Effect of landscape position on wheat yield and soil nitrogen management under rainfed conditions in Koohrang area

Wheat is planted in several million ha of hummocky land of Zagros area. Considering high precipitation in this area, it is important to study nitrogen application management with respect to soil, water and environmental protection. This study was conducted in rainfed wheat fields located on different slope positions. Soil properties, crop yield, N uptake and residual soil N were determined in 100 points of rainfed cultivated wheat. The results showed that soil characteristics and crop yield varied in different slope positions. The highest and the lowest crop yields were obtained in toeslope and shoulder, respectively. Maximum and minimum N uptake and residual soil N were also observed in the same slope positions. Soil N in toeslope had a movement toward downhill and was higher than wheat requirement. Thus, residual soil N in this position may be exposed to the soil surface erosion and move on to the waterways and deep percolation to ground water during intermittent years, and thus the excess N in the soil would probably lead to soil and water contamination. Based on the results of this investigation and in order to prevent N losses, it is recommended that N application should be managed to use less N in all slope positions, especially in the toeslope, to split application of N fertilizers in appropriate times, and to use organic.