby, increasing soil Fe bio-availability (iron and lead competitive effect) cannot be ignored.