Effects of long-term fertilization on soil particles and microaggregate distribution in the loess area

Based on the particle volume fractal theory, effects of 15 years fertilization on soil particle distribution, microaggregate distribution and organic carbon content of farmland in the loess area were studied using field sampling and experimental analysis. Results show that the fertilization has a significant effect on the particle and microaggregate distribution in 0-20 cm soil layer, and the fractions of 0.02-0.05 mm are predominant in different treatments. The organic fertilizer (M), phosphoric fertilizer (P), the combination of organic and nitrogen fertilizer (MN), and the combination of organic, nitrogen and phosphoric fertilizer (MNP) significantly improve the contents of 0.1-0.2 mm fractions, and. the combination of organic and phosphoric fertilizer (MP) and MNP treatments are contribute to the formation of large soil microaggregate. Among the treatments, the biggest dispersion rate is found in the treatment of nitrogen and phosphoric combination (NP), the smallest in the M treatment. There are no significant differences among treatments. The soil particle fractal dimension is positively correlated with clay particle (0.002 mm), and fine silt (0.002-0.02 mm) and negatively correlated with coarse silt (0.02-0.05 mm) and fine sand (0.05-2 mm). The soil aggregate degree is negatively correlated with 0.05 mm aggregate and positively correlated with 0.05 mm aggregate. The soil organic carbon is negatively correlated with in 0.01-0.05 mm microaggregate and positively correlated with 0.1-0.5 mm microaggregate in 0-20 cm layer.