Effect of Crop Rotation Systems on Wheat (Triticum aestivum L.) Yield and some Soil Properties

In order to study the effect of different crop rotation systems on wheat grain yield and some soil properties, this experiment was conducted with seven rotation treatments in a randomized complete block design with four replications in Darab Agriculture Research Station. The experiment was repeated in two rotation frequencies: the first from 1999 to 2002 and the second one from 2002 to 2005 with the same crop treatments. Cropping systems were included 1. broad bean (Vicia sativa L.), corn (Zea mayse L.), chick ling vetch (Vicia villosa L.), and wheat (Triticum aestivum L.) (CS1) 2. clover (Trifolium sp. L.), cotton (Gossypium hirsutum L.), chick ling vetch, wheat (CS2) 3. broad bean, corn, sugar beet (Beta vulgaris saccharifera L.), wheat (CS3) 4. cotton, wheat, cotton, (CS4) 5. corn, wheat, corn, wheat (CS5) 6. wheat, canola (brasica compestris L.), wheat (CS6) 7. wheat, wheat, wheat (CS7). At the end of each rotation frequency, wheat grain yield and its components, soil organic carbon, phosphorous, potassium and bulk density was measured. At the end of second cropping cycle core index of soil different layers was also measured. Results of the experiment showed that CS2 had the highest amount of wheat grain yield in the first rotation frequency, without any significant difference with CS8, CS6 and CS4. The lowest wheat grain yield was for CS5 and CS3, respectively. In the second rotation frequency, wheat grain yield of CS6 was significantly higher than those of other crop systems, and the lowest was for CS5. The higher wheat grain yield of superior cropping systems such as CS2 and CS6 was due to higher kernel weight, more spike number per unit area and more kernel number per spike. The lower O.C. quality, lack of any follow and high nutritional requirements in CS5, resulted in lower wheat grain yield. Some soil chemical and physical properties, including O.C, P and K was also increased in high yielding cropping systems such as CS2 and CS7 in the first rotation frequency and CS6 in the second rotation frequency. Finally it could be concluded that presence of clover as a legume green manure in both short and long-term cropping cycle and canola with summer follow in rotation with wheat in long-term cropping cycle could result to increasing of wheat grain yield.