Stubble management and seeding rate effects on irrigated winter wheat yield in central Iran

Soils in central Iran are low in organic carbon and consequently have weak structure. Managing crop residues is an importance practice for improving soil structural stability. However, for suggesting the method of incorporation of surface-residue cover by tillage to the farmers, knowledge of the effect of different stubble disposal methods (leaving wheat stubble on or mixing with the soil surface, or incorporation of stubble by plowing) on the yield of a subsequent crop is essential. The experiment was conducted in split plot design with three replications. Three seeding rates of 100, 130 and 160 kg ha(-1) were used as main plots. Five tillage and planting systems were used as split plots. Tillage and planting systems used for different stubble disposal methods were: a) no-tillage (direct drilling into the. standing stubble), b) seedbed and planting combination with a wing-tined cultivator combined with rotovator, drilling machine and roller (mixing wheat stubble with the soil surface by rotavation), c) plowing (incorporating the stubble) + disking + seed distributed by hand + shallow disking, d) disking the stubble + plowing (first, mixing wheat stubble with the soil surface and then incorporating it by plowing) + disking + planting with a grain drill and f) burning the stubble + plowing (incorporating the ash) + disking + planting with a grain drill. Treatments were compared by measuring wheat yield and yield components of an irrigated winter wheat (Triticum aestivum L.) cultivar (Ghouds). The experiments were conducted on a silty clay loam soil. Differences in grain yields among three seeding rates were not statistically significant. The presence of stubble influenced yield. The highest yields were produced after the stubble was burnt; yields were reduced when stubble was present, especially when it was mixed with the soil surface using a rotovator to a depth of 8 cm. In non-burning stubble disposal methods, incorporation of stubble by plowing to a depth of 25 cm and planting with a broadcasting method had the highest yield. The grain yield was 11% more in direct drilling compared to the rotovator combined seeding where stubble was mixed with the soil surface. On this soil, incorporation of the stubble by plowing to a depth of 25 cm and planting with a broadcast seeder is recommended to improve reliability of crop production.