Silicon rich agro industrial wastes for sustainable management of iron toxicity and acidity of lateritic rice wetlands

Abstract Non-conventional organic Si sources, rice milling waste char (TRMWC) and diatomaceous earth (TDE) were tested against burnt lime (TBL) and calcium silicate (TCS) for amending Fe toxicity and acidity at tillering (TI), panicle initiation (PI) and harvest (HA) of a short duration rice variety Manuratna in lateritic rice wetlands of Kerala. Irrespective of the growth stages of rice, the TRMWC recorded the lowest water-soluble (WS-Fe), acid-soluble (AS-Fe), MnO occluded Fe (MN-Fe), and residual Fe (RS-Fe) fraction of Fe. WS-Fe indirectly enhanced Fe adsorption into specifically adsorbed lead displaceable Fe (SP-Fe) and AS-Fe, whereas AS-Fe abridged the Fe adsorption between WS-Fe and MN-Fe > OM-Fe. A strong negative influence of organic Si amendments was observed for organic matter occluded Fe (OM-Fe) (P=-0.94), amorphous FeO occluded Fe (AM-Fe) (P=-0.74) and crystalline FeO occluded Fe (CR-Fe) (P=-0.53). Fe fractions and forms of acidity were significantly (p=0.05) and positively correlated. TBL maintained the highest soil pH in all critical growth stages (5.90, 6.04, and 5.99) of rice, which was statistically on par with that at TRMWC (5.90, 6.02, and 5.96). Highest reduction of Fe in rice was recorded in TBL at TI (16%) and PI (18.76%), while at HI (21%) in TRMWC. TBL and TRMWC were statistically on par in reducing the WS-Fe (at PI and HA), exchangeable acidity and extractable acidity (at TI), and total acidity (at HI).