Evaluation of the effect of land use change from forest lands into agricultural lands on some chemical properties of soil (Case study: Zarin Abad, Sari, Iran)

Land use change and its effect on soils is one of the important factors in decreasing soil quality. Nowadays because of rapid growth of the population، vast areas of the forest lands are changed into agricultural lands but chemical properties of the soils are commonly affected by changing in land usage. Converting the forest lands into agricultural lands is one of the prevalent issues in Iran، especially in north of Iran، nevertheless، relevant studies considering the effects of land use change is very limited and lack of enough and suitable studies due to quantifying of these effects is so significant. Because of that، this study was carried out in order to investigate the impact of changing in usage of forest lands in to the dry farming lands (canola) and paddy lands on some chemical properties of soil such as: pH، organic carbon، total nitrogen، available phosphorous and potassium، electrical conductivity and cation exchanging capacity in Zarin Abad area of Sari، in north of Iran. In order to study the effect of changing in usage of forest lands (Hyrcanian forest) into the dry farm lands (canola) and paddy lands on some chemical properties of soil in Zarin Abad area of Sari، Iran، this research was conducted as factorial design in complete randomize block. samples of soil from each land use were collected in four replications from 2 depths of 0-20 and 20-50 centimeter. Samples were dried and passed from the 2mm sieve، then amount of the organic carbon was determined by the method of wet oxidation. Total nitrogen of the soil was measured by Kejeldal method. To calculate the soil available phosphorous، samples were extracted in two ways: Olson (for measuring available phosphorous in soil samples with pH=7) and Bray-Kortz (for measuring available phosphorous in soil samples with pH=7). then the amount of phosphorous in each extraction was determined with Expectrophotometer device. Available potassium was measured by extraction with Ammonium acetate with pH=7 and Flame photometer device. Cation Exchanging Capacity was also determined by Bawer method. To measure the reaction and the electrical conductivity of the soil’samples، after making saturation mud، the amount of reaction (pH) was measured by pH meter in each sample. The amount of electrical conductivity after extracting from saturation mud was determined in extractions from each sample by Ec meter. Then the analysis of data was done after doing normalization test with Colomogrof-Smirnof test in SPSS program. Comparison of the averages of data was done with Duncan test. Results showed that land use change from forest lands (Hyrcanian forest) into paddy lands، increased soil reaction from 6. 43 to 7. 52 but change to dry farming lands (canola) had no significant effect on soil reaction. Land use change from forest lands into dry farm lands caused decrease in the amount of organic carbon about 46. 5 percent which was about 38 percent in paddy lands. Amount of total nitrogen was decreased in land use change from forest usage into dry farm usage but this decrease was not significant in forest lands change into paddy lands. While land use change caused increase about 4 times in amount of available phosphorus in dry farming lands and increased about 2 times in lands that converted to paddy lands but it had no effect on amount of available potassium and cation exchanging capacity. The lowest amount of electrical conductivity was observed in dry farming lands. Correlation coefficients between parameters showed positive and significant correlations between organic carbon with available potassium and electrical conductivity. There were positive correlations between electrical conductivity with amount of available potassium and soil reaction. Amount of available phosphorus showed a positive relationship with cation exchanging capacity too. Land use change caused changes in some soil chemical properties and each property affected the amount of others so considering the ecological importance of Iran’s northern forests، results of this study showed the necessity of more accuracy and attention to adjust the unfavorable effects of land use change by applying efficient methods of land management in these areas.