(1) Topographic slope
1. Acquisition of terrain slope
The terrain elevation data is extracted from the county (district) topographic map, DTM is established through GIS system, and the slope attribute of each classification unit is extracted by superimposing it with the agricultural land classification unit map. According to the grading standards of grading factors in the Regulations on Agricultural Land Grading, Guangdong Province divides the terrain slope into six grades: Grade I, terrain slope.
2. General situation of terrain slope distribution
Cultivated land in Guangdong Province is mainly distributed in flat and relatively flat areas, among which agricultural land with topographic grade I is the most, accounting for about 47.0% of the total area. More than 70% of cultivated land in the Pearl River Delta Plain and Chaoshan Plain has topographic slopes.
Figure 3- 14 Scale Map of Cultivated Land Grading Area in Guangdong Province
Table 3-7 Distribution Table of Topographic Slope Grade and Area of Cultivated Land in Guangdong Province
(2) Slope of field surface
1. Acquisition of field slope
According to the supplementary field investigation data of counties (districts), the present situation of agricultural land utilization and soil characteristics, the slope of grading unit field is comprehensively interpreted. Paddy field, irrigated land, Wang Tiantian land and vegetable land are all treated as flat land, and only the slope of dry land is graded. The slope of cultivated land in Guangdong Province is divided into five grades: Grade I, slope of cultivated land.
2. General situation of site slope distribution
85.0% of agricultural land in Guangdong Province has a grade I slope; The second level accounts for 9.9%; Grade III accounts for 4.9%, mainly distributed in Xinyi, Leizhou, Xuwen, Lechang and Nanxiong, accounting for about 20% of the local cultivated land area; The gradient of the site is less than 0.2%, which is Grade IV, scattered in mountainous areas such as Xinyi, Gaoyao, Yangxi, Xinxing, Lechang, Wuhua, Plain, Guangning, Huaiji and Fengkai (Figure 3- 15). See Table 3-8 for the area distribution of cultivated land gradient grades in various prefecture-level cities in Guangdong Province.
Figure 3- 15 Scale Map of Cultivated Land Grading Area in Guangdong Province
Table 3-8 Distribution Table of Cultivated Land Slope Grade and Area in Cities of Guangdong Province
sequential
(3) Groundwater level
1. Acquisition of groundwater level
According to the field investigation data and the groundwater level distribution map of hydrogeological departments in various places, combined with the soil inspection of grading units, the groundwater level data are obtained comprehensively. The activity of soil groundwater level directly affects the development and fertility level of soil layer. Low-lying land has high groundwater level and difficult soil drainage, which often leads to water accumulation in the field, poor soil ventilation and strong reducibility, and produces reducing toxic substances, which is not conducive to crop growth. If the groundwater level is too deep, there is often insufficient water, which is easy to cause drought, such as hillsides. The groundwater level is between 0.6 ~ 1 m, and the soil is wet and dry alternately, which is beneficial to soil material renewal and soil layer development. Guangdong province divides the groundwater level into three levels: the groundwater level is above 0.6 meters from the surface, which belongs to the first level; Between 0.3 and 0.6 meters, it is the second level; Less than 0.3 meters is level 3.
2. General situation of groundwater level distribution
About 75% of the cultivated land in Guangdong Province has a groundwater level of Class I; Grade II accounts for about19%; Less than 7% is Grade III, mainly distributed in coastal areas, low reclamation areas, river banks and potholes in Tian Yang (Figure 3- 16). Table 3-9 shows the proportional distribution of the groundwater level area of cultivated land in various prefecture-level cities in Guangdong Province.
Figure 3- 16 Scale Map of Graded Area of Cultivated Land Groundwater Level in Guangdong Province
Table 3-9 Proportional Distribution Table of Groundwater Level Area of Cultivated Land in Guangdong Province
sequential
(4) Effective soil thickness
1. Obtain effective soil thickness.
Effective soil layer thickness refers to the soil layer closely related to plant growth at the soil profile level, and refers to the sum of soil layer and loose parent material layer. Generally speaking, the soil layer within 1 m can be considered as an effective soil layer and one of the important indexes to evaluate soil fertility. The data of effective soil layer thickness in Guangdong province are directly taken from the results of the second national soil survey and cultivated land fertility survey. According to the grading standards of grading factors in Agricultural Land Grading Regulations, the effective soil layer thickness in Guangdong Province is divided into four grades (including the upper and lower limits of effective soil layer thickness grading): the first grade, the effective soil layer thickness is ≥100 cm; Grade Ⅱ, the effective soil thickness is 60 ~100 cm; Grade ⅲ, the effective soil thickness is 30 ~ 60cm；; Grade 4, effective soil thickness
2. General situation of effective soil thickness distribution
The vast majority of agricultural land in the plain area of Guangdong Province has deep soil layers, which can fully meet the needs of crop rooting and growth. Only the effective soil layer of some soil species in mountainous and hilly areas is shallow (80 cm), belonging to thin soil layer (
Generally speaking, the cultivated land with deep effective soil layer in Guangdong Province is mainly distributed in the Pearl River Delta Plain and Chaoshan Plain, among which the effective soil layer thickness in Zhongshan, Zhuhai, Shantou, Guangzhou and Foshan is greater than 100 cm, accounting for 89. 1%, 88.8%, 78.7%, 67.4% and 6/kloc-respectively. The graded area of effective soil thickness of cultivated land in Guangdong Province is shown in Figure 3- 17. See Table 3- 10 for the area proportion distribution of effective soil thickness of cultivated land in various prefecture-level cities in Guangdong Province.
Figure 3- 17 Scale Map of Graded Area of Effective Soil Thickness of Cultivated Land in Guangdong Province
Table 3- 10 Proportion Distribution Table of Effective Soil Thickness Area of Cultivated Land in Guangdong Province
Source: Wan Hongfu et al. Atlas of Soil Resources and Crop Suitability in Guangdong Province. Guangzhou: Guangdong Science and Technology Press, 2005.
(5) Surface soil texture
1. Acquisition of surface soil texture
Topsoil texture generally refers to the sandy viscosity of topsoil, which affects soil fertility, fertility, ventilation, water permeability and other production characteristics, and is one of the signs to identify soil fertility. The texture of surface soil can be obtained by distinguishing soil types and properties and field verification. The distribution map of soil species is one of the results of the second national soil survey. By superimposing the classification unit and the soil species distribution map, the soil species attributes of the classification unit can be interpreted, so as to determine the surface soil texture type. According to the classification standard of agricultural land classification factors in the Regulations on Agricultural Land Classification, the soil texture in Guangdong Province is divided into five grades: light soil/middle soil/heavy soil, sandy loam, clay, sandy soil and gravelly soil.
2. General situation of surface soil texture distribution
Most paddy soils in Guangdong Province are loam, accounting for 57.6% of the total paddy soil area, of which Shaoguan, Meizhou, Shantou, Chaozhou, Jieyang, Maoming and Shenzhen account for more than 64.8% of the local paddy soil area. The sticky paddy soil accounts for 26.3% of the paddy soil area in the province, among which Foshan, Huizhou, Dongguan, Zhongshan, Shanwei, Guangzhou, Jiangmen, Qingyuan, Zhanjiang and Zhuhai have the most sticky soil, accounting for 60% ~ 80% of the local paddy soil area; Sandy paddy soil accounts for 16. 1% of the paddy soil area in the province, mainly distributed in Huizhou, Shanwei, Heyuan, Zhanjiang and other places, accounting for more than 24.5% of the local paddy soil area.
48.4% of the dry land in Guangdong Province belongs to loam, and the loam areas in Shaoguan, Qingyuan, Guangzhou, Meizhou, Zhaoqing, Yunfu and Shenzhen all reach more than 54%. There are not many dry lands with sticky texture, accounting for only 16.2%. Except Foshan, Zhongshan and Zhanjiang, the area of dry land with sticky texture is less than 20%. Dry farming soil with sandy texture accounts for 35.4%, and the area of Huizhou, Dongguan, Heyuan, Shanwei, Maoming, Shantou, Chaozhou, Jieyang and Zhuhai exceeds 47%. Natural soils in the whole province are mainly distributed in hills and mountains, and are mostly developed from parent rocks, and their texture is closely related to the types of parent rocks. For example, the soil developed by granite and shale has a lot of sand and a rough texture; The soil developed by shale, limestone and basalt has less sand content and sticky texture. There are many basalts in Zhanjiang area, and the natural soil texture is mostly sticky. The soil on the beach is sticky. The soil texture developed by different parent material types is very different. Generally speaking, the soil in delta and coastal alluvial plain is relatively sticky, mainly from heavy soil to middle soil, such as paddy soil in alluvial plain of northwest river delta is relatively sticky; Paddy soil in river alluvial plain and hilly area is light in texture, mainly light soil and middle soil; In the soil with shale parent material, there are few gravels, mainly silt, accounting for about half, and the rest are sand and clay. Granite parent soil is rich in gravel; There are not many soil gravels with sandstone parent material, and the particle size is between shale and granite parent material; The soil developed from limestone, Quaternary laterite and basalt is relatively viscous, mostly from heavy soil to clay. See Figure 3- 18 for the graded area ratio of cultivated land surface soil texture in Guangdong Province. See Table 3- 1 1 for the proportion distribution of cultivated land surface soil texture area in various prefecture-level cities in Guangdong Province.
Figure 3- 18 Scale Map of Grading Area of Topsoil Texture of Cultivated Land in Guangdong Province
Table 3- 1 1 Proportional Distribution Table of Topsoil Texture Area of Cultivated Land in Guangdong Province
(6) Profile configuration
1. Acquisition of configuration file configuration
Through the comprehensive analysis and interpretation of soil types, typical soil physical and chemical analysis results and landforms, the soil profile configuration attributes of agricultural land classification units in counties (districts) were obtained. The soil profile in Guangdong Province is mainly divided into whole texture (including whole soil, whole sand, whole clay and whole gravel), interlayer texture (including sand/clay/sand, clay/sand/clay, soil/sand/clay) and cushion texture (including sand/clay/clay, clay/sand, soil/clay).
2. Profile Configuration Distribution
There are 14 kinds of soil profile configurations in Guangdong province, among which homogeneous profile configurations are the most, accounting for more than 79% of the cultivated land area in the province. In the profile configuration with uniform texture, "all soil" is the most, accounting for 68.0% of the total cultivated land area in the province, and "all soil" accounts for 9. 1%. Secondly, the profile structure of cushion texture accounts for 16.6% of the total cultivated land area in the province, among which "soil/sticky/sticky" is the most, accounting for 1 1.4% of the total cultivated land area in the province, and "soil/sand/sand" accounts for 3. 1%. Interlayer structure profile configuration is the least, accounting for less than 5% of the province's cultivated land area. In the profile configuration of interlayer texture, "soil/clay/soil" accounts for 2.4%, and soil/sand/soil accounts for about 2.0%. The topsoil cultivation conditions are superior, and the land with good profile configuration is mostly distributed in two alluvial plains (Pearl River Delta Plain and Chaoshan Plain) and valley flat land with low altitude and flat terrain, while the topsoil cultivation conditions in hilly and mountainous areas are limited to some extent, and its profile configuration is generally poor. See Table 3- 12 for the configuration composition of cultivated land profiles in various prefecture-level cities in Guangdong Province.
Table 3- 12 Table of Proportional Distribution of Cultivated Land Profile in Guangdong Province
(7) Organic matter content
1. Acquisition of organic value content
The content of soil organic matter is obtained from the data of the second soil survey in various places, the data of cultivated land fertility investigation in the Pearl River Delta and the data of field investigation. The content of soil organic matter in Guangdong province is mainly divided into five grades (including the upper and lower limits of the classification limit of organic matter content): the first grade, the organic matter content is ≥ 3%; Grade Ⅱ, with organic matter content of 2% ~ 3%; Grade ⅲ, organic matter content1%~ 2%; Grade 4, organic matter content 0.6% ~ 65438 0%; Grade 5, organic matter content
2. Distribution of organic value content
Soil organic matter content is an important index reflecting soil nutrient status and soil fertility. The average content of soil organic matter in Guangdong Province is 2.35%, which is slightly higher in natural soil (2.52%), followed by paddy soil (2.45%) and dry land soil (1.49%).
Organic matter content of paddy soil in Guangdong province >: 3.0% accounts for 26.8%, 2.0% ~ 3.0% accounts for 44.0%, 1.0% ~ 2.0% accounts for 26.8%, and less than 1.0% accounts for 3.7%. The organic matter content of paddy soil in the whole province is above average. Due to the different parent materials of paddy soil in different regions of the province, the organic matter content of paddy soil in different regions of the province is also different. The soil-forming parent materials of paddy soils in Guangdong are mainly slope deposits, proluvial, wide valley alluvial proluvial, river alluvial deposits, delta deposits and coastal deposits. Among them, paddy soil developed from parent materials such as delta deposits and wide valley alluvial floods has high organic matter content because of its sticky texture. Paddy soil formed by parent materials, such as residues and alluvium, has low organic matter content, because the sediment at the top of the mountain is accumulated on the hillside with flood erosion, and the texture is sandy, and fine organic matter is alluvial downward with running water. Paddy soils in Foshan, Zhongshan, Zhuhai and other places are mostly developed from delta sediments and coastal sediments, and the soil organic matter content is high, with an average content of more than 2.82%. The paddy soils in Shantou, Chaozhou, Jieyang, Huizhou, Dongguan, Shanwei and Zhanjiang are mostly developed from parent materials such as delta deposits, alluvial deposits and shallow sea deposits. The soil texture is mostly sandy soil or loam, and loam is less. The land area with high soil organic matter content in these areas only accounts for about 20%, especially in Shantou, Chaozhou, Jieyang and Zhanjiang. The organic matter content is salty and acidic > halophytic type > latent type >. Flushing type > infiltration type >; Submerged paddy soil, decreasing in turn.
The content of organic matter in dry land soil in the whole province is >: 3.0% accounts for 8.3% of the total dry land area, 19.8% accounts for 2.0% ~ 3.0% of organic matter, 36.8% accounts for 1.0% ~ 2.0%, and 35. 1% is insufficient/kloc. The average content of soil organic matter in dry land of the whole province; 2.0% area accounts for 9% ~19% of dryland soil area; 2.0% area accounts for about 3% of dryland soil area; 1.0% ~ 2.0% soil organic matter content accounts for more than 30%; organic matter content: base water > yellow mud land > red mud land > tidal sand mud land > lateritic red soil.
Organic matter content of natural soil in the whole province >: 3.0% accounts for 27.9% of the total natural soil area, 29.4% contains 2.0%-3.0% organic matter, 28.6% contains 1.0%-2.0% organic matter, and the organic matter content < 1.0% accounts for/kloc-. It can be seen that the organic matter content of natural soil in this province belongs to the upper-middle level. Due to different parent materials, the content of organic matter in natural soil varies from place to place. The organic matter content of natural soils in Shaoguan and Qingyuan, which are located in the middle subtropical zone >: 2.0% accounts for more than 75% of the natural soil area. : 2.0% accounts for about 70% of the local natural soil area, and 1.0% ~ 2.0% accounts for about 20%. : 2.0% accounts for about 30% of the local natural soil area, and 1.0% ~ 2.0% accounts for about 40%. : yellow soil > calcareous soil > red soil > lateritic soil > purple soil > latosol, decreasing in turn.
The average content of soil organic matter in the whole province is 2. 17%, and the average content of organic matter is >: 2.0%, accounting for 58.8% of the total beach area, and the average content of organic matter is 1.0% ~ 2.0%, accounting for 16.6%. : coastal swamp saline soil (grass flat) > coastal intertidal saline soil (mud flat) > coastal saline soil > coastal sandy soil decrease in turn.
See table 3- 13 for the organic matter content of paddy soil and dry land soil in each prefecture-level city.
Table 3- 13 Table of Organic Matter Content of Paddy Soil and Dryland Soil in Guangdong Province
Source: Guangdong Soil Survey Office. Guangdong soil. Beijing: Science Press, 1993.
(8) pH value
1.Acquisition of pH value
The soil pH value in Guangdong Province is mainly obtained according to the analysis results of typical soil physical and chemical properties in the second soil survey. The soil pH value in Guangdong Province is mainly divided into five grades: the first grade, the pH value is 6.0 ~ 7.9; Grade Ⅱ, with pH values of 5.5 ~ 6.0 and 7.9 ~ 8.5; Grade iii, pH 5.0 ~ 5.5, 8.5 ~ 9.0; Grade iv, pH 4.5 ~ 5.0, grade v, pH 9.0.
2.2. General situation of pH value distribution
The average pH value of soil in Guangdong Province is 5.7, in which the average pH value of paddy soil is 5.8, that of dry land is 5.9, and that of natural soil is 5.2. Most soils in Guangdong Province are acidic. As can be seen from Table 3- 14, the cultivated land area with soil pH below 6.5 accounts for 93.92% in the whole province, among which pH 4.5 ~ 5.5 and pH 5.5 ~ 6.6 account for the largest proportion, accounting for 55.9% and 37.63% respectively; PH < 4.5 is strongly acidic, and pH >; 7.5 The soil area of alkaline and neutral cultivated land with pH value of 6.5 ~ 7.5 is small, accounting for only 6.47%, of which pH value is
Table 3- 14 Proportional Distribution Table of Cultivated Soil pH Grading Area in Guangdong Province
sequential
In terms of geographical distribution, Chaoshan, Huizhou, Shanwei, Heyuan, Zhaoqing, Dongguan, Shenzhen, Meizhou, Yangjiang and Guangzhou have the largest proportion of cultivated land with soil pH below 6.5. The soils in these areas are mostly weathered acid parent rocks, and mostly paddy soils developed from alluvial and river alluvial parent materials. The neutral cultivated land in Zhuhai and Zhongshan has the largest soil area, accounting for 865,438 0.26% and 365,438 0.87% of the local cultivated land soil respectively. Most of the cultivated soils in these areas are developed from alluvial parent materials in the Pearl River Delta, and some of them are salty fields which are influenced by seawater. Alkaline arable soil is mainly distributed in Qingyuan and Shaoguan, accounting for 17.04% and 15.43% of the local arable soil area, respectively. These areas are located in limestone areas, which are influenced by limestone parent rocks or caused by excessive application of lime.
Acidic dryland soils mainly include: ① lateritic red soil, Songka land and red mud land, which are mainly distributed in hilly platforms in Zhanjiang area; ② Red mud land, lateritic red soil land and yellow mud land are widely distributed; ③ Carbonaceous black mud land, mainly distributed in Zhanjiang and Maoming areas; (4) Tidal sand mud land, mainly distributed in alluvial terraces on both sides of the river and downstream. Alkaline and neutral dryland soils mainly include: ① red fire mud, mostly neutral or weakly acidic, mainly distributed in limestone areas such as Yingde, Yangshan, Lechang, Lianzhou, Wengyuan, Luoding and Qingxinbei; (2) Alkaline beef liver land, mainly distributed in gentle slopes of Zhongshan in the Hongyan basin, such as Nanxiong, Shixing, Conghua, Lianshan, Yangshan, Lechang, Wuhua, Xingning and Meixian; ③ Coastal sandy land and coastal muddy sandy land are mostly neutral or weakly acidic. In addition, due to the influence of parent material and artificial high maturity, the soil in basic waters and vegetable fields is mostly neutral or weakly acidic.
(9) Irrigation guarantee rate
1. Acquisition of irrigation guarantee rate
The irrigation guarantee rate is based on the present situation of land use, the information of local water conservancy department and field investigation. Irrigation guarantee rate is one of the important indexes to evaluate the quality of agricultural land. According to the conditions of irrigation water sources and irrigation facilities, the irrigation guarantee rate is divided into four grades: first, it is completely satisfied, including paddy fields, vegetable fields and irrigated land that can be irrigated at any time; Grade II, basically satisfied, with a good irrigation system and irrigation land with irrigation guarantee in the key water demand growth season; Grade 3, generally satisfactory, with irrigation system to irrigate the land, but irrigation cannot be guaranteed in severe drought years; Grade 4, no irrigation conditions, including dry land and Wang Tiantian.
2. Distribution of irrigation guarantee rate
The irrigated land area in Guangdong Province is 37,090.06 hectares, accounting for 1.2 1% of the total cultivated land area in the province, mainly distributed in Zhanjiang, Guangzhou, Jiangmen and Shanwei. The dry land and Wang Tiantian covers an area of 876,627.64 hectares, accounting for 28.66% of the total cultivated land in the province, mainly distributed in Zhanjiang, Qingyuan, Yangjiang, Shaoguan and Maoming, especially Zhanjiang, and 55% of the cultivated land is dry land and Wang Tiantian. The irrigated paddy fields and vegetable fields cover an area of 2144,635,438+0 hectares, accounting for 70.438+03% of the total cultivated land in the province. Therefore, according to the classification, in theory, more than 70% of the cultivated land in Guangdong Province should have a first-class irrigation guarantee rate, 28.66% of the cultivated land has no irrigation conditions, and less than 1.2% of the cultivated land has a second-class irrigation guarantee rate and a third-class irrigation guarantee rate. But in fact, due to the destruction of irrigation facilities, uneven distribution of water resources and shortage of water resources, not all paddy fields and vegetable fields can fully meet the irrigation requirements. For example, Leizhou Peninsula area 198064.30 hectares, due to perennial drought, the groundwater level is deep, the evaporation is greater than the rainfall, and nearly 70% of paddy fields are not fully irrigated. In addition, vegetable fields in some places are transformed from hilly dry land (for example, 80% of vegetable fields in Shenzhen are transformed from hilly dry land), resulting in the cultivated land area with the first irrigation guarantee rate in the whole province accounting for about 8 1% of the irrigated paddy field area, accounting for about 60% of the cultivated land area in the whole province, mainly distributed on both sides of rivers and near the irrigation water sources in the whole province; The cultivated land with secondary and tertiary irrigation guarantee rates accounts for about 14% and 5% of the total cultivated land area in the province respectively. The irrigation guarantee rate is about 22% of Grade IV, which is basically consistent with the distribution of dry land (Figure 3- 19).
Figure 3- 19 Scale Map of Farmland Irrigation Guarantee Rate in Guangdong Province
(10) Drainage conditions
1. Acquisition of drainage conditions
Drainage conditions are generally obtained according to the groundwater level distribution map of hydrogeological units around the country. If there is no hydrological survey data, we can collect farmland water conservancy data and make a comprehensive judgment based on field survey results, geomorphological characteristics and soil types. Drainage condition refers to the situation of surface water accumulation after rain, which is influenced by topography and drainage system. According to the Regulations on Agricultural Land Classification and the reality of Guangdong Province, the drainage conditions of agricultural land classification in Guangdong Province are divided into four grades (including upper and lower grades): first, there are sound drainage channels for trunk, branch, bucket and agriculture (including pumping), and there is no flood disaster; Grade II, the drainage system (including pumping and drainage) is basically sound, and there is short-term flood after heavy rain in wet years (site 1 ~ 2 days); Grade III, the drainage system (including drainage) is general, and there is flood after heavy rain in wet years (the site is flooded for 2 ~ 3 days); Grade IV, no drainage system (including pumping and drainage), generally flood after heavy rain in the year (water accumulated in the site for more than 3 days).
2. Distribution of drainage conditions
It can be seen from the table 3- 15 of the area distribution of cultivated land drainage conditions in various prefecture-level cities in Guangdong Province that the overall drainage conditions of cultivated land in northern Guangdong, central Guangdong, southwestern Guangdong and Leizhou Peninsula with low groundwater level are good, while the drainage conditions of cultivated land in coastal platforms, plain lowlands, Pearl River Delta Plain, Chaoshan Plain and coastal areas in eastern Guangdong are poor.
Table 3- 15 Distribution Table of Area Proportion of Cultivated Land Drainage Conditions in Cities of Guangdong Province
Source: Wan Hongfu et al. Atlas of Soil Resources and Crop Suitability in Guangdong Province. Guangzhou: Guangdong Science and Technology Press, 2005.
(XI) Restrictive factors
Judging from the soil types and their distribution in Guangdong Province, the number of soil types affected by obstacle grade, outcrop of surface rocks and soil salinization degree is very small and scattered. Rock outcrop is affected by cultivated calcareous soil and cultivated purple soil, barrier layer is affected by lime field (with lime hardening layer) and eel mud field (with albic soil layer), and salinization degree is affected by acid sulfate saline soil, saline-alkali soil and salty acid field.
Through the results of the second soil survey and field verification, the limiting factors are obtained. According to its influence on cultivated crops, the value is revised in the range of 0.4-0.8.
1. Soil barrier layer
Soil barrier layer refers to the layer below the tillage layer that hinders the extension of crop roots or affects water infiltration, such as latent layer, lateral infiltration layer, iron sublayer, white slurry layer, lime hardening layer, mud tray and iron tray layer. According to its distance from the surface, it can be divided into two degrees of influence (illumination: 30 ~ 60cm；; Weight:
2. Surface rock outcrops
Surface rock outcrop refers to bedrock outcrop, which interferes with farming. According to the degree of disturbance to farming, it is divided into three levels (light: the distance between rock outcrops is 35 ~ 100 m, which has affected farming; Medium: rock outcrop spacing 10 ~ 35 meters, which can be used for non-mechanized farming; Weight: Rock outcrop spacing is 3.5 ~10m, which is not mechanized farming. Correction coefficient range: 0.4 ~ 0.8). The cultivated land affected by rock outcrops is mainly distributed in limestone areas in northern Guangdong, involving Yangshan, Lechang, Shixing, Ruyuan and Liannan, accounting for 50%, 24%, 1 1%, 9% and 8% of the local cultivated land area respectively.
3. The degree of soil salinization
The salinized soils in Guangdong Province include coastal saline soil, acid sulfate saline soil and saline-alkali paddy soil. The degree of soil salinization is generally divided into different salinization degrees according to the content of soluble salt in soil and its relationship with crop growth. The degree of salinization is divided into three grades: mild, moderate and severe. The correction factor ranges from 0.4 to 0.8. The cultivated land affected by salinization is mainly distributed in coastal areas such as Shantou, Haifeng, Lufeng, Zhuhai, Yangjiang, Jiangmen and Dongguan in Shanwei.