Cropland
Characteristics of cropland: China and Zhang Jiachong
Author: Honghu LiuEditor's note 30 Apr 2012: Text source D111-2.4. To be edited again to avoid overlap with D131.
According to the first survey of land resources (Zhao et al. 2010), in 1996 the total area of cropland in China was 130 Mha but by 2007 the area had decreased to less than 122 Mha; a decrease of 8 Mha (Table 1).
Table 1. Change in area of cropland in China between 1998 and 2007
| Year | 1998 | 1999 | 2000 | 2001 | 2002 | 2003 | 2004 | 2005 | 2006 | 2007 |
| Quantity of cropland (Mha) | 129.30 | 128.86 | 128.24 | 127.62 | 125.97 | 123.39 | 122.44 | 122.08 | 121.80 | 121.74 |
Source: (Zhao Yuling et al. 2010)
Currently, the quality of cropland in China is very poor (Wu, 2009) and degradation is severe. The area of soil loss in China is 3.67 Mkm², which is a third of the land area and as a result, there is a severe lack of land resources in China. In 2001, the per capita area of arable land was about 0.10 hectares, which is 40% of the average per capita arable land area in the world (0.250 ha). Eleven provinces have a per capita area of arable land of more than 0.13 ha. These provinces are mainly distributed in the northeast and west of China. Seven provincial administrative units have a per capita area of arable land of less than 0.07 ha. These provinces include: three municipalities directly under the control of Central Government (Beijing, Tianjing and Shanghai); Hunan; Zhejiang; Fujiang; and Guangdong in southern China. Sixty six percent of cropland in China is located on mountains, hills and plateaus while only 34% of cropland is distributed on plains and in basins. According to statistical data in 2003, the area of sloping farmland in the Yangtze River basin is 9 Mha, which is 42.5% of the sloping farmland in the whole of China. Of this sloping farmland, 7.67 Mha is in the upper reaches of the Yangtze River, which is 88.3% of the Yangtze River basin (Hu 2009). In the middle and lower reaches of the Yangtze River, the total land area is 0.92 MKm², which is 9.54% of the total land area in the whole of China. Cropland accounts for 19.56 MHa, which is 20.6% of the total cropland in China (Qi 2009).
The source region of the Yangtze River
The data on land use change in this section of the report is derived from remote sensing images. The remote sensing images used are landsat-5 TM image in 1986 and landsat-7 ETM image in 2000, which is in summer and autumn (August and October) (Pan 2005).
Between 1986 and 2000, the main characteristics of land use change in the source region of the Yangtze River are a rapid increase in the area of land under cultivation and a sharp decrease in the area of wetlands, forests and glaciers, which regulate the ecosystem in high cold regions. Over the 15 year period, the area of urban construction land and bare earth rose by between 184.2% and 151.3%, which represents two trends: (1) human activity has strongly influenced the land cover; (2) both abandoned land and grassland degradation have caused an increase in secondary barren land. Table 2 below shows that in 1986, grassland covered the largest area, followed by unused land, wetland, water, forest land, cropland and construction land. In 2000, land use cover had changed and the order of individual land use was; grassland, unused land, wetland, water, forest land and construction land. The categories with maximum spatial variation of individual land use change were grassland and water bodies. These results indicate that in the past 15 years, grassland degeneration and degradation have become a serious problem, and the use of grassland has declined. In the meantime, large areas of glacier have disappeared and lakes have shrunk in area, which has resulted in changes in the spatial position of large areas of grassland and water.
Table 2. Changes in individual land use categories between 1986 and 2000.
| Type | Area(km²) | Yearly change ratio (%) | Roll-in (km²) | Roll-out (km²) | Variation (km²) | |
| 1986 | 2000 | |||||
| Construction land | 2.2 | 4.8 | 8.6 | 2.6 | 0 | 2.6 |
| Cropland | 3.2 | 4.6 | 3.1 | 1.5 | 0.1 | 1.4 |
| Grassland | 78469.6 | 75818.1 | -0.2 | 4395.1 | 7046.6 | 2651.5 |
| Forestland | 23.7 | 10.8 | -3.9 | 0 | 12.8 | 12.8 |
| Wetland | 7220.4 | 4138.0 | -3.1 | 33.9 | 3116.3 | 3082.1 |
| Water | 6934.2 | 6606.0 | -0.34 | 777.6 | 1105.7 | 328.2 |
| Unused land | 28766.6 | 34837.5 | 1.5 | 7835.5 | 1764.6 | 6070.8 |
| Total | 121419.9 | 121419.9 | 0 | 13046.2 | 13046.2 | 12149.8 |
Source: (Pan 2005)
The upper reaches of the Yangtze River
The data used for this report is mainly sourced from the resource and environment database covering the whole of China, which includes: the Landsat TM/ETM remote sensing images from 1980, 1990 and 2000; land use maps; administrative maps; 1:250000 DEM; and the statistical data of the related economic development (Wu et al. 2008). The 1:100000 land use database in 1980, 1990 and 2000 has been constructed using RS and GIS technology. As can be seen from Table 3 below, in the past 20 years cropland in the upper reaches of the Yangtze river has shown a significant decrease, followed by an increase which has been caused by the development of small towns, township enterprises, and the ratio and spatial distribution of agricultural land changed by household contract management.
Secondly, forest land and grassland shows a different trend to cropland. Forest land has decreased by 0.14×104 km² whereas grassland has increased by 0.17×104 km². Forest land is the category of land use showing the largest decrease in area and grassland shows the maximum increase. The sharp reduction in forest land is caused by long-term extensive deforestation. The degradation of forest ecosystems is also one of the main reasons for the increase in grasslands. Third, water area shows changes up to 3.42%, but this is due to the fact that some water storage facilities were built and glacier and snow cover changes with seasonal change. Fourth, construction land shows the maximum change and fastest increase, with an increase ratio of 96.29%, which is caused by rapid economic development in the 1990s. Fifth, although the change in the unused land category is small, at only 0.18%, this category has also experienced a significant increase and subsequent decrease as a result of increasing animal husbandry and cultivation. Unused land decreased by 0.8×104 km² in the upper reaches of the Yangtze River in the 1980s. Vegetation deterioration results in increasing soil loss and desertification of land. As a result, land use capability locally has decreased.
Table 3. Basic land use situation of upper reaches of Yangtze River
| Landuse type | Area (104 km²) | Yearly change of area (104 km²) | Yearly change ratio of area (%) | ||||||
| 1980 | 1990 | 2000 | 1980-1990 | 1990-2000 | 1980-2000 | 1980-1990 | 1990-2000 | 1980-2000 | |
| Cropland | 21.99 | 21.60 | 21.91 | -0.39 | 0.3 | -0.08 | -1.77 | 1.43 | -0.36 |
| Forestland | 33.77 |
33.95 | 33.63 | 0.18 | -0.32 | -1.14 | 0.53 | -0.94 | -0.41 |
| Grassland | 35.47 | 36.89 | 35.64 | 1.42 | -1.25 | 0.17 | 4.00 | -3.39 | 0.48 |
| Water | 1.46 | 1.20 | 1.41 | -0.26 | 0.21 | -0.05 | -17.81 | 17.50 | -3.42 |
| Construction land | 0.42 | 0.27 | 0.53 | -0.15 | 0.26 | 0.11 | -35.71 | 96.29 | 26.19 |
| Unused land | 5.54 | 4.74 | 5.53 | -0.80 | 0.79 | -0.01 | -14.44 | 16.67 | -0.18 |
Source: (Wu et al. 2008)
The relative change in the rates of land use in nine provinces of the upper reaches of the Yangtze River has been calculated. The results showed an obvious spatial difference of land use across these provinces. Among them, change in the area of cropland in Qihai province was the highest. Its relative change rate is 36.18. The next is 6.32 in Gansu province. Guizhou province is the lowest, with only 0.26. The change of forest in Chongqin city is the highest, in which the relative change ratio is 6.88. The next is Sichuan and Xizang province, which are 2.59 and 1.26, respectively. The lowest is 0.05 in Yunan province. The change in grassland in Chongqin is the highest. Its relative change rate is 16.48. Next are Yunan and Sichuan provinces, with 3.56 and 2.78 respectively. Lowest in terms of change are Shanxi and Qihai provinces, with 0.44 and 0.07 respectively. The change of water in Yunan province is the highest and its relative change rate is 7.42 while the change in other provinces is lower than the mean change in the water bodies in the upper reaches of Yangtze River. This means that in provinces other than Yunan province, there is no spatial difference in the area of land covered by water. The change in area of construction land in Hubei province is the highest, with a relative change ratio of 9.54. Next are Chongqin and Sichuan Provinces. The former three provinces belong to a well developed area. The other provinces such as Gansu and Qinhai province belong to a developing area. The change in the area of unused land in Qihai province is the lowest, at 23.94. Next is Chongqin, which is 7.59. The lowest is Hubei and Guzhou province, at only 0.06.
In the upper reach of the Yangtze River, four sample areas were measured. The first (105°33'45″ - 37'30″, 33°35'00″- 37'30″) is located in western Chengxian, which belongs to western Qinling region of southeast Gansu province. The second (106°48'45″-52'30″, 30°40'00″-42'30″) is located in the north-eastern Gangan, which belongs to east Sichuan province, the west of the middle of Huaying mountain. The third (108°26'15″-108°30'00″, 30°52'30″-30°55'00″) is located in north-eastern Wanzhou, which belongs to the middle of the Three Gorges in the east of the Sichuan basin, paralleled ridge-valley of east Sichuan. The fourth is located in the middle of Yuanmong County, which belongs to the western part of the middle Yunnan plateau, including the Three Gorges Dam Area, the low hill and middle mountains (Ren et al. 2007).
Based on field surveys, data on land use in the four sample areas of the upper reaches of the Yangtze River was obtained. Using a weighted average method, land use in four sample areas was computed (Table 4 below). The results indicated that in the upper reaches of the Yangtze River, agricultural land (cropland, forest land and ponds) is the dominant land use. The total area of the four sample areas is 111 km². Agricultural land covers 88.01 km², which is 79.29% of the whole sample area. Next is unused land, which is 17.1 km² or 15.41% of the whole sample area. Construction land is the lowest, covering 5.89 km² or 5.31% of the whole sample area. Cropland covers the largest area within the agricultural land category, with 63.87 km² or 72.57% of agricultural land; 57.54% of the sample area. Next is forest land, which covers 18.32 km² or 20.82% of agricultural land; 16.5 % of the sample area.
Due to the difference in terms of the type of environment in the four sample areas, the land use in these areas is different (Table 4 below). The Longnan mountain area, the hill region of middle Sichuan and the ridge-valley of east Sichuan have very similar land uses. Agricultural land in these three sample areas is the dominant land use type, which is 92% of the whole sample area. The land use in the Arid-hot river valley of Jinshajiang is special. The dominant land use is unused land, which is 53.15% of the whole sample area. Next is agricultural land, which is 12.5 km² or 43.22% of the whole sample area. In the four sample areas, the ratio of construction land in the Longnan mountain area is the highest, at 8.65% of the whole sample area. Next is the hill region of the middle Sichuan, which is 5.97% of the area. The others have almost the same ratio of construction land, which is about 3%. Unused land in the hill region of the middle Sichuan and ridge-valley of east Sichuan is 2.21% and 4.06% respectively, while there is no unused land in the Longnan mountain area. In the hill region of the middle Sichuan area, cropland is the dominant land use covering 25.09 km² or 90.71% of the sample area. In the Longnan mountain area and the ridge-valley of east Sichuan, the area covered by cropland is very similar at about 55% of the sample area. The area of forest land in the Longnan mountain area is relatively larger, covering 9.82 km² or 36.60% of the whole sample area. The area of forest land in the ridge-valley of east Sichuan is 4.50 km², which is 16.3% of the whole sample area. The ratio of cropland in the arid-hot river valley of Jinshajiang is the largest within the category of agricultural land, accounting for 63.20% of the agricultural land. Next is forest land, which covers 30.56% of the sample area. In the four sample areas, a large proportion of cropland is sloping land. The minimum proportion appears in the hill region of the middle Sichuan, which is up to 32.21%. The maximum is in the Longnan mountain area, which achieves 53.71%. The other two areas are 39.24% and 48.72% respectively.
Table 4. Statistics for land use in the upper Yangtze River regions
| Land use type | Longnan mountain area | Hill region of the middle Sichuan | Ridge-valley of east Sichuan | Arid-hot river valley of Jinshajiang | Mean | |||||
| Area/km² | Ratio/ % | Area/km² | Ratio/ % | Area/km² | Ratio/ % | Area/km² | Ratio/ % | Area/km² | Ratio/ % | |
| Cropland | 14.69 | 54.75 | 25.08 | 90.71 | 16.2 | 58.7 | 7.9 | 27.32 | 63.87 | 57.54 |
| Forest land | 9.82 | 36.6 | 0.18 | 0.65 | 4.5 | 16.3 | 3.82 | 13.21 | 18.32 | 16.5 |
| Pond |
0 | 0 | 0.1 | 0.36 | 0.07 | 0.25 | 0.01 | 0.03 | 0.18 | 0.16 |
| Construction land | 2.32 | 8.65 | 1.65 | 5.79 | 0.87 | 3.15 | 1.05 | 3.63 | 5.89 | 5.31 |
| Unused land | 0 | 0 | 0.07 | 0.25 | 1.12 | 4.06 | 14.75 | 51 | 15.94 | 14.36 |
| River | 0 | 0 | 0.54 | 1.95 | 0 | 0 | 0.62 | 2.14 | 1.16 | 1.05 |
| Total | 26.83 | 100 | 27.65 | 100 |
27.6 | 100 | 28.92 | 100 | 111 | 100 |
Source: (Ren et al., 2007)
The middle reach of the Yangtze River
The data for this area was sourced from statistics yearbooks of Xianning city (1995-2007) and data on land use change from the Land and Resources Bureau of Xianning city (Xia et al. 2009). The character of land use change is shown in Table 5 and discussed below.
Table 5. Variation of land use in Xianning in 1996 to 2006
| Land use type | Cropland | Vegetable field | Forest | Grassland | Other agricultural land | Construction land | Roads | Water conservancy |
| 1996-2000 | -0.1830 | -0.1492 | -0.0257 | 0.0000 | 0.1613 | 0.7476 | 3.8582 | 0.1335 |
| 2000-2005 | -1.3472 | -0.1596 | 0.7208 | 0.0000 | -0.1554 | 0.6788 | 0.9141 | -0.0003 |
| 1996-2006 | -0.6754 | -0.2558 | 0.3209 | 0.0000 | 0.0265 | 0.8281 | 3.4309 | 0.0596 |
Source: (Xia et al. 2009)
- Change in transportation (road) land: The change in the area of road land is the largest at 3.4309. The next is construction land, which is 0.8281. Another is land for building water conservancy facilities;
- Change in agricultural land: Change in cropland shows a decline. Change in forest land is next to cropland, and shows that area of land covered by land changes increasingly
- Generally, the change of road land is very strong. The next is residential area, land for industrial and mining use. Another is cropland.
The Yangtze River Delta
The land area in the Yangtze River delta is 844.1×104 ha. The area of arable land per capita is 0.048 ha, which is less than that of the whole country and is one fifth of the world average (Peng and Gao 2004). Based on statistics yearbooks and data from detailed land surveys, the ratio of cropland is the largest land use. Second to this island used for water storage. According to statistics between 1980 and 1995, 24.7×104 ha of cropland was lost through soil and water loss, which represents 5.6% of total soil loss in China. The average rate of decline in cropland is up to 0.55%, which is double the mean value between 1980 and 1995. The maximum soil loss ratio per year is 1.47%, which occurred in 1993. The rate of erosion in cropland is more than 0.2 ha/km²yr-¹, which is 6.7 times higher than the average rate of erosion (0.03 ha/km²yr-¹ in the corresponding period. The ratio of construction land is up to 14.8%, which is far greater than the average level countrywide. The cultivation index of cropland rises 38.5%, which is close to four times as much as the average national level. The change of land use structure has the obvious spatial difference. In the 1990s the average decrease rate of cropland per year in the different towns or cities has differs 10 times for each other. The towns and cities in which the decrease rate per year is more than 2% are mainly distributed around Tailu lake. In particular in the Su, Xi and Chang districts, the decrease in cropland per year is 5.64%, 4.57% and 4.06%.