Changes in Area and Quality of Cultivated Land in China

Transcription

1 1 Changes in Area and Quality of Cultivated Land in China Qinxue WANG* and Kuninori OTSUBO* * National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaraki , Japan Abstract: In this paper we discuss the changes in cultivated land in China, both quantitatively and qualitatively, by using agricultural statistical data and a soil database of China established by the Nanjing Institute of Soil Science, Chinese Academy of Sciences. We found that the area of cultivated land increased from 1661 to its maximum at the end of the 1950s; it then began to decrease from the 1960s, and has kept decreasing up to the present. Lost land was mostly high quality cultivated land located in the eastern part of China, while reclaimed and new areas of cultivated land were mostly marginal lands in the northern and western parts of China, where soil erosion, desertification, and salinization have been very severe. Keywords: cultivated land change, land quality, soil erosion, desertification, salinization. 1. Introduction The total area of China is km 2, which makes it the third largest territory in the world. However, only 13.5% ( km 2 ) is cultivated land; the cultivated land per capita is only ha, or 43% of the world average. Pressures on land resources continue to grow owing to rapid population increase, economic development, and environmental changes. Under such heavy pressures, there have been large changes in cultivated land resources, both quantitative as well as qualitative. Since the 1960s, the area of cultivated land has been continually decreasing as it becomes nonproductive or is transferred to other non-agricultural land-use patterns. In this study, we have attempted to use as many data as possible from different sources to discuss these changes in both quality and quantity. For this purpose, we developed a GIS that includes a county-level statistical database 1) and a set of 1-km-resolution digital maps of soil degradation 2) (such as soil erosion, desertification, and salinization) in China, based on a soil database of China developed in 1997 by the Nanjing Institute of Soil Science, Chinese Academy of Sciences. 2. Changes in Area of Cultivated Land 2.1 Temporal changes China has one of the oldest histories of agricultural cultivation in the world, and most of the land suitable for cultivation has been under cultivation for hundreds of years. The cultivation rates in the basins of the middle and lower reaches of the Yellow River, the Yangtze River, the Sichuan Basin, and the Zhujiang River Basin had already reached a very high level hundreds of years ago 3). Changes in the area of cultivated land in the past 300 years are shown in Figure 1. We can see that the largest increase in area of cultivated land in China occurred between 1888 and 1957, with an annual increase of between 1.2% and 1.7% (Table 1), and the peak appeared at the end of the 1950s. Since then, the total area of cultivated land has begun to decrease, especially during the last two decades, owing to heavy pressures of rapid population increase and socioeconomic development. While cultivation in the basins of the middle and lower reaches of the Yellow River, Yangtze River, Sichuan Basin, and Zhujiang River Basin has a long history spanning thousands of years, cultivation in the Northeast, Northwest, and Qingzang Plateaus has a relatively short history of between 100 and 300 years (Figure 1).

2 2 1, ,000.0 (1,000 km 2 ) Qingzang Plateau Southwest South Yangtze River Basin Northwest Yellow River Basin Northeast Figure 1 Changes in area of cultivated land over the last 300 years (Data sources: Shi et al ) and Chinese Agricultural Statistics 1987 and ) ) Table 1 Rate of annual increase in cultivated land during the past 300 years (Unit: %) Region Northeast Yellow River Basin Northwest Yangtze River Basin South Southwest Qingzang Plateau China Total Spatial changes Chinese agricultural statistical data at a county scale were used to analyze spatial changes between the distribution of cultivated land in 1985 (Figure 2a) and the distribution of cultivated land in 1995 (Figure 2b). Both figures show that the cultivated land is distributed mainly in the eastern and northeastern areas of China, which are the main grain producing regions in China. The difference in the area of cultivated land between the two years (Figure 3) clearly shows that the area of cultivated land has increased in western and northeastern China, but has decreased in eastern China. From among 3 2 provinces, the area of cultivated land has decreased in 20 provinces, including Beijing, Tianjin, Hebei, Liaoning, Shanghai, Jiangsu, Zhejiang, Fujian, Shandong, Henan, Hunan, Guangdong, and Hainan. The total area of cultivated land decreased by about km 2, in which about km 2 decreased in Guangdong province. The main cause of the decrease the eastern and coastal areas is attributed to the increase of urban and industrial areas. In addition, because of land degradation caused by over-cultivation and reckless conversion from cultivated land to grassland, cultivated land in arid and semi-arid areas, such as Shanxi, Gansu, Qinghai Provinces, and Ningxia Huizu and Xinjiang Uygur Autonomous Regions in the north, has also been decreasing. The total area of cultivated land in these areas decreased by about km 2.

3 3 (a) Figure 2 Distribution of cultivated land in 1985 (a) and 1995 (b) at county level (b) Figure 3 Difference in the area of cultivated land between 1995 and 1985 (Positive values mean that the area of cultivated land in 1995 was greater than that in 1985) In terms of natural conditions, the eastern and coastal areas of China are warm, water resources are abundant, and the land there is very flat. The decrease of such good quality cultivated land in these areas has led to a decline in the quality of cultivated land. To compensate for the rapid decrease of good quality cultivated land in the eastern and coastal areas, wastelands, grasslands, wetlands, and woodlands have been developed as cultivated land in the Northeast district, the Yungui Plateau, and the Northwest district. Cultivated land has increased by ha in the Northeast Provinces (Inner Mongolia, Heilongjiang, and Jilin), mainly by reclaiming grasslands and wetlands, and has increased by 8046 ha in Yunnan and Guizhou provinces, mainly by burning forest. Cultivated land has increased in Hubei, Jiangxi, and Anhui provinces mainly by converting grassland or reclaiming cultivated land from lakes.

4 4 3. Changes in the Quality of Cultivated Land In general, the quality of cultivated land in China has improved over the past 50 years owing to the development of various agricultural infrastructures, such as irrigation system, fertilizing and land flatting. However, because of unsuitable land use or over-cultivation in hilly and mountainous areas, degradation of cultivated land by soil erosion, desertification, or salinization, is still occurring, threatening grain production, the environment, and sustainable agricultural development. To study the situation of soil degradation, we produced a 1-km-resolution digital map of soil degradation in China (Figure 4). The map is based on the Soil Database of China created in 1997 by the Nanjing Institute of Soil Science, Chinese Academy of Sciences. From the map, we can see that the main factors limiting agricultural production are soil erosion by water and wind, terrain deformation (or desertification), salinization, and gleization. Among them, soil erosion by water is the most severe problem. According to s tatistical analysis of the map, the total area of soil degradation in China is km 2, in which the area of soil erosion (including the loss of topsoil by water, gully erosion by water, and loss of topsoil by wind) is km 2, accounting for 70% of the total area of soil degradation. Further, among the three types of erosion, gully erosion, which is the most harmful and difficult to protect against, accounted for km 2 or 27.8% of the total area of soil degradation. Gully erosion is mainly distributed throughout the Loess Plateau, and in Sichuan, Yunnan, and Guizhou provinces. Soil erosion causes a thin soil layer, coarse soil texture, and poor nutrient content. As a result, the capacity for storing soil moisture declines, and productivity of the land and stability of crop production falls sharply. Moreover, eroded soil and sand accumulates in down-stream regions, riverbeds, lakes, and dams in the cultivated areas. As a result, the drainage capabilities of the rivers decline and the risk of flood increases. In China, especially in the northwestern area, damage to natural vegetation and cultivation on the slopes are the main causes of soil erosion. Desertified areas account for km 2 (6.7%) of the total area of degraded soil in China. The most seriously desertified areas are mainly located in arid and semi-arid regions, such as the Inner Mongolia, Xinjiang and Ninxia Autonomous Regions, and Qinghai province. Desertification destroys soil texture and creates conditions that allow severe wind erosion. Desertification is considered to be caused mainly by human-driven factors, such as over-grazing, over-cultivation, over-explo ring, and misuse of water resources. Although the situation of salinization in the North China Plain has greatly improved in recent decades, the total area of salinization is still increasing 4). According to the statistics in Table 2, the total area of salinization is km 2, which accounts for 10.5% of the total area of degraded soil. The areas affected by salinization are mainly distributed in northern and northwestern China, where unsuitable irrigation practices and inadequate drainage are the main causes. Finally, we overlaid the map of soil degradation with the map of cultivated land and obtained a map of soil degradation in cultivated areas of China (Figure 6). From this map, we can estimate the area of each type of degradation occurring on cultivated land. The estimated result shows that 39.2% of cultivated land currently has soil degradation problems (Table 3). Among all degradation types, soil erosion is the major problem, adversely affecting the quality of more than 30% of cultivated land.

5 5 Figure 4 Digital map of soil degradation in China Figure 5 Structure of soil degradation in each province Figure 6 Soil degradation in cultivated areas of China

6 6 Table 2 Area of soil degradation in each province (km 2 ) ADMIN_NAME Degraded Area Salinization Wind Erosion Water Erosion Gully Erosion Gleization Desertification Whole China Hong Kong Anhui Zhejiang Jiangxi Jiangsu Jilin Qinghai Fujian Heilongjiang Henan Hebei Hunan Hubei Xinjiang Xizang Gansu Guangxi Guizhou Liaoning Inner Mongolia Ningxia Beijing Shanghai Shanxi Shandong Shaanxi Sichuan and Chongqing Tianjin Yunnan Guangdong Taiwan Table 3 Proportions of soil degradation throughout China and proportions of soil degradation in cultivated land Soil DegradationType Area and proportion of degraded land throughout China Percentage of total territory affected by soil degradation Area and proportion of degraded land in cultivated areas Percentage of cultivated land affected by soil degradation (km 2 ) (%) (%) (km 2 ) % % Salinization Wind Erosion Water Erosion Gully Erosion Gleization Desertification Soil degradation

7 7 4. Conclusions Changes in both area and quality of cultivated land in China have been discussed. It was found that the area of cultivated land increased rapidly from 1661 to the end of the 1950s, and then decreased from the 1960s up to the present owning to heavy pressures of population increase and socioeconomic development. The lost cultivated land was mostly high quality land located in the eastern part of China, while reclaimed new cultivated land was mostly located in marginal areas in the northern and western parts, where soil erosion, desertification, and salinization are deteriorating the quality of cultivated land. References 1) Department of Agriculture of China (1987, 1997): Agricultural Statistics of China, China Agriculture Press, Beijing, China. 2) China Office of Soil Survey (1998): Soil of China, Chinese Agricultural Press, Beijing, China. 3) Shi Y., Q. Kang, C. Zhao, L. Zhong and Z. Shi, (1985): Cultivated Rough Land Resources in Ch ina (In Chinese), Beijing Science & Technology Press, Beijing, China. 4) Institute of Natural Resources and Regional Planning, Chinese Academy of Agricultural Sciences (1995), Cultivated Land in China, Chinese Agricultural Sci. & Tech. Press, Beijing, China.