3.1 Distribution Characteristics of Soil Particle Size under Different Profile Configurations
According to the distribution of soil texture (Fig. 4), the soil texture in the study area is silty loam and silt. It can be seen from Table 2 that the clay content of the soil treated with plot 1 ranges from 13.37–26.18%, with an average value of 20.46%, the silt content ranges from 67.78–73.37%, with an average value of 70.24%, and the sand content ranges from 5.78–14.75%; Compared with plot 1, the average content of clay and sand decreased by 18.57% and 4.13% respectively, and the average content of silt increased by 6.99%; The average content of clay and silt in plot 3 treatment increased by 6.66% and 1.17% respectively, and the average content of sand decreased by 0.17%; The average content of clay decreased by 31.28%, and the average content of silt and sand increased by 2.62% and 38.66% respectively; The average content of clay decreased by 23.02%, and the average content of silt and sand increased by 5.77% and 12.86% respectively; The average clay content of plot 6 treatment increased by 12.45%, and the content of silt and sand decreased by 1.15% and 14.99% respectively.
Among different treatments, the clay content of plot 3 in 0-10cm soil layer was significantly higher than that of other treatments (P < 0.05), followed by plot 1; In this soil layer, the content of silt in plot 2 treatment was significantly higher than that in plot 3, plot 4 and plot 5 (P < 0.05), and the content of sand in plot 4 treatment was significantly higher than that in other treatments (P < 0.05); In 10-20cm soil layer, the clay content of plot 6 treatment was significantly higher than that of other treatments, the powder content had little difference among treatments, and the sand content of plot 1 treatment was significantly higher than that of other treatments (P < 0.05); In 20-30cm soil layer, the clay content of plot 3 and plot 6 treatment was higher, there was no difference between the two treatments, but it was significantly higher than that of other treatments (P < 0.05), the silt content of plot 2 treatment was significantly higher than that of other treatments (P < 0.05), and the sand content of plot 4 treatment was the highest in this soil layer; In 30-40cm soil layer, there was no difference among the treatments of plot 1, plot 2 and plot 6, but it was significantly higher than other treatments. The difference of silt content in this soil layer was significant (P < 0.05). The silt content was the highest in plot 5 treatment, and the sand content was the highest in plot 4 treatment.
Under the treatment of plot 1, the clay content of 30-40cm soil layer was significantly higher than that of other soil layers (P < 0.05), and its content was 26.18%. The silt content of 0-10cm soil layer was the highest, and its content was 73.37%. The sand content of 10-20cm soil layer was significantly higher than that of other soil layers (P < 0.05), and its content was 14.75%; Under plot 2 treatment, the difference of clay content was significant (P < 0.05), the highest content was 25.80% in 30-40cm soil layer, the content of silt in 10-20cm soil layer was significantly higher than that in 0-10cm and 30-40cm soil layer (P < 0.05), the content was 80.42%, and the content of sand in 0-10cm soil layer was significantly higher than that in others (P < 0.05), the content was 12.07%; Under the treatment of plot 3, the content of clay in 10-20cm soil layer was significantly lower than that in other soil layers (P < 0.05), and its content was 13.35%. The content of silt and sand in this soil layer was significantly higher than that in other soil layers (P < 0.05), and their contents were 77.16% and 9.48% respectively; Under plot 4 treatment, there was no significant difference in clay content among all soil layers. The content of silt in 0-10cm soil layer was significantly lower than that in other soil layers (P < 0.05), which was 70.39%. The content of sand was significantly different among all soil layers (P < 0.05), and the highest was 15.69% in 0-10cm soil layer; Under plot 5 treatment, the clay content in 20-30cm soil layer was significantly higher than that in other soil layers (P < 0.05), the content was 23.05%, the silt content was significantly different among different soil layers (P < 0.05), the highest was 79.45% in 30-40cm soil layer, and the sand content was significantly different among different soil layers (P < 0.05), and the highest was 15.48% in 0-10cm soil layer; Under the treatment of plot 6, the clay content in 20-30cm soil layer was significantly higher than that in 0-20cm soil layer, with the highest of 28.46%, and the content of silt and sand in 0-10cm soil layer was significantly higher than that in other soil layers (P < 0.05), with the highest of 73.75% and 13.23% respectively.
The order of d-means of soil volume fractal dimension in the test area is plot5 (2.484) > plot6 (2.417) > plot3 (2.381) > plot4 (2.361) > plot2 (2.349) > plot1 (2.229), indicating that the overall roughness of soil increases gradually in this order.
Table 2
Soil mechanical composition and single fractal dimension under different management modes
Covering type | Sampling depth(cm) | Clay content (%) | Silt content (%) | Sand content(%) | D |
Plot1 | 0–10 | 19.32 ± 0.89Bc | 73.37 ± 1.76Aa | 7.31 ± 1.94Cb | 2.112 ± 0.023Bb |
10–20 | 13.37 ± 0.57Bd | 68.55 ± 4.35Cc | 14.75 ± 1.24Aa | 2.459 ± 0.021Aa |
20–30 | 22.96 ± 0.86Bb | 71.26 ± 0.74Bab | 5.78 ± 0.38Cb | 2.120 ± 0.956Cb |
30–40 | 26.18 ± 0.86ABa | 67.78 ± 0.80Dc | 6.04 ± 0.14Bb | 2.225 ± 0.025Aab |
average | 20.46 ± 0.80 | 70.24 ± 1.91 | 8.47 ± 0.93 | 2.229 ± 0.256 |
Plot2 | 0–10 | 12.89 ± 0.07Cc | 75.04 ± 0.68Ab | 12.07 ± 0.61Ba | 2.320 ± 0.023ABa |
10–20 | 13.17 ± 0.13Bbc | 80.42 ± 2.22Aa | 6.41 ± 2.32Db | 2.384 ± 0.017BCa |
20–30 | 13.59 ± 0.31Cb | 79.00 ± 1.10Aa | 7.41 ± 0.82Bb | 2.337 ± 0.025Ba |
30–40 | 25.80 ± 0.53ABa | 67.63 ± 0.36Dc | 6.57 ± 0.23Bb | 2.354 ± 0.015Aa |
average | 16.36 ± 0.26 | 75.52 ± 1.09 | 8.12 ± 1.00 | 2.349 ± 0.020a |
Plot3 | 0–10 | 22.28 ± 0.66Aa | 69.89 ± 1.09Bb | 7.83 ± 1.61Cab | 2.360 ± 0.030ABa |
10–20 | 13.35 ± 5.22Bb | 77.16 ± 5.89ABa | 9.48 ± 0.79Ca | 2.411 ± 0.052Ba |
20–30 | 27.64 ± 2.46Aa | 67.24 ± 2.56Cb | 5.13 ± 1.35Cc | 2.418 ± 0.064ABa |
30–40 | 24.41 ± 2.34Ba | 69.99 ± 1.23Cb | 5.60 ± 1.28Bbc | 2.336 ± 0.088Aa |
average | 21.92 ± 2.67 | 71.07 ± 2.69 | 7.01 ± 1.26 | 2.381 ± 0.059 |
Plot4 | 0–10 | 13.92 ± 0.67Ca | 70.39 ± 0.84Bb | 15.69 ± 0.62Aa | 2.445 ± 0.058ABa |
10–20 | 14.48 ± 0.45Ba | 73.25 ± 0.85BCa | 12.27 ± 0.44Bc | 2.225 ± 0.209Cc |
20–30 | 14.14 ± 0.39Ca | 72.53 ± 0.86Ba | 13.34 ± 1.09Abc | 2.458 ± 0.030Aa |
30–40 | 13.71 ± 0.51Ca | 72.34 ± 1.22Ba | 13.95 ± 0.73Ab | 2.314 ± 0.071Ab |
average | 14.06 ± 0.51 | 72.13 ± 0.94 | 13.81 ± 0.72 | 2.361 ± 0.092 |
Plot5 | 0–10 | 13.30 ± 0.34Cb | 71.22 ± 1.12Bc | 15.48 ± 1.02Aa | 2.489 ± 0.005Ab |
10–20 | 12.97 ± 0.30Bb | 75.70 ± 0.84ABb | 11.34 ± 0.69 BCb | 2.525 ± 0.254Aa |
20–30 | 23.05 ± 0.52Ba | 71.77 ± 0.33Bc | 5.18 ± 0.35Cd | 2.467 ± 0.024Ab |
30–40 | 13.67 ± 0.30Cb | 79.45 ± 1.14Aa | 6.88 ± 0.86Bc | 2.453 ± 0.029Ab |
average | 15.75 ± 0.37 | 74.54 ± 0.86 | 9.72 ± 0.73 | 2.484 ± 0.078 |
Plot6 | 0–10 | 13.02 ± 0.31Cc | 73.75 ± 0.89Aa | 13.23 ± 0.64Ba | 2.353 ± 0.075ABb |
10–20 | 24.72 ± 1.18Ab | 71.91 ± 1.21BCb | 3.36 ± 0.32Ec | 2.447 ± 0.157ABa |
20–30 | 28.46 ± 0.85Aa | 65.99 ± 0.39Cc | 5.56 ± 0.61Cb | 2.548 ± 0.118Aa |
30–40 | 27.27 ± 0.55Aa | 66.07 ± 0.66Dc | 6.65 ± 0.87Bb | 2.321 ± 0.074Ac |
average | 23.37 ± 0.73 | 69.43 ± 0.79 | 7.20 ± 0.61 | 2.417 ± 0.106 |
Note: different capital letters indicate the same soil layer, and there is significant difference between treatments (P < 0.05); Different small letters indicate the same treatment, and there are significant differences among different soil layers (P < 0.05). |
3.2 The Physical and Chemical Characteristics of Soil under Different Profile Configurations
In the 0-10cm soil layer, the content of total nitrogen in plot6 treatment was the highest (Fig. 5), which was 0.54g/kg, and that in plot2 treatment was the lowest, which was 0.33g/kg, and the content of total nitrogen in plot6 treatment was significantly higher than that in plot1 and plot2 (P < 0.05); In 10-20cm soil layer, the content of soil total nitrogen under plot 6 treatment was the highest, which was 0.44g/kg, and the content of soil total nitrogen under plot 1 treatment was the lowest, which was 0.24g/kg, and the content of soil total nitrogen under plot 6 treatment was significantly higher than that of plot 1 (P < 0.05); The content of soil total nitrogen was the highest under plot 6 treatment in 20-30cm soil layer, which was 0.41g/kg, and there was no significant difference among the treatments; In the 30-40cm soil layer, the change of soil total nitrogen content between treatments was consistent with that in the 0-10cm soil layer. The soil total nitrogen content under plot 6 treatment was the highest, which was 0.37g/kg, and the soil total nitrogen content under plot 2 treatment was the lowest, which was 0.13g/kg, and the soil total nitrogen content under plot 6 treatment was significantly higher than that of plot 2 (P < 0.05). In general, with the increase of soil depth, the content of soil total nitrogen decreased under each treatment.
In 0-10cm soil layer, the content of soil organic matter in plot6 treatment was significantly higher than that in other treatments (P < 0.05) (Fig. 5), which was 11.98g/kg, followed by plot2, which was 10.44g/kg; In the 10-20cm soil layer, the content of soil organic matter under plot 3 treatment was the highest, which was 8.45g/kg. There was no significant difference in soil organic matter among the treatments in this soil layer; In 20-30cm soil layer, the content of soil organic matter in plot 1 treatment was significantly higher than that in plot 3, and the corresponding contents were 6.71g/kg and 5.20g/kg respectively.
In 0-10cm soil layer, the content of available potassium in plot1 treatment was the highest, which was significantly higher than that of plot2, plot3 and plot5 (P < 0.05) (Fig. 5), and the corresponding contents were 175.24, 150.34, 151.07 and 155.54mg/kg respectively; In the 10-20cm soil layer, the content of soil available potassium in plot 1 treatment was the highest, 156.49mg/kg, and the content of soil available potassium in plot 3 treatment was the lowest, 145.05mg/kg. There was no significant difference in soil available potassium among treatments in this soil layer; In 20-30cm soil layer, the available potassium in plot 6 treatment was significantly higher than that in plot 1 (P < 0.05), and the corresponding contents were 145.98 and 132.22mg/kg respectively; In 30-40cm soil layer, the content of available potassium in plot 1 treatment was significantly higher than that in plot 2 and plot 5 (P < 0.05), and the corresponding contents were 147.50, 131.62 and 132.92mg/kg respectively.
In 0-10cm soil layer, the available phosphorus of soil treated with plot5 was significantly higher than that of plot2 (P < 0.05) (Fig. 5), and the corresponding contents were 25.94 and 12.85mg/kg respectively; In the 10-20cm soil layer, the content of soil available phosphorus in plot 5 treatment was the highest, which was 18.56mg/kg. There was no significant difference in the content of soil available phosphorus among the treatments in this soil layer; In 20-30cm soil layer, the content of available phosphorus in plot 2 was significantly higher than that in plot 4 (P < 0.05), and the corresponding contents were 14.66 and 10.42mg/kg respectively; In 30-40cm soil layer, the soil available phosphorus of plot 2 treatment was significantly higher than that of other treatments (P < 0.05), and its content was 15.11mg/kg.
In the 0-10cm soil layer, the content of ammonium nitrogen in the soil of plot 4 treatment is the highest (Fig. 5), which is 9.21mg/kg. There is no significant difference in the content of ammonium nitrogen between this soil layer and the treatment; In 10-20cm soil layer, the content of ammonium nitrogen in plot 1 treatment was significantly higher than that in plot 3 and plot 6 (P < 0.05), and the corresponding contents were 8.78, 6.02 and 6.37mg/kg respectively; In 20-30cm and 30-40cm soil layers, the content of ammonium nitrogen in plot 1 was significantly higher than that in plot 6 (P < 0.05).
In 0-10cm soil layer, the content of soil nitrate nitrogen in plot1 treatment was significantly higher than that in plot3 (P < 0.05) (Fig. 5), and the corresponding contents were 7.49 and 4.89mg/kg respectively. In 10-20cm, 20-30cm and 30-40cm soil layers, there was no difference in the content of soil nitrate nitrogen among all treatments.
3.3 Relationship among Soil Texture, Fractal Dimension and the Physical and Chemical Characteristics of Soil
According to the correlation analysis of soil fractal dimension D, soil texture and soil physical and chemical properties (Fig. 6), it can be seen that the fractal dimension D of soil volume in the experimental area has a significant positive correlation with soil organic matter, total nitrogen and silt particle content (P < 0.01), and a significant negative correlation with soil gravel content (P < 0.05). When D increases, soil silt particle content increases and soil gravel particle content decreases. It has no significant correlation with soil available phosphorus, available potassium, clay particles content, nitrate nitrogen or ammonium nitrogen. The fractal dimension D of soil volume can be regarded as a judgment index of the variation of soil quality in the experimental area. Soil clay particle content is positively correlated with soil silt particles content (P < 0.01), and negatively correlated with soil organic matter, total nitrogen and gravel particle content (P < 0.01). There is no significant correlation between particles composition and soil available phosphorus, available potassium, ammonium nitrogen and nitrate nitrogen.