Soil Classification and Area in Neijiang City

Terrain: Neijiang City is dominated by hills, surrounded by low mountains in the southeast and southwest. Hills with an altitude of 350~450 meters account for about 90%. The geological structure belongs to a part of the Neocathaysian subsidence zone, and the fold scale is small. The surface is composed of gentle purple sandstone and mudstone, which are mostly round and ridged shallow hills after long-term running water erosion and cutting. The valleys between hills are long, narrow and straight, mostly trapezoidal gentle slopes from the top of the mountain to the valley, forming a grain field with layers of steps. Mud is mainly composed of soil, coarse sand, red sand, soybean powder soil and yellow sand. These soils have good water retention and strong drought resistance, which is beneficial to crop growth. Land use has a long history, mainly cultivated land. Other land uses are garden, woodland, grassland, urban-rural fringe, residential land, industrial and mining land, traffic land, water area, special land and some land that is difficult to use.

Climatic hydrology

Climate Neijiang City is influenced by the basin and local natural environment, and has the characteristics of mild climate, abundant rainfall, sufficient light and heat and long frost-free period. It is warm in winter and hot in summer, with moderate rainfall. The average temperature is 15℃-28℃, the monthly average temperature is 6℃-8℃, the July average temperature is 26℃-28℃, the highest temperature is 4 1℃, the lowest temperature is -5.4℃, and the active accumulated temperature is about 598℃. China is rich in heat resources, with an average annual total solar radiation of 89.6 kcal/cm2, annual total sunshine hours 1 100- 1300 hours and a frost-free period of 330 days. The number of frost days in the whole year is generally about 4-8 days, and the disastrous weather is mainly drought, alternating with drought and flood; Spring, summer, autumn and winter, low temperature, strong wind and heavy rain occur from time to time, and the rain is remarkable. The annual temperature is obviously dry in winter and dry in spring, while summer drought and summer drought also occur from time to time. The annual rainfall is below 1000 mm, mostly distributed in summer, accounting for about 60% of the annual rainfall. The high temperature period is basically the same as the rainy season, accounting for about 17% in spring and only 4% in winter. Hydrological Tuojiang River is the main river in the urban area, which flows through Zizhong, Dongxing and Shizhong, and is the main waterway transportation route in the urban area. Since ancient times, there has been a description of the busy scene of "a ship with thousands of hooves". The Tuojiang River flows alternately in a rapid and slow order, alternating between the beach and the Tuotuo River, with an average annual flow of 375 cubic meters per second, a natural drop of 135.5 meters and an average gradient of 4.5 ‰. The hydropower reserves available for development are145,000 kilowatts. Larger tributaries include Qiuxi River of Hippo Chef and Daqingliu River of Neijiang. These rivers are conducive to irrigation, shipping and power generation, and the water reserves are about 35 thousand kilowatts for development. Coupled with the hydropower resources of Tuojiang River, the annual power generation can reach 920 million kWh, and the developed hydropower resources only account for 2 1.7% of the exploitable amount. At the same time, because the Tuojiang River runs through the north and south, with a long basin, many tributaries and a large area of accumulated water, it is easy to cause floods in the rainy season. Hydrology Neijiang City belongs to the Tuojiang River system in the Yangtze River basin. Tuojiang River is a first-class tributary of the Yangtze River, Liu Qing and Xiaoqinglong are second-class tributaries of the Yangtze River, and Wulong River enters Fuxi and still enters Tuojiang River.

Vegetation tree species

Neijiang is a subtropical evergreen broad-leaved forest belt with mild climate and abundant rainfall, which is suitable for the growth of all kinds of trees. There are more than 60 families, 1 10 genera and 190 tree species. Because of the low altitude difference, Neijiang terrain is mostly hilly and low mountains. The species, community composition and community dynamic characteristics of forest vegetation change obviously with the different physical and chemical properties of soil, and are relatively stable in the corresponding range. Its forest vegetation mainly includes coniferous forest, broad-leaved forest, bamboo forest and shrub forest. From the use point of view, the forest vegetation in Neijiang is mainly timber forest, of which Weiyuan County is the largest and downtown area is the smallest. Economic forests are rich in tree species, mainly including tung tree forest, camellia oleifera forest and citrus forest, as well as other deciduous fruit trees, such as pear, apple, peach, plum, apricot, cherry, grape, mulberry forest, tea forest, olive, palm, walnut and Fraxinus mandshurica. Fuelwood forest is an important means of subsistence in rural areas of Neijiang City, which is widely distributed and has high yield, and most of it is renewable. The main tree species are Alnus cremastogyne, Sophora japonica, Coriaria sinica and Vitex negundo. There are other special-purpose environmental protection forests, experimental forests, parent forests, scenic forests, historical sites, revolutionary holy land forests, nature reserves and so on. Dominant tree species are Pinus massoniana, Cinnamomum camphora, Phoebe bournei, Pistacia chinensis and Cypress, which are mainly distributed in urban areas and scenic spots in Zizhong.