| The Hetao Irrigation District(HID)is an important food production area,where irrigation is essential for agriculture.Because of water shortages,it is crucial to study the suggested border irrigation schedule,the sprinkler irrigation mode,the conjunctive use of saline and non-saline water irrigation mode,and to adjust cropping structure to preserve the water resource and maintain sustainable crop production.In addition,it is significant that changing ditches to pipe drain,which would increase the number of cultivated lands and ensure agriculture production.In this study,a distributed Soil-Water-Atmosphere-Plant World Food Studies model(SWAP-WOFOST)was conducted sensitivity analysis,calibration and validation;and then used to simulate water productivity(WP)for spring wheat,spring maize,and sunflower under the suggested border irrigation schedule,the sprinkler irrigation mode,the conjunctive use of saline and non-saline water irrigation mode,and the suggested pipe designs of farmland drainage in the HID during 2000-2010;finally,the recommended cropping structures were zoned respectively based on improving WP in the above different simulation scenarios by the "Z-Scores normalization" method.The main research contents and results are as follows:First,for calibration,the general agreement between the simulated and measured data suggested that the model reasonably simulated soil moisture,salinity,and crop growth at the five experimental stations.For validation,the model performed rationally with regard to crop yield,field evapotranspiration,groundwater depth and drainage amount on a regional scale.In a word,the calibrated and validated model has the potential to help in future decision making for irrigation and drainage management in the HID,Second,based on the suggested border irrigation schedule,if all the cultivated lands were planted with a single crop,the average annual amounts of irrigation in the suggested border irrigation scenario for spring wheat,spring maize,and sunflower were about 38.2%,5.3%,and 21.9%lower,respectively,than those in the basic scenario.At the same time,the average annual crop yields of spring wheat and sunflower increased by about 11.2%and 5.3%,respectively,whereas the spring maize yield decreased by about 0.9%,compared with those in the basic scenario.The average annual WPs of spring wheat,spring maize,and sunflower changed by about 2.3%,-0.4%,and 3.8%,respectively,compared with those in the basic scenario.In the recommended cropping structure based on the suggested border irrigation schedule,the average annual yields of spring wheat,spring maize,and sunflower increased by about 17.3%,1.2%,and 10.5%,respectively,and the WPs increased by about 9.5%,3.7%,and 16.5%,respectively,compared with those in the basic scenario.On the whole,the multiyear(2000-2010)average amount of field irrigation water(irrigation amount xcultivated areas)could be saved was about 4.890×108 m3 in the suggested border irrigation scenario,and the estimated the total amount of irrigation water required for agriculture was approximately 3.939×10 m3 per year in the HID,which reduced by about 21%compared with present irrigation amount from the Yellow River.Third,based on the sprinkler irrigation mode,if all the cultivated lands were planted with a single crop,the irrigation amounts in the sprinkler irrigation scenario for spring wheat,spring maize,and sunflower were about 45.8%,0.8%,and 41.8%lower,respectively,than those in the basic scenario.At the same time,the crop yields of the three crops were changed by about 8.3%,2.7%,and-0.7%.The WPs of spring wheat and sunflower were increased by about 0.9%and 1.9%,respectively,whereas the spring maize WP was decreased by about 1.5%,compared with those in the basic scenario.Compared with those in the suggested border irrigation scenario,the irrigation amounts in the sprinkler irrigation scenario for spring wheat,spring maize,and sunflower were changed by about-11.6%,6.1%,and-26.2%.At the same time,the crop yields of the three crops were changed by about-3.1%,3.7%,and-5.0%.The WPs of the three crops were about 1.4%,1.1%,and 1.2%lower,respectively,than those in the suggested border irrigation scenario.After division in the sprinkler irrigation scenario,compared with those in the basic scenario,the annual average yields of spring wheat,spring maize,and sunflower were increased by about 16.9%,8.0%,and 11.4%,respectively,and the WPs were increased by about 7.9%,5.0%,and 14.1%,respectively.At the same time,the multiyear(2000-2010)average amount of field irrigation water could be saved was about 4.090×1008 m3 after zoning in the sprinkler irrigation scenario.Compared with those in the suggested border irrigation scenario,the annual average yields of spring wheat,spring maize,and sunflower were increased by about 2.1%,10.%,and 3.6%,respectively,and the WPs were increased by about 4.7%,5.8%,and 3.7%,respectively.Meanwhile,the multiyear(2000-2010)average amount of field irrigation water could be saved was about 0.200×108 m3 after zoning in the sprinkler irrigation scenario.As above the estimated the total amount of irrigation water required for agriculture was approximately 4.215×109m3 per year in the HID,which reduced by about 16%compared with present irrigation amount from the Yellow River.Fourth,the conjunctive usage of saline and non-saline irrigation water mode based on the allowable yield of shallow groundwater,if all the cultivated lands were planted with a single crop,the annual average crop yields and WPs of spring maize and sunflower basically maintain stable,only changed by about-1.2%and-1.6%,and the annual average yield and WP of spring wheat approximately decreased by 12.4%and 12.3%,compared with those in the basic scenario.Moreover,the averaged root-zone salt would not continuously accumulate for the period of 2000-2010.After division in the conjunctive usage of saline and non-saline water scenario,the annual average yields of spring maize and sunflower were approximately increased by 5.3%and 8.2%,and the annual average WPs were approximately increased by 2.6%and 7.6%,but the yield and WP of spring wheat was only decreased by about 0.2%and 5.5%.On the whole,the multiyear(2000-2010)average required groundwater amount was about 3.970×108m3 per year,which was in the range of the allowable yield of shallow groundwater in the HID,therefore,annual average groundwater depth would maintain stable.The estimated total average amount of required irrigation for agriculture was about 4.082×109m3 per year,which reduced by about 18%compared with present irrigation amount from the Yellow River.Fifth,based on the suggested pipe design of farmland drainage,if all the cultivated lands were planted with a single crop,the average annual yields of spring wheat,spring maize,and sunflower were about 15.1%,1.7%,and 7.8%higher,respectively,than those in the basic scenario,and the WPs increased by about 6.5%,1.1%,and 5.1%,respectively,compared with those in the basic scenario.After zoned under the suggested pipe design of farmland drainage,the average annual yields of spring wheat,spring maize,and sunflower increased by about 18.6%,7.1%,and 10.6%,respectively,and the WPs increased by about 13.2%,4.9%,and 9.7%,respectively,compared with those in the basic scenario.In general,the suggested border irrigation schedule,the sprinkler irrigation mode,the conjunctive use of saline and non-saline water irrigation mode,and the suggested pipe design of farmland drainage and the corresponding recommended cropping structures in this study could provide the references to decrease agricultural water usage as well as maintain sustainable food production in the HID. |
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