Distribution of Chemical Fractions of Micronutrient Cations in Some Vertisols under the Agro-Eco-Sub Region 4.2 of Eastern Rajasthan

The agro-eco-subregion (AESR) 4.2 encompasses Aravalli foot hills, central Rajasthan plains and adjoining areas. Four pedons of Vertisols from benchmark soil series classified as Calcic Haplusterts (Bhupalsagar soils series), Petrocalcic Haplusterts (Taswaria soil series), Sodic Haplusterts (Bhatewar soil series) and Typic Haplusterts (Sanwata soil series) occurring mostly on dolomitic and gneissic sub-surface were subject to fractionation of Cu, Zn, Mn and Fe into organic bound (OB), crystalline (C), complexed (CD), amorphous (AM) and exchangeable (EX). The results showed that the major portion of the Cu, Zn, Mn and Fe resided in the residual fraction. The trends for the mean values of Cu, Zn, Mn and Fe observed were OB (4.89) > C (2.20) > CD (1.70) > EX (0.51) > AM (0.48); OB (10.84) > C (4.14) > CD (1.20) > AM (0.92) > EX (0.66); C (58.56) > AM (42.26) > OB (31.52) > CD (18.90) > EX (1.51) and AM (1194.8) > OB (745.4) > C (194.0) > CD (11.71) > EX (0.46) mg kg−1, respectively. Bhupalsagar soil series had higher content of crystalline Cu due to higher pH and low organic carbon. The coefficients of correlation for Cu and Zn fractions responded significantly amongst the fractions and soil properties viz., silt, clay and organic carbon. For Fe, the organic and amorphous components had significant relationship with soil properties (R2 = 0.81 and 0.97); amongst the different fractions the complexed and crystalline forms showed significant relationship (R2 = 0.78 and 0.80). In the manganese fractions the amorphous and complexed fractions had a significant relationship with soil properties (R2 = 0.88 and 0.80). The organically-bound fractions showed positive relationship with different forms of Mn (R2 = 0.86).