Strategies and approaches for high water use efficiency of crops

towards sustainable use of groundwater in the piedmont of

Mt. Taihang, China

 

1)Hu Chunsheng*,  1)Xiying Zhang,  2)Zhao Shidong

1)Institute of Agricultural Modernization, Chinese Academy of Sciences,

Shijiazhuang, 050021, China

2)Institute of geographic science and natural resources, Beijing, 100101, China

*:corresponding author, Tel: 86-311-5871762, Fax: 86-311-5815093

Email: xyzhang21@hotmail.com

 

 

Abstract

 

Crop yield is greatly affected by irrigation in the plain located in front of Mt.Taihang, China, where the rainfall is far less than the water needed by winter wheat and summer corn as two crops a year system. Irrigation water in this area is mainly coming from groundwater that contributes to a significant overdraft problem. Recently, groundwater table has been decreasing at the rate of about 1m per year. The overdraft problem has become a limiting factor to the sustainable development of agriculture in this region.  The main elements to lead water table decrease are precipitation decreased by 130mm since 1950, expanding of wheat area which is irrigated with groundwater, lateral flow decreased from Mt.Taihang and low WUE of crops. The most effective way to slow the groundwater table decrease is to increase water use efficiency of crops to reduce irrigation water use.

Many years experiments have been carried out to study the effects of different field management practices on water use efficiency of crops. This paper summarized the results of optimizing irrigation schedule, straw mulching, hoeing soil surface for preventing soil evaporation and management of root system for efficiency water use at Luancheng Station, China. Results showed that partially or limited irrigation schedules based on the sensitive growth stages of winter wheat to water stress didnt reduce crop yield compared with fully irrigation schedule, while the water use efficiency was greatly improved. By this practice, the conventional 3 to 5 numbers of irrigation during the growing period of winter wheat can be reduced to two or even to one number of irrigation, a great quantity of groundwater can be saved. Critical soil moisture contents at various growing stages for winter wheat has been decided for irrigation scheduling. By using straw mulching, soil evaporation could be reduced by 30%, and by hoeing soil surface to winter wheat after over-wintering, 20mm soil water could be saved. Combining all those water-saving measures, the water use efficiency of crops can be greatly improved.

 

 

Key words: Water use efficiency,  Optimum irrigation scheduling, Straw mulch, Root system, Piedmont of Mt. Taihang

 

 

   Piedmont of Mt. Taihang is typical high-yield region in North China Plain. The groundwater is basic water source for irrigation. The groundwater overdraft has led to continuously decline of water table since 70s and decline rate is up to about 1m per year(Table1). The fact raises the doubts on the sustainability of agriculture based on the groundwater overdraft in this region. How long the agricultural production of high productivity can be maintained under the water deficit? How about the sustainable yield of water resources for agriculture is? Where is way out to alleviate the crisis? What measures should be taken? These questions urgently need

researchers to give definite answer. So it is very important to study the relationship between the agricultural development and water resources exploitation, analyze the reason to lead decline of


groundwater table and put forward the strategies and approaches for sustainable use of groundwater resources.

 

 


1.  The main elements affects groundwater resources overdraft

 

1.1. Supplemental irrigation is necessary for two crops of wheat and corn one year in Piedmont of Mt.Taihang.

 

The Piedmont of Mt.Taihang, high-production agricultural plain, is a major grain production region in North China Plain, China. Soil is rich and climate is favorable for growing winter wheat and summer corn as two crops a year system in this area. However, agricultural production in the area is limited by a lack of rainfall during a large portion of the year and need supplemental irrigation. The groundwater is basic water source for irrigation.

The mean annual rainfall is about 480-500mm. The amount of rainfall fluctuates greatly from year to year, and the distribution within a year is also very uneven. About 70% of the total rainfall occurs during July to September, the growing season of summer corn. The average rainfall during the wheat growing season, which is from October to June of the following year, ranges from about 60mm to 150mm. Supplemental irrigation is required to support wheat production because the consumptive use of water by winter wheat is about 400 to 450mm(table 1). Farmers in this region generally irrigate winter wheat 3 to 5 times each season. They also irrigate corn one or two times per year(table2).

 

Table. 1. Water requirements by winter wheat calculated by Penmen equation recommended by FAO in the piedmont of Mt. Taihang, China

Month

Oct.

Dec.

Nov.

Jan.

Feb.

March

April

May

First ten days of June

Total growth period

(mm)

Etomm/day

2.2

1.3

0.9

0.8

1.2

2.2

3.6

4.6

5.1

566.9

Kc

0.85

0.92

0.54

0.33

0.24

0.42

1.14

1.22

0.73

---

Etcmm/day

1.87

1.2

0.49

0.26

0.29

0.9

4.1

5.5

3.7

----

Etcmm/month

58.0

35.9

15.1

8.2

8.1

28.6

123.1

173.8

37.2

488.2

Rainfallmm/month

22.5

8.8

6.4

2.6

6.8

11.2

18.3

34.2

16.0

126.8

Rainfall-Etcmm

-35.5

-27.1

-8.7

-5.6

-1.3

-17.4

-104.8

-139.6

-21.2

-361.4

*Eto is reference evapotranspiration calculated by Penmen equation using data from 1971 to 1998, Kc is crop coefficient, Etc= Eto*Kc. Monthly rainfall was the average from 1971 to 1998.

 

Table.2. Water requirements by summer corn calculated by Penmen equation recommended by FAO in the piedmont of Mt. Taihang, China*

Month

11 to 30 of June

July

Autumn

1 to 20 of Sep.

Total growth periodmm

Etomm/day

5.5

4.4

3.8

3.2

460.2

Kc

0.5

0.81

1.1

1.07

---

Etcmm/day

2.75

3.56

4.18

3.42

---

Etcmm/month

55.0

110.4

129.6

68.4

363.4

Rainfallmm/month

40.6

136.5

119.6

34.9

331.6

Etc-rainfallmm

-14.4

+26.1

-10.0

-33.5

-31.8

*Eto is reference evapotranspiration calculated by Penmen equation using data from 1971 to 1998, Kc is crop coefficient, Etc= Eto*Kc. Monthly rainfall is the average from 1971 to 1998.

1.2.Planting area of wheat irrigated by groundwater increasingly expand since1970's

 


The changes of monthly average groundwater table from 1974-1998 (as Fig 3) show that decline period of groundwater table is during March to Aug. which is main growth period of winter wheat. The monthly decline rate of groundwater table became much bigger especially in April since 1975 which means that amount of groundwater irrigated for wheat increased (Fig4.).

 


The groundwater table decreases with increasing planting area of wheat (see Fig5). The planting area of wheat has expanded from 8000 hm2 to 25000 hm2 since 1950 (see Fig.6). The amount of water consumption for winter wheat growth by irrigated with groundwater is important reason to lead decline of water table. 

 

1.3.The rainfall decreased by about 130mm since 1950's

 

The climate enter into drought and warm stage since late of 1960's and the precipitation decreased since 1950's (see Fig7). The average rainfall is 555.42 mm in 1950's, 514 mm in 1960's, 493.96 mm in 1970's, 436.44 mm in 1980's, 420.77 mm in 1990's. The rainfall decreased by 135mm during 1950-1990 and decreased 27 mm every 10 years. The reduced precipitation has significantly impacts on decline rate of groundwater table (see Fig8). The relationship between precipitation and decline rate of groundwater table express as follow formula.

                           Y=2.4144-0.0037X


The Y is decline rate of groundwater table (m), the X is precipitation (mm). When decline rate of groundwater table is zero, the precipitation is 652mm. Every 100mm rainfall reduced will lead 0.37m decline rate of groundwater table.

The effects of reduced rainfall on the groundwater table have two aspects, one is that reduced rainfall lead exploitation of groundwater increase and rainfall infiltration decreased, another is that reduced rainfall lead lateral flow reduced from Mt. Taihang.

 

1.4.Low lateral flow from Mt. Taihang

 

The runoff enter into the plain is decreased from 275.3 mm to 44.1 mm(see table 3), the reason is that precipitation reduced and some runoff blocked by reservoir in mountain area. Supposed the precipitation reduced 100mm in mountain, the human activities lead to reduce 130mm of runoff to plain. 

 

 

 

 

 

 

Table. 3.  The result of water resources balance estimation in Hebei Plain during 1950's-1980's 

   Year         P(mm)        RI(mm)        RO(mm)            T( )

 

  1950-1959        600.5        275.3         247.3            10.1

  1960-1969        577.5        160.7         142.5            10.2

  1970-1979        560.2        108.7         107.6            10.3

  1980-1989        496.7         44.1          11.1            10.4

 


 

It is less irrigation and rainfall season during Nov. to next Feb.. The changes of groundwater table depends on the regional groundwater resource balance. The ascending of water table is mainly caused by lateral flow from upriver region. From Fig.9, the ascending rate of water table has the decreasing trend since late of 1970's, which means the lateral flow decreased.


 

 


1.5.Low water use efficiency of crops

 

Lack of application and popularization of advanced irrigation facilities and techniques for high WUE of crops, the WUE is low compared with developed countries. According to the traditional management, seven times of irrigation in the growing season of winter wheat and summer corn are needed totally, the amount of water for each time of irrigation is about 70-80mm. The water production efficiency for this system is only 1kg/m3, which is much lower than 2kg/m3 in some of the developed countries.

 

2.      The strategies and approaches for sustainable use of grounwater resources

 

It involves many aspects to establish a water-saving system towards to sustainable use of water resources. One basic way is to reduce water exploitation such as reducing area of crops need much water for irrigation, limiting water exploitation intensity by suitable policies. Another is to increase WUE of crops such as implementing advanced irrigation technologies, selecting rational irrigation schedule and demonstrating water-saving techniques.

 

2.1 Selecting rational farming systems suitable to capacity of water resources.

 

According to analysis above, the winter wheat area has high correlation with the water table decline (Fig.5). Amount of water (about300mm) used for irrigation in growing period of winter wheat is 70% of the annual rainfall in this region. But because there is a little rainfall in the growing period of winter wheat, planting it more means exploring more groundwater. So taking the winter wheat and summer corn as the principal crops of the farming system in Piedmont of Mt. Taihang is inevitable to pose high press on the underground water resource. For this reason, dwindling planting area of winter wheat, expanding the drought-tolerate crops and establishing a farming system adapting to the limited water resource is a rational choice. According to preliminary results, if dwindling 20% of winter wheat area and applying rotation of crops (cotton-wheat-corn), the amount of water-saving could be up to 8.9%.

 

2.2  Developing comprehensive agricultural water-saving techniques and effective demonstration model

 

The comprehensive agricultural water-saving techniques are basic and effective ways to save water resources. Its approach is to reduced water resources exploitation by increasing reducing water waste and increasing WUE. These technologies include irrigation schedule, tillage system such as mulching and hoeing, drought-tolerate crop varieties, rational application of fertilizer and irrigation ways such sprinkler, drip and tube irrigation.

   

2.2.1        Optimization of irrigation schedule for high WUE of winter wheat

In the piedmont of Mt. Taihang, winter wheat is the main irrigated crop. During its growth period, approximately more than 300 mm irrigation water is needed for high yield of this crop(table 1). Average yield of this crop is about 6 to 7 tons/ha. WUE is about 13-15kg/mm.ha. Generally 3-5 numbers of irrigation are applied to winter wheat: at over-wintering, turning green to jointing, booting to heading and milky filling stages, respectively. For a grain crop, whose yield may depends as much on when water is used as on the amount, and plant water deficits do not necessarily reduce crop yields and that mild water deficits can in fact stimulate yields (Turner, 1990). This implies that partially or limited irrigation may not reduce crop yield. Figure 10 is the total water consumption(ET) of winter wheat with grain yield and WUE at Luancheng station. The results showed that the highest ET didnt produce the highest yield, and WUE is decreasing with the increasing in ET. Then it is possible to optimize the irrigation schedule to reduce irrigation water use, at the same time to achieve high yield and high WUE.


 

 


2.2.1.1  Irrigation scheduling based on sensitivity stages of winter wheat

Adequate soil moisture is essential for maximum crop production. It is well-accepted fact that the various crop development stages possess varying sensitivity to moisture stress(Turner, 1990). Figure 11 is the effects of water stress at its different growth stages on the reduction of winter wheat yield, which showed that water stress at jointing has caused the highest reduction in yield, following is from booting to flowering, while the water deficit at turning green and maturing had no effects on the crop yields. By using Jensen water production function model(Jensen, 1968):

 

Y/Y0=P(Wa/W0)ili         (1)

 

Where Y is the actual yield under partial irrigtation, Y0 is the yield under non-limiting water use from fully irrigation, n is the number of growth stages, Wa is the actual amount of water used by the crop, W0 is the non-limiting crop water use or potential water requirement, and li is the relative sensitivity of crop to water stress during the ith stage of growth (sensitivity index). The value of li for a given crop is different at the various stages of growth. A more sensitive growth stage has a higher value of li. The sensitivity index of winter wheat to water stress at its different growth period were calculated based on field results (Table 4). The highest of li appears at jointing stage. The negative li value at turning green stage and maturing may shows that at this two stages moderate water stress is favorable for crop yield.


             

Table. 4. The sensitivity index(li) of winter wheat to water stress at its various growth stages(Luancheng)

Growth stage

Turning green to start of noding

Jointing

Booting

Heading to early milky filling

Maturing

li*

-0.1213

0.3145

0.2721

0.1016

-0.087

li**

-0.09831

0.2823

0.201

0.1188

-0.0211

*:reults from 1996-1997 experiments; **:results from 1988-1989 experiments

 

Table. 5.  The effects of irrigation scheduling on winter wheat yield and WUE in 1996-1997(Luancheng)(seasonal rainfall was 87.5mm)

Irrigation time(month-day)

Total irrigation

mm

Total water onsumption (mm)

Grain field

kg/ha

WUE

kg/mm.ha

11-21

67.5

364.7

5500.6

15.08

11-21, 4-22

144.4

428.6

6900.8

16.10

11-21, 4-29

153.5

434.5

6164.3

14.19

11-21, 3-274-22

171.4

428.9

6494.3

15.14

11-21, 3-274-29

200.1

475.9

6308.6

13.26

11-21, 3-275-7

186.7

460.0

6503.3

14.14

11-21, 3-275-14

193.7

476.1

6219.8

13.06

11-21 ,4-185-14

194.8

470.1

7170.0

15.25

11-21, 4-295-22

176.7

413.2

6236.6

15.09

11-21, 3-274-225-14

252.5

474.7

6503.3

13.70

Table. 6.  The effects of irrigation scheduling on winter wheat yield and WUE in 1997-1998(Luancheng)(seasonal rainfall was 126.5mm)

Irrigation time(month-day)

Total irrigationmm

Total water consumption (mm

Grain Yield

kg/ha

WUE

kg/mm.ha

 

 

Non irrigation

0.0

299.4

5413.8

18.08

 

3-254-21

95.0

338.4

5954.9

17.60

 

3-255-20

151.3

366.0

5958.0

16.28

 

4-15

84.7

333.7

6088.2

18.24

 

3-254-215-20

175.9

375.6

5650.7

15.04

 

4-74-215-20

166.6

389.8

6066.0

15.56

 

Table 7  The effects of irrigation scheduling on winter wheat yield and WUE in 1998-1999(Luancheng)(seasonal rainfall was 60.4mm)

Irrigation time

(month-day)

Total irrigation

mm

Total water consumptionmm

Grain Yield

kg/ha

WUE

kg/mm.ha

 

 

Non-irrigation

0

323.0

5325.8

16.49

 

3-16

80

366.4

7023.8

19.17

 

4-3

80

338.2

6697.5

19.79

 

4-24

80

370.4

7058.3

19.06

 

3-44-24

160

444.2

7592.0

17.09

 

3-114-24

160

438.4

7422.5

16.93

 

3-175-6

160

399.0

6915.0

17.33

 

3-175-14

160

403.9

7344.6

18.18

 

11-214-24

160

400.3

6923.0

17.29

 

3-315-5

160

442.5

7296.0

16.49

 

11-213-314-245-5

240

478.5

6937.5

14.51

 

Table 5, 6, 7 were the results from different irrigation scheduling in three seasons. In 1996-1997 and in 1998-1999 seasons, the rainfall was less than in normal years, two number irrigation applied at jointing stage and booting to flowering stages had achieved higher yield and higher WUE than the fully irrigated treatments. In 1997-1998 season, since the rainfall was higher, a single irrigation at jointing stage achieved the highest yield and highest WUE. The results showed that the conventional irrigation practice in the region doesnt get highest yield of winter wheat, and the WUE is also very lower. So it is necessary to re-scheduling the irrigation based on the sensitivity index to water stress of winter wheat.

 

2.2.1.2  The critical soil water contents at various stages of winter wheat

Results from several studies suggest that in many situations about two-thirds of the extractable soil water can be used before the rate of photosynthesis is decreased(Turner, 1990). Sometime irrigation to replace water lost from soil may be wasteful of water. This implies that when soil moisture is higher than a certain level, decreasing of soil moisture may not reduce yield, only when soil water contents is lower than that level, water stress will begin to cause yield reduction.

 

Table 8 the critical soil moisture level (lower limit)for winter wheat at its various growth stage(Luancheng,China)

Growth stage

Seedling

Turning green to start of noding

Jointing

Booting

Heading to early milky filling

Maturing

Percentage over field capacity

60%

55%

65%

60%

60%

50%

 

Since there are varying sensitivity to moisture stress at different growth stage of winter wheat, there are different critical soil moisture levels. For example, at jointing stage, the most sensitivity stage to water stress of winter wheat, when irrigation was postponed by 7 days (soil moisture for 0-50cm decreased from 22.5% to 17.4% by volume), yield was reduced about 11%. While at maturing, soil moisture decreased to 16.5% by volume, no effect was found on yield in 1997. Table 7 is the list for the critical soil moisture level at various stages of winter wheat by summing up several years experiments at Luancheng Station.

 

2.2.1.3  The optimum irrigation practice

Based on the experimental results at Luancheng Station, the optimizing irrigation practice in the piedmont of Mt. Taihang shall be:

(1)  It is very important that soil moisture condition at sowing is good for better germination and emergence of winter wheat.

(2)  According to soil conditions to decide whether the irrigation before over-wintering is needed. If the soil moisture content is over the critical level, this irrigation can be omitted.

(3)  One number of irrigation shall be applied at jointing stage.

(4)  If rainfall is less than normal years, another irrigation shall be applied at heading to flowering stage, otherwise, this irrigation can be omitted.

By this irrigation scheduling, the conventional three to five number of irrigation practice in this region can be reduced to two numbers of irrigation or even to one number of irrigtaion, a great quantity irrigation water can be saved. Yield of winter wheat and WUE can be increased by 10% and 15-20%, respectively.

 

2.2.2        Reducing soil evaporation to increase WUE

ET is composed of soil evaporation (E) and plant transpiration (T). WUE can be efficiently improved by reducing soil evaporation. Figure 12 was the E and ET of winter wheat during 1995-1996 season measured by using large-scale weighing lysimeter(depth 2.5m, area 3m2) combining with micro-lysimeter at Luancheng Station. The results showed that about one-third of the total ET were E, for other crops, the percentage of E over ET was also nearly the same (table 9). In this region, for the main cropping pattern of winter wheat plus summer corn as two crops a year system, the total E is about 250mm annually. This value equals to three numbers of irrigation. If reducing E by 30%, WUE of crops can be increased, and one or two numbers of irrigation can be saved. This will be a great importance in easing the overdraft problem in the area.

 

Table. 9.  The percentage of soil evaporation over the total evapotranspiration for different crops(Luancheng, 1998)

Crops

Total evapotranspiration(ET)mm

Soil evaporation(E)mm

E over ET %

Winter wheat

461.8

137.4

29.8

Corn

364.6

114.5

31.4

Cotton

519.6

141.8

27.3

Soybean

328.1

77.8

23.7

Millet

319.7

73.1

22.8

Sorghum

235.5

86.4

36.7


* Soil evaporation was measured by micro-lysimeter, except for winter wheat and cotton, all other crops were planted in summer, and cotton was planted in spring

 

 


2.2.2.1  Straw mulching in reducing soil evaporation

The piedmont of Mt. Taihang is a high production area. Its straw sources are abundant. For a hectare farmland, about 15-17tons of straw can be produced annually. Some of the straw is used as composed organic manure, and others, farmers just burn them. Results from field experiments at Luancheng Station showed that the WUE could be improved by 10% when the summer corn is covered with wheat straw and the winter wheat is covered by straw either from winter wheat or corn (Table 10). The 10% increase in WUE equals about 80-100mm water saved, which is about one third of the total soil evaporation. Then it is necessary to extend this practice to the farmland in the region.

 

Table. 10.  The effects of straw mulching on increasing of WUE of summer corn(Luancheng, China)

Year

treatment

Rainfall (mm)

Irrigation (mm)

Total water used (mm)

Grain yield (t/ha)

WUE (kg/ha.mm)

Increase in WUE(%)

1987

Mulching

139.1

120

366.0

5.57

15.3

7.8

CK

139.1

120

360.3

5.09

14.1

1988

Mulching

343.2

40

312.1

4.78

15.3

10.9

CK

343.2

40

333.5

4.65

13.8

1989

Mulching

243.2

48

321.8

6.52

20.3

10.7

CK

243.2

48

345.1

6.32

18.3

1990

Mulching

393.4

0

326.0

6.32

19.4

9.3

CK

393.4

0

342.6

6.00

17.6

1992

Mulching

210.3

140

342.0

6.33

18.5

6.0

CK

210.3

140

350.4

6.12

17.4

 

For straw mulching practices, it is relatively easier to cover the summer corn with the wheat straw, since farmers usually plant maize to the wheat field ahead of 5 to 10days before harvesting of wheat. And combine harvester is widely used. After harvesting, farmers just spread the straw evenly in the field. But for covering the winter wheat using straw, it is relatively labor costing. Generally when the winter wheat grows three leaves, the straw which has been cut up is spread between rows. The wind will not blow off the straw since the existence of the wheat seedlings. Besides, the straw mulching practice can also increase soil organic contents.

 

2.2.2.2  Reducing soil evaporation by hoeing soil surface

Hoeing is a traditional practice in history in China for wiping out weeds and reducing soil evaporation. By hoeing soil surface, water transfer to soil surface can be cut off. Especially, when the winter is over, soil begins thawing, and soil water flows from deeper layer of soil to soil surface, hoeing lightly to the soil surface between rows of winter wheat can reduce soil evaporation, since at this time the leaf area index of winter wheat is very lower. Figure 13 compared of soil water contents with and without hoeing. The results showed that the water content of hoed soil was higher than the one without hoeing. By calculation, From late of February to the beginning of April, about 20mm evaporation from soil surface could be reduced.


 

 


2.2.3        Managing root system for reducing irrigation by deep tillage

The amount of water available to a crop depends both on the amount of water stored in soil profile at sowing and on rainfall and irrigation during the life of the crop (Passioura, 1983). The role of roots in miniming both water evaporation directly from soil during the growth season, and that left behind in the soil at the end of the growth season has important implication in increasing WUE and yield for limited water supply of crops.

After irrigation or rainfall, the water uptake activity of roots at soil surface will influence the proportion of the water supplied that is extracted by roots before it has been evaporated directly from soil. Generally, root length density at top layer of soil is much higher than that at deep layer of soil profile. This distribution of root system is favorable for root extracting water at soil surface, that is why sometime crop can utilize soil water below wilting point at top layer of soil, while substantial water at deep layer of soil still left at harvest, even to water limited crops. Figure 14 shows the distribution of soil moisture at sowing and harvest for non-irrigated winter wheat. Though the winter wheat had been affected by water stress, there was still some available water stored at deep layer of soil, while at top layer of soil, the water contents was nearly the same with wilting point. The water uptake pattern of crops is closely related to their root distribution along soil profile.

Availability of soil water to plants depends on how fast the roots are extracting the water. The rate of this extracting from a given volume of soil is proportional to rooting density, diffusivity of soil water and the water potential gradient between soil and root(Tinker, 1976). When soil water content is not the limiting factor, root length density (RLD) will be the main factor influencing


 


soil water utilization rate for a given soil layer. Several years experiments at Luancheng Station showed that when RLD is lower than 0.8cm/cm3 for winter wheat, the root will be the main factor limiting soil water use.(Zhang and Yuan, 1995).

Figure 15 shows the distribution of root system at harvest for winter wheat and maize in the piedmont. The average maximum root depth of winter wheat can reach 2m, for maize, it is about 1-1.2m because of its relative short growth period. Generall, the RLD of winter wheat below 80cm of soil surface is less than 0.8cm/cm3. In this high production plain, water contents of the 2m root zone is near field capacity because of the rainy season in July, August and September at sowing. And at harvest, a substantial available soil water (generally about 100 to 150mm) stored at soil layer below 1m hasnt been utilized. Then if improving the root growth at deep layer of soil, more stored soil water will be utilized by winter wheat, irrigation water may be reduced.


             

For increasing root growth at deep layer of soil, one effective method is to break the soil pan by deep tillage (Barracloghu and Weir, 1988). Figure 16 shows that the root growth of winter wheat in deep layer of soil was greatly improved by deep tillage( plough depth was 50cm) than that the conventional tillage(plough depth about 30cm) and yield was improved by 10% to the one number of irrigation treatment for the dry season of 1998-1999. More soil water was used from deep layer of soil..


 

 


2.2.4        Implementing the relatively advanced technologies like sprinkling and driping irrigation to reduce water waste as transfer and increase WUE

 

The different irrigation ways have different water transfer efficiency and different effects on water-saving. The results from Tab.11 show that spray irrigation could greatly reduce water amount of irrigation and increase WUE. The spray irrigation could increase WUE by 20% than that of the furrow irrigation. Agricultural scientists should demonstrate these advanced irrigation ways to farmers and government should increase input for improving irrigation facilities to replace the traditional method like the overflowing irrigation

 

 

 

 

 

 

Table 11  Effects of irrigation ways on the yield and water use efficiency of winter wheat*

Treatments     Rainfall  Irrigation  Consumption of  Total water use   yield       WUE

              (mm)     (mm)    soil water (mm)    (mm)       (kg/hm2)  (kg/hm2.mm)

Spray irrigation  93.6     140.0        170.8        404.4        7812       19.35

Pipe irrigation   93.6     170.0        168.2        435.8        7953       18.30

Furrow irrigation 93.6     241.6        138.8        474.0        7608       16.05   

    

*by Chen Suying.

 

2.3  Making the suitable policies to control the over use of the water resources

 

Water price is one of key elements effecting the implementation of the results. It will provide very positive influences on the water conservation and sustainable to increase the water price to control the over-exploration of the underground water resource. So local governments should develop new relative policies to ensure sustainable use of water resources.

 

 

3.      Summary

 

The yield of a crop is the outcome of myriad process occurring at many time scale((Passioura, 1976). And in many crops the extractable soil water content can be reduced by 50% before there is any influence on physiological activity leading to loss of crop productivity(Turner, 1990). Results showed that irrigation can be reduced and mild water deficits will not reduce winter wheat yield at some stages in the piedmont of Mt. Taihang in China. The critical soil water contents and the sensitivity to water stress at the different water growth stages of winter wheat can be used as indicators for irrigation scheduling. Also by improving deep root growth, more soil water stored during the rainy season before sowing can be utilized by winter wheat for the purpose of reducing irrigation water use. Other effective methods such as straw mulching and hoeing soil surface can improve WUE by reducing soil evaporation. Combining all those measures, the water use efficiency of crops can be improved. This has an important implication in sustainable utilization of the groundwater resource in the region.

For farmers to adapt those water-saving management practices, public policies are very important. Presently, farmers in this region only pay the electricity cost in drawing groundwater for irrigation. To control the descending of groundwater table, besides the field management practices, public policies, such as imposing a per-unit tax on use of groundwater, raising electricity price for pumping when water use per field area exceeds a specified amount, should also be used to promote farmers to use water-saving measures to increase WUE and to reduce the demand for irrigation water.

 

 

Acknowledgements

 

This project is jointly supported by Key Projects of Chinese Academy of sciences (KZ95T-04-01 and KZ951-A1-301), National Scientific Program of 96-006-02-03-3 and the cooperation research project of LWR!/95/07 founded by ACIAR of Australia.

 

 

References

 

Barraclough PB, Weir, AH,1988. Effects of a compacted subsoil layer on root and shoot growth, water use and nutrient uptake of winter wheat, J. Agri. Sci. Cam., 110:207-216

Carl C, 1993. Use of microlysimeters to measure evaporation from sandy soils, Agri. and For. Mot., 65:159-173.

Chen Suying et al., 1998, Effect of comprehensive water-saving techniques on water wheat in Taihang Piedmont, Chinese Eco-Agriculture Research,6(2):61-63.

Doorenboss J, Pruitt WO, 1977.  Crop water requirements, FAO Irrigation and Drainage Paper, 24, Rome.

Doorenboss J, Kanssan, A,. 1979. Yield response to water, FAO irrigation and drainage paper, 33 Rome, 1979, p193.

English MJ, Nakamura B, 1989. Effects of deficit irrigation and irrigation frequency on wheat yields, J. Irri. Drain. Eng., ASCE, 115:172-184.

Ghahraman B, Sepaskhah AR, 1997. Use of a water deficit sensitivity index for partial irrigation scheduling of wheat and barley, Irri. Sci., 18:11-16.

Hu Chunsheng et al., modeling dynamics of groundwater in Luancheng County, Progress in Geography, 17(supp.): 26-31.

Hu Chunsheng et al., An analysis on structure succession of farmland ecosystems and its function changes in Luancheng County, Chinese Eco-Agriculture Research, 6(2):51-54.

Jensen ME, 1968. Water consumption by agricultural plants, in: Kozlowski TT(ed.), Water deficit and plant growth, Vol.2, Academic Press, New York, pp1-22.

Liu CM, Zhang XY and You MZ, 1998. Determination of daily evaporation and evapotranspiration of winter wheat field by large-scale weighing lysimeter and micro-lysimeter, J. of Hydrology, 10:36-39 (in Chinese).

Passioura JB, 1983. Root and drought resistance, Agric. Water Mana., 7:265-280.

Zhang XY, Yang XL, 1995. Afield study on the relationship of soil water content and water uptake by winter wheat root system, ACTA Agriculturae Boreali-Sinica, 10(4):99-104 (in Chinese).