The effect of climate change on soil organic carbon storage using the Roth C model in the agricultural lands of Golestan province

Increasing concerns about global warming and climate change have led to special attention to soil and its capability in carbon sequestration in recent years. About 540,000 hectares of soils in Golestan province are under agronomic activities and so far no studies have been conducted on soil organic carbon changes and its interactions with climate change. The total organic carbon in soils is approximately twice the amount of carbon atmosphere, so changes in soil carbon have significant effects on climate change. On the other hand, factors such as climate change or changes in land use and management affect soil organic carbon changes. As soil temperature increases, the rate of organic carbon decomposition will increase, which potentially increases the average release of soil carbon dioxide emission into the atmosphere. Therefore, finding low-cost and rapid methods for estimating soil organic carbon in large ranges and predicting its changes in the future has became a necessity.
Modeling is a tool that can be used to evaluate the feasibility of various land management techniques, and with the help of the results, the best methods can be selected and researched. In the field of soil organic carbon studies, the RothC model is one of the most widely used models, which is of great interest to researchers due to its simplicity and availability of inputs. Climatic changes are also investigated using the output of general circulation models (GCMs) under greenhouse gas emissions scenarios. These data are used after exponential microscale, in which Lars-WG statistical method has been used in this research.

The purpose of this study is to investigate the status of soil organic carbon storage in agricultural lands of Golestan province and the effect of climate change on soil organic carbon storage in the coming decades. Therefore, in order to conduct this research along the northeast_southwest of the province were selected 3 points in 3 arid climates, semi-arid and Moist climate. In selected points, soil samples were collected by digging 3 profiles and several augers and soil organic carbon, soil texture and soil apparent specific weight were measured (year 2018). The Roth C model has been used to investigate changes in soil organic carbon storage in the future. Roth C model has been used to investigate future changes in soil organic carbon storage. In order to validate the Roth C model, the results of previous studies (1997 and 2004) were used. Also, the climatic data used in this project were extracted from the statistics of 1371 to 1398 weather stations of Chat, Kalaleh and Ramyan and using the output of general circulation models (GCMs), scaled by Lars WG6 model and precipitation and temperature data were predicted of future decades.

The study of temperature changes showed that by 2040, based on scenario 4.5, the temperature will increase between 0.6 and 0.8 and based on scenario 8.5 between 0.6 and 1.3 °C. Also, by 2080, based on scenario 4.5, the temperature increase was predicted between 1.5 and 2.3 and based on scenario 8.5 between 2.2 and 3.2 °C. Climate change in different regions can reduce, increase or no change in precipitation. According to the forecast of the third report of the InterGovernmental Panel on Climate Change, precipitation will increase in winter and decrease in the summer. Based on the findings of this study, the amount of precipitation in the studied stations will increase in the future (in 2040 and 2080) based on two scenarios of 4.5 and 8.5. The results of prediction of soil organic carbon storage show that in 2040 based on scenario 4.5 the amount of soil organic carbon storage in agricultural land use will decrease between 0.5 and 5.3 tons per hectare. Also, based on scenario 8.5, the reduction of soil organic carbon storage in these lands was predicted between 0.8 and 6 tons per hectare. Based on these results, the greatest reduction in soil organic carbon storage was predicted in the humid and rainy areas of the province in 2040. According to this research, in the three investigated stations, in 2080, based on scenario 4.5, the amount of soil organic carbon storage in agricultural land use will decrease between 1.5 and 13.1 tons per hectare. However, in this year, based on MIROC5 and MPI-ESM-MR climate models in Sufian station, we will see an increasement in soil organic carbon storage between 0.6 and 3.9 tons per hectare. Also, according the scenario 8.5, in 2080, the reduction of soil organic carbon in these lands is predicted between 0.5 and 10.5. According to these results, the greatest reduction in soil organic carbon storage in 2080 was calculated in wet and rainy areas (Ramian station).

According to the obtained results, the Rothamsted model has been able to simulate the dynamics of soil organic carbon storage in the study area with appropriate accuracy. The output of the four climate models showed that future temperature changes will increase in 2040 and 2080 based on scenarios 4.5 and 8.5. these findings are consistent with the results of most climate studies that have predicted temperature enhancement in the future decades. According to the findings of the current research, the amount of precipitation in the studied stations will increase in the future (in 2040 and 2080) based on two scenarios of 4.5 and 8.5. The results of Roth C model simulations for predicting soil organic carbon storage showed that soil organic carbon storage will decrease in 2040 and 2080 in both climatic scenarios. According to these results, with increasing of temperature, the rate of decomposition of soil organic carbon increases. Increasing the rate of decomposition in agricultural land use due to the lack of surface vegetation in periods of the year causes the waste of soil organic carbon in the form of CO2 in the upper layers of the soil. Some studies have shown that low vegetation cover (agricultural compared to rangeland) areas will be severely affected by climate change and will lead to soil organic carbon waste in these areas.