Effect Of Limited Irrigation And Nitrogen Rate On Photosynthetic Performance And Yield Of Maize In Hetao Irrigation District And Its Regulation Mechanism

Hetao Irrigation District(HID)is a main grain production region in China.Water shortage,soil secondary salinization and excessive application of chemical fertilizer are the main factors that limiting the sustainable development of agriculture in HID.Therefore,under the background of border irrigation as the main irrigation method in HID,it is a promising way to relieve these problems by investigating the mechanisms of saving water and fertilizer and building reasonable water and fertilizer managing patterns.In this study,the maize of border irrigation was taken as the research object,and the coupling mechanism of water and nitrogen of maize was revealed in the perspective of photosynthetic performance in saline soil in HID.Then,the field experiments were carried out to explore the response of maize yield to water and nitrogen regulation under different salinization farmlands and different precipitation years,and the reasonable amount of water and nitrogen in saline soil was put forward.Finally,the effect of water and nitrogen regulation on the dynamics change of water and salt and the water consumption process of maize was simulated under water and nitrogen regulation,and the influence mechanism of water and nitrogen regulation on maize yield in different salinization farmlands and different precipitation years was analyzed.Main conclusions are as follows:1.The external influencing factors and the influencing mechanism of photosynthesis of maize in moderate saline soil were expounded under different water and nitrogen levels.At the end of irrigation period,border irrigation maize is prone to water,nitrogen and salt stress in HID.At the end of the irrigation period,compared with the local conventional water and nitrogen(W3N3 treatment),the treatment of reducing 25%irrigation and nitrogen application(W2N2 treatment)improved the water storage capacity,the groundwater recharge,the soil salinity,and the alkali-hydrolyzed nitrogen content.Therefore,W2N2 treatment improved soil moisture and nitrogen status and reduces soil salinity,which was beneficial to the photosynthesis of maize in later growth period.Increasing the irrigation and nitrogen could improve the photosynthetic indexes,such as light energy utilization and intercellular CO2 concentration during tasseling-grouting stage.When the irrigation amount exceeded 225mm and the nitrogen application exceeded 258.8 kg·m-2,the photosynthetic indexes of maize would not significantly improve,and even showed a decreasing trend in the grouting stage.Compared with the W3N3 treatment,the W2N2 treatment significantly promoted the utilization of light energy and the concentration of intercellular CO2 at the later stage of maize.2.The effect of limited water and nitrogen rate on photosynthetic performance of maize in moderate saline soil was discussed,and the coupling mechanism of water and nitrogen was revealed.Increasing the irrigation and nitrogen not only could improve the photosynthetic rate,area,time and the products of maize during the grain filling stage,but also could increase the accumulation of photosynthetic products and the proportion of photosynthetic products distributed to grain organs of maize.When the irrigation amount exceeded 225mm and the nitrogen application exceeded 258.8kg·hm-2,the increase of these photosynthetic performance indexes was not significant,or even decreased.Compared with the W3N3 treatment,the W2N2 treatment significantly increased the photosynthetic rate,maintained a higher photosynthetic area,prolonged the photosynthetic time,and significantly increased the accumulation of photosynthetic products.Therefore,the W2N2 treatment was not only beneficial to the photosynthetic performance of maize in the late growth period,but also could improve the accumulation of photosynthetic products and their distribution to grain organs.3.In order to further understand the response mechanism of photosynthetic performance of maize to water and nitrogen regulation,the effect of limited water and nitrogen rate on the antioxidant system of maize in moderate saline soil was discussed.Increasing the irrigation and nitrogen could alleviate the adversity stress and improve the antioxidant capacity of maize in the middle salinized soil in HID.When the irrigation amount exceeded 225mm and the nitrogen application exceeded 258.8kg·hm-2,it would aggravate the adversity stress and reduce the antioxidant capacity of maize in the filling stage.Compared with the W3N3 treatment,the W2N2 treatment significantly alleviated the stress of adversity during the filling stage of corn,and was beneficial to improve the antioxidant capacity.4.The response of maize yield,water use efficiency(WUE)and nitrogen use efficiency(PFPN)to water and nitrogen regulation in HID was clarified.Moderate increase of irrigation amount or nitrogen application amount was beneficial to increase maize yield,WUE and PFPN.When the irrigation amount exceeded 225mm and the nitrogen application exceeded 258.8kgm2,the improvement effect was not significant,and even had a decreasing trend.Compared with the W3N3 treatment,in 2016 and 2017,the maize yield of the W2N2 treatment increased by 4.01%and 23.35%,respectively,and the WUE and PFPN were significantly improved(P<0.05).5.The response of maize yield to water and nitrogen rate in three salinization farmlands was discussed,and the response of maize yield in moderate salinized soil to water and nitrogen rate in different precipitation years was also studied.The reasonable amount of water and nitrogen for border irrigation maize in saline soil in HID was put forward.With the increase of soil salinity,the interactive effect of water and nitrogen on yield enhanced.The maximum yield could be obtained only when the water was better and nitrogen was suitable,but the moderate reduction of irrigation and nitrogen application rate would not significantly reduce the yield in non-saline land.The suitable water and nitrogen supplying are needed in middle saline soil.The higher yield could be obtained when suitable water and less nitrogen are supplied in heavily saline soil.Through the model optimization,the water-saving and nitrogen-controlling management for higher yield of maize in HID are as follows:non-saline soil(irrigation 255.2?284.8mm,nitrogen 258.9?313.8kg·hm-2),moderately saline soil(irrigation 227.6?269.5mm,nitrogen 215.5?267.6kg·hm-2),heavily saline soil(irrigation 197.4?252.6mm,nitrogen 158.1?221.4 kg·hm-2).Under the current irrigation conditions in HID,a relatively high yield of maize could be obtained through reasonable water and nitrogen regulation in different precipitation years.In low flow year,it was necessary to supply suitable water and nitrogen.In normal flow year,it could get maximum yield when the water was better and nitrogen was suitable,but the moderate reduction of irrigation and nitrogen rate would not significantly reduce the yield.In high flow year,the maximum yield could be obtained only when the amounts of water and nitrogen were higher.Through the model optimization,the water-saving and nitrogen-controlling management for higher yield of maize in the moderate saline soil are as follows:low flow year(irrigation 227.6?269.5mm,nitrogen 215.5?267.6kg·hm-2),normal flow year(irrigation 259.1?292.9mm,nitrogen 232.1?285.4kg·hm-2),high flow year(irrigation 267.8?302.2mm,nitrogen 278.1?342.9 kg·hm-2).6.The dynamic process model of soil water and salt in salinized farmland was established under the regulation of water and nitrcgen.Through the modified HYDRUS-1D model,the effect mechanism of water and nitrogen regulation on maize yield in different salinized soils and different precipitation years were discussed from the aspects of soil water and salt dynamics and water consumption process.In this study,we modified the actual soil evaporation as well as potential transpiration in the HYDRUS-1D model using the improved FAO-56 Dual Crop Coefficient model.Then,the dynamic process model of soil water and salt in salinized farmland under the regulation of water and nitrogen(the modified HYDRUS-1D model)was established.The modified HYDRUS-1D model were calibrated and validated using the field observation data in 2016 and 2017.The results showed that the soil water and salt calculated by the modified HYDRUS-1D model were in good agreements with the measured values.The W3N3 treatment was beneficial to the growth of maize in the corn irrigation period in non-saline land(S1),middle saline soil(S2)and heavily saline soil(S3).But at the end of the corn irrigation period(the middle and late grain filling stage),compared with the W3N3 treatment,the W2N2 treatment improved soil water status in S1,soil water and salt status in S2,and salt environment of shallow soil and groundwater recharge in S3.In addition,the transpiration of the W2N2 treatment in S1,S2 and S3 soil increased by 10.15%,20.87%and 26.58%,respectively.The main difference of the effect of water and nitrogen regulation in different precipitation years was during the middle and late grain filling stage.Compared with the W3N3 treatment,the W2N2 treatment improved the soil water and salt conditions in low flow year,mainly improved the soil water status in normal flow year,but the soil water and salt status was poor in high flow year.In addition,the transpiration of maize with the W2N2 treatment increased by 20.87%in low flow year and 6.83%in normal flow year,but decreased by 6.38%in high flow year.