Understanding the variability in crop yield and identification of the factors affecting crop yield is necessary to achieve sustainable increase in agricultural productivity in agro-ecosystems. Crop production systems become very complex in rainfed conditions under variable topography. Knowledge of the relationships between topographical parameters, soil properties, management factor and crop yield can be used for developing appropriate management practices for enhanced productivity of the dry land production systems. In rolling landscapes, topography is the most important factor controlling soil water redistribution and physicochemical soil properties that affect plant growth and yield. Wheat ( Triticum aestivum ) is the most important crop that can be grown in the arid and semiarid regions of Asia . Little investigation has been made to identify important factors that influence wheat production using non-linear statistical approaches in the semiarid hilly regions. Moreover, no attempt has been made to predict the variability in grain protein of wheat in the hilly regions. Therefore, the objectives of this study were to predict biomass, grain yield, thousand seed weight and grain protein of wheat in hilly regions under rainfed agriculture using ANN model and to identify the most important edaphic and topography parameters affecting the variability of wheat yield in the semiarid region of western Iran . The study was conducted on a farmer–operated wheat field in 900ha size, located in Ardal district of Chaharmahal and Bakhtiari province, west of Iran . The study area is located within 50 ° 12 ? to 50 ° 37 ? E longitude and 31 ° 58 ? to 32 ° 03 ? N latitude. The mean elevation of the area is approximately 1860m above the sea level. The mean annual temperature at the site is 15 ْ C. The average annual precipitation is 600 mm which mainly falls from November through April. The hillslopes of the study area have been developed by extensive dissection of sedimentary Eocene deposits and have 20-30% lateral slope. Generally, the soil texture is silty clay and silty clay loam in the 0-30 cm soil layer; and the soils of the study area are dominantly path="m,l,21600r21600,l21600,xe" o:spt="202" coordsize="21600,21600" as curvature, wetness index and stream power index that related to moisture distribution over the
