Effects Of Lateral Spacings,Irrigation Scheduling And Nitrogen Application Modes On Growth,Yield And Water Productivity Of Drip Irrigated Winter Wheat

Uneven water distribution and the injudicious application of nitrogen fertilizer are the two main problems threatening the sustainable agricultural development in North China Plain（NCP）,a largest alluvial plan which is contributing more than 60%of winter wheat production in China.Irrigating as soon as possible on water requirement during wheat production is essential to attain a higher grain yield.Water management practices like irrigation frequency,proper wetting soil volume and irrigation scheduling may regulate the soil moisture status and then ultimately affect the grain yield and water use efficiency（WUE）.Therefore,it is necessary to properly design the irrigation source and the irrigation scheduling to achieve the higher grain yield and water use efficiency.Furthermore,nitrogen management strategies are also necessary to avoid the nitrogen losses and groundwater pollution in NCP.A study was conducted during 2017-2018 and 2018-2019 winter wheat growing seasons to quantify the response of soil and wheat plants under different drip irrigation lateral spacings,irrigation scheduling levels（ISLs）and nitrogen application modes（NAMs）.This study was consisted of three drip irrigation lateral spacings of 40,60 and 80 cm(referred as D₄₀,D₆₀ and D₈₀ respectively),three ISLs(irrigating the winter wheat when soil water consumption（SWC）reached to 20,35 and 50 mm,referred as I₂₀,I₃₅ and I₅₀ respectively),three NAMs(basal and top dressing application ratios as 50:50,25:75and 0:100,referred as N_50:50,N_25:75 and N_0:100 respectively).The study was designed with aims to evaluate the effects of different drip irrigation lateral spacings,ISLs and NAMs on winter wheat growth,yield parameters and WUE in NCP.The main findings of the study are as follows:1.The growth characteristics of winter wheat were observed at 7-10 days interval and found that drip irrigation lateral spacings,ISLs and NAMs have significantly influenced the winter wheat growth.It was observed that higher irrigation scheduling treatment（I50）under 40 cm later spacing always exhibited the better growth of winter wheat during both growing seasons.At winter wheat re-green,higher growth was observed under N50:50 treatment followed by N25:75 NAM.But as the nitrogen was fertigated at tillering,jointing and early grain filling stage,growth tend to increase faster in N0:100as compared to other NAMs.Aboveground biomass at harvest was recorded in each treatment and found that drip irrigation lateral spacings,ISLs and NAMs markedly affected the aboveground biomass of winter wheat.It was measured that,D40 increased the aboveground biomass by 10%and 24%in2017-2018 and by 9%and 23%in 2018-2019 seasons than D60 and D80 lateral spacing respectively.However,irrigating the winter wheat at I50 increased the biomass by 6%and 23%in 2017-2018 and by6%and 23%in 2018-2019 season than I35 and I20 respectively.Furthermore,in case of NAMs,applying all the nitrogen as top dressing at tillering,jointing and early grain filling stage was beneficial in increasing the aboveground biomass as N0:100 significantly increased the biomass by 9%and 20%in 2017-2018 season and by 8%and 19%in 2018-2019 season than N25:75 and N50:50 treatment respectively.2.It was observed that proper drip irrigation lateral spacing,ISL and NAM has the potential to improve the yield components of winter wheat.The study results revealed that,higher yield components（spike length,number of spikelets per spike,number of grains per spike and 1000-grain weight）were achieved under 40 cm drip lateral spacing with conjunct influence of I35N25:75 treatment followed by60 cm lateral spacing under same treatment.However,the lowest yield components were observed at 80cm lateral spacing under I20 ISL and NAM of N50:50.In our study,irrigating the winter wheat at I35ISL significantly increased the spike length,spikelets per spike,number of grains per spike and 1000-grain weight by 6%,10%,21%and 7%than I20 during 2017-2018 season.While these corresponding values during 2018-2019 growing season were 5%,10%,17%and 4%respectively.In case of NAM,N25:75 increased the spike length,spikelets per spike,number of grains per spike and 1000-grain weight by 8%,8%,19%and 7%than N50:50 during 2017-2018 season respectively.However,during2018-2019 season these values were 6%,8%,18%and 4%respectively.Thus,it can be concluded that I35+N25:75 treatment have the potential to improve the yield components of winter wheat in NCP.3.The study results showed that drip irrigation lateral spacings,ISLs and NAMs significantly affected the winter wheat yield and WUE during both growing seasons.Compared with D60 and D80,D40 increased the grain yield by 4%and 9%in 2017-2018 and by 4%and 8%in 2018-2019 season respectively.Irrigating the winter plants under ISL I35 significantly improved the grain yield by 15%and 3%,and by 14%and 4%as compared to I20 and I50 during both growing seasons respectively.Among the three NAMs,N25:75 significantly increased the grain yield by 6%and 2%,and by 8%and4%than N50:50 and N0:100 in both seasons,respectively.In case of WUE,D40 increased the WUE by5%and 13%in 2017-2018,and by 5%and 13%in 2018-2019 season than D60 and D80 respectively.Comparing to I20 and I50,I35 significantly increased WUE by 4%and 12%in 2017-2018 season,while by 3%and 11%in 2018-2019 seasons.On the other hand,comparing to the greatest WUE in NAM N25:75,the WUE in N50:50 and N0:100 both decreased by 5%and 4%in 2017-2018 season,and by 6%and 5%respectively in 2018-2019 season respectively.The results referred that irrigating the winter wheat at I35 ISL and N25:75 NAM could be the best option to achieve the higher grain yield and WUE.4.Soil moisture and nitrogen contents were also studied during both growing seasons and it was found that drip irrigation lateral spacings and ISLs considerably affected the soil moisture and nitrogen contents.It was noticed that,higher soil moisture contents were observed under 40 cm drip irrigation lateral spacing followed by D60 under I50 ISL.Compared to I20 and I35,I50 distributed more soil moisture in deeper soil layers during both growing seasons.Interestingly,lower soil moisture contents were observed under 30-70 cm soil layer and this might be due to more extraction of water in this layer.But this higher soil moisture did not increase the grain yield and reduced the WUE.In case of I20 ISL,it was noticed that soil moisture depleted earlier in I20 than other ISLs and it might create a water stress condition among wheat plants.Soil nitrogen contents were also recorded during both growing seasons and it was found that drip irrigation lateral spacings,ISLs and NAMs significantly affected the nitrated nitrogen during both seasons.Higher soil nitrate nitrogen was measured in N0:100 treatment during whole growing season.It was noticed that,N0:100 with I50 ISL distributed more nitrogen in deeper soil layers which can be a reason for groundwater pollution.However,lowest nitrogen was observed under N50:50 treated plots.5.Keeping in view the above-mentioned results,this study strongly recommends using the 40 cm drip irrigation lateral spacing or if enough resources are not available then D60 could also be a good choice for winter wheat production.However,irrigating the winter wheat at I35 ISL and choosing the N25:75 NAM is beneficial in increasing the grain yield and WUE of winter wheat.