Cost-effective enhanced iron bioavailability in rice grain grown on calcareous soil by sulfur mediation and its effect on heavy metals mineralization.

Calcareous soil, high pH, and low organic matter are the major factors that limit iron (Fe) availability to rice crop. The present study was planned with the aim to biofortified rice grain with Fe, by integrated use of chemical and organic amendments in pH-manipulated calcareous soil. The soil pH was reduced (pHL2) by using elemental sulfur (S) at the rate of 0.25 % (w/w). The organic amendments, biochar (BC) and poultry manure (PM) [1 % (w/w)], along with ferrous sulfate at the rate of 7.5 mg kg-1 soil were used. The incorporation of Fe with BC in soil at pHL2 significantly improved plant biomass, photosynthetic rate, and paddy yield up to 99, 97, and 36 %, respectively, compared to control. A significant increase in grain Fe (190 %), protein (58 %), and ferritin (400 %) contents was observed while anti-nutrients, i.e., polyphenols (37 %) and phytate (21 %) were significantly decreased by the addition of Fe and BC in soil at pHL2 relative to control. Among the organic amendments, PM significantly increased Cd, Pb, Ni, and Cr concentrations in rice grain relative to control but their concentration values were below as compared to the toxic limits of hazard quotients and hazard index (HQ and HI). Hence, this study implies that Fe applied with BC in the soil at pHL2 can be considered as an effective strategy to augment Fe bioavailability and to reduce non-essential heavy metal accumulation in rice grain.