(Gansu
Desert Control Research Institute, Wuwei 733000)
1 Preface
Drought is a global
problem. The arid area in the world is over 3.0×107km2, making up 20% of the total area. The
arid area in China, covers 1/4 of the total area of land territory (excluding
the semi-arid area), is mainly distributed in northwest China (in the west of
Helan Mountain-Wushaoling region).
Water shortage is
one of the main constraints for the economic development in arid areas.
However, its very
important for the arid areas to promote public awareness rising in water-saving
so as to develop the social sustainability.
Great efforts on the research, demonstration and extension of water resource management, rational allocation of water resources and water-saving irrigation technologies have been made in many arid provinces/regions, and a series of efficient measures on these issues have been worked out. All these measures and technologies have been widely applied in agriculture, forestry and animal husbandry productions, and great social and economic benefits have been gained, which made great contribution for the development of arid areas in the world.
2.1 Improve the water-saving irrigation regime
There are great
problems in the crop irrigation in arid areas. Intensive and irrational water
resource allocation and management have caused great waste of water resources.
In order to solve the problems, a method named four changes and one establishment is generally adopted, that is to change the water allocation regime
(from regional allocation to channel allocation), to change the rotation flow
method (from centralized one to dividing into groups), to change flood
irrigation into ditch irrigation or strip irrigation, to change water charge
unit (from mu to m3) and to establish and strengthen the water
management organization.
In addition, its essential to make rational water-saving irrigation regime based on
local conditions and crops grown, and to comply seriously with the regime so as
to reduce the leakage and infiltration in the soil and to raise the water
utilization efficiency. The trials of wheat, maize irrigation in the oasis of
Hexi corridor show that if the regime can be complied with seriously, 2-3 times
of irrigation can be reduced and 30-40% of water can be saved, comparing with
the traditional irrigation regime.
2.2 Rational
water reservation for irrigation
In
arid areas, water reservation is widely applied for the crop irrigation in
spring and growing season, and to relieve the contradiction of water usage in
summer. The research shows that in the oasis of Hexi Corridor, the optimum
water need to be reserved is 1,200-2,250m3/ha, and irrigation quota
is 1,200-1,500m3/ha in winter while 1,800-2,250m3/ha
in summer and autumn. Comparing with the traditional irrigation quota of
2700-4500m3/ha, 1,500-2,250m3/ha water can be saved.
There is a great potential to save water.
2.3 The complementary utilization of surface and underground water
for irrigation
In arid areas, the surface runoff is less from April to June while more from July to September, this will cause the lacking of irrigation water from April to May. For example, in the oasis of Hexi Corridor, the runoff of surface water from April to June is only 22-27% of the total in whole the year, while crops water requirement in this period accounts for 50-60% of the total in whole the year; from July to September, the runoff is 45-50% of the total. Thus, its essential to extract the underground water to irrigate crops, combining with the surface water; and to adjust the proportion of summer and autumn crops (from concurrently 7:3-8:2 to 6:4) so as to make full use of the surface water resources in July and September.
3.1 Technologies on preventing channels from leakage
Limited
by the economic conditions, most of the channels in arid areas were built with
earth, this caused the great loss of water from leakage and evaporation and the
water utilization ratio is only more or less than 50%. In recent years, U-shape
concrete channels are widely used in Xingjiang, Gansu, Ningxia, Shannxi,
Qinghai, etc. and great effect has been gained.
As
the channel size and channel grade are different, the design standards of
U-shape concrete channels are different. Take the sublateral canal as an
example, its flow control range is 0.3-1.5m3/s, the bottom slope of
the channel can be changed based on the surface relief condition, but generally
is 1/50-1/2000, the roughness coefficient of the prefabricated face is over
0.013, the ratio of depth and width of channel section is 1.0 to 1.2, the
radian angle of channel bottom is about 163°, the channel body, with the thickness of 5-15cm, is made into
70-100cm long prefabrication with 150# concrete or made directly.
U-shape
concrete channel has the optimum water section, good flow conditions and fast
flow; and its very
strong in the conveying of water and sands; it has high cold-resistance and
need little invest. Comparing with channel built with earth, it can reduce 75%
of water leakage, and comparing with ladder-shape channel built with concrete,
water loss can be reduced by 3.7% per kilometer. U-shape channel is very useful
in preventing water from infiltration.
3.2 Irrigation
through low-pressure pipes
Its a new water-saving technology to irrigate fields with low-pressure
water through pipes instead of channels. The pipes are PVC pipe with the
diameter of 110-160 mm and the thickness of 1.8-3.3 mm. The qualified pipes
should be made complying with the following 5 indexes:
(1) pull resistance
δ≥42MPa
(2) flat rigidity PS = (0.92-0.64)×105kPa
(3) shock
resistance of low temperature, over 20N.m
(4) explosive
resistance of momentary inside pressure (20-14)×105KPa
(5) elasticity modules E = (3.1-3.9)×103MPa
After being selected, the pipes will be installed according to the irrigation design. Pipes are generally buried under the ground and above frozen earth. The furrows should be straight and can not be deviated±3。 from central line, and the furrow bottom is arc-shaped. Pipes are connected through thermoplastic stress method and the temperature should not be over ±3。, the length of lap joint is 1.2 -1.5 times of pipe diameter.
Irrigation through low-pressure pipes can save energy and land, reduce evaporation and leakage, and is convenient for management; PVC pipes are easy to transport as they are light, it is corrosion-resistant and need little invest. So, theres a great potential to extend this technology.
3.3 Irrigation
through permeable pipes
With this kind of irrigation, water can seep into soil through special permeable pipe, and then provides moisture to plant root according to the movement dynamics of water in the branch pipes. Pipes for permeable irrigation are usually made from PVC pipe, brick and clay products. The property and water power of pipes are different as they are made from different materials. As far as clay product concerned, it has good permeability and corrosion-resistance and need little invest.
The pipes are generally buried under the ground and the depth depends on the soil characteristics and plant species, etc., generally is 40-60 cm. When installing, pipes should be straight and flat and the lap joint should be fixed. Permeable irrigation is efficient to reduce evaporation and invalid leakage and can save water, land and energy. Comparing with traditional flood irrigation and ditch irrigation, it can save water by 83.1%, 63.1%, respectively.
3.4 Strip
irrigation
Its one of the field irrigation applied in arid areas. The technical
points of this irrigation are fine preparation of land, reasonable design of
irrigation area and to control the flow and time of irrigation water.
Irrigation area generally is ( 30-100)×(2-4)m2, water flow entering into the unit area should be
controlled within the range of 3-6L/s/m, and the slope of each plot is
0.001-0.003. Table 1 analyzes the relationship between land area and irrigation
effect.
|
Land area (m2) |
66 |
133 |
213 |
300 |
400 |
660 |
1,200 |
2,241 |
|
Irrigation quota (m3/m2) |
0.510 |
0.528 |
0.543 |
0.556 |
0.589 |
0.615 |
0.622 |
0.642 |
|
yield(kg/m2) |
0.637 |
0.636 |
0.631 |
0.664 |
0.623 |
0.624 |
0.610 |
0.593 |
|
Irrigation effect (kg/m3) |
1.25 |
1.20 |
1.16 |
1.14 |
1.06 |
1.01 |
0.96 |
0.92 |
The result shows that strip irrigation can increased crops yield by 10.9%, 11.7% and 29.1%, respectively, and with the same yield, water can be saved by 13.73%, 22.9% and 48.43%, comparing with plot irrigation, flood irrigation and series irrigation.
3.5 Irrigation on plastic film strip
This technology is
to change the flowing water from beside the film to on the film and water crops
through the holes (used for the ventilation of seedlings). Its a partial irrigation as it water crops through holes, just like drip
irrigation. Comparing with the irrigation beside film and without film,
irrigation on the film is useful to make the irrigation uniform and raise the
quality. Irrigation on the film is an advanced water-saving technology, its suitable for arid areas as it need little invest, can raise yield,
is easy to operate and to control the water flow, can speed water flow and
reduce the water loss from leakage and infiltration.
The technical
points of this kind of irrigation are soil types, field slopes, irrigation
intensity, water flow and its speed, irrigation area, irrigation quota and
irrigation time, etc.. Irrigation intensity is relevant to water flow and soil
characteristics, and can be calculated with the formula: q = 0.001 knvw
where
q=irrigation intensity L/ (N.m), k=coefficient
of side infiltration, it has direct proportion to the water on the film and
adverse proportion to the length of plot. For those without side infiltration
belt, k = 1.48 1.86, average is 2.66;
n - holes on the film of each meter,
including the holes for the seedling ventilation and holes special for
irrigation;
v - infiltration speed of soil. It
reduces with the increasing of irrigation times and can be defined through
field measurement, cm/h;
w - average area of irrigation holes, m2.
This technology has been extended at a
large scale in such arid areas as Gansu and Xingjiang. Comparing with
traditional irrigation, it can save water 40-60% and can raise yield by 25%. Concurrently,
the main forms of filmstrip irrigation extended in Gansu, Qinghai and Xinjiang
are as follows:
A. Strip irrigation on the plastic film
Plant crops in the
strip and cover it with plastic film. When irrigation, flow water into the
strip, water will flow on the film and infiltrate into soil through holes. It
includes strip irrigation on the plastic film with ridge and strip irrigation
on the plastic film through holes.
B. Furrow irrigation on the plastic film
Prepare
the land as intervals of ditch and ridge, put film at the bottom and back of
ditch, plant crops there. This pattern is especially suitable for melons and
vegetable plantation. Ditch size depends on different crops, e.g., for the
seed-melon plantation in Minqin, the ditch is 30cm deep, 40cm wide for upper
mouth and the interval of furrows is 90cm.
3.6 Drip-irrigation technology
Drip irrigation is
an advanced mechanical technology for water-saving. It is to water the soil
near the crops roots timely and quantitatively based on the crops water
requirement and through the pipes and the dripper fixed at the end of pipe.
Drip irrigation system is composed of water source, capital section (pump,
power, filter, fertilizer injector, measurement meter), water-conveying pipes
and dripper.
The advantage of
drip-irrigation is that the dripping water will just wet the soil with the
force of capillary without destroying soil structure, thus, the moisture, air,
fertilizer and heat are always suitable for crop growth. Drip irrigation,
almost with no water loss caused by deep leakage and evaporation, is the best
one among various technologies in watersaving.
China has now had
its own drip irrigation products through the study and introduction of advanced
technologies outside China. For example, drip irrigation in Yanshan has been
widely used in the irrigation of crops, melons, vegetables and the shelterbelt;
at Wuhai railway station, drip irrigation is applied in the afforestation for
desert control along the railway and great returns have been gained. They
installed the 0.99 mm pipes at the roots of 1.12 million of Caragana korshinskii, Headysarum scoparium, C. mongolicum, this
can raise the well utilization efficiency by 4 times and save money 0.65
million RMB Yuan per year. In Minqin of Gansu, drip irrigation is applied in
the plantation of seed-melon and there are great economic and ecological
returns. Not only can the yield be raised by 32.8%, also water and labor can be
saved by 62.8% and 37.7%, respectively, input can be reduced by 2.8%.
3.7 Spray irrigation technology
It is to divert water into field through the pressure pump or water
drop, and then spray water evenly through spray head. It is mainly used in the
big farm in arid areas and in those places where land is plain, water
permeability of soil is good and difficult for flood irrigation. Concurrently,
three forms of spray irrigation as fixed one, semi-fixed one and
equipment-moving one are extended at a large scale in China. Comparing with
flood irrigation, spray irrigation can save water by 30-50% and raise yield by
10-30%.
4.1 Preservation of soil moisture
It
is to preserve soil moisture by deep plowing, loosing soil, compacting,
harrowing, inter-cultivation, weeding, fertilizer application, improving soil
structure, etc. to enlarge vital soil, to increase the speed and amount of
rainfall, to reduce runoff loss and water evaporation. Thus not only the
rainfall conservation capacity can be strengthened; also water evaporation can
be reduced. So, its a
very efficient measure for watersaving.
4.2 Cover field with plastic film and crops straws to save water
Cover field with plastic film and crop straw can reduce water evaporation and surface runoff, preserve soil moisture, raise ground temperature, and improve soil fertility. It is useful to raise water utilization efficiency and increase crops yield. At present, this technology is widely applied in arid areas, and plastic film covering technology has been extended successfully in the plantation of vegetables, cotton, melons, sugar-beet, maize and wheat, etc. with the area of 6.0×104ha
Research shows that the technology on crop cultivation through plastic film is an effective measure to save water and increase yield. It can increase the moisture in the soil by 1- 4%; in arid areas and during the growing season, it can save water 1,500-2,250m3/ha and increase yield by 30-40%. In the irrigation areas of Hexi oasis, comparing with the traditional pattern, wheat planted in the plastic film can reduce 1-2 irrigation, irrigation quota is only 2,250-2,700 m3/ha, which can save water 900m3 per ha In the same conditions, comparing maize without film, maize with film can save water 1,950m3/ha, increase yield 975 kg/ha, yield increasing rate reaches 11.5%, water efficiency raise 1 kg/m2 For cotton with plastic film , through the irrigation on the film, over 2% water can be saved. With the same yield, wheat, cotton and maize plantation with the covering of crop straws can save water by 23.3%, 14.2% and 29.8%, respectively, comparing with the traditional pattern.
Gansu Desert Control Research Institute is implementing an UNDP donor-assisted project-Gansu Integrated Desert Control and Sustainable Agriculture, trials within the project show that through the application of plastic film covering technology, 3.5×107m3 water can be saved per year, which is equal to 1/3 of the over-exploited underground water in Minqin per year. The effect of water-saving is very great.
4.3 Chemical measures for water-saving
Reasonable
utilization of chemical agent for moisture preservation is useful to restrain
over-evaporation, improve the moisture preservation in the soil and strengthen
root system to absorb moisture in deep soil. The chemical agent widely used in
arid areas are: agent for moisture
preservation in the soil, invented by
Chinese Academy of Sciences; yellow acid, invented by Chinese Academy of
Agriculture Science and ABT root-promoting agent, invented by Chinese Academy
of Forestry. These chemical agents have all played an important role for crops
growing, e.g., the wheat and maize seeds, after the treatment of agent for moisture preservation in the soil,
the emergency rate raised 10-20% and yield increased 15-25%; applying yellow
acid, the evaporation rate of leaves can reduce by 19-27%, water consumption in
the field reduce by 7-9%, yield increase by 9-12%, water utilization efficiency
raised by 25-35%; if seeds treated with ABT root-promoting agent, the rate of
water conservation can raise over 20%.
4.4 The selection of drought-resistance species
The selection of drought-resistance species is essential for the development of water-saving agriculture and forestry in arid areas. Based on local conditions of rainfall distribution, drought occurrence regular and moisture characteristics, select species that need little water and can fully absorb moisture, and enlarge the area of autumn crops. For example, Haloxylon ammondendron, planted at a large scale in the afforestation for desert control in arid areas, has very strong ability of drought-resistance and has played an important role in the establishment of “three north shelterbelt”in China and the fixation of sand dunes. The research shows that through the selection of drought-resistant species, water utilization efficiency can be raised by 1.5-2.25 kg/(mm·ha) yield increased by 15-30%.
5.1 Reasonable allocation of water resources
It is to make a comprehensive assessment of water resources and then put forward a reasonable regime for the full use of water resources so as to raise water utilization efficiency. For example, Lanzhou University and other institutions conducted researches on the allocation of water resources in agriculture, industry, forestry and animal husbandry in Hexi irrigation areas, then put forward a regime of rational allocation of water resources in Hexi region in light of local water resources. This has provided a scientific base for the reasonable utilization of water resource in Hexi region.
5.2 The utilization of underground water
In the arid areas of northwest China, (2.0-3.0)×1010m3 underground water can be exploited per year. So, its very important to exploit underground water reasonably at a premise of maintaining the ecological balance of underground water.
Its also important on how to exploit underground water. Reasonable exploitation can avoid excess exploitation and waste. The research shows that the distance between single wells should be over 500-800m, between group wells 300-500m. However, something wrong has been done in the exploitation of underground water in recent years, e.g., its not suitable to dig wells in such areas as Minqin of Hexi Corridor, Andonghu region of Shule River basin and the downstream of Tarim River, etc., the exploitation of underground water in these places led to the decrease of water table, the degradation of underground water and eco-environment.
1. Chen Longxiang, Qu Yaoguang, 1992. Rational Development and Utilization of Water Resources in Hexi Region, Science Press;
2. Li Baoxing, 1982. Rational Development and Utilization of Underground Water in Arid Areas of Northwest China, Journal of Desert Research, 2 (1).
3. Li Shouqian, Lan Nianjun, 1992. Research on the Crops Water Requirement and Water-Saving Irrigation. Gansu Scientific Technology Press, Lanzhou.
4. Li Yingneng, 1998. Research on the Water-saving Agriculture in China. Water-saving Irrigation, 2.
5. Mi Menen, 1998. Technology of Irrigation on Plastic Film, Water-saving Irrigation, 2.
6. Tang Xingxin, 1992. Water-saving Technology in Agriculture, Water & Electricity Press, Beijing.