(1) Soil formation conditions
According to the second soil census classification system of Guangdong Province from 1979 to 1985, soil types are divided into 16 soil types and 36 sub-soil types. Category, 131 soil genera, 522 soil species, the total soil area of ??the province is 178,000 square kilometers (267 million acres). The distribution of soil types is shown in Figure 1-1.
Most of Guangdong Province has a subtropical monsoon climate. The Tropic of Cancer crosses the central part of the province. Because it is located in the low latitude zone, the southeast monsoon is obvious, with abundant heat, abundant precipitation, and a wide variety of plant species. They grow lushly and are zonally friendly. There are obvious regional differences. In addition, the geological types and soil-forming parent materials are diverse, and the soil formation conditions are relatively complex. In addition to being affected by the above topography, climate, hydrology and vegetation conditions, it is also affected by the conditions of parent rock and human factors.
Figure 1-1 Map of soil types in Eastern Province
1. Conditions of parent rock and parent material
Soil-forming parent material is an important factor in determining soil development and soil fertility characteristics Base. Guangdong Province has diverse soil-forming rocks and parent materials. Mountains and hills are mainly composed of granite, sand shale, and some schist, gneiss, limestone, etc.; valleys, plains, and terraces are mainly composed of modern river alluvial deposits, while mountains, hills, valleys, and small basins are composed of alluvial deposits. The platform is dominated by shallow marine sediments and basalt weathering. The pedogenic rock parent material in Guangdong Province can be summarized into four major categories: magmatic rocks, sedimentary rocks, metamorphic rocks and modern sediments.
Granite, the intrusive rock type, is the most widely distributed igneous rock type in Guangdong Province, forming the main framework of the mountains in Guangdong Province. There are roughly two invasion periods of granite, one is the Paleozoic Era, and the other is the Mesozoic Era. Mesozoic granites had the greatest impact on Guangdong Province, mostly intruding along major faults and folds. For example, the three-arc mountains in northern Guangdong were formed by granite intrusions. Extrusive rocks include rhyolite, andesite, quartz porphyry, tuff, etc., some of which were formed in the Paleozoic Era, but most are in the Mesozoic Era. The eruption area is mainly in eastern Guangdong, forming a strong eruption zone, such as Lianhua Mountain and Yinna Mountain.
Sedimentary rocks are also widely distributed in Guangdong Province, mainly including sandy shale, red sandstone, shale, conglomerate, purple calcareous sandstone, shale, conglomerate, limestone and fourth Ji red clay. Among them, sand shale (mostly Devonian sediments) is the most widely distributed, usually forming folded hills and mountains. Red sand shale is mainly distributed in low hills and basins and was formed from the Cretaceous to the Tertiary period. Limestone types were formed in both the Paleozoic and Mesozoic eras, and are mainly distributed in northern and western Guangdong. Quaternary red clay is Quaternary alluvial, diluvial, slope and residual material. It is a soil-forming parent material formed under warm and humid environmental conditions. It has a high degree of weathering and is mainly distributed on terraces and hills on both sides of the river. On the platform in the basin, a few are distributed on low hills or platform in the piedmont, with a smaller area.
Metamorphic rocks are scattered in Guangdong Province, with a small area. They mainly include gneiss and schist, followed by slate, phyllite, quartzite and marble. They are scattered in western Guangdong, Mountainous and hilly areas such as northern Guangdong and eastern Guangdong.
The modern sediments in Guangdong Province mainly include river alluvial sediments, delta sediments, coastal sediments, ancient shallow sea sediments, alluvial sediments, alluvial sediments and slope sediments. River alluvial deposits are distributed on both sides of the river, forming alluvial plains on both sides of the river; delta sediments are mainly distributed in the downstream areas of major rivers, especially the junction areas of the Haihe River, forming delta plains; coastal sediments are mainly distributed in the coastal areas of Guangdong Province, starting with Leizhou The northern part of the peninsula is the most widely distributed; alluvial deposits are distributed in hills, valleys and piedmont areas, forming hill pits, fields and piedmont alluvial fans. Alluvial and alluvial deposits are distributed in the basins; the foothills are formed by slope deposits. composition of matter.
2. Human factors
Soil is a historical natural body. In the process of interaction with natural environmental factors, it gradually develops from instability to stability, and finally forms a relatively stable and balanced soil. Various soils. In the process of agricultural production and utilization of soil, people use a series of agricultural technical measures to improve and cultivate the soil in a targeted manner, turning raw soil into mature soil, and turning mature soil into fertile soil, thus promoting soil maturation and improving soil fertility.
But on the other hand, due to long-term unreasonable reclamation and utilization of soil, especially severe deforestation, the ecological environment has been destroyed, the natural fertility and artificial fertility of the soil have been destroyed, and the trend is opposite to improvement and cultivation. Evolution in the direction of poverty and fertility degradation. This fully demonstrates that human activities are one of the important factors in soil formation. In the process of transforming nature, humans have changed certain natural conditions, thus causing soil changes. Human activities can make the soil evolve in the direction of developing soil fertility and continuously building and improving soil fertility. For example, the unique stacked soil (basic water land) in Guangdong Province is created by continuous accumulation of fertilizers on low-lying waterlogged land through human activities. Human beings are soil. However, human activities can also lead to deterioration of soil properties, soil erosion, and reduction of soil fertility.
(2) Soil distribution patterns in Guangdong Province
Guangdong Province is located in the southeast of my country, spanning the central subtropical zone, the southern subtropical zone and the northern tropical zone. The bioclimatic conditions are affected by the southeast monsoon. Mainly low mountains and hills, the terrain is undulating, and the bioclimatic conditions change significantly in the horizontal and vertical directions. Differences in soil formation conditions lead to obvious horizontal zonation, vertical zonation and composite regionality in soil distribution.
1. Horizontal distribution pattern of soil
Guangdong Province is located at low latitudes, with a terrain high in the north and low in the south. It faces the South China Sea and spans the central subtropical zone, the southern subtropical zone and the northern tropical zone. It is rich in heat and abundant rainfall. In a high temperature and rainy environment, soil formation is mainly based on desilicification and aluminum enrichment. From north to south, a series of ferro-bauxite soils are formed in horizontal zones of red soil, red red soil and brick red soil. The distribution boundaries of these three types of zonal soils are roughly as follows:
Red soil is a typical zonal soil in the mid-subtropics. It is distributed in the area north of 24° to 24°50′ north latitude in Guangdong Province, and its southern boundary Roughly from Shuangji Mountain in Jiaozhong District of Huaiji County to Tailai, Zhongzhou and Fenggang, Chikeng and Beishi in Guangning County, Hengshishui, Dazhen, Shakou, Babaoshan, Dawan, Yanbei and Wengzhou in Yingde City. Nanfu, Jiangwei, Liuli, Sanhua, Wengcheng, and Xinjiang in Yuan County; Xintian, Chiyan, and Chetian in Longchuan County; Beidun, Yousheng, and Heshui in Heping County; Gaoguan, Youxi, Banjiang in Heyuan City, Luogang in Xingning City, Shizheng in Pingyuan County, Xinbu and Jiaocheng in Jiaoling County, Songkou in Meizhou City, and the north of Sanhe and Dadong in Dabu County . The average annual temperature in this zone ranges from 17°C to 21°C, the average temperature in the coldest month is 7°C to 12°C, and the extreme minimum temperature is -3.6°C to 6.9°C. Low-temperature frosts often occur at this time in winter. The summer is sultry, with the average temperature in the hottest month ranging from 26°C to 29°C, and the extreme highest temperature reaching over 40°C. Sweet potatoes cannot survive the winter in this zone, and tropical fruits such as lychees, longans, papayas, and bananas cannot grow normally and survive the winter.
The red soil belt is located in the central part of Guangdong Province, and the Tropic of Cancer runs through the middle of this belt. Red soil is a typical zonal soil county in the south subtropics. The northern part of this zone is connected to the southern boundary of the red soil belt, and the south is adjacent to the brick red soil. Its boundary is located near 21°30′-22° north latitude. Roughly starting from Anpu, Puling, Pingpo, Kuang, Jishui, and Baiteng in Lianjiang County in the west, Xin'an, Guanqiao, and Zhen'an in Huazhou City, Shigu in Gaozhou City, the southern end of Gaozhou County, Yangjiao, and Dianbai County Xiadong, Guanzhu, Daya, Diancheng, Magang, Lingmen, and the north of the Rudong connection in Yangjiang City. This zone is located to the north and south of the Tropic of Cancer, and is the transition zone between the tropics and subtropics. It has richer heat than the mid-subtropics, with an average annual temperature of 20°C to 23°C, an average temperature of 10°C to 15°C in the coldest month, and an extreme minimum temperature of 0°C. The average temperature in the hottest month is 28℃～29℃. Sweet potatoes in this zone can survive the winter.
Brick red soil is a typical zonal soil in the tropics. It is distributed on the low hilly platform of Leizhou Peninsula and some coastal islands south of the southern boundary of red soil. It is located in the northern part of the tropics. The annual average temperature is 23°C ~ 24°C, the average temperature in the coldest month is 15°C ~ 18°C, the extreme low temperature averages around 5°C for many years, and the average temperature in the hottest month is 28°C ~ 29°C. In this zone, perennial tropical crops grow normally throughout the year.
2. Vertical distribution of soil
High mountains and cold water are the climate characteristics of mountainous areas. As the terrain rises, the temperature drops and the rainfall increases, so does the bioclimate and soil development. Corresponding changes occur, forming different series of soil vertical band spectra.
Since the mountainous areas of Guangdong Province are mainly concentrated in two climate zones, the southern subtropical zone and the central subtropical zone, two corresponding vertical soil spectrums are formed.
In the mid-subtropical zone, the base soil is red soil, and the vertical band structure of mountain soil from low to high is red soil - yellow red soil - yellow soil - southern mountain shrub meadow soil. The altitude of distribution of various types of soil is roughly as follows: the upper limit of red soil is 350 to 400 meters, the yellow and red soil is distributed between 350 and 700 meters or 400 and 800 meters, the yellow soil is distributed above 750 meters, and the southern mountain shrub meadow soil appears sporadically. On ridges and peaks above 1100 meters above sea level.
In the southern subtropics, the base soil is red soil, and its soil vertical band structure from low to high is red soil - red soil - yellow soil - southern mountain shrub meadow soil. The altitude of distribution of various types of soil is generally: the upper limit of red soil is 350-400 meters, red soil is distributed between 350-750 meters or 400-800 meters, yellow soil is distributed above 750 meters, and mountain shrub meadow soil is scattered in Ridges and peaks above 1000 meters.
Due to the influence of habitat factors such as aspect and slope, the soil type and distribution height of the vertical soil spectrum also change to a certain extent. For example, on the north slope, due to relatively less sunlight and being affected by the north wind, the climate is cold and rainfall is less, while the south slope is windward and sunny, warmer and wetter than the north slope, and the height of the same type of soil is 100 meters lower than in the south slope mountains. about.
3. Regional distribution rules of soil
In addition to the characteristics of horizontal distribution affected by bioclimatic zones, soil distribution rules are also affected by landform types, soil-forming parent material and complex hydrology. Affected by geological conditions and human activities, soil distribution also has various types of regional distribution patterns. According to the characteristics of different soil combinations, it can be divided into two types of soil combinations: medium domain and micro domain.
The distribution of soil mesodomains is based on the zonal distribution of soil and is affected by topography, parent rock, parent material, hydrological conditions and human activities. Guangdong Province mainly has three types of soil combinations: plain area soil combination, red rock basin soil combination and limestone mountain soil combination.
The plain area has flat and open terrain, sufficient light, heat and water, and frequent human activities. Rice cultivation is the main area. According to its different landform types and composition materials, it can be roughly divided into valley and plain soil combinations, Delta soil combination and coastal sandy plain soil combination. The soil combination of river valleys and plains extends from the river to the gentle slopes of hills on the edge of the plain. Its composition is river alluvial sediment and diluvial sediment. Affected by the gravity of river flow and sedimentary sorting, its soil distribution pattern is fluvoid-tidal sand mud. Land - river sand mud field - mud field - sand mud field - red land. The delta soil combination refers to the estuary alluvium and sea plains from the estuary bifurcation to the coast. The composition is river alluvium and delta sediment. It is formed by the river carrying a large amount of sediment and being continuously deposited in the estuary area. Its soil distribution pattern It is coastal saline soil and acidic sulfate soil, coastal intertidal marsh soil - saline type rice soil, saline acid type rice soil, latent type rice soil - retention type rice soil. The coastal sandy plain soil combination is a coastal sandy soil formed by the sand deposited on the coast and accumulated inland from the coast under the action of ocean currents, waves and wind. The composition material is coastal sediments, and its soil distribution pattern is from the coast to the inland. It is mobile sand - fixed sand - coastal sand - coastal sand and mud fields.
The soil combination of the Hongyan Basin is composed of purple sand shale, such as Nanxiong, Dengtaeng, Luoding, etc., and the soil parent material is purple sand shale and its alluvial alluvial deposits. Because the soil is purple in color, it is called purple soil; and due to the differences in the composition of the parent rock, alkaline, neutral, and acidic purple soil are formed respectively. Through artificial reclamation and planting, alkaline, neutral and acidic beef liver fields have been formed in water-scarce and arid areas. After artificial planting of rice in the middle part of the basin and in places with water sources, alkaline and acidic beef liver soil fields often develop.
The limestone mountain soil combination is mainly distributed in Yangshan, Lianshan, Liannan, Lianzhou in Qingyuan City and Lechang in Shaoguan City.
The soil-forming parent material is mainly limestone. The rock mass in this type of area is exposed, with dense clusters of peaks. Various landform types such as isolated peaks, clear land, funnels, and shafts coexist. There is very little contiguous soil, and the soil is mostly alternated with rock outcrops, forming red lime. Soil and black lime soil. Due to the lack of water sources, drought is the main problem. After artificial reclamation and dry farming, it often develops into red stone cave land, red fire mud land, black mud land, etc. It is distributed in areas with eroded valley troughs and seasonal rivers passing through it. It is mostly cultivated for rice cultivation, forming limestone parent material flooded rice soil.
(3) Distribution rules of agricultural soil in Guangdong Province
Based on the characteristics of agricultural soil origin, soil properties, fertility and agricultural production traits, agricultural soil in Guangdong Province can be divided into seaside fields, sandy soil and other agricultural soils. There are 12 soil areas including encircled fields, foreign fields, dong fields, pit fields, terraced fields, hillside fields, terraces, tunnel fields, dam fields, basic water fields, and beach salty gardens. The distribution rules of soil in each soil zone are described below.
1. Seaside farmland
Distributed along the coast of Guangdong Province. Since it is close to the sea, the soil parent material is mostly coastal alluvial deposits and is easily affected by salt tides, so it is cultivated and planted with rice. Most of the paddy fields are salty fields and salty-sour fields, accounting for about 5% of the province's paddy field area. The soil fertility in this soil area is not high. Fresh water must be used to wash away salt water, desalinize and deswamp, in order to improve soil fertility.
2. Shaweitian District
Shaweitian is a paddy field formed by farmers in the delta alluvial plain who built embankments and fenced it to prevent salt water. It accounts for about 10% of the paddy field area and is mainly distributed in The major rivers along the coast of Guangdong Province are located in alluvial plains, among which the Pearl River Delta has the largest area, followed by the Hanjiang Delta, in addition to the Jianjiang Delta and the Xiantian area in the coastal plain. The Shawei field area has low and flat terrain, sufficient sunlight and heat, fertile soil, intertwined river networks, and convenient irrigation. It can make full use of tidal gravity drainage and irrigation, which is extremely beneficial to growing rice. However, crop growth in the Shawei field area is greatly affected by unfavorable factors such as wind, salty water, drought, and waterlogging.
The development of soil and fertility in the Shawei field area is closely related to the farming history and terrain changes during the formation of the beach. It can be divided into low field area, middle field area and high field area. In the low-enclosed fields, there are salty fields, salty-sour fields, Youni fields, and Jisui fields; in the middle-enclosed fields, Youge fields are the main ones, and Youni fields also occupy a certain area; in the high-enclosed fields, there are Nirou fields. Field, Nigu field, Ni nail field, Iron nail field, etc.
3. Yangtian District
Yangtian, also known as riverside field, accounts for about 16% of the paddy field area and is distributed in the alluvial plains on both sides of major rivers in the province. The terrain of Yangtian District is open and flat, with sufficient sunlight and heat. The groundwater level near the river bed is high and irrigation is convenient. However, far away from the river, the groundwater level is low, lacking water sources for irrigation, and is prone to drought. Yields are low, the population is densely populated, and the soil is frequently cultivated.
The soil distribution pattern in the Yangtian area is closely related to the material precipitation in the river alluvial plain. In the cross section of Yangtian District, from the river bank to the mountainside, soil types such as sandy fields, sandy mud fields, mud fields, and clay fields are distributed in sequence; in the longitudinal section of Yangtian District, from upstream to downstream, sandy fields are distributed in sequence. Field, sandy mud field, mud field, clay field and other soil types.
4. Dongtian District
Dongtian is a wide and flat paddy field surrounded by hills on three sides and with a gap on one side, accounting for about 45% of the province's paddy field area. Dongtian District is located on hilly terraces or lowlands with wide valleys between mountains. The terrain is slightly open and flat. There are small streams flowing through the fields. The agricultural production environment is superior, with sufficient sunshine and convenient irrigation. The terrain is not undulating. There are natural barriers around it, and natural disasters are relatively low. With a small population, dense farming, and relatively stable output, it is an important base for grain production in Guangdong Province.
Due to different locations in Dongtian District, the texture of various fields is also different. Generally, the riverside in Dongzhong is mostly river alluvial deposits, while the mountain sides are mostly slope deposits. The paddy fields on the hillside are yellow mud fields; rust paddy fields are formed at the foot of the slope due to the influence of rust springs; low-lying areas in the fields are soaked in water for a long time due to poor drainage, forming stagnant paddy fields or rotten fields; those near villages and towns, After artificial improvement, most of them have been turned into meat fields. Therefore, the soil distribution pattern in the field area from the river to the foot of the mountain is dam land - sandy soil - sandy field - sandy mud field - clay field - cold bottom field - yellow mud field.
5. Kengtian District
Kengtian is distributed in mountains, hills, valleys and lowlands, accounting for about 22% of the paddy field area.
Because it is sandwiched between two mountains, the mountains are high and the valleys are deep, and the sunlight is insufficient and the light time is short. Therefore, the air temperature, soil temperature, and water temperature in the pit field area are all low, forming the unique mountain pit cold bottom field. Generally, mountainous pit farm areas are sparsely populated, with inconvenient transportation, extensive farming, shallow, thin, cold field bottoms, and low crop yields.
The soil-forming parent material of Kengtian is valley bottom alluvial deposits. The soil distribution pattern is generally that the mouth of the pit is mud and clay fields, the middle of the pit is mostly sand and mud fields, and the tail of the pit is mostly sandy fields. The edge of the pit is often affected by the seepage of spring water, forming rotten paddy fields, rusty paddy fields and cold bottom fields.
6. Terraced fields
Terraces are artificial terraced fields built step by step along the hillside, accounting for about 3% of the paddy field area. The terraces are distributed on slopes and have sufficient light and heat. Generally, mountain terraces have sufficient water resources, while terraces on hilly slopes lack water resources, most of which are Wangtian fields. Terraced fields far away from villages require difficult farming and fertilization management, resulting in low soil fertility. Terraced fields near villages and towns require intensive cultivation and higher soil fertility.
Terraces are vertically distributed in mountains with an altitude of tens to thousands of meters. Generally, the red soil developed on the weathered parent material of granite is turned into terraces, often forming sandy mud fields, sandy fields, yellow mud fields, etc. The terraces formed by the red soil developed on the shale form shallow yellow mud fields and yellow mud fields. For slope terraces with the same soil parent material, the distribution sequence from the foot to the top of the slope is sand mud field - yellow mud bottom field - shallow foot yellow mud field, etc.
7. Hillside area
Slope area refers to the dry land soil distributed on the slopes of mountains, hills and terraces. The slope is mostly between 5° and 15°, accounting for the area of ??dry land soil in Guangdong Province. of around 61.
The dry farming soils on slopes include yellow soil, yellow-red soil, red soil, terracotta, yellow terracotta, red-brown sandy soil and beef liver soil. Generally, the slopes in mountainous areas are composed of yellow Ni soil and yellow-red Ni soil, while hilly lands are mostly red Ni soil. In some areas, beef liver soil, red brown sandy soil, etc. are also distributed.
8. Taiwan area
The dry farming soils in Taiwan area include terracotta, yellow terracotta, red brown sandy soil and carbonaceous black soil, etc., which are distributed in the platform hills of Leizhou Peninsula. The slope is relatively gentle, but the area is often hit by droughts and typhoons, which affects agricultural production.
9. Hole area
Mainly distributed in the limestone areas of northern Guangdong. The soil in the area includes black stone hole soil and red fire soil. Its distribution pattern is that the black stone hole soil is between the stone gaps on the saucer-shaped ground, and the red fire soil is on the gentle slope. The organic matter and plant nutrient content were high when first cultivated, but in areas far away from the village and with little fertilization, the organic matter and plant nutrient content decreased, and the fertility declined.
10. Dam areas
Ba areas are mainly distributed in alluvial plains and sand bar areas in river valleys. Dry farming soils in dam areas include sandy soil, tidal sand soil, tidal sand soil, etc. Generally, there is more sand and less mud, with loose structure and low water and fertilizer retention capacity.
11. Jishui area
Jishui area is an artificial landform formed by the working people in the Pearl River Delta region who transformed the soil according to local conditions. It is mainly distributed in Shunde, Nanhai, Panyu, Zhongshan and other Pearl River areas. delta region.
The soil in the base water field is essentially stacked soil. Its soil was formerly depression swamp soil or meadow swamp soil. Therefore, its soil evolution is formed by artificial excavation and accumulation of swamp soil or meadow swamp soil. It is divided into sandy base, sandy base, Nie bone base and Nie base. Rouji et al. Nirouji is distributed near villages and towns and is made from intensive cultivation of Shaniji and others; Niguji is far away from the villages and is the product of extensive farming.
12. Beach salty gardens
Beach salty gardens are mainly distributed in coastal areas, with a small area, accounting for less than 1% of the province's dry land area.
The salty beach area has been separated from the influence of the tide, but the subsoil still contains a lot of salt. Representative soils are salty bottom sand and salty bottom clay.