**5. Use of slag as an iron fertilizer**

The problem of iron (Fe) chlorosis can affect many crops on calcareous soils, resulting in substantial yield losses. Generally it has been corrected through the addition of Fe synthetic chelates, but these have resulted very expensive. Various studies have been focused on applying different Fe sources, in order to reduce the economic burden and to recycle some industrial by-products, such as converter slag (Wallace et al., 1982) (Sikka & Kansal, 1994). They are used not only as soil amendment but also as source of important plant nutrients, such as P, K, Mg and Fe oxides.

An investigation pursued on 1984 showed that the application of a steel by-product (dust containing 430 g Fe kg-1) as fertilizer to alkaline soils, with o without sulphuric acid, increased dry matter yield of sorghum (Anderson & Parkpian, 1984). A similar treatment, through a mixture of sulphuric acid and iron sulphates, has allowed to correct Fe chlorosis in corn and alfalfa (Stroehlin & Berger, 1963).

While converter sludge has been used as Fe fertiliser in calcareous soils with positive results, recently the use of converter slag as source of Fe fertiliser in some calcareous soils incubation studies has led to relevant achievements. On this subject, pot experiments in a greenhouse have been carried out in China (Wang & Cai, 2006). Relevant results of this study have shown that the use of moderate steel slag or acidified slag as Fe fertilizer leads to the increase in Fe uptake and corn dry matter yield. This phenomenon is proportional to the application rate and is enhanced by the acidification of slag, although increasing application rates do not produce further improvements in yield and in Fe uptake. This suggests a possible optimized rate of these applied substances. On the other hand, in experiments conducted with the sandy loam dry matter yield significantly decreased. This can be explained because the Fe availability decreases with salt levels increase, resulting in a yield decrease and an increase of chlorosis in plants.

Although further studies still have to be conducted in order to investigate the correct rates of converter slag for different crops and its possible residual environmental impacts to the soil, important results have been achieved by using this by-product as a source of available Fe (Torkashvand, 2011). In an incubation study, by adding to the soil converter slag (from Isfahan steel factory, Isfahan, Iran), containing about 24% of Fe oxides, along with elemental sulphur and organic matter, the soil pH has increased, due to the alkaline pH of slag. But

reactions. On the other hand, the foliar concentration can be influenced by soil solution changes, competitions for root uptake and root-to-shoot transfer. In particular the soil pH has increased from 5.6 to 9.8, and the soil conductivity has proportionally risen from 0.14 mS cm-1 to 0.82 mS cm-1 by applying increasing rates of basic slag, probably due to the basic slag composition, particularly to the Ca content. Furthermore the foliar Cu concentration has probably caused a phytotoxic effect in plants grown in Cu-contaminated soil. After the basic slag addition at 1% rate the bean growth, along with the decrease of foliar Cu concentration, has been observed. Moreover while the Ca foliar concentration has increased after applying increasing rates of basic slag, the foliar P concentration has not been improved. These results suggested that the use of basic slag at 1% addition rate is effective as a liming material but, is not effective as P fertiliser. Furthermore, the basic slag addition in contaminated soil does

The problem of iron (Fe) chlorosis can affect many crops on calcareous soils, resulting in substantial yield losses. Generally it has been corrected through the addition of Fe synthetic chelates, but these have resulted very expensive. Various studies have been focused on applying different Fe sources, in order to reduce the economic burden and to recycle some industrial by-products, such as converter slag (Wallace et al., 1982) (Sikka & Kansal, 1994). They are used not only as soil amendment but also as source of important plant nutrients,

An investigation pursued on 1984 showed that the application of a steel by-product (dust containing 430 g Fe kg-1) as fertilizer to alkaline soils, with o without sulphuric acid, increased dry matter yield of sorghum (Anderson & Parkpian, 1984). A similar treatment, through a mixture of sulphuric acid and iron sulphates, has allowed to correct Fe chlorosis

While converter sludge has been used as Fe fertiliser in calcareous soils with positive results, recently the use of converter slag as source of Fe fertiliser in some calcareous soils incubation studies has led to relevant achievements. On this subject, pot experiments in a greenhouse have been carried out in China (Wang & Cai, 2006). Relevant results of this study have shown that the use of moderate steel slag or acidified slag as Fe fertilizer leads to the increase in Fe uptake and corn dry matter yield. This phenomenon is proportional to the application rate and is enhanced by the acidification of slag, although increasing application rates do not produce further improvements in yield and in Fe uptake. This suggests a possible optimized rate of these applied substances. On the other hand, in experiments conducted with the sandy loam dry matter yield significantly decreased. This can be explained because the Fe availability decreases with salt levels increase, resulting in a yield

Although further studies still have to be conducted in order to investigate the correct rates of converter slag for different crops and its possible residual environmental impacts to the soil, important results have been achieved by using this by-product as a source of available Fe (Torkashvand, 2011). In an incubation study, by adding to the soil converter slag (from Isfahan steel factory, Isfahan, Iran), containing about 24% of Fe oxides, along with elemental sulphur and organic matter, the soil pH has increased, due to the alkaline pH of slag. But

not increase the foliar concentrations and accumulations for Cd, Cr, and Zn.

**5. Use of slag as an iron fertilizer** 

such as P, K, Mg and Fe oxides.

in corn and alfalfa (Stroehlin & Berger, 1963).

decrease and an increase of chlorosis in plants.

during the incubation time the pH decreased. This can be due, according to some previous studies, either to the precipitation of the free carbonates as calcium carbonate (Abassapour et al., 2004) or to the hydrolysis of Fe3+ in the soil (Rodriguez et al., 1994). The decrease of soil pH probably results from the decomposition of organic matter applied and subsequent organic acids and CO2 release as well as the buffering ability of the calcareous soils. The observed yield increase in these soils may be due to the some nutrients availability as a consequence of pH increase.

The converter slag application has proportionally increased ammonium bicarbonatediethylenetriamine pentaacetic acid (AB-DTPA) extractable Fe, although in some incubation soils Fe extractable decreased, maybe due to the temporary fixation of iron by organic matter. Further in the pot experiment converter slag has been shown to be very effective in correction of Fe chlorosis in calcareous soils.
