A field experiment was conducted at farmer's field, Durgadevigudi near Dharwad city to study the direct and residual effect of iron management practices for groundnut-maize cropping sequence in calcareous Vertisol during Kharif season of 2002-03 and rabi season of 2003 and 2003-04.

The characterization study revealed that, the distribution of available iron was found to be associated with clay content, organic carbon, soil pH and calcium carbonate and the percentage contribution of soil iron fractions to total iron were in following order: Residual iron > amorphous Fe-oxide occluded iron > organically bound iron > Mn-oxide occluded iron > Pb-displaceable iron > exchangeable iron > acid soluble > water soluble iron.

The incubation study indicated that, the effect of varying levels of FeSO₄ was significant with respect to water soluble iron, acid soluble iron, exchangeable iron and Pb-displaceable iron in soil. However, increase in CaCO₃ levels in soil significantly decreased all iron fractions in soil at varying days after incubation period.

The field experiment revealed that, direct and residual effects of pyrite application @ 50 kg per ha was superior in terms of growth, yield, quality and biochemical parameters and nutrient uptake by groundnut and maize and it was on par with 100 kg FeSO₄ per ha and significantly superior over rest of the treatments.

The iron fractions (water soluble iron, acid soluble iron, exchangeable iron, Pb-displaceable iron) were higher due to direct and residual effect of pyrite application @ 50 kg per ha and it was on par with 100 kg FeSO₄ per ha and significantly superior over rest of the treatments.

Path analysis indicated that, soil and plant iron fractions, which were important for groundnut (acid soluble, ferrous iron at 60 and 80 DAS) and those, which were important for maize (water soluble, Pb-displaceable and ferrous iron at 30 DAS ) are different to attain higher yield.