Study On Irrigation System And Comprehensive Effects Of Shallow Covered Drip Irrigation For Maize In Tongliao City,Inner Mongolia

Due to the stresses of low agricultural irrigation efficiency and excessive groundwater extraction,Shallow Covered Drip Irrigation Project was completed which replaced the traditional surface irrigation（pipe irrigation）in 6.73×10⁴hm² farmland in Keerqin district of Tongliao City,in recent years.Improving the system of shallow covered drip irrigation for water saving and high yield,and studying the comprehensive effect of shallow covered drip irrigation technology can provide theoretical and practical basis for its promotion.In this experiment,choosing"Jingke 968"as the test object,experimental study on irrigation system of maize was carried out.Setting up shallow covered drip irrigation[SCDI-ck(3000m³·hm^-2),SCDI-1,SCDI-2 and SCDI-3 irrigation amount were 80%,65%and 50%of SCDI-ck respectively],and pipe irrigation[SI-ck(3750m³·hm^-2),SI-1,SI-2 and SI-3irrigation amount were 2700m³·hm^-2,and water control was carried out successively in the spinning-grouting,the tassel-spinning and the jointing,and SI-0 was irrigated in the sowing].The effects of different water deficit treatments on maize growth,yield and water use efficiency under two irrigation modes were analyzed,and the best irrigation system was determined.According to the field investigation and groundwater monitoring data in Keerqin district,and taking the conventional pipe irrigation as the contrast,the comprehensive benefit evaluation of the shallow covered drip irrigation project was carried out from the aspects of water saving,economy and ecology.And the change and impact of groundwater depth were analyzed.The main conclusions were as follows:（1）With the growth period,the plant height and leaf area index of maize increased first and then decreased slightly,while the dry matter accumulation increased gradually.Under shallow covered drip irrigation,the plant height,leaf area index and dry matter accumulation of maize were positively correlated with the irrigation quota,which showed as SCDI-ck>SCDI-1>SCDI-2>SCDI-3.Except for the jointing stage,the plant height,leaf area index and dry matter accumulation of SCDI-ck and SCDI-1 were higher than those of pipe irrigation.Under pipe irrigation,the effects of different water deficit treatments on maize growth index was basically the same,SI-ck and SI-1 were always at a higher level,while SI-0 and SI-3 were lower.（2）Under shallow covered drip irrigation and pipe irrigation,maize consumed more water during jointing and spinning-grouting period.Under shallow covered drip irrigation,there was a positive correlation between maize water consumption and irrigation quota,expressed as:SCDI-ck>SCDI-1>SCDI-2>SCDI-3.Under pipe irrigation,the water consumption of maize was closely related to controlled irrigation.The water consumption of SI-ck was at a high level,while SI-0 was always low.In addition to SCDI-ck and SI-0,the total water consumption of maize treated by shallow covered drip irrigation was lower than that of pipe irrigation in 2019.（3）Under shallow covered drip irrigation,silage yield and grain yield were positively correlated with irrigation quota,while irrigation water use efficiency（IWUE）was negatively correlated,and water use efficiency（WUE）had no obvious regularity.The yield of SCDI-ck was the highest,but WUE and IWUE were the lowest.SCDI-3 had the highest IWUE,but the yield was severely reduced,while SCDI-1 had the least yield reduction and the highest WUE.Under this condition,SCDI-1 could be the optimal treatment of shallow covered drip irrigation.Under pipe irrigation,only SI-1 increased the yield,and the others showed different degrees of yield reduction compared with the SI-ck.SI-0 had the highest WUE and IWUE,while SI-ck had the lowest.The IWUE and WUE of SI-0 were higher than SI-1,but the yield was severely reduced.Under this condition,SI-1 could be the optimal treatment of pipe irrigation.（4）The yield,water use efficiency,and irrigation water use efficiency of SCDI-1were higher than those of SI-1.Therefore,SCDI-1 was the optimal irrigation system,which the irrigation quota was 2400m³·hm^-2,and irrigation was performed 9 times under shallow covered drip irrigation.（5）Water-saving of shallow covered drip irrigation were 41.83%and 37.66%,and the yield increased by 32.60%and 28.63%compared with pipe irrigation in 2018 and 2019,respectively.Shallow covered drip irrigation saved 2.34×10⁸m³ of water and increased3.28×10⁸kg of yield in total.And irrigation water use efficiency was more than doubled compared with pipe irrigation.The net income under shallow covered drip irrigation increased by 51.96%and 49.88%and the production-to-investment ratio increased by24.17%and 22.65%compared to pipe irrigation in 2018 and 2019,respectively.（6）Under the premise of ensuring ecological benefits,shallow covered drip irrigation can significantly improve the water-saving and economic benefits of maize.The comprehensive benefits of shallow covered drip irrigation in 2018 and 2019 were higher than those of pipe irrigation,which were 1.57 times and 1.53 times of pipe irrigation.（7）The groundwater depth in Keerqin district gradually increased from the southwest and northeast sides to the middle area,forming an obvious funnel area in the middle.After the implementation of the shallow covered drip irrigation project,the decline rate of the underground water depth decreased from 0.36m·a^-1 to 0.24m·a^-1in maize growth period.The decline rate of groundwater depth was slowed down,and the groundwater level even rose in some areas.Furthermore,the rate of decrease in the area of the groundwater with a depth of<10m and the rate of increase in the area of the groundwater with a depth of≥10m were reduced.