Influence of fulvic acid on transport of iron in soils and uptake by paddy seedlings

The influence of fulvic acid (FA) on the porous system self diffusion coefficient (Dp) of Fe in Calciorthent soils of Bihar, India, was determined with the half cell technique. Significantly higher values of Dp were observed when Fe was applied as Fe–FA to the soil compared to FeCl₃. The capacity factor of Fe decreased considerably due to its complexation by fulvic acid, resulting in an increase in the Dp of Fe. The organic carbon content of the soils correlated positively with Dp of Fe while it showed a negative relationship with active CaCO₃ and the clay content of soils. A soil culture system simulating acquisition of Fe by rice was developed to investigate transport of Fe from the soil solution to the surface of the plant roots through diffusion and mass flow. Mass flow contributed only 5–9% of the total Fe uptake by rice, with the remainder being ascribed to diffusion and root interception. A significant relationship ( r =0.96^**) between Dp- and Fe-uptake by rice was observed. The uptake of Fe by the crop and the percentage of tissue iron content derived from fertilizer were higher in the case of Fe–FA in comparison with FeCl₃, indicating the superiority of organically complexed Fe fertilizers over inorganic salts.