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

Non-conventional organic Si sources, rice milling waste char (T _RMWC ) and diatomaceous earth (T _DE ) were tested against burnt lime (T _BL ) and calcium silicate (T _CS ) 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 T _RMWC 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. T _BL 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 T _RMWC (5.90, 6.02, and 5.96). Highest reduction of Fe in rice was recorded in T _BL at TI (16%) and PI (18.76%), while at HI (21%) in T _RMWC . T _BL and T _RMWC 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).