The use of alum sludge to improve cereal production on a nutrient-deficient soil

Alum sludge from wastewater treatment was applied at five rates on a phosphorus-deficient sand, and the effects on cereal growth and nutrition were investigated over 2 years. An inorganic fertilizer treatment, reapplied in the second year, was also included. The grain yield for inorganic fertilizer was 44% higher than the control in year 1 and 58% higher in year 2. Alum sludge was an adequate source of nitrogen for crop growth, and supplied sufficient residual nitrogen to meet crop requirements in year 2. However, grain yield in the alum sludge treatment applied at an equivalent available nitrogen rate to the inorganic fertilizer was 62% (year 1) and 69% (year 2) of the yield achieved by the inorganic fertilizer, though greater than the control. No toxic forms of aluminium were detected in the soil at any rate of alum sludge application. Plant shoot tissue analysis indicated that wheat sown in alum sludge-amended soil and the control were phosphorus deficient, whereas phosphorus was adequate in the inorganic fertilizer treatment. There was no evidence of any other nutrient deficiency. Alum sludge amendment resulted in an increase in soil phosphorus; however, further soil analysis indicated that forms of phosphorus present in alum sludge-amended soil may not be available for crop uptake; this is consistent with phosphorus deficiency observed in plant tissue in alum sludge-treated soil. It is suggested that on this nutrient-poor sand, the ability of alum sludge to provide sufficient phosphorus for plant production was limited in the 2 years after application.