مجله آب و خاک (Sep 2016)
Relationships between some soil physical and chemical properties with magnetic properties in different soil moisture regimes in Golestan province
Abstract
Introduction: Soil moisture regime refers to the presence or absence either of ground water or of water held at a tension of less than 1500 kPa in the soil or in specific horizons during periods of the year. It is the most important factor in soil formation, soil evolution and fertility affecting on crop production and management. Also, it widely is practical in soil classification and soil mapping. The soil moisture regime depends on the soil properties, climatic and weather conditions, characteristics of natural plant formations and, in cultivated soils, is affected by the characteristics of crops grown, as well as the cultivation practices. Determination of soil moisture regime within a landscape scale requires high information and data about moisture balance of soil profile during some years according to Soil Survey Manual (2010). This approach is very expensive, labor, time and cost consuming. Therefore, achievement to an alternative approach is seems essential to overcome these problems. The main hypothesis of this study was to use capability of magnetic susceptibility as a cheap and rapid technique could determine the soil moisture regimes. Magnetic properties of soils reflect the impacts of soil mineral composition, particularly the quantity of ferrimagnetic minerals such as maghemite and magnetite. Magnetic susceptibility measurements can serve a variety of applications including the changes in soil forming processes and ecological services, understanding of lithological effects, insight of sedimentation processes and soil drainage. Materials and Methods: This study was conducted in an area located between 36°46َ 10˝ and 37° 2’ 28˝ N latitudes, and 54° 29’ 31˝ and 55° 12’ 47˝ E longitudes in Golestan province, northern Iran. In the study region mean annual temperature varies from 12.4 to 19.4 °C. The average annual rainfall and evapotranspiration varies from 230 mm and 2335 mm in Inchebrun district (Aridic regime), to 732 mm and 846 mm in Touskstan uplands (Udic regime), respectively. this study was conducted in four soil moisture regimes (Aridic, Xeric, Udic and Aquic), for exploring the relationships between soil properties and magnetic measures. In each regimes, 25 soil profiles were drug, described and soil samples were collected from each of soil horizons. Soil samples were air-dried and sieved using a 2 mm sieve. The dithionite-citrate bicarbonate (DCB) method was used to measure Fed and acid ammonium oxalate for Feo. In this study, a set of environmental magnetic parameters including magnetic susceptibility at low frequency (χlf), saturation isothermal remnant magnetization (SIRM), isothermal remnant magnetization (IRM100 mT) were measured. Magnetic susceptibility (χ) was measured at low frequency (0.47 kHz; χlf) and high frequency (4.7 kHz; χhf) using a Bartington MS2 dual frequency sensor using approximately 20 g of soil held in a four-dram clear plastic vial (2.3 cm diameter). Frequency dependent susceptibility (χfd) was determined by the difference between the high and low frequency measurements as a percentage of χ at low frequency. IRM was measured at the field of 100 mT generated in a Molspin pulse magnetizer (IRM100mT) and at the back field of 100mT (IRM−100mT). The IRM acquired in the maximum field of 1000 mT was measured and defined as the saturation isothermal remnant magnetization (SIRM) of the soil sample. Results and Discussion: The results showed that moisture regime induced significant differences for soil physical and chemical properties. Diversities in genetic soil horizons and soil development degree have been increased from Aridic to Udic soil moisture regime. The results also indicated that selected properties including magnetic measures and physical and chemical properties were significantly different in four soil moisture regimes. With increasing rainfall and reducing temperature from aridic to udic soil moisture regime, soil organic matter was increased. Otherwise, in arid environment Gypsic, Calcic and Salic horizons were observed in the near of soil surface. Fed and Fed-Feo were the highest in udic and the lowest in udic soil moisture regime, respectively. Moreover, higher soil development because of climate effect leaded to higher amount of pedogenic ferromagnetic minerals, as well as the highest were observed in the Udic regime. Otherwise, in Aquic moisture regime, the lowest value of magnetic susceptibility was obtained because of dissolution of ferromagnetic minerals (magnetite and maghemite) under supersaturating condition. In overall, close relationships were observed between soil physical and chemical properties and magnetic measures in various soil moisture regimes.
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