Dynamics of Copper Fractions and its Bioavailability in Soils under Mulberry Cultivation

The present study assessed the influence of varying fertilization rates on the distribution of chemical fractions of Cu and bioavailable Cu. Nutrient management practices viz., unfertilized control, 100% recommended doses of fertilizers for mulberry (100% RDF), 80% RDF and 60% RDF besides a fallow plot were considered for the study. Sequential fractionation of Cu was carried out for measuring the different Cu fractions in soil while the bioavailable Cu was extracted with Mehlich-3 extractant. Nutrient management practices influenced the distribution of Cu fractions and bioavailable Cu. Residual Cu was the dominant fraction accounting 71.5% of total Cu in soil across the nutrient management practices. Relative to 100% RDF, unfertilized control, 80% RDF and 60% RDF resulted in declined Cu contents in all fractions. Principal component analysis (PCA) suggested that water-soluble + exchangeable Cu fraction exhibited a higher association with bioavailable Cu indicating its importance in mulberry nutrition although the Cu fraction contributes hardly 1% to total soil Cu. Also, the path analysis showed the importance of organically bound Cu fraction explaining 99.2% of the variation in plant Cu concentration alone. Further, the positive correlations of bioavailable Cu with different Cu fractions indicate their relative contribution to mulberry’s Cu nutrition. The study concludes that recommended doses of fertilizers for mulberry improved the bioavailability of Cu in soil.