Fixing critical limits of boron in rice soils of Karaikal region, Puducherry union territory, India

Boron is relatively immobile in plants and its deficiency can cause serious yield reduction in rice by retarding panicle formation. Karaiakal region of Puduchuerry union terittory includes different soils with varying fertility status thus supplying boron at optimum level is a must concern to enhance the rice productivity.A pot experiment was conducted to fix critical limits of boron in soils and rice of this Karaikal region. Forty surface soil samples (0-15 cm) were collected from Inceptisol, Entisol and Vertisol soil orders of different locations in Karaikal region. The experiment was conducted with three levels of boron viz., 0, 1 and 2 ppm applied through borax in a factorial completely randomized design with three replications. The available B content of soil was estimated with five extractants. The critical limits of hot water, hot 0.01 M CaCl2, 0.05 M HCl, 1.0 M NH4OAc, 0.01M CaCl2+ 0.05 M Mannitol extractable B were found to be 0.50, 0.58, 0.46, 0.45 and 0.39 ppm in Inceptisol, 0.48, 0.59, 0.44, 0.39 and 0.48 ppm in Entisol and 0.45, 0.54, 0.45, 0.44 and 0.41ppm in Vertisol and a critical limit of 31.0, 39.0 and 34.0 ppm B in rice plant for Inceptisol(0.5ppm), Entisol(0.48 ppm) and Vertisol(0.45 ppm) as determined by Cate and Nelson’s graphical procedure. Among the extractants the hot water extractant showed the highest significant and positive correlation with Bray’s percent yield(0.48,0.47and 0.48), plant B content(0.041*, 0.019* and 0.271*) and B uptake(0.012*, 0.646* and 0.293*), respectively in Inceptisol, Entisol and Vertisol. From this study, the indicating knowledge of critical limit of boron will help to avoid yield loss of rice in the study region.