| Land resources, as the principal resource, were the foundation for realizing the sustainable development. Since 1970s, problems, such as the declining of arable lands area and the severity of conflict between human and land, had been becoming more and more obvious, due to the increasing of population, accelerating of urbanization and industrialization, and frequently change of climate. Land consolidation project, harmonized relationship between human and land resources, is one of important measures to realized optimize allocation in land resources. The acreage of arable lands increased by land consolidation project but few studies focus on the impact of that on soil fertility, especially in soil particle distribution and water-holding capacity. So, taking land consolidation project in Xiaomian County, Hechuan District, Chongqing Municipality as object, the changes of soil particle distribution, fractal dimensions, and water-holding capacity before and after land consolidation were studied, and then discussed the impact of land consolidation practices on properties of soil physics, to enriching the researches of land consolidation project effect on soil physics properties in purple soil in hilly areas and providing scientific evidence to carry out land consolidation. The results showed followed as:1. The effect of land consolidation project on the distribution of soil particle and soil aggregatesThe practices of land consolidation had a significant effect on the distribution of soil particle and soil aggregates. Through land consolidation project, the change of gravel content ranged from 72% to 131%. After carrying out land consolidation, the content of gravel in the dry land which was transforming from the paddy field was increased in most area. In traditional dry land after descending grade treatment, the content of gravel was decreasing with the decreasing of slope gradient, with the decline of gradient constantly reduced, and the rock slightly increased at the bottom of slope. There were two causes of the results. Firstly, during the process of land consolidation project, the steep region and the area with thin soil layer should be covered with soil in order to raise the thickness of soil layer and improve the content slit and clay. Secondly, building stone linchs, which effectively reduced the flow speed, played a pivotal role in relieving the water loss and soil erosion, furthermore, the slit and clay in soil would to be preserved.There was an obvious change on the distribution of soil particle after implementing the land consolidation. The change ratio of particle content with the diameter>0.25 mm,0.05-0.25 mm, 0.02-0.05 mm,0.002-0.02 mm, and<0.002 mm was ranged from 0.34 to 3.32,0.58 to 1.71,0.77 to 1.38,0.63 to 1.56, and 0.71 to 1.40, respectively.The practices of land consolidation also had a significant effect on the distribution of soil aggregates. Compared with the distribution of soil aggregates before and after land consolidation, the result suggested that the change ratio of soil aggregates content with the diameter>5 mm,2-5 mm,1-2 mm,0.5-1 mm,0.25-0.5 mm and<0.25mm was ranged from 1.07 to 1.32,0.76 to 1.25, 0.91 to 1.44,0.94 to 1.38,1.08 to 1.16 and 0.80 to 1.00, respectively. The soil aggregates with diameter> 5mm most evidently increased and the effect had a close relationship with the gradient. The more the gradient was, the more evidently it increased.2. The effect of land consolidation project on soil water holding capacityThrough determing the soil moisture feature curve before and after implementing land consolidation, van Genuchten equation was fitted to calculate the specific water capacity, and discussed the relationship between the moisture content and the soil particles. The results from fitting of van Genuchten equation suggested that after land consolidation the change interval at A-zone almost kept the same level and land consolidation had little effect on theθr. The change interval ofθs,α, and n before land consolidation was obviously larger than that after land consolidation. Furthermore,θs and a tend to be more concentrated. It showed that the discrepancy of soil water-holding capacity among the dry lands which was transformed from paddy field after land consolidation significantly reduced. In B-zone, the variations ofθr,θs, a, and n, were nearly unchanged, evidently decreased, markedly enlarged, and reduced, respectively, which showed the difference of hold water characteristics of consolidated steep traditional upland was also narrowing. The change interval at C-zone, there was faintly reduced inθr, enlarged inθs andα, and reduced in n. It showed that the discrepancy of soil water-holding capacity among the steep traditional dry lands significantly increased. The specific water capacity of soil in 0.1-0.33×105Pa was an order of magnitude higher than 1.0-3×105Pa, and the specific water capacity of soil in 1.0-3×105Pa was an order of magnitude higher than 10-15×105Pa. It showed that as the pressure increasing quickly than water capacity decreasing, and the more the pressure built the less obvious reduced trend. The specific water capacity and the water release were big when the soil water potential higher than-0.33x105Pa, while the specific water capacity of soil was obviously small in-10×105Pa--15x105Pa. The correlation between soil water-holding capacity and soil physical properties showed that when pressure was 0.33x105 Pa, content of soil water had negative correlation with 0.05～0.02 mm and 0.002 mm size fraction, had positive correlation with 0.02～0.002 mm size fraction and soil bulk density, but had no significant correlation with the size fraction of>0.25 mm and 0.25～0.05 mm. which indicated that soil water-holding capacity was mainly affected by soil bulk density. When pressure was 15×105P, content of soil water had positive correlation with soil bulk density (P<0.05) and 0.02～0.002 mm size fraction, had positive correlation with the size fraction of 0.05～0.02 mm and<0.002 mm, but also had no significant correlation with the size fraction of>0.25 mm and 0.25～0.05 mm. With the increasing of pressure, the positive correlation between content of soil water and the size fraction of 0.02～0.002 mm was increased. And the negative correlation between content of soil water and the size fraction of 0.05～0.02 mm was increased. But there was no significant change among other size fractions. In addition, the positive correlation between content of soil water and soil bulk density was decreased. In conclusion, the soil water-holding capacity was significantly changed by land consolidation, and the degree of influence was closely related to the specific measures of consolidation.Therefore, the engineering measures of land consolidation seriously disturbed the matured soil layer and obviously changed the soil gravel distribution, particle distribution, structure, and water holding characteristic. The change degree was closely related to the gradient of consolidation area. In the future, the land consolidation should be observed constantly from the aspects such as soil biology, soil chemistry and soil physics, in order to analyze the evolution of soil physical fertility at the consolidation region and discuss the mechanism. Moreover, it should to ascertain the evolution discipline of soil physical fertility after implementing the engineering measures of land consolidation, and impulse the research on the improve of soil fertility and sustainable agro-ecosystems development.
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