Cadmium Availability to Rice in Sludge‐amended Soil under “Flood” and “Nonflood” Culture

Abstract

AbstractRice plants (Oryza sativa var. ‘Colusa’) were grown to maturity in pots containing a soil (Domino silt loam, pH 7.5, Xerollic calciorthid) amended with 1% sewage sludge enriched with variable amounts of CdSO4 ranging up to 640 µg Cd/g. Two sets of soil cultures were used, one for rice under continuous flood and the other under nonflood conditions. Grain production for rice under flood management was relatively unaffected by the Cd treatment; 25% yield decrement was associated with a treatment of 320 µg Cd/g. Under nonflood management, however, a comparable decrement in grain production was observed with a treatment of only 17 µg Cd/g. The Cd content of mature leaves at early flowering varied from approximately 0.3 µg Cd/g for the controls to 2.8 µg Cd/g for plants receiving the highest Cd treatments. Leaf Cd values were slightly higher under the nonflood culture. The Cd content of the grain under nonflood management was approximately 55% greater than that of grain under flood management. The Cd content of mature leaves correlated with grain production (r = 0.872***) for rice produced under either flood or nonflood culture. Chemical analysis of saturation extracts revealed greatly reduced Cd concentrations in soil solutions under flood management which may account for the greater tolerance of the cultivar to soil Cd under flood culture. This reduced availability of Cd in flooded soils is attributed to precipitation of CdS.