Abstract:

Soil structure affects the water, fertilizer, gas and heat situation of soil, and soil micro-aggregate is the most important material basis of it. Many factors can affect the status of micro-aggregate, so as tillage system. Fractal dimension offers a new means to quantitatively investigate the soil structure. By using fractal model of soil micro-aggregate, soil structure based on a long-term (19 years) experiment with various tillage systems were studied in a purple paddy soil at the farm of Southwest University, Chongqing, China. The experimental plots included five tillage treatments: conventional tillage with rice only system (DP), conventional tillage with rotation of rice and rape system (SH), no-till and ridge culture with rotation of rice and rape system (LM), no-till and plain culture with rotation of rice and rape system (XM), and tillage and ridge culture with rotation of rice and rape system (LF). Soil samples were collected at depths of 0-10 cm, 10-20 cm, 20-30 cm, 30-40 cm, 40-50 cm, 50-60 cm and 60-70 cm. The results showed that the contents of soil micro-aggregate in each soil depth decreased with the decrease of particle size under LM, XM, LF and SH, while showed the trend of increase firstly and then decreased under DP treatment. There were highly significant positive correlation between the contents of 2-0.25 mm soil aggregate and soil organic carbon, total nitrogen, available nitrogen, total phosphorus and other nutrients, while the contents of 0.05-0.01 mm and 0.01-0.005 mm soil micro-aggregates with these types of nutrients were significantly or highly significant negative correlation, indicating that these nutrients are mainly rich in 2-0.25 mm soil aggregate. The fractal dimension and the content of grain size of soil micro-aggregates were highly significantly correlated. Fractal dimension, and (<0.005 mm)/(>0.005 mm) grain size ratio of micro-aggregate content both can quantitatively characterize the structure of purple paddy soil. In 0-70 cm soil layers, the fractal dimensions under LM, XM and LF treatments were highly significantly lower than DP treatment, showing that the ridge or no-tillage can improve soil structure.