Crop Rotation Effects on Soil Physico-chemical Properties and Rain Fed Wheat Crop Yield

In order to evaluate the effects of various crop rotations on soil physical and chemical properties in drylands، three sites with Sahand (Fluventic Haploxerepts)، Rajol Abad (Typic- Calcixerepts)، and Darab (Calcic Haploxerepts) soil series were chosen in Maragheh and Hashtroud، North West of Iran. The treatments including continuous wheat cropping (T1)، wheat–chickpea rotation (T2)، wheat-fallow-wheat-wheat-wheat (T3) and wheat–fallow rotation (T4)، were executed for 5 cropping years from autumn 2003 to summer 2008. Disturbed and undisturbed soil samples from 0-10، 10-20، and 20-40 cm depths were taken at these sites on June 2008. Selected soil physical and chemical properties such as texture، pH، EC، carbonate calcium equivalent (CCE)، wet-aggregate stability (WAS)، bulk density (Db)، organic carbon (OC)، saturation hydraulic conductivity (Ks)، CEC and concentration of available P، K، Mn، Fe، Cu، Zn، and total nitrogen were measured by common laboratory methods. For assessing the moisture content soil samples were taken at four growth stages of wheat. Sampling for assessing the biomass was carried out at harvest (late June 2008). The lowest Ks occurred in T1 and T3 (2. 01 cm. hr-1) and had significant difference with T2 and T4. The highest (4. 79 mg kg-1) and lowest (3. 88 mg kg-1) Fe concentration occurred in T4 and T1، respectively، which significantly (p< 0. 05) differed from those of other treatments. Soil WAS in T4 (71. 54%) became significantly (p<0. 05) greater than those of other treatments. Db in T2 (1. 16 g cm-3) and T4 (1. 15 g cm-3) was significantly (p< 0. 05) lower than T1 (1. 29 g cm-3) and T3 (1. 29 g cm-3). Biological yield in T2 (3. 096 t. ha-1) and T4 (3. 052 t. ha-1) significantly (p< 0. 05) differed from that of T1 (1. 501 t. ha-1) and of T3 (1. 573 t. ha-1). In other measured properties and soil moisture content no significant differences among treatments were appeared. Based on the results، alteration from wheat-fallow or wheat-chickpea rotation to continuous wheat cropping، may gradually degrade soils of the region.