Changes in Soil Structure and Soil Organic Matter Due to Different Severities of Fire

The effect of different fire severity on the changes of the soil organic matter (SOM) and soil structure was evaluated. Soil samples were collected (May 2010) in the locality of Nitra-Dražovce (Slovakia) from the following plots: 1) control (unburned place), 2) low severity of fire and 3) higher severity of fire. The results showed that the content of water-stable microaggregates (WSAmi) increased by 20% in the area with a low severity of fire, but on the other hand, it decreased by 42% in the area with the higher severity of fire in comparison to control. The higher severity of fire resulted in a decrease of smaller size fractions of water-stable macroaggregates (WSAma) (0.5−0.25) and a low severity of fire resulted in the decrease of WSAma 2−0.5 mm. On the other hand, the content of WSAma in the size fraction >5 mm was higher by 54% and by 32% in the lower and higher severity of fire, respectively, than in unburned soil. The higher severity of fire had a more positive effect on increases of the structure coefficient and coefficient of aggregate stability, as well as on the decrease of the vulnerability coefficient compared to the low severity of fire. After burning, the contents of soil organic carbon (Corg) and labile carbon were significantly increased by the severity of fire. However, the low severity of fire affected more markedly the increase of hot water-soluble and cold water-soluble carbon than the higher severity of fire. After burning and due to the severity of fire, both the carbon of humic and carbon of fulvic acids ratios and SOM stability increased. The parameters of SOM due to fire significantly increased also in WSA with the least changes in WSAmi. The results showed that a low severity of fire increased Corg mainly in WSAma >2mm and WSAmi, whereas high severity fire increased Corg content in the smaller fraction of WSAma