Chemical Forms and Phytoavailability of Copper in Soil as Affected by Crop Residues Incorporation

Abstract

Preceding crops as a source of organic matter are important sources of micronutrient and can play an important role in the soil fertility and soil cycling of micronutrients. In addition to the role of the organic matter in increasing the concentration of micronutrients in soil solution, attention should be also paid to the role of the kind and the quantity of the root’s exudates released in response to the incorporation of different plant residues in the rhizosphere. Present research was conducted with the objective of studying the effect of the kind of preceding crops: Trifolium ( Trifolium pretense L) and Sorghum ( Sorghum bicolor L) on chemical forms of copper (Cu) in solid phases of a calcareous soil in a completely randomized block field experiment with split plot (3 m × 5 m) arrangement, consisting of 3 replications and 3 treatments. After incorporation of the residue, wheat (genotype back cross) was planted. After harvesting the wheat, soil samples were collected from root zone of wheat. Selected soil properties and chemical forms of Cu were determined in the solid phases of the soil samples. Incorporation of plant residues significantly increased the concentration of DTPA-extractable Cu, in the soil. The highest effect was obtained for Trifolium treatment. Incorporation of plant residues decreased the carbonate-bound Cu (Cu-Carb) fraction in the solid phase and increased oxide-bound Cu (Cu-Ox) as compared to the control (fallow treatment). Fraction of organic-bound Cu (Cu-Org) in the soil increased with incorporation of plant residues as compared with the fallow treatment. Trifolium was the most effective in increasing Cu-Org. Cu-Ox and Cu-Residual (Cu-Res) forms showed a significant negative correlation and Cu-Org showed a significant positive correlation with the concentration of DTPA-extractable Cu. Incorporation of Trifolium residues decreased the fraction (%) of Cu-Carb and Cu-Ox (less soluble forms) and consequently increased the fraction (%) of Cu-Org which in turn elevated the concentration of DTPA-extractable Cu. Trifolium was the most effective in increasing the phytoavailability of Cu in soil.