| Irrigation is an important way to maintain and increase winter wheat-summer maize production.However,there are still many problems in using agricultural irrigation water,such as water shortages,over-exploitation of groundwater,lacking of efficient irrigation technology and low efficiency of irrigation water.Therefore,the development of efficient water-saving irrigation technology for grain crops of winter wheat-summer maize and its corresponding irrigation management are very important to cope with regional agricultural water crisis,improve resource utilization efficiency and ensure food security.This research studied the effects of irrigation methods and irrigation levels on the growth characteristics,physiological characteristics,soil water consumption dynamics,root water uptake,yield,and water use of winter wheat-summer maize in Henan Province.The objectives of this research are,on the one hand,to reveal the mechanism of water saving and yield increasing of subsurface drip irrigation on winter wheat-summer maize;on the other hand,to optimize the irrigation strategy for subsurface drip irrigation of winter wheat-summer maize.At the same time,the system design parameters that match the subsurface drip irrigation of winter wheat-summer maize were constructed through simulation of water movemement law,numerical simulation,and field experiments.1.Subsurface drip irrigation increased soil water content in the middle and lower layers and reduces soil water fluctuations,enhanced the physiological characteristics of plants in the middle and late growth period of winter wheat-summer maize,promoted dry matter accumulation after anthesis and its transport to grains as compared to surface drip irrigation.Compared with surface drip irrigation,the yield of winter wheat and summer maize was increased by 5.8~12.5% and 3.4~19.9%under deficit irrigation conditions,respectively.Compared with surface dirp irrigation,subsurface drip irrigation increased water extracted from deep soil layers and reduced irrigation water requirements;the irrigation amount of winter wheat and summer maize in subsurface drip irrigation was decreased by 7.0~13.9% and 1.6~11.4%,respectively.Subsurface drip irrigation did not significantly increase crop evapotranspiration,so its water use efficiency of winter wheat and summer maize increased by 10.1~11.3% and 4.8~8.7% as compared to surface drip irrigation,respectively.2.There is a complementary effect between the upper root system(20~50 cm)and the lower root system(60~100 cm)of winter wheat and summer maize on root water uptake.Except for severe drought treatment(0.4ETc),the root water uptake rate of the upper soil layers first increased and then decreased during each irrigation event,while the root water uptake rate of the lower soil layers decreased first and then increased from the second irrigation event.The root water uptake rate of the upper soil layers increased with the increase of drip irrigation amount,and it showed the oppsite trend in the lower soil layers which decreased with the increase of drip irrigation amount(except to 0.4ETc treatment)under subsurface drip irrigation conditons for winter wheat and summer maize.The total root water uptake of winter wheat and summer maize increased with the increased of drip irrigation amount.Compared with the 1.0 ETc treatment,the 0.8 ETc reduced the cumulative root water uptake in the early filling stage for winter wheat and in the late filling stage for summer maize;consequently,its total root water uptake was decreased by 11.6% and5.8% in the winter wheat and summer maize growing seasons,respectively.Proper deficit irrigation(0.8ETc treatment)increased root water uptake in the deep soil layers(> 70 cm).3.Compared with flooding irrigation,the 1.0ETc treatment enhanced the physiological activity of plants,increased the dry matter accumulation after anthesis(or after silking),and ultimately yield and biomass.Furthermore,the fluctuation of root water uptake rate in the 1.0ETc treatment was smaller when compared to that in flooding irrigation.The total root water uptake of winter wheat in the 1.0ETc treatment was increased by 9.8% as compared to that in flooding irrigation.Compared with flooding irrigation,the 0.6ETc treatment saved irrigatioin water by 73~84 mm with similar winter wheat yield;the 0.6ETc or 0.8ETc treatment saved irrigation water by 32~98 mm with similar summer maize yield.4.Compared with 1.0ETc treatment,0.6ETc or 0.8ETc treatment had no or little effect on physiological characteristics of winter wheat plants under subsurface drip irrigation conditions,but they promoted grain filling and finally achieved similar or slightly lower yield as 1.0ETc treatment.0.6ETc or 0.8ETc treatment reduced ineffective tillers,reduced evapotranspiration and biomass,and ultimately improved water use efficiency and harvest index of winter wheat.1.0ETc treatment could maintain high physiological activity and obtain higher biomass and yield.Compared with 1.0 ETc treatment,0.8ETc treatment could reduce the physiological activity of summer maize plants in some growth stages and had the risk of reducing yield;however,0.8ETc treatment could increase soil water extraction,reduce evapotranspiration and obtain higher water use efficiency.5.The suitable irrigation strategy for subsurface drip irrigation of winter wheat was to guide irrigation with 0.6~0.8ETc: for wetter areas,drip irrigated 5~6 times after jointing and turning green(drip irrigated 2~3 times before flowering,irrigation period was 15~20 days;drip irrigated 3 times after flowering,irrigation period was10-15 days),irrigation quota was 25-35 mm,irrigation should be postponed appropriately when rainfall occurs,and irrigation should be ended in the mid-filling stage;for drier areas,drip irrigated 6 times after jointing and returning green(drip irrigated 3 times before flowering,irrigation period was 15-20 days;drip irrigated 3times after flowering,irrigation period was 10-15 days),irrigation quota was 25-35 mm,and irrigation should be ended in the mid-filling stage.The suitable irrigation strategy for summer corn under subsurface drip irrigation was to guide irrigation with0.8~1.0ETc: drip irrigated 6~7 after jointing(drip irrigated 3 times before flowering,irrigation period was 10-15 days;drip irrigated 3~4 times after flowering,irrigation period is 10~ 15 days),the irrigation quota was 35-45 mm,irrigation should be postponed appropriately when rainfall occurs,and irrigation should be ended in the mid-filling stage;.6.The HYDRUS-2D model can well simulate soil water movement under subsurface drip irrigation with point-source.The determination coefficient of the model and model efficiency were 0.96~0.99 and 0.90~0.96,respectively.The root mean square error of soil water content and the moving distance of the wet front were0.029~0.032 cm3·cm-3 and 0.69~2.01 cm,respectively.The model simulation optimization and field test verification showed that bured depth of drip tape with 30 cm and drip tape distance with 60 cm were the reasonable parameters for subsurface drip irrigation system of winter wheat-summer maize under sandy loam conditions of Henan Province.The water-saving and yield-increasing mechanisms of winter wheat-summer corn under subsurface drip irrigation conditions were as follows:(1)increased the soil water content in the middle and lower soil layers,decreased soil evaporation,reduced the fluctuation of soil water and root water uptake rate,and created a more stable growth environment for the crop root zone;(2)increased soil water extraction in the deep layer and the entire soil profile,and reduced the amount of irrigation;(3)enhanced the physiological activity of plants after anthesis,promoted dry matter accumulation after anthesis and its transport to the grain.Under subsurface drip irrigation conditions,irrigated with 0.6~0.8ETc for winter wheat and 0.8~1.0ETc for summer maize can achieve the purpose of water-saving and high-yield;under sandy loam conditions,the suitable burial depth and spacing of drip tape for subsurface drip irrigated winter wheat-summer maize was 30 and 60 cm,respectively. |
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