The impact of land use on soil water repellency in the central part of Mazandaran province

Soil water repellency reduces soil infiltrability, water availability for plants, and can increase surface runoff, soil erosion and preferential flows, and reduces environmental fertility. Land use is one of the factors affecting soil water repellency. Soil water repellency can increase runoff in areas where land use change occurs. Thus, knowledge about the soil water repellency properties is necessary for effective environmental management. Changing the soil properties upon reduction of soil wettability can affect crop growth and yield, and water use efficiency. However, relations between soil water repellency and physical and chemical properties among different land uses in the large scale have not been studied yet. Therefore, the objectives of this study were: i) to investigate the persistence and severity of soil water repellency in different land uses, and ii) to develope regression relations between the water repellency indices and soil physical and chemical properties in the central part of Mazandaran province.

In this study, the persistence and severity of soil water repellency were investigated in the paddy fields located in the plains to mountainous areas consisting of four land uses of pasture, citrus garden, paddy field, and forest located in Amol city in the central part of Mazandaran province. Ninety-two soil samples were collected to determine soil water repellency and physical and chemical properties in the dry season of the year. The persistence of soil water repellency was determined using the water droplet penetration time (WDPT) test, and water repellency index (RI) and soil-water contact angle (β) were measured using the intrinsic sorptivity test in the laboratory. Correlation between water repellency indices and soil properties was studied. Relations between the water repellency indices and soil properties were derived by multiple regression.

Soil water repellency in all the land uses was sub-critical and all of the soil-water contact angle values were less than 90°. The highest mean values of soil water repellency indices in all methods were found in the forest land use, so that Log WDPT value was significantly different from paddy field land use. Log WDPT showed positive and significant correlations (r = 0.33**) with RI, indicating that the water repellency persistence (i.e., Log WDPT) and water repellency severity (RI) are directly related in the studied soils. The correlation between soil organic matter content and calculated β in the citrus garden land use was positive and significant (r = 0.42*). There was also a positive and significant correlation between Log WDPT and soil organic matter content (r = 0.36***). Negative and significant correlations were found between calcium carbonate equivalent (CCE( and Log WDPT in the whole study area (r = -0.28**) and in the paddy field land use (r = -0.29*)

The results showed that the land use through the effect on the soil organic matter content can induce and intensify water repellency in the studied soils. Moreover, the derived regression relations indicated that soil organic matter content, total nitrogen and CCE are important properties affecting water repellency in the studied soils.