Wheat in Iran used to be cultivated in rotation with other crops periodically. So there was enough time for decomposition of plant residue. Recently in most areas, wheat is cultivated intermittently. We should consider soil quality and organic matter to have a sustainable agriculture. Soil quality is the capacity of the soil to act as an alive component in ecosystem. There are several agronomic methods to improve qualitative properties of soil such as crop rotation and application of plant residues. The plant residue application methods have great effects on physical, chemical and biological properties of soil that lead to constant soil production. The aims of this study were to determine the effect of preceding crops and their residues on some soil qualitative (physical, chemical and biological) properties and soil quality index in a farm setting. This research includes two separate studies performed in two fields at Rudasht agricultural research station. Pre-crop treatments consisted of four different plants species, Sunflower ( Heliantus annus L .), Sorghum ( Sorghum bicolour L .), Trifolium ( Trifolium pretense L .), Safflower ( carthamus tinctorirus L .) and without pre-crop plant treatments. The preceding crops were harvested after 70 days and their residues were air dried, chopped and incorporated in to the soil at seven ton dry matter weights per hectare. Two weeks after addition of the preceding crops, the Back Cross genotypes of wheat were planted. The wheat crops were harvested after 7 months. Results showed that using preceding crops and crop residues increased soil organic matter in both tillering and harvesting stages in two fields(with different agricultural sequence) comparing with control treatment. In the first field all treatments had more organic matter than second field. Using mentioned treatments (preceding crops and crop residues) in both fields led to increased zinc concentration (measured by DTPA) and soil Fe in both tillering and harvesting of wheat in comparison with control treatment. Total nitrogen and phosphoru concenterations raised in the first field. In second field all treatments had increased phosphorus and total nitrogen concenterations except for the treatment of Safflower without residue. Soil in the first field had much total nitrogen, DTPA-zinc and phosphorus than the second one. Totally in second study there were better physical properties, available water, soil hydrolic conductivity and less bulk density than the first study. In the first field the Soil Quality index in all treatments were higher than the second field.
