Relation of soil aggregate fractal dimension and organic carbon in purple-soil slope farmland

Abstract: For better understanding the effect of soil organic carbon on soil aggregate characterization, the relationship between soil aggregate fractal dimension (D) and soil organic carbon (SOC) were studied in purple soil under different fertilization treatments using the dry sieving, potassium dichromate external heating method and correlation analysis. The results showed that the difference existed in both D and SOC in the treatments (CK, NPK, OM, RSD) and in soil layers (0-10, >10-20, >20-30 cm) ranging from 2.376 to 2.603, 3.54-12.07 g/kg, respectively. The average values both declined following the soil layer. Fractal dimension D of all the samples (n=36, no differences for the treatments or soil layers) were significantly correlated with soil organic carbon (SOC) (p=0.01). Further analysis of the correlation of D and the fraction organic carbon content (fSOC) showed that the correlation was significantly for all the samples and the relevant degree increased with smaller grain size. However, the correlation showed distinction in various treatments or soil layers compared with all the samples: there was no significance in CK and weak correlation for almost all groups of the cultivated horizon (0-20 cm). And most groups of the plow pan (>20-30 cm) were significantly correlated. From the results, it was believed that the different effects in the formation of the aggregates caused by carbon source were from various fertilization treatments. Thus would lead the aggregates to own their characteristics and then show their own fractal feature. And the difference of correlation between D and fSOC reflecting the similarity degree of aggregates size structure and whether the primary factors had coherence in the formation of aggregates were also caused by the fertilization. These results signified that the correlation has characterizing function on the dominant factors in soil structure formation. The results are helpful to recognize the affecting factors of the fractal dimension of soil aggregate, physical characterization and the indication factor of soil structure.