Effect of phosphogypsum amendment on fluoride content of soil and plants under rice (Oryza sativa)–wheat(Triticum aestivum) system in sodic soil of Indo-Gangetic plains

Abstract

An experiment was conducted during 2006–07 to study the fluoride enrichment in soil as well as crops after phosphogypsum application in the sodic soil and compared with the mineral gypsum treated soils. It was found that the addition of phosphogypsum increased both the total water soluble fluoride (Ftw) and total CaCl2 extractable fluoride FtCa in the sodic soil over mineral gypsum treated fields. The Ftw in 0–15 cm of the soil layer varied between 3.2 and 3.9 mg/kg, whereas total CaCl2 extractable fluoride varied between 5.6 and 9.0 mg/kg. The total water soluble fluoride were positively correlated with total fluoride concentration (r=0.76, P<0.05) and exchangeable sodium percentage of soil (r=0.75, P<0.05). The fluoride added through phosphogypsum accumulated in the top 30 cm of the soil profile. The yield of rice and wheat indicated that phosphogypsum application resulted higher yield of rice and wheat over the equivalent dose of mineral gypsum. Fluoride concentration in grain, straw of rice and wheat was higher in phosphogypsum treated field. It was 13.5 and 14.3 mg/kg in rice and wheat grain, respectively. Multiple regression analysis showed that Ftw together with exchangeable sodium percentage explained fluoride concentration in rice (oryza sativa L.)–wheat (Triticum aestivum L. emend. Fiori & Paol.) grain better than Ftw alone.