Determining soil organic carbon and fractions under different climete and managemet conditions using century model

In the last century, the rapid increase in atmospheric CO2 concentration, global warming, and climate change have made important C management in the terrestrial ecosystem. The aim of this study was to estimate the changes in soil organic C under pasture and agricultural use in humid, semi-arid and arid climates with two years field measurements and long-term model use. In addition, the effects of 10% increase in temperature, 10% decrease in precipitation, different textures and pH groups on soil organic C content were tested independently in the three climatic conditions. The study was conducted in Samsun, Tokat, and Sivas to represent humid, semi-arid, and arid climate conditions. In each site, two land uses representing pasture and agricultural use and four randomly selected sampling locations were identified and samples were taken from 0-20 cm depth. Particle distribution, bulk density, wilting point, field capacity, pH, EC, lime content, organic matter, organic C, mineralized C, microbial C and passive C contents were determined in soil samples. The long-term changes in the amount of organic C in the study area by using climate, soil and plant data were modeled with the Century 4.6 program. It was observed that the two years land measurements and the estimated values of the model were close to each other. In general, there is a linear relationship between measured and estimated values. However, it was seen that there is an inverse relationship between Sivas and Tokat agricultural use and estimated values. The 10% reduction in monthly rainfall and the 10% increase in monthly maximum and minumum temperatures in the three climatic conditions had no significant effects on organic C content alone. This can be considered as the reason of the insignificant effect of the changes of precipitation and temperature on organic C. The highest organic C was determined in clay texture. The amount of soil organic C increased when the soil reaction went towards acid condition and decreased when the soil reaction towards basic reaction. It was determined that the estimation of soil organic C under different climate and uses were consistent with the actual land measurements. Unless there is a significant change in the current climate and management, the soil organic C content will remain at a certain level of equilibrium in the three study sites. KEYWORDS: Century model, organic carbon, Carbon fractions, Global worming, Carbon storage