Grain sorghum response to banded acid‐type fertilizers in iron‐deficient soil

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Abstract
Two fluid acid‐type fertilizers made by mixing urea with H3PO4 or urea with H3PO4 and H2SO4, an ammonium polyphosphate (APP) fluid, and granular triple superphosphate (TSP) and diammonium phosphate (DAP) were banded alone or with FeSO4 in an Fe‐deficient Epping silt loam soil (Ustic Torriorthent) in two greenhouse pot experiments. Grain sorghum (Sorghum bicolor L. Moench) forage yields and Fe uptake increased with band application of FeSO4 alone or with these fertilizers except with DAP. Forage yields and Fe uptake with band application of fertilizers alone (no FeSO4) were somewhat higher with all three fluid fertilizers and TSP, indicating that Fe availability in this soil may have been increased by band application of these fertilizers or that Fe contaminants in these fertilizers may have been available to plants. Each fertilizer also was banded to soil in plexiglass cells in the laboratory. Soil in radial increments around the fertilizer bands was sampled after 7, 21, and 35 days. Within 1 cm of the band, soil pH decreased more with the acid‐type fertilizers than with APP. DTPA‐extractable Fe near the fertilizer band was higher with APP than with the acid‐type products and decreased with distance from the band. Research is needed on other soils to determine if banded acid‐type fertilizers affect levels of available soil Fe sufficiently to correct Fe chlorosis of crops on Fe‐deficient soils and if these fertilizers are effective carriers of FeSO4.