Evaluation of preflooding effects on iron extractability and phytoavailability in highly calcareous soil in containers

Previous pot cropping and laboratory incubation experiments were consistent with field observations showing that temporary flooding before cropping can increase the availability of soil Fe to plants. To study the effect of temporary flooding on changes in soil Fe phytoavailability we used 24 highly calcareous, Fe chlorosis-inducing soils to carry out a pot experiment where peanut and chickpea were successively grown after flooding for 30 d. At the end of the cropping experiment, the preflooded soil samples exhibited higher concentrations of acid oxalate-, citrate/ascorbate- and diethylenetriaminepentacetic acid (DTPA)-extractable Fe (Fe-ox, Fe-ca, and Fe-DTPA, respectively) than the control (nonflooded) samples. Also, Fe-ox and Fe-ca exhibited no change by effect of reflooding of the cropped soils or three wetting-drying cycles in freeze-dried slurries of soils previously incubated anaerobically for several weeks. Leaf chlorophyll concentration (LCC) in both peanut and chickpea was greatly increased by preflooding. The best predictor for LCC was Fe-ox, followed by Fe-ca and Fe-DTPA. The LCC-soil Fe relationships found suggest that the Fe species extracted by oxalate and citrate/ascorbate from preflooded soils were more phytoavailable than those extracted from control soils. However, the increased phytoavailability of extractable Fe forms was seemingly limited to the first crop (peanut). Flooding dramatically increased Fe-DTPA; however, high Fe-DTPA levels did not result in high LCC values, particularly in the second crop. Therefore, this test is a poor predictor of the severity of Fe chlorosis in preflooded soils.