Effect of Topography Indices and Soil Characteristics on Rainfed Wheat Yield in Loess Lands of Toshan Area, Northern Iran

Topography by affecting soil quality can significantly affect the production of agricultural products. This study was conducted in Toshan area of Golestan province to evaluate the spatial variation of wheat production and to create regression models between the crop, soil, and topography characteristics. Wheat and soil sampling from different slope positions were collected randomly from 100 points. Soil physical-chemical analyses and wheat yield parameter measurements were carried out. The digital elevation model was prepared, and topographic attributes were calculated. The results showed that the highest total yield (14.53 t/ha) and grain yield (4.41 t/ha) were observed in <10% slope class, which showed a significant difference compared to steeper slopes. The highest (15.82 t/ha) and the lowest (5.68 t/ha) total mean yields were corresponded to paw slope and shoulder slope, respectively. The highest grain yield was obtained from the foot slope and paw slope. The amounts of mean grain yield were 4.61 t/ha in foot slope and 4.66 t/ha in paw slope. Curvature and wetness index had a remarkable relationship with wheat yield. According to the regression analyses, topography indexes have been able to explain the spatial variability of yield, indicating the importance of these factors' impact on water distribution in yield production process in the studied area. Increasing yield productions in low slope positions in this study was probably due to increasing in soil depth and plant available water, as well as accumulation of organic matter and nutrient elements such as nitrogen and potassium due to deposition of eroded materials in these positions.