effect of incorporation of crops residue into soil on some chemical properties of soil and bioavailability of copper in soil

objective: returning crop residue to the soil exerts favorable effects on physical and chemical properties of soil. in fact, the plant residues can affect soil conditions such as ph and important role in soil fertility and cycling of elements in the soil may have. in addition to the role of the organic matter from decomposition of crop residue in increasing the concentration of micronutrients in soil solution is very important.  present research was conducted with the objective of studying the effect of the kind of crop residues: sunflower (helianthus annnus l. cv. allstar), sudan grass (sorghum bicolor l. cv. speed feed), trifolium (trifolium pretense l.) and safflower (carthamus tinctorius l. cv. koseh-e-isfahan), with control on chemical properties of soil and effect on bioavailable of copper. methods: in this study complete randomized block field experiment, consisting of 3 replications and 5 treatments. after 3 weeks, increasing crop residues, soil samples collected and were used to measure some properties of soil and concentration of cu in soil. results: results showed that crop residues significantly decreased soil ph and the largest increase was observed for trifolium treatment. ec significantly increased by affected crop residues application. the crop residues significant increased the concentration of dissolved organic carbon (doc). the largest effect was dependent  for trifolium treatment. the crop residues significant increased the concentration of dtpa-extractable cu. the highest effect was obtained for trifolium treatment. therefore, trifolium residues application decreased the amount of soil ph and consequent increase of doc which in turn elevated the concentration of dtpa- extractable cu. trifolium was the most effective in increasing the phytoavailability of cu in soil.