Zinc (Zn) deficiency is one of the important nutritional problems in arid and semi-arid regions of the world where cereal crops are the main staple food in these regions. Agronomic biofortification is a new strategy combating Zn deficiency that increases Zn bioavailability in the soil for plant uptake through agronomic methods such as crop rotation and application of plant residues into the soil. The aims of this study were to determine the effect of preceding crops and their residues on some soil chemical properties, yield, Zn concentration and uptake of two wheat genotypes with different Zn efficiency. Safflower ( Carthamus tinectrius L.), clover ( Trifolium pretense L.), sunflower ( Heliantus annus L.) and sorghum ( Sorghum bicolor L.) were used as preceding crops. The preceding crops were harvested after 70 days and their residues were air dried, chopped and incorporated into the soil at 6.5 ton dry matter weights per hectare. Two weeks after addition of the preceding plants, two wheat genotypes Back Cross (a Zn-efficient genotype) and Kavir (a Zn-inefficient genotype) were planted. The wheat crops were harvested after 7 months. Results showed that incorporating plant residues did not significantly affect P and K but significantly increased DTPA-Zn, organic matter content and dissolved organic carbon (DOC) in the soil. Zinc concentration in shoots and grain of wheat were higher after incorporating of safflower and clover residues in comparison with other treatments. Incorporating plant residues into the soil had a significant effect on transfer factor of Zn from soil to wheat shoot and grain. There was also higher transfer factor of Zn after incorporating of safflower and clover residues into the soil. Shoot dry matter and grain yield of wheat were reduced after incorporating of sorghum and sunflower residues into the soil in comparison with the other residues. There was a positive correlation between Zn concentration of shoot and grain of wheat and DOC and also between Zn uptake by shoot and grain of wheat and DOC. There was a significant difference between Back Cross and Kavir genotypes in shoot and grain yield. Wheat plants grown after clover and safflower accumulated greater Zn in their grains as compared with those grown after sorghum and sunflower. The residues of safflower and clover had the highest effect on Zn uptake and its traort to grain of wheat.
