| Under the severe shortage of water and soil resources,and frequent drought events,maize production is facing great challenges.It is an effective scheme to ensure the sustainable development of agriculture by enhancing crop yield and water use efficiency using efficient and reasonable water-saving irrigation technology.With the development of plant physiology,it is an inevitable trend to explore how to realize biological water saving through the physiological response mechanism of crops.Alternate partial root-zone irrigation is an effective technology to realize biological water saving by regulating the physiological and biochemical processes of crops.However,the effects of vertical partial root-zone alternative irrigation on maize growth,morphological structure and physiological and biochemical metabolism are not clear.In this study,there are three irrigation methods,including conventional drip irrigation(CDI),subsurface drip irrigation(SDI)and vertical partial root-zone alternative irrigation(ADI);and three irrigation levels,including 100% ETc(W1;ETc summer maize evapotranspiration),80% ETc(W2)and 60% ETc(W3),9 in total.Through two consecutive years of field summer maize experiments,the effects of vertical alternate root-zone irrigation on yield and water use of summer maize were studied.Also,this paper tries to explore the mechanism of water-saving and yield increasing from the perspectives of growth,physiology and biochemistry,photosynthetic characteristics,biomass accumulation and grain filling characteristics,and choose the irrigation mode suitable for summer maize in the semiarid areas of Northwest China to provide theoretical support for the application and popularization of vertical alternate root zone irrigation at field scale.The main conclusions are shown as follows:(1)The response law of summer maize growth index to vertical partial root-zone alternative irrigation was clearedCompared with the CDI group,the treatment in the ADI group can alleviate the adverse effects of water stress,improve root growth and activity of summer maize,and uniformly regulate the distribution of roots in the soil layer.The improvement of root characteristics is conducive to the absorption of water and nutrition for roots and further promotes the growth of the shoot.Compared with the CDI and SDI groups,the plant height stem diameter and leaf area index of summer maize in the ADI were increased.A standardized root sampling depth-root length density model can be used to accurately simulate the distribution of root length density of summer maize under different irrigations.(2)The response law of antioxidant enzyme activity and osmotic adjustment substance to vertical partial root-zone alternative irrigation in summer maize was elucidatedBoth the irrigation methods and levels showed significant effects on the antioxidant enzyme activities of summer maize(P<0.05).Compared with the SDI and CDI treatments,the activities of superoxide dismutase(SOD),peroxidase(POD)and catalase(CAT)in summer maize leaves in the ADI were increased,and the content of MDA in leaves was significantly decreased(P<0.05).The linear-plateau equation was used to quantitatively simulate the changes of leaf relative water content(Lrwc),SOD and POD activities during the gradual decrease of soil water.The results showed that Lrwc,SOD and POD activities remained relatively stable at the initial stage,and changed significantly when the relative soil water content decreased to a certain threshold.The threshold for obvious changes in the SOD activity was higher than that of the POD activity,indicating that SOD was more sensitive than POD under water stress.In the ADI treatments,when the value of Lrwc changed,the relative soil moisture content reached the lowest,indicating that vertical alternate root zone irrigation can enhance the ability of leaf water retention and drought tolerance of summer maize.Because the threshold for the changes of SOD activity in the ADI treatment was the highest,and the overexpression of ROS can be more sensitively observed,so that the antioxidant defense system was started in time to resist the oxidative damage caused by water stress.(3)The effect of vertical partial root-zone alternative irrigation on leaf photosynthetic characteristics was studiedCompared with the SDI and CDI groups,in the ADI group,the total chlorophyll and net photosynthetic rate of leaves were significantly increased(P<0.05),the photosystem II,the photochemical quenching coefficient(q P)and the actual quantum yield(?PS ?)of photosystem II were maintained at the maximum photochemical efficiency(Fv/Fm),and the non-photochemical quenching coefficient(NPQ)was decreased,indicating that vertical alternate root zone irrigation can maintain the stability of photosynthetic structure under water stress to alleviate photoinhibition and improve the adaptability of photosynthesis.Compared with the CDI group,the ADI group significantly reduced the leaf transpiration rate of maize,indicating that vertical alternate root zone irrigation can reduce water loss in plants by reducing transpiration rate and enhancing its adaptability under water stress.(4)The response law of summer maize yield and water use to vertical partial root-zone alternative irrigation was provedIn the ADI treatment,the total biomass was increased and the contribution rate of biomass to grain was increased after silking;At the same time,in the ADI group,the effective and active grain-filling periods were prolonged and the maximum and average grain filling rates were increased by regulating the grain filling process,which laid a foundation for a higher yield.Under the same irrigation level,the yield of the ADI group was the highest.The irrigation water use efficiency(IWUE)of the ADI group was the highest,and higher than that of the SDI and CDI groups by 5.9% and 11.2% on averagely and respectively in 2018 and2019.(5)The best irrigation mode of summer maize was put forward according to the fuzzy Borda combination evaluationThe irrigation patterns of summer maize were comprehensively evaluated by various methods as well as indexes like growth,drought resistance physiology,photosynthetic characteristics,yield and water use of summer maize.There were differences in the ranking results of irrigation patterns among the evaluation methods.Therefore,a fuzzy Borda combined evaluation model was established according to the above evaluation results;and the optimal combinations for summer maize in a semi-arid area of Northwest China were ADI+100ETc.Given in its capacities in enhancing drought resistance,coordinating plant growth and improving field adaptability of summer maize,vertical partial root-zone alternative irrigation is a feasible method for saving water and increasing yield and provides an effective guarantee for the production purpose of high-efficiency water use and yield increase of Summer Maize in Northwest semi-arid area. |
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