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.

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 km², 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 <3°C is 5,300°C, higher than that needed for the triple-cropping of wheat-rice rice (5,000°C). The average January temperature of 3-4°C 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.

(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 16°C, the January average is 3.3°C, and the low 8.9°C. Normally, tangerines require an average annual temperature of not less than 15°C, a January average higher than 5°C and a lowest temperature of not less than - 5°C. 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.