Sugar Processing Residuals as an Iron Source for Grain Crops Grown in Calcareous Soil

Iron (Fe) deficiency is common when grain crops are grown in calcareous soils. The study was conducted to determine if the DTPA-extractable Fe concentration and Fe uptake of sorghum and corn were greater when Fe fertilizers were co-applied with sugar processing residuals than without residuals. The glasshouse pot experiment was a 3 x 3 x 3 complete factorial with three Fe fertilizer sources (none, 5 mg Fe kg(-1) of FeSO4, 5 mg Fe kg(-1) of Fe-EDDHA (Fe-ethylene diamine-N,N'-bis (2-hydroxyphenylacetic acid)) combined with three residuals (filtercake, bagasse and sugar beet) that were applied at rates of 0, 1.5 and 3% (w/w) and cropped continuously with sorghum-sorghum-corn. Cumulative shoot Fe uptake was greater in pots amended with filtercake and sugar beet than bagasse. Application of 3% bagasse reduced the cumulative shoot Fe uptake by 36%, compared to the unamended control (P .05). Application of Fe-EDDHA or FeSO4 increased cumulative shoot Fe uptake by 9%, compared to the unfertilized control. The DTPA-extractable Fe concentrations were consistently higher in soil amended with filtercake and Fe-EDDHA, and declined with time. Since co-application of Fe fertilizer and residuals did not increase Fe uptake, this practice is not expected to improve Fe availability in calcareous soils. Filtercake and sugar beet residuals are alternative Fe sources for grain crops in calcareous soils.