Determining the effect of plant species type on some soil properties in the mountain rangelands in Kakhk watershed

Abstract Background and objectives: Biological control of erosion in sloping lands and recognizing the effects of plant species, which are used for rangeland improvement, is the most effective and sustainable method for stabilizing and controlling soil fertility in rangeland.Variations of plants composition cause extensive changes in the soil so that in the short term return to the original state is limited .The interactions of plant species on soil have been studied in various research.Tree species with creating litter, have positive effects on physical and chemical properties of soil, and their loss due to various factors leads to a decrease in soil quality characteristics. The aim of this study is investigation the effects of plant species  planted to improve and rehabilitation slope lands on recovering of soil characteristics of Kakhk watershed. Methodology: Kakhk watershed with 37.2 Km2 area in northeastern of Iran is located between 58° 31ʹ 12ʺ to 58° 37ʹ 08ʺ E longitude and 34° 02ʹ 13ʺ to 34° 05ʹ 04ʺ N latitude. The average annual rainfall of the basin is 243 mm. The project of improving and rehabilitating the destroyed lands and pastures in this watershed including sub-projects of planting fruit tree and non-fruit trees, shrub planting, range seeding, seeding, and mount culture Which started in 1993 and has continued until 2006. Slope, direction of slope, altitude, and geology maps of the basin was prepared with GIS software and by overlying them homogeneous work unit maps was obtained.Sampling sites were selected under similar condition of geology and topography. Soil sampling was done randomly and systematically from 0-30 and 30-60 cm depth of understory soil of Prunus amygdalus, Pinus eldarica, Rhus Coriaria and bare area (control treatment). soil texture by hydrometric method, amount of organic matter by Valky block method, pH of saturated soil extract with pH meter, electrical conductivity of saturated soil extract with EC meter, total nitrogen by Kjeldahl method, absorbable phosphorus by Olsen method, lime, potassium, and Bicarbonate of soil samples was measured in soil science laboratory. One-way analysis of variance was used to compare between several independent groups.Also, the comparison of means and differences between groups was investigated using LSD and Dunnett t3 test. Results: The highest percentage of Nitrogen (0.054), Potassium (270 mg/kg), Phosphorus (6.6 mg/kg), and the percentage of organic matter (0.96) were observed in understory soil of R.coriaria and the highest percentage of lime (7.91) was observed in P. eldarica understory soil. Their lowest values were 0.017, 96.33, 1.92, 0.3, and 2.87, respectively, in the soil of control area. The analysis of variance results showed that there was no significant difference at the level of 5% between the amount of acidity, salinity in all soil depth, and bicarbonate in depth of 30-60 and 0-60 centimeters of soil in different treatments. The percent of sand, silt, and clay also have a significant difference at the level of 5% between treatments in total soil depth (0-60 cm). The average amount of Nitrogen and organic matter of control area in depth of 0-30 cm have a significant difference at a 5% level with P. Amygdalus, P. Eldarica, R. Coriaria treatments. There are a significant difference at a 5% level between the average of potassium (137.67 mg/kg), organic matter (0.55 %), and lime (8.04 %) in understory soil (0-30cm) of P. Eldarica treatment with R.Coriaria region (278.67 mg/kg, 1.07 % and 4.38% respectively) and only in term of lime have a significant difference with P. Amygdalus treatment. The mean of phosphorus (6.26 mg/kg) and organic matter (0.84%) in P.Amygdalus treatment are significantly different from the control area (1.82 mg/kg and 0.32% respectively) but not significantly different with P.Eldarica and R. Coriaria. The soil of 0 to 30 cm depth in the R.Coriaria cultivation area was the most different from the control area in terms of studied chemical parameters. The average amount of Nitrogen, potassium, phosphorus, organic matter and silt  of control area in depthes of 30 to 60 cm showed a significant difference at 5% level with P. Amygdalus, R. Coriaria treatments. Soil pH and EC in none of the treatments and studied depths did not show a significant difference with the soil in the control area at the level of 5%. Conclusion: The results of this research showed the planting of different trees species in Kakhk watershed has been causes changes in some physical and chemical properties of soil.The R. Coriaria and P. Amyigdalus species more than P. Eldarica provide soil fertility by increasing the minerals Such potassium, nitrogen, phosphorus and organic matter in the their understory soil without significant increasing unhelpful indicators such as salinity. Since Rh.coriaria has better ability for establish and growth in the slopping lands, so it can be used as a suitable species to repairing and rehabilitation of destroyed mountain pastures in Gonabad County.