Ningxia is high in the south and low in the north. Mountains and plateaus account for about 3/4 of the whole region, and the rest are plain areas, of which desert accounts for 8% of Ningxia. From the perspective of topographic distribution, from north to south are Helan Mountain, Ningxia Plain, Ordos Grassland, Loess Plateau and Liupanshan Mountain. , the average altitude 1000 meters above. Helan Mountain in the north stretches for 250 kilometers, becoming a natural barrier of Ningxia Plain, while Liupanshan Mountain in the south is lush. The ancient Yellow River flows northward through the north-central part of Ningxia, with a total length of 397 kilometers in Ningxia and flows through 12 counties and cities. The Ningxia section of the Yellow River has a wide water surface and is irrigated and cultivated. Their hard work has made Ningxia a "plug in the south of the Yangtze River" with criss-crossing ditches, fragrant rice and fish, fragrant melons and fruits and beautiful scenery. This can be confirmed by the poem of the Tang Dynasty poet, "Orchard under Helan Mountain, Old Famous in the South of the Saibei River".
● Climate overview
The topography of high in the south and low in the north determines the climate of Ningxia, with cold in the south and warm in the north. In addition, Ningxia is located at a high latitude, with a large temperature difference between day and night. During the day, the direct sunlight temperature is high, and the temperature of the residual heat of blast at night is obviously reduced. In summer, the temperature difference between day and night is about 15 degrees. The rainy season is concentrated in summer, but the precipitation is not great. The sky in Ningxia is clear. "Blue sky and white clouds floating, white clouds dismounting and running" is a true portrayal of the weather and customs in Ningxia.
● Related introduction
Ningxia is located in the middle of the upper reaches of the Yellow River, which is narrow from east to west and long from north to south. The terrain is low in the north and high in the south, with an altitude of 1000 meters or more. On the west side of the plain is the magnificent and beautiful Helan Mountain, which was called "the protector of the north and the throat of the desert" by the ancients. It has prevented Tengger Desert from moving eastward and weakened the invasion of northwest cold current, which is a natural barrier of Ningxia Plain. Here is rich in rice, wheat, square meters, beets and fruits, especially rice with high quality and high yield, which has a long reputation and is known as "Jiangnan".
Qin Qu was first carved in Qin Dynasty, hence its name. The mouth of the canal is in the north of Qingtongxia, and the Yellow River flows northeast through Wuzhong to Lingwu County. Han Qu was named after the legend that it was carved in the Han Dynasty. The mouth of the canal is also in the north of Qingtongxia, leading the Yellow River to flow northeast to Balang Lake. Tang Laiqu, also known as Tang Qu, is said to have been carved in the Han Dynasty and cultivated in the Tang Dynasty. The mouth of the canal is near Qingtongxia, and the Yellow River flows northward through Yongning County, Yinchuan City, Helan County and Pingluo County. After the establishment of New China, Qingtongxia Water Control Project was completed, drainage and irrigation channels were arranged, saline-alkali land was improved, irrigation area was expanded, and "Jiangnan" became more abundant.
Songnen Plain is located in the southwest of Heilongjiang Province, bounded by Songliao Basin in the south, Xiaoxing 'anling in the north, and the eastern mountainous area and Daxinganling in the east and west respectively. The whole plain is slightly rhombic. The land area of Heilongjiang Province is 103200 square kilometers, accounting for 2 1.6 1% of the total area of the province. Songnen plain is a geological structural depression area, which belongs to a part of Songliao fault depression zone. The southwest of the depression is still sinking and the northeast is rising. The tertiary and quaternary sediments rose to a platform, which was locally called a ridge. Songnen plain is also called undulating plain because of its undulating surface. Plain surface elevation120-300m. There are many wetland lakes in the middle, and the terrain is relatively flat. Nenjiang River and Songhua River flow through the west and south, and the floodplain is wide. The southwest of the plain is a closed flow area with a tailless river. On the east bank of Nenjiang River, sand dunes are distributed from Fuyu to Dorbod Mongolian Autonomous County.
Songnen Plain is mainly formed by alluvial of Songhua River and Nenjiang River. Nenjiang, Nehe, Yi 'an, Keshan, Dedu, Wudalianchi, Bei 'an, Kedong, Baiquan, Helen, Suiling, Qing 'an, Suihua, Wangkui, Cyclobalanopsis glauca, Mingshui, Fuyu, Lin Dian, Qiqihar, Gannan, Longjiang, Tailai, Dulbert, Daqing and Zhaoyuan. The Songnen Plain has 5.59 million hectares of arable land and fertile soil, with black soil and chernozem accounting for more than 60%, and is rich in soybeans, wheat, corn, beets, flax and potatoes, making it an important commodity grain base. In addition, grasslands are concentrated, animal husbandry is developed, and underground oil resources are abundant.
The south-central part of Songnen Plain is a relatively flat area, and chernozem is widely developed on the surface, with an organic matter content of 4-8%, humus is mainly humic acid, and exchangeable base ions are mainly calcium and magnesium, which belongs to salt-based saturated soil. Except humus layer, other layers are slightly alkaline, with PH value of 8-8.5, moderate texture and good structure, second only to black soil, which is suitable for agriculture.
There are alluvial and diluvial platforms in the piedmont and eastern mountainous areas of Xiaoxing 'anling, such as the wave platforms in Keshan, Baiquan and Bei 'an, the ridge platform between Keluo River and Namur River, the flat and oblique platforms in Hailun and Suihua, and the hilly platform east of Ashe River. The altitude is about 200-300m, and the relative altitude is 30- 100m. The surface erosion is serious, and many places are criss-crossed by running water. In this area of Songnen Plain, the upper part of the composition material is loess loam and the lower part is gravel layer, and black soil is widely developed on the surface. It is formed by the process of black soil, a special meadow, under the conditions of vegetation and loess-like parent material in temperate humid shrub meadow or middle grass meadow. Before reclamation, the organic matter content was as high as 10%. Humic acid is the main component of humus, and the ratio of surface humic acid to fulvic acid is 1.38- 1.6, with a maximum of 2. Soil is rich in nutrients, has strong ability of water and fertilizer conservation, and is suitable for the growth of many crops. It is the main agricultural soil resource in Heilongjiang Province.
In front of the Daxinganling Mountains, the undulating erosion platform is about 200-250 meters above sea level. The relative height is 10-30m. There are many weathered clastic materials and clay in the platform, which belong to Baitushan Formation formed from the end of Tertiary to the beginning of Quaternary. The soil belongs to erosion and leaching type, with thin soil layer, rough texture and acidic reaction.
The middle and lower reaches of Nenjiang River are alluvial plains covered with sand dunes, which cover the floodplain and the first and second terraces on both sides. The terrain is low and the slope is very small. Width of floodplain10km. Tens of centimeters to three or five meters above the river bed. The upper part of the composition material is clayey silt and the lower part is gravel. The first terrace is about10m higher than the riverbed, and the surface is covered with loess loam and clayey silt. The second terrace is 30-50 meters higher than the river bed, and the composition is loess loam or gravel layer. There are aeolian sand dunes, sand dunes, sand ridges and wavy sand fields on the surface of this area. Although these soils can be cultivated, they leak water and fertilizer, and it is easy to bury fertile fields when wind erosion is serious. Therefore, it is advisable to plant trees and grass and apply organic fertilizer as land for forestry and animal husbandry, but not for reclamation.