Soil fertility decline and sustainable production of pure plantations of fast growing trees in long time, are the main reasons fore utilization of trees with the ability of nitrogen fixation in mixed plantations. The objective of this study was to survey the effect of pure plantation of Populus eurmaericana (Dode) Guinier and mixed whit Alnus subcordata C.A.Mey on soil properties. In order to investigate soil chemical and physical properties, soil were sampled at 0-15, 15-30 and 30-60 cm depths from the plantation that were located in the next of Chamestan station and also some blank samples were collected (3 samples from the soil that were located out of plantation). The collected samples were transferred to the laboratory and several properties of them such as: texture, pH, Ec, organic matter, organic carbon, total nitrogen and some available nutrients (K, P, Ca, and Mg) were determined. Results showed that, the maximum amount of Nitrogen, C/N ratio, organic matter and electrical conductivity were observed in 0-15 and 15-30 cm depths of mixed plantations. Totally, the presence of Alnus in plantations of populus was an important factor in improvement of soil fertility and sustainable production.
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