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5. Land use on the Lake Taihu Plain

She Zhixiang, Chen Yuee, and Tang Zhenfu
Nanjing Institute of Geography, Chinese Academy of Sciences,
Nanjing, Jiangsu Province

Abstract

Almost all the land on the Lake Taibu Plain has been brought into productive use, so the only way to increase agricultural production is to raise the per-unit yield. Since 1965 triplecropping systems have become widespread in the region and the per-unit grain yield has increased greatly Crops must be planted and harvested precisely on time to maximize resource use. Among the problems of triple-cropping are seasonal labour shortage, soil deterioration, and the poor quality of some grains. The hills around Lake Talbu are used for fruit growing, of which tangerine production is the most important. Future expansion of tangerine production should consider carefully local microclimatic conditions, to avoid frost damage.

Fig. 5.1. Land-Use Patterns on the Taihu Plain, Southern Jiangsu Province

The Lake Taibu Plain, in the southern Yangzi Delta, includes counties and towns located in Jiangsu and Zheliang Provinces and Shanghai Municipality. The plain has an area of about 36,355 km, a population of 30 million (60 per cent in agriculture), and 1.44 million ha of cultivable land. Urban settlements on the Taihu Plain range in size from Shanghai, the world's largest metropolis, to small towns, and include Hangzhou, Suzhou, Wuxi, Changzbou, Jianxing and Huzhou. Having excellent land and water communications, this region has emerged as the most economically advanced and developed region in East China (fig.5.1).

Although the Lake Taihu Plain accounts for only 0.3 per cent of China's total area, the region's agriculture is highly productive yielding 11.5 million t/yr of grain, an amount far in excess of that produced by many provinces. The plain is now China's most important area for grain production. It is also a major silkwormbreeding area with an annual output of 50,000 t/yr cocoons. It is also noted for the production of freshwater fish, pearls and for sheep. Moreover, it produces 10 million/yr head of pigs, 125,000 t/yr of cotton, 290,000 t/yr of rapeseed, and 60,000 t/yr of various fruits. Traditional household handicraft industries, such as embroidery and woven items for everyday use, flourish, and industries run by the People's Communes and Brigades have also developed rapidly in recent years.

One reason for the high levels of agricultural productivity in the Taibu Plain region is the intensity of land use commonly found in the lower and middle Yangzi Valley. This chapter examines the condition of land resources and the present-day land use patterns in the Lake Taihu Plain. A better understanding of the land use patterns will contribute to a more rapid development in this area as well as in other densely populated regions of China, and may also be a useful example to assist in the development of many Third World regions. Two aspects of land use will be discussed in detail, intensive cropping systems and the use of hilly land.

Intensive Cropping Systems and Land Use

Almost all land on the Taibu Plain has been fully used for centuries and no large areas remain to be reclaimed for cultivation. Thus the only way to raise agricultural productivity in this region is to increase the per-unit productivity. For many years Taihu Plain farmers have made great efforts to extend the area under multiple cropping and have invested a large amount of labour to make better use of time and the limited land area. Immediately following a harvest, the sowing and transplanting of the next crops is done. No farmland is left unused for any appreciable time because of the use of double- or triple-cropping systems.

Before 1965, two crops per year (rice and wheat) were generally harvested. After six to eight years of experimenting and practice in some localities, a triplecropping system based on wheat (or rape or green manure) and two crops of rice entered widespread use in the early 1970s. As a result, intensive land-use entered a new stage. With the improvement of cultivation techniques, grain yields have increased from 6,000-6,800 kg/ha to 9,500-10,000 kg/ha, making the Lake Taihu Plain one of the most productive agricultural regions of China.

The frost-free period on the plain is about 220-245 days, and the accumulated temperature of <3C is 5,300C, higher than that needed for the triple-cropping of wheat-rice rice (5,000C). The average January temperature of 3-4C is suitable for winter wheat. The annual rainfall of 1,100-1,200 mm, which falls mostly in the summer, provides adequate water during the growing season. Such ideal conditions for multiple cropping are rarely found elsewhere in China. In north China, for example, temperatures do not permit the maturation of two rice crops per year, whereas in south China the winter temperature is not everywhere suitable for the common winter wheat. In the south, during its mature stage, wheat may also suffer seriously from excessive temperature and moisture, insufficient sunshine, and crop diseases, each of which affects yield. On the Lake Taihu Plain the high yields of wheat, rice and rapeseed are closely related to the favourable climatic conditions, dense population, efficient irrigation, prosperous economy, and intensive cultivation.

Development of the wheat-rice-rice system of triplecropping, which requires an aggregate growing period of 450 days, was complicated since even the production of two crops of rice per year requires a frost-free period of 220-245 days in a growing season of 240-250 days. Given such a serious constraint to triplecropping and the high risks of crop failure, the correct temporal organization of cropping is of the utmost importance.

Throughout the Lake Taihu Plain, therefore, the crop calendar is extremely tight. All farming tasks, including the selection of crop strains with different maturation periods (fig.5.2), are meticulously planned and scheduled for each season.

Under the triple-cropping system used southern Jiangsu Province, barley, planted in mid-November, is the major earlymaturing crop. This permits the early planting of the first rice crop, the strains of which must be high-yielding and have either an early or intermediate maturation period, whereas the second rice crop is sown and transplanted strictly according to season. Transplanting takes place as seedlings reach the earing stage.

Improvements have been made in rice-crop management. The seedlings of the middle- and late-maturing strains of the first crop are often raised after early sowing under a thin nylon cover, which gives the crops an early start. In addition, many communes have adopted a two-step method of raising the seedlings of the latematuring strains of the second crop. The first step is to raise the seedlings as usual in a seedbed. Because such seedlings require a longer growing season than do those of the first rice crop before they reach the transplant stage, some are moved from the seedbed to a temporary seedbed where they remain until ready for transplanting (fig. 5.3). They will not be transplanted until all the first crop has been harvested and after seedlings of the secondcrop rice, raised in the usual way, have been transplanted. This method makes it possible to use the original seedbed as a field for transplanting. The use of a temporary seedbed compensates for the lack of sufficient fields for rice growth, prolongs the transplanting period, regulates the tight working schedule of the growers, and saves on the space devoted to seedbeds.

At present, the Lake Taibu Plain is one of the largest areas in China where a triple-cropping system producing two rice crops per year is practiced. This intensive system has two main advantages: it effectively maximizes the use of the limited agricultural land and fully employs farm labour, and, more importantly, it has resulted in drastically increased grain yields. But a number of problems have recently become evident, especially the higher demand for labour that has followed the overexpansion of triplecropped areas. Under the present conditions of farm mechanization, most production teams require more than 1,500 working days/yr/ha of triple-cropped land. Labour demand is especially heavy at planting and harvest times. Production costs are often too high to enable commune members to increase their income. Also, the physical properties of the soil tend to deteriorate, particularly as a consequence of prolonged immersion which leads to poor aeration and to secondary gleyization. Further, in the race against time early-maturing crop strains have been overemphasized, which has contributed to a decline in crop quality. In the last several years, however, a diversified triplecropping system with two dry crops (wheat, rapeseed or green manure) plus one crop of maize, soybean or rice has been developed.

As a result of those problems, disputes have arisen about the prospects of the triple-cropping system in southern Jiangsu. There is no need to repeat the arguments here. However, it may be useful to point out that in the past the disputes centred on exposing the weaknesses of the system. The task now should be to consolidate the experience and to seek an agricultural system that would better fit the physical and economic conditions of the region and would yield a higher regional income. In the last few years, efforts have been made in the Lake Taihu Plain to reduce the area devoted to triple-cropping, which has reduced demands made on both the scarce labour and fertilizer during the growing season. On the other hand, the area under wheat has been increased, reducing the supply of winter green manures, a practice that gains profit in summer at the expense of autumn crops. Solutions to the issue of the most appropriate farming system for a region will not be found by looking only at the problems at hand. A broad perspective on the issue must be maintained, and the potential problems of the cropping system to be adopted must be anticipated. Only when all the ramifications of the cropping systems have been thoroughly studied can an optimum solution be expected to emerge.

Fig. 5.2. Stages of Grain Crop Growth in the Triple-Cropped Areas of the Taibu Plain, Southern Jiangsu Province

Fig. 5.3. The evolution

(a) Ca. 20 July. Fields devoted to three types of first rice crop (early, middle, and late maturing). A seedbed is used to raise the seedlings for the second crop. Before fields are planted to rice, they are planted with wheat, rapeseed, or a green manure crop.
(b) Ca. 25 July. The early-maturing first rice has been harvested, followed by the immediate transplanting of the second crop. Some of the seedlings are moved temporarily to a field transplanted with an early maturing second crop.
(c) Ca. 30 July. After the harvest of the middle-maturing variety of the first rice crop, a second crop of rice is transplanted. At the same time the seedling bed becomes available and is used for transplanting the second crop.
(d) Ca. 15 August. Seedlings temporarily raised in the field are transplanted to the field from which a late maturing variety of the first rice has just been harvested. Although such transplanting is rather late, it usually does not affect crop maturing since the seedling period has been long enough.

Use of Hilly Land

In Lake Taihu there are a number of small islands, and along its borders are to be found mostly quartzitic hilly areas with elevations of 100-300 m above sea-level, and some peaks higher than 300 m. These hills and islands are mostly scattered and isolated, but are important agriculturally for various kinds of fruit, including tangerine, loquat (Eriobotrya japonica), arbutus (Arbutus sp.) chestnut, plum, persimmon (Diospyros sp ), peach, apricot (Prunus sp ), pomegranate (Punica granatum), and ginkgo (Ginkgo biloba) sweet osmanthus (Osmanthus fragrans), and roses, as well as for the provision of stone used in construction. Their renowned scenery makes them a locally important recreation area. Contrary to the common belief that upland areas are economically more backward than plain regions, the economy of the communes of the densely populated hilly areas on the Lake Taibu Plain is highly developed.

Regularities of land-use occur along the East and West Dongting Hills and in the Dengwei Hills. In general, the higher elevations are under grass, below which are mixed forests and small patches of bamboo. Both the valleys and the hillsides support fruit farms where the land-use patterns are highly complex, meticulously planned and well managed. These factors are closely interrelated. The fruit farms derive their water from the dense vegetation at higher elevations, and should that vegetation be destroyed, the orchard environment would be seriously affected and production would decline.

Fruit-growing, an important form of land use in the hilly regions of the Taibu Plain, is distinguished by four main characteristics. The first is that production areas of many fruits and flowers are well defined. The sweet osmanthus flower, for instance, is a special product of the DengweiXiji Hills, one of the three largest osmanthus-producing regions of China, and its flowers are noted for their colour, fragrance, appearance, and taste. The East and West Dongting Hills are known for such fruits as arbutus, loquat, plum, persimmon, ginkgo, and chestnut. Hengshan and Yinshan islands, in the middle of Lake Taihu, produce high-quality pomegranates.

Second is that, with the exception of tangerine groves, which occupy fairly large areas devoted to one type of fruit, most fruitproducing regions grow a variety of fruits or combine fruits with such economic plants as tea and mulberry to ensure harvests and to meet market demands. In the planting of fruit trees, the following measures are taken: rough fruits (such as arbutus) are combined with delicate ones (such as loquat); nuts (such as chestnut and ginkgo) are combined with fruits eaten fresh (such as peach and plum); and trees requiring a longer growing period (such as tangerine) are combined with those requiring a shorter period (such as peach).

Such combinations are complex and display characteristics of the traditional small-scale farm economy. However, trees are arranged so that different species receive the correct amount of sunlight. Such artificial plant communities are both comparatively stable and ecologically sound.

The third characteristic is that the East and West Dongting Hills have 2,800 ha under various kinds of fruit trees. Some of the subtropical evergreen fruits are of geographical significance. The tangerines of the Lake Taihu area occupy about 1,000 ha in total, which produce 15,000 t/yr, and are located on the northern margin of the south China tangerine-producing region. The Taibu Plain is one of the three largest (and the northernmost) loquat-producing areas of China, and its arbutus production is one of the largest in the lower and middle Yangzi Valley. These three evergreen fruits all show a strong preference for hilly or valley locations where the thermal and moisture conditions are more suitable for their growth. Important in this region is the moderating effect of Lake Taibu on local microclimates, which, together with local topography, affects the growth of the evergreen fruit trees.

The final characteristic is that fruit production has been affected by market prices at different times. In recent years, tangerine production has been expanding rapidly whereas loquat, chestnut, ginkgo, plum, and peach outputs are gradually declining. Such changes affect farm land-use patterns. Tangerine production continues to expand because the market value of tangerine is high, the demand large and close at hand, and advanced cultivation techniques introduced to this area ensure a large and steadily increasing production per unit.

These characteristics facilitate study of the possibility of expanding the tangerine production areas in the uplands of the Taibu Plain. Being located in the transitional zone between the northern subtropical and central subtropical regions, the thermal conditions of the plain barely meet the requirements of the earlyripening and cold-resistant tangerine trees that are commonly grown. In the Dongting Hills, for example, the average annual temperature is 16C, the January average is 3.3C, and the low 8.9C. Normally, tangerines require an average annual temperature of not less than 15C, a January average higher than 5C and a lowest temperature of not less than - 5C. Thus the region's January average and the lowest temperature tend to be on the low side, which easily damages the fruit.

Records indicate that in the 600-year period from the Song Dynasty to the Qing Dynasty (eleventh to seventeenth centuries), the Dongting Hills suffered 12 times from frost damage, during five of which the loss was nearly total. Over the past 30 years, especially in 1955, 1969, and 1977, severe frost has also greatly reduced production. In view of the existing unstable physical conditions for the growth of tangerines in this area, great importance should be attached to the microregional differences in temperature, radiation, moisture, and wind caused by local geomorphological factors. Such considerations can play a critical role in the selection of areas suitable for tangerine cultivation. Other factors such as local experience with cultivation, the selection of earlyripening and cold-resistant strains, as well as socioeconomic conditions, are also of significance.

Based on a detailed investigation, we have compiled maps on the current distribution of tangerine cultivation, the distribution of areas damaged by frost, and on the general patterns of land use. We have ascertained that the lake islands, valleys and hillsides are the localities most suited for orange cultivation, since there the microclimate is regulated by the lake. Cultivation is also possible on some of the sunny slopes and in some valleys that do not experience the climate-modifying effects of the lake. In the interior parts of valleys, however, local conditions may either facilitate air circulation or contribute to its stagnation. With the arrival of a cold wave, the tangerines on both sides of a valley often suffer from relatively minor frost damage whereas on the floor of the valley, where the cold air penetrates easily but flows out with difficulty, the fruit is more readily damaged.

The results of our research have shown how and where to select the best areas for tangerine growing in the hilly regions around Lake Taihu as well as in the East and West Dongting Hills. A total area of about 1,700 ha is suitable for tangerine cultivation, of which 42 per cent has been rated as first-class, with excellent conditions.

At present, the Taihu Plain is entering a new stage of agricultural development. To bring into full interplay the natural and economic conditions of the region an adjustment of the structure and spatial distribution of agricultural production is now under way. Changes in land use patterns will inevitably take place. For this reason, comprehensive investigations of the land resources of the Lake Taihu Plain and a thorough understanding of the region's historical processes of land utilization are essential.

6. Salt-marsh resources of China

Song Daquan
Institute of Forestry and Soil Sciences, Chinese Academy of Sciences, Shenyang, Liaoning Province

Abstract

In China salt-marsh resources have been used for more than 4,000 years. Coastal marshlands offer a variety of ecological niches where crops. aquatic products, salt and grasses are produced. Detailed studies have been conducted along the coasts of the northern Yellow Sea and southern Zhejian Province, using LANDSAT images and aerial photographs to analyse soil and water conditions as well as land-use patterns. An interdisciplinary study should be conducted in each coastal province to understand better the resource endowment and the problems of its utilization.

Introduction

China has about 18,000 km of coastline and some 6,000 coastal islands. The coastal zone of China is ecologically complex and economically highly productive, and includes extensive marsh areas. Based on coastal geomorphology, three major categories of coast can be recognized in China: plain (deltaic), rocky, and biological.

The plain coast comprises mostly the deltas of large rivers, such as the Huanghe, Yangzi, and the Zhu. This type of coast is subdivisible into a depositional type and corrosional type. The former occurs where large quantities of silt have been deposited in estuaries, largely as a consequence of the misuse of upstream resources. In the estuaries of these three rivers, nearly 2,000 million t/yr of silt and sand are deposited, causing continuous seaward progradation. Only a few areas are corrosional-type coastal plains, the best example being the estuary of the old Yellow River, in north-eastern Jiangsu Province.

A rocky coast occurs mainly along the Liaodong and Shandong peninsulas on the Yellow Sea and the Gulf of Bohai. In south China, rocky coast predominates from Hangzhou Bay to Guangdong and Guangxi, and on the southern coast of Hainan Island, except for some estuarine and deltaic areas.

Biological seacoasts occur in northern Fujian Province, on Hainan Island, and on some islands in the South China Sea. That in Fujian Province consists mainly of mangrove and tobira (Pittosporaceae) forests, the dominant species of the latter being Aegiceras comiculatum and Scaevola hainanensis. Those in the South China Sea consist mostly of mangrove forests and coral reefs.

Salt-marsh Resources in China and Problems of their Utilization

Salt-marsh resources in the coastal plains of north and east China have been used by farmers and fishermen for more than 4,000 years. The large coastal plains formed by the major rivers of China have, over the millennia, gradually been developed into fertile agricultural lands where rice, wheat, corn, soybean, and cotton are highly productive. Abundant aquatic products are produced in the many ponds, lakes, and waterways of these plains. The population density of the long-urbanized and highly developed lower Yangzi and Zhu valleys is 100-200 persons/km

In the lower Liao delta of north-east China, where irrigation and drainage systems have been constructed and salinized soils reclaimed, the application of green manures and commercial fertilizers has greatly increased productivity, and the rice yields are now 6-7.5 Vha. In South China, sugar-cane, citrus, and rice thrive in reclaimed areas of former salt marsh. Double and triple cropping is practiced there, and average rice and wheat yields may reach 10-20 t/ha/yr 2

For centuries Chinese farmers have made tidal flats by enclosing salt marshes. Coastal marshlands offer a variety of ecological niches suitable for cropping, aquaculture, salt-making, and the cultivation of Phragmites sp. and other useful grasses (fig. 6.1). The inter-tidal zone of the higher beach, beyond 3 m in elevation, is suitable for the cultivation of rice, other crops, or for pasture. Aquaculture of prawns, clams, mussels. oysters, and razor clams can be practiced 2-3 m below sea level, where mud or silt deposits are abundant in nutrients and biological products. This middle tidal zone is also suitable for cultivating Spartina anglica, which may grow in tidal water with up to 3 per cent salt content. Because of its rapid propagation this valuable grass hastens the deposition of salt marsh and increases its depth at the rate of between 0.120.40 m/yr. This grass also protects dikes along shores, and its leaves and stems can be fed to livestock, used for green manure or for making paper.

Fig. 6.1. Schematic Diagram of Resource Potentials of Tidal Flats in South Zhejiang Province

It can also increase the fertility of the tidal salt marsh, in which the total organic matter can be increased from 1.2 to 1.3 per cent while the salt content of the surface horizons decreases 0.45-0.20 per cent. In estuaries where the salt content of the water is less than 0.5 per cent, phragmites may form reed beds.

At depths of 1-15 m below the middle tidal zone, fertile muds are suitable for the cultivation of kelp, laver (Porphyra spp.) and sea cucumber, all rich in protein. The area lying below the tidal zone, at depths of -5 to -15 m, may be several times as wide as the intertidal zone, and can be used to cultivate kelp and other edible seaweeds.

Fig. 6.2. Land Use near Yingkou City, Liaoning Province

The salt-marsh water in the upper part of the middle tidal zone has a salt content of about 3 per cent. Here salt pans may be constructed. Coastal salt production in China amounts to about 10 million t/yr. The country has more than 2 million ha of salt pans, mostly in north China, especially along Bohai and Liaodong Bays. About 20 per cent of China's salt is produced along the East China and South China Seas.

The development of salt marshes must be based on detailed studies to assist in the better understanding of the alternative uses of coastal resources; thus Chinese teams have conducted comprehensive research on the natural resources and economic conditions of the coastal zone, and have examined coastal geology, geomorphology, hydrology, meteorology, sedimentation, biology, soils, and land use. Maps of coastal resources have been prepared, based on field data, aerial photography and LANDSAT images. Researchers have studied the chemical, physical, biological, and mineralogical characteristics of the marshes. evaluated the quality of different kinds of coastal natural resources, and conducted research on the protection of the ecological systems of the coastal environment. In the final report, suggestions are made for the comprehensive development and use of salt-marsh resources in different parts of China.

Coastal Resources along the Northern Yellow Sea

Black-and-white 1:30,000 aerial photographs, 1:50,000 topographic maps and marine charts and colour LANDSAT images were used to compile soil and land-use maps along the Yellow Sea coast.3 Figures 6.2 and 6.3 show parts of land-use maps of two study areas along the coast of Liaoning Province.

Fig. 6.3. Land Use between Donggou and Zhuanghe, Northern Yellow Sea Coast

TABLE. 6.1. Salt Content of Salt Marsh Soils. Northern Yellow Sea Coast. North-east China

Type of Salt Marsh Depth (cm) Total
Salt
pH Ion Content (m.e./100g)
        HCO3-
(%)
Cl-
(%)
SO4-
(%)
Ca++
(%)
Mg++
(%)
Na++K+
(%)
Salt-marsh soil (sample from Tongkou) 0-15 1.40 7.0 0.14 20.88 2.62 0.42 2.33 20.75
15-30 1.38 7.0 0.12 20.53 2.71 0.49 2.71 20.17
30-50 1.55 7.6 0.12 22.79 3.20 0.58 2.80 22.74
50-70 1.45 7.8 0.14 21.23 0.06 0.49 2.44 21.50
Groundwater 70 49.17a 7.6 5.8a 830.9a 31.8a 39.6a 221.6a 607.2a
Salt-marsh soil with salt (Sample from Xingging) 0-15 5.86 8.3 0.33 63.42 30.20 2.091 0.39 81.47
15-30 2.65 8.2 0.38 40.31 4.03 1.23 4.92 38.23
30-50 2.82 8.1 0.28 43.65 4.03 1.23 5.47 41.26
50-70 3.07 8.2 0.38 47.50 4.29 1.35 5.90 44.92
70-100 2.60 8.2 0.40 39.80 3.94 1.17 4.49 38.48
Groundwater 135 77.70a 7.8 6.8a 1071.2a 24.8a 50.8a 224.9a 829.3a
Desalinized salt-marsh soil

(Sample from Tongkou)

0-15 0.86 6.8 0.47 11.81 1.96 0.37 1.44 12.44
15-30 0.48 6.9 0.47 6.42 1.26 0.21 0.69 7.26
30-50 0.43 6.7 0.28 6.29 0.58 0.18 0.25 6.72
50-70 0.49 6.8 0.28 6.93 0.92 0.21 0.53 7.40
70-100 0.63 6.7 0.28 8.78 1.41 0.34 0.70 9.43
Groundwater 120 31.90a - 1.4a 484.7a 23.9a 18.3a 63.8a 427.0a

a. The unit of total salt content in the Groundwater is Img/l), as is the unit of anion and cation

TABLE 6.2 Nutrient Content of Paddy Soils and Salt Marsh Soils, Northern Yellow Sea Coast, North-east China

Locality and
Soil No.
Soil
Type
Depth (cm) Organic matter (%) pH Total N (%) Total P2O5 (%) Water soluble N (mg/1009) (%) AvailableP2O5 (%) (mg/100g) (%) Available K(mg/100g) (%)
Tongkou
80-100
Paddy
soil
0-20 1.3 6.39 0.21 0.08 6.97 2.60 29.9
  20-40 1.0 6.72 0.23 0.08 5.96 2.54 47.2
  40 60 0.6 6.74 0.14 0.115 4.47 3.60 50.0
Zhuanghe
80-66
Paddy
soil
0-20 1.2 6.58 0.15 0.07 7.18 2.08 10.6
  20-50 1.0 6.69 0.15 0.05 3.87 1.22 14.2
  50-70 0.8 6.73 0.12 0.07 2.06 1.20 19.2
Tongkou
80-96
Salt
marsh
0-18 1.5 6.94 0.07 0.15 3.38 7.40 146.0
  18-45 1.3 6.52 0.05 0.11 1.98 4.38 104.5
  45 0.7 6.40 0.06 0.09 1.48 4.12 121.0
80-5 Salt
marsh
0 32 0.5 7.74 0.14 0.01 3.02 1.54 30.0
  32-62 0.2 7.72 0.09 0.02 2.15 1.32 35.6
  62-80 0.1 7.34 0.14 0.02 1.46 1.56 62.7
80-12 Salt
marsh
0-10 1.6 7.74 0.16 0.03 4.94 0.94 12.4
  10 16 1.3 8.60 0.10 0.02 3.00 0.92 12.0
  16-55 0.9 7.38 0.11 0.02 3.90 0.78 15.6

The land-use patterns of the salt-marsh region near Yingkou are shown in figure 6.2. Desalinized former salt marsh soils along the Liaohe delta are used for rice-fields. Phragmites beds and ponds are located near the estuary, the latter being used for raising prawns and fin fish. South of Yingkou City is a salt pan of approximately 20,000 ha. East of the city are extensive areas of dry farmland developed on former salt-marsh deposits and used to grow maize, sorghum, and millet, usually with high yields. Low hills with meadow brown forest soil are scattered over the plain, and support apple orchards. Larger hills with moderate slope are covered mostly by secondary forest, with Ouercus liaotungensis and Pinus tabulaeformis as the dominant species.4 Land use around the Dayanghe estuary, on the Yellow Sea coast, is shown in figure 6.3. Along the coast are salt marshes of 5-10 km in width. Some salt pans and fish ponds are distributed along the coast. The slightly elevated land is used mostly for dry farming, whereas stony hills are under broad-leaf forests, and the few small hills are planted with apple trees. Phragmites beds are located along the estuary, and rice fields are widespread in the flat lowland that has been developed from the former salt marshes. Many reservoirs for irrigation and raising freshwater fishes lie in the northern part of the area.

To evaluate land resources we analysed the salt content of different kinds of salt-marsh soils (table 6.1 ) and investigated the nutrient content of the salt marsh and paddy soils (table 6.2). The coastal paddy soils have a medium organic matter content, high N content, and modest P content. The productivity of rice is either moderately high or high. The organic matter as well as the N content of the salt marsh soils are medium to high, and the pH ranges between 6.4 and 7.7, mostly neutral in reaction. The texture of the paddy soils and salt-marsh soils ranges from silty clay loam to silty clay.

Fig. 6.4. Coastal Soils and Land Use near Wenzhou, Zheliang Province

Land Use in the Wenzhou Area, Southern Zheiiang Province

A soil and land-use map along the coast around Wenzbou, a city in southern Zheiiang Province, is given in figure 6.4. This map was prepared in connection with a 1979 comprehensive survey of the salt-marsh resources of the area, and was based on blackand-white LANDSAT images, aerial photographs, and two months of fieldwork.6,7 7 The red-earth soil sub-group (1 a) is derived

from red clay, sandstone, shales, and acidic crystaline rocks, and the Young red-earth sub-group (1 b) is derived from coarse granitic rocks. These two soils are surrounded by paddy soils, some of which have been formed from former salt-marsh deposits dating back to the Tang, Song, and Ming dynasties (about A.D. 600-1600), but for the most part the soils and the coastal plain along the East China Sea have developed only in the last 200300 years.

Paddy soils developed on clay deposits are usually old rice soils, whereas those developed on silty clay or silty clay loam deposits are usually new rice soils which are distributed behind the sea dikes. These soils are highly productive and can yield rice at about 15 t/ha/yr. On the other hand, the fertility of the desalinized paddy soils near the sea dikes is only modest, and they produce rice at a rate of about 7-8 t/ha/yr.

TABLE 6.3 Nutrient and Physical Properties of Salt March Wenzhoru Zhejiang Province

Soil type Locality and field No. Depth (cm) pH Nutrient content (%) humus Total N (%) Total P (%) Physical sand >0.01 mm (%) Physical clay <0.01 mm (%) Soil texture Clay minerals
Meadow
Saline soil
Salt marsh of Lingguan Island
  79-W-16 0-20 8.28 1.66 0.11 0.11 29.6 70 4 Light clay -
Salt marsh
Soil
Salt marsh of Wugisa 0-20 8.24 1.01 0.08 0.10 43.2 56.8 Heavy clay loam Hydrated mica
  79-W - 4 20-40 8.18 - - - 41.6 58.4 Light clay loam Vermiculite Kaolinite
Salt-marsh
Soil
Pazou salt-marsh soil 0-20 8.41 1.22 0.09 0.09 45.2 54.8 Light clay loam  
    20-40 8.16 - - - 49.0 51.0 Light clay loam  
  79-W-48  

 

TABLE 6.4 Salt content of Salt Marsh Soils, Wenzbou, Zheiiana Province

Soil type Locality and field No. Depth (cm) Total salt (%) Ion content (m.e./100g)
        CO3-
(%)
HCO3-
(%)
Cl-
(%)
SO4-
(%)
Ca++
(%)
Mg++
(%)
Na+ + K+
(%)
Meadow saline soil Lingguan Island 0-20 0.91 - 0.47 12.56 1.97 0.47 1.09 13.44
79-W-16 40-60 0.87 - 0.39 13.80 2.09 0.66 1.71 9.74
Salt-marsh soil Wugisa 0.20 1.00 - 0.37 14.06 2.32 0.82 1.74 14.20
79-W-4 20-40 1.00 - 0.32 12.95 3.31 0.89 1.76 13.93
Salt-marsh soil Pazou 0-20 0.85 - 0.33 11.94 1.93 0.62 1.50 12.09
79-W-48 40-60 1.03 - 0.43 11.62 3.03 0.76 1.80 14.52

Immediately behind the sea dikes are salinized meadow soils with a pH value of 8.28. They are calcareous in reaction. Their humus content is 1.66 per cent, and the total N and total P both 0.1 1 per cent. The texture is mostly light clay. The clay mineral composition of the saltmarsh deposits are hydrated mica, vermiculite and kaolinite, ail detected by X-ray defection and by using an electron microscope. These clay minerals are quite similar to those found in deposits near the Yangzi delta. The nutrient content and the physical properties of the salt marshes near Wenzhou are listed in table 6.3, and the salt content of the meadow saline soils and sea marsh soils is shown in table 6.4.

Conclusion

Preliminary estimates show that China has some 2 million ha of tidal flats. Research on coastal and saltmarsh resources and their proper use is still going on. It is recommended that an interdisciplinary investigation be conducted in each coastal province better to understand its coastal resources and the problems of their utilization. Such knowledge is basic to the better planning, use and management of resources.

References

1. Chen Jiyu, " Comments on the Comprehensive Survey and Rational Utilization of Tidal Flat Resources, " Ziran Ziyuan [Natural resources] 1(1979): 53-57 (in Chinese).

2. Song Daquan, "The Significance of Strengthening the Investigation and Research on China's Tidal Flat Resources and the Prospect for the Study of Coastal Ecosystems," Ziran Ziyuan [Natural resources] (1978): 48-52 (in Chinese).

3. Institute of Forestry and Soil Sciences. Chinese Academy of Sciences, Shenyang, " Using LANDSAT Images for the Study of Salt Marsh Resources in Liaoning Province." Unpublished research paper, 1973 (in Chinese).

4. Pei Yong, " Land Types along the Coast of Southern Liaoning Province, North east China." Unpublished research paper, Institute of Forestry and Soil Sciences, Chinese Academy of Sciences, Shenyang, 1980 (in Chinese.)

5. Luo Xuan, "Characteristics of Tidal Flats in Liaoning Province, and Their Improvement and Utilization," Turang Tongbao [Soils bulletin] 1(1980): 17-21 (in Chinese).

6. Cai Ouinquan et al., "Land Use in the Wenzhou Area, Zhejiang Province." Unpublished research paper, Institute of Geography, Chinese Academy of Sciences, Shenyang, 1980 (in Chinese).

7. Song Daquan et al., "Soils and Land Resources in the Wenzhou Area, Zhejiang Province, East China." Unpublished research paper, Institute of Forestry and Soil Sciences. Chinese Academy of Sciences, Shenyang, 1980 (in Chinese).


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