Document Type : Research Paper

Authors

• Alireza Abdollahpour ¹
• Mojtaba Barani Motlagh ²
• Amir Bostani ³
• Farshad Kiani ²
• Farhad Khormali ⁴
• REZA GHORBANINASRABADI ²

¹ PhD student, Department of Soil Science and Engineering, Gorgan University of Agriculture and Natural Resources

² Associate Professor, Department of Soil Science and Engineering, Gorgan University of Agriculture and Natural Resources

³ Associate Professor, Department of Soil Science and Engineering, Faculty of Agriculture, Shahed University

⁴ Professor of the Department of Soil Science and Engineering, Gorgan University of Agriculture and Natural Resources

Abstract

Introduction Soil organic carbon (SOC) is the largest source of terrestrial organic carbon and small changes in its components have many effects on global warming and carbon cycle. Soil organic matter (SOM) is considered as the most complex and least known component of soil, because it consists of plant, microbial and animal masses in various stages of decomposition and is a mixture of heterogeneous organic materials that are closely related with mineral components. Soil organic matter has beneficial effects on the chemical (buffering and changes in pH) and biological (precursor and supply of nutrients for microbes) properties of the soil and thus affects the fertility capacity of the soil. The quality and quantity of soil organic matter is the most important criterion for sustainable soil management. Total organic carbon (TOC) consists of labile and non-labile forms of SOC and have different degrees of sensitivity to different types of land use changes and management operations. The purpose of this research is to investigate the effect of changing land use on the chemical components of soil organic carbon and carbon recalcitrant index in Toshan Watershed, Golestan province
Materials and Methods For this research, four major and dominant types of land use were considered in the study area, including forest, cropping land, garden and abandoned lands in the Toshan watershed in the northwest of Gorgan city of Golestan province. The soil organic carbon and total C of soils were measured. Furthermore, the soil carbon fractionation was performed by Young's method (using hydrolysis methods with HCl and Labile fraction). In this research, Acid hydrolysis method was used to separate the recalcitrant SOM pool. For this purpose, one gram of SOM sample was treated with 25 ml of 6 M hydrochloric acid solution at 105°C for 18 hours in a Pyrex tube in a hydrolysis package. After cooling, the remaining non-hydrolyzed materials were separated by centrifugation. Then, they were dried in an oven at a temperature of 60 degrees Celsius and considered as a part of resistant organic matter. The resistant part of the soil organic carbon was determined with the CHNS Analyzer device. The Labile fraction consists of water soluble carbon, microbial biomass carbon and mineralizable carbon are measured using the following methods and the labile part of carbon is calculated from their sum. Water-soluble organic carbon is extracted by adding 20 ml of distilled water to 10 grams of wet soil. The mixture will be shaken and centrifuged, filtered. Then they will be quickly analyzed by TOC Analyzer. Microbial biomass carbon will be determined by the chloroform fumigation-extraction method. Mineralizable carbon determined as follow. The amount of CO2 will be measured by titration of NaOH solutions with 0.1 M HCl in the presence of BaCl2. Cumulative amount of CO2-C emitted in 30 days of incubation is called Mineralizable carbon. The data were analyzed based on the factorial test in the form of a completely randomized design (CRD) with two levels of soil depth and four land uses with five replications. Correlation between traits was also estimated. Statistical analyzes were performed using SAS software. Therefore, it can be concluded that depending on the climatic conditions and the condition of the soil, the forest, in terms of natural cover, the correct management of agricultural lands (using modern methods of no-tillage or low-tillage) can be a potential practice. It is to store carbon in the soil as well as various soil components and increase soil formation, which will subsequently reduce the concentration of carbon dioxide in the atmosphere.
Results and Discussion The results showed that the first depth of forest use has the highest amount of total carbon and soil organic carbon (6.12% and 3.5% respectively). Also, the highest amount of resistant organic carbon (HCl hydrolysis), water-soluble organic carbon, microbial biomass carbon, and microbial mineralizable carbon were observed in forest land use. The second depth (10-20 cm) of forest land use had the highest and the second depth (10-20 cm) of garden land use had the lowest organic carbon resistance index (82.1% and 50.17%, respectively). In all land uses, except for the forest, the soil organic carbon resistance index decreased with increasing sampling depth. Due to the fact that the carbon management index can be easily calculated, it can be a suitable index for quick assessment of soil quality.
Conclusion The results showed that with the change of land use and cultivation, the soil organisms received more oxygen and the speed and intensity of respiration in the soil increased in the short term, which caused more decomposition of organic matter and with the decrease of organic matter in the long term, the quality of soil decreases after a while.

Keywords

• Chemical Fractionation
• acid hydrolysis
• soil organic carbon resistance index
• labile component
• resistant component

Main Subjects

• Soil Chemistry and Pollution