|Freshwater Resources in Arid Lands (UNU, 1997, 94 p.)|
|4: Water resources and agricultural environment in arid regions of China|
Water resources are the most important condition for agricultural development and hence economic development and progress of the society in arid regions. Water management and utilization have made great contributions to agriculture, but were accompanied by some environmental and social problems because of the misuse of water resources. At present, developing agricultural production is limited by the degree to which the water supply occurs in the right amount and at the right moment in the arid regions of China. Consequently, the urgent challenge before us is the improvement of water management and utilization, which not only is required to ensure the sustainable development of the economy, but also is needed to protect the agricultural environment. Some suggestions based on typical examples of good water management in the region can be made as follows.
1. Take the Continental River Basin As an Integrated Ecological System to Unify Water-Use Planning with Due Consideration for All Concerned
In the arid regions, the formation, distribution, and transformation of water resources originate from each continental river basin through the link between surface run-off and groundwater, which constitute an integrative valley ecosystem from the upper to the lower reaches of the river. The oasis agriculture in the river basin depends on the water supply. Any unsuitable water use will cause an imbalance of the ecosystem and environmental degradation, and consequently endanger the agricultural production. So it is a vital task to take the river basin as a whole ecosystem to unify the water-use plan. In accordance with the principles of overall consideration of all factors in the upper, middle, and lower reaches of the river, of unified management and utilization of surface and groundwater resources, and of centralized distribution of water supply along the river, the former intensive water use should be regulated and the scope of land use should be maintained at the level of the maximum water capability for irrigation. A good example is the well management of the Manas River basin in the south-western fringe of the Gurbantunggut Desert in Xinjiang in the aspects of water use and water-conservation projects.
Figure 2 Diagram of Degradation of the Agricultural Environment by the Misuse of Water Resources in the Arid Regions of China
2. Increase the Utilization Ratio of Water Use and Establish a Stable and Highly Efficient Artificial Ecosystem in Each River Basin
In the arid regions, agriculture can be practiced only in the oases, and over 90 per cent of farmland relies on irrigation. The average grain yield is 2,100-2,500 kg/ha, but 3,700-4,000 kg/ha in many high-yield fields (Wang and Zhu 1989).
The land's productivity has a great potential to be exploited. Under the present conditions of available water and favourable heat and light resources, along with gigantic efforts to increase the production so as to increase the multiple crop index, to choose crops in the light of water-supply variation in different seasons, to ameliorate the soil, and to control salinization, a stable and highly efficient artificial ecosystem will not be so difficult to establish. Again, the example is the artificial oasis ecosystem in the Manas River basin in Xinjiang. Here, the utilization ratio of water use was increased to as high as 85 per cent in the 1980s. The areas of artificial oasis agriculture expanded from 1,200 km² in the 1950s to 7,200 km² in the 1980s.
3. Improve the Conveyance System and Irrigation Technique
Although many water-conservation facilities have been constructed, most of them still need to be completed by adding conveyance systems, and the trunk and branch canals also have to be treated with seepage-proof materials, so that more benefits of water use can be obtained. For example, in the Shihezhi reclamation area of Xinjiang, the irrigation system with over 40 per cent seepage-proof canals has effectively saved water since the canal utilization coefficient reached 0.63 and the irrigation quota decreased to 5,460 m³/ha.
The irrigation techniques, such as flood and string irrigation, are very backward in the arid regions, too, which results in the large gross quota of irrigation (table 9); capital construction on farmland and better techniques (furrow and border method of irrigation) should therefore be carried out. A series of experiments on the Yarkant River of Xinjiang shows that the gross quota of irrigation could be decreased on average to 2,300 m³/ha when the better technique was practiced, and about 3.87 x 108 m³ of water could be saved annually over a total of 167,000 ha land if spring-sown crops were adapted to the border method of irrigation along the river only. Information regarding the advanced technique of spray and drip irrigation should be spread and applied, although we would not expect that to be on a large scale at present because of the higher cost.
4. Protect the Natural Vegetation and Develop an Artificial Shelter Belt for a Better Agricultural Environment
The oasis is the foundation of agriculture. But only 3-15 per cent of the river basin area is constituted by oases in the arid regions, which are surrounded by deserts and face many natural disasters such as drought damage, frost injury, hail, flooding, sandstorms, dry and hot winds, and wind erosion. Vegetation serves to withstand these disasters; thus, on the one hand, it is a foundation to safeguard the stability of the oasis and on the other hand it is the most stable part of production in the arid ecosystem. It is, consequently, very necessary to ensure a volume of water for use on woodland and range land, which will certainly have the effect of protecting the oasis ecosystem.
Based on the experience of oasis shelter-belt construction in the arid regions, the forestry should keep a certain proportion in the oasis area. In the Shihezhi reclamation area of Xinjiang, the shelter-belt covers 7-15 per cent of the irrigation area on the edge of deserts and 5-10 per cent in the oases. In the Hexi Corridor Region the proportion is 5-10 per cent. Under normal conditions, the shelter forest is planted along the canal or around the crop land, so the seepage water from the canal and land can be used by the forest. That being the case, the forest can fully save and utilize the farmland irrigation water, as well as providing biological drainage to avoid salinization. At present, the total forest land in the arid regions comprises about 5-10 per cent of irrigation land, which still should continue to increase. The water supply for the shelter-belt and woodland should be about 10 15 per cent of total irrigation water in the oases.