Relationship between Soil Productivity and Erodibility in Rainfed Wheat Lands in Northwestern Iran

Soil erosion by water is the main factor of land degradation, particularly in semi-arid regions where soil productivity is usually low and lowering soil quality can severely decrease crops yields. This study was done in an area of 900 km(2) in the semi-arid agricultural region of Hashtroud in northwestern Iran to determine the relationship between soil productivity and soil erodibility. Wheat grain yield (WGY) and soil erodibility factor (K) were measured separately at 108 plots in 36 dry-farming lands under natural rainfall conditions for a two-year period from March 2005 to March 2007. Based on the results, significant differences were observed among the lands in WGY (P < 0.001) and K (P < 0.001). These differences were attributed to variations of soil properties among the lands. There was a negative relationship between WGY and K (R-2 = 0.77). Multiple regression analysis indicated that both WGY and K were significantly related to aggregate stability and infiltration rate, with a determination coefficient (R-2) of 0.74 and 0.90, respectively. Organic matter and calcium carbonate equivalent were the most effective soil properties that enhanced both aggregate stability and infiltration rate. The study revealed that soils with a lower percentage of water-stable aggregates and a lower infiltration rate also tended to have a higher susceptibility to erosion and a lower potential for crop production.