Effects of soil moisture and phosphorus fertilization on iron chlorosis of sorghum

Abstract

Pot experiments were conducted in the growth chamber using two calcareous soils from western Oklahoma: Quinlan silt loam (Typic Ustochrept) and Spur silt loam (Fluventic Haplustoll). In the first experiment, sorghum (Sorghum bicolor (L.) Moench) variety RTx428 was grown at four soil matric potentials (‐0.5, ‐2.69, ‐14.1, and ‐75 kPa) to study the influence of soil moisture on the severity of Fe chlorosis. In the second experiment, RTx428 was grown under three different P sources (ammonium polyphosphate, APP; NH₄H₂PO₄, MAP; and KH₂PO₄) at two rates, with and without a soil application of Fe as FeSO₄.7H₂O. Increases in soil moisture resulted in increases in soil solution HCO₃ ^‐ and soil pCO₂; however, these increases did not result in increases in the severity of sorghum chlorosis as has been observed in dicots. The amount of total chlorophyll (Chl_T) and dry matter increased when APP was applied to the Quinlan soil relative to the MAP and KH₂PO₄ treatments. Increases in Chl_T in the APP treatments were associated with increases in plant tissue Fe and uptake of Fe. Ammonium polyphosphates appear to play a role in stimulating uptake of Fe in soils deficient in available Fe.

Key words:

• Bicarbonate
• carbon dioxide
• ammonium polyphosphate
• monoammonium phosphate
• potassium phosphate
• P/Fe ratio
• chlorophyll content
• calcareous soils