Effects of sewage sludge on iron chlorosis and yield of grain sorghum grown on calcareous soils

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Abstract
A greenhouse study was conducted to evaluate the effects of sewage sludge on Fe‐chlorosis and yield of grain sorghum. Different rates of sewage sludge (0, 2.5, 5.0, 7.5, 10.0, 12.5, 15.0, 20.0 and 25.0 g sludge kg‐1 soil) were added to three calcareous soils; Clareville cl (Pachic Argiustoil), Orelia c (Typic Ochraqualf) and Pernitas fsl (Typic Argiustoil). Visual chlorosis ratings decreased with increasing sludge rates on all three soils. However, more than 25 g sludge kg‐1 was needed to correct Fe‐deficiency in Orelia soil. Dry matter yields increased with increasing sludge rates in Orelia soil. On Pernitas soil, dry matter yields increased with increasing sludge rates up to 12.5 to 15.0 g sludge kg‐1 soil and then leveled off or slightly decreased. On Clareville soil, dry matter yields increased with sludge rates up to 10 g sludge kg‐1 soil and then decreased, indicating a possibility of heavy metals toxicity. The data in this experiment indicate that in calcareous soils with high pH it is possible to use sewage sludge to correct Fe‐deficiency and increase yields.