Nitrogen And Manure Fertilizers Regulate The Water And Nitrogen Use Of Winter Wheat In Dryland

Wheat?Triticum aestivum L.?is one of the most important food crops and is extensively grown through the arid and semi-arid areas.Tapplication of nitrogen?N?is one of the most important techniques increase the yield to gain enough food to fed the world.However,with the global climate change and increase application of nitrogen fertilizers,the drought and environmental pollution are becoming more and more serious.Therefore,highly efficient use of water and N are becoming more and more important for agricultural production in the arid and semi-arid areas and have become an important task for both sustainable agriculture and global ecosystem stability.To understand the effects of N and manure fertilizers on the water and N use of winter wheat in dryland,a field study with four rates of N fertilizer(0,60,120and 180 kg N ha^-1)was conducted to determine soil water balance,root growth,water uptake,dry matter?DM?and N accumulation,partitioning and remobilization.A pot experiment was conducted to understand the responses of the activities of antioxidative enzymes,water conditions,photosynthetic parameters,DM and N accumulation,partitioning and remobilization to manure fertilizer application,the wheat was grown under the identical N level?urea-N,CF;and manure plus urea-N,MC?and under two watering regimes?WW,well-watered;and WS,water stress?imposed after anthesis.The main results are as follows:?1?The soil water content at harvest was lower and evapotranspiration?ET?was higher with N fertilization than without fertilization.With an increase in N fertilization,precipitation storage efficiency?PSE?and root growth in deeper soil layers significantly increased;thus,water uptake from deeper soil layers significantly increased,which resulted directly in increases in biomass accumulation at anthesis,post-anthesis dry matter?DM?accumulation,pre-anthesis DM remobilization and grain number per m².Therefore,N60,N120 and N180significantly increased WUE during vegetative growth stage?WUEb??by 16.6,37.2 and47.4%,whereas WUE during grain filling?WUEb??significantly reduced with increasing N fertilization.Therefore,N60,N120 and N180 significantly increased grain yield by 12.8,25.4and 34.8%and WUEg by 5.1,13.8 and 29.3%,respectively,compared with N0.Based on these results,the larger rooting systems resulting from N fertilization produced remarkable improvement in biomass accumulation by promoting the efficient use of soil water during vegetative growth stage,thus improving WUEg.However,adverse effects also resulted from N fertilization,such as the depletion of soil water and loss of soil organic C.?2?N accumulation at anthesis,remobilization of restored N to grain?NR?and the contribution of pre-anthesis stored N to the grain?CNR?were increased as N increased,thus,resulting in significant increases in grain N concentration,grain protein yield and grain yield.N remobilization efficiency?NRE?and N harvest index?NHI?were decreased as N rate increased,therefore,treatments of N120 and N180 reduced the NUtE by 19.4 and 23.0%,respectively,compared with N0,and with corresponding reduction in partial factor productivity of N?PFP?by 44.8%and 61.4%for N120 and N180 treatments,respectively.Drought significantly reduced N accumulation at anthesis,thus resulting in significant lower biomass accumulation,grain yield and NRE.Therefore,NHI was decreased under drought,with the result that NUtE reduced by 23.0%,and PFP decreased by 53.6%.These results suggest that high N application and drought reduced N use efficiency?PFP?,mainly because of the lower NRE and NHI under high N application and drought,leading to significant decrease in NUtE.?3?We investigated the response of N use efficiency to organic manure partial substitution for chemical fertilizer.The results showed that total N accumulation at harvest?NAH?and N-uptake efficiency?NUpE?in organic manure partial substitution for chemical fertilizer were similar to those of control treatment.However,organic manure partial substitution for chemical fertilizer improved N accumulation and optimized pre-anthesis N allocation in canopy and improved post-anthesis N uptake,and thus resulting in significant increase in photosynthetic enery transport rates,photosynthetic capacity and nitrogen-use efficiency?PNUE?,that contributed to resulting in the post-anthesis DM accumulation,grain number per plant and gain yield,and with the significant increases in N remobilization efficiency?NRE?and N harvest index?NHI?.The N-utilization efficiency?NUtE?in organic manure partial substitution for chemical fertilizer treatment significantly increased by 17.0%and 13.5%under WS and WW,respectively,compare with control treatment,with corresponding improvement in NUE by 23.5%and 15.0%respectively.These results suggest that organic manure partial substitution for chemical fertilizer increased NUE through enhancing photosynthetic nitrogen-use efficiency via optimising N parttioning in canopy.Our results highlight organic manure partial substitution for chemical fertilizer enabled plants to use N more efficiently under drought stress.?4?We investigated the response of water use efficiency to organic manure partial substitution for chemical fertilizer.The results showed that organic manure partial substitution for chemical fertilizer had a higher P_n and lower g_s and T_r than control treatment under both water conditions,in particular,it significantly increased WRC and?w,and decreased EWLR and MDA under WS.Also,organic manure partial substitution for chemical fertilizer increased post-anthesis N uptake by 81.4 and 16.4%under WS and WW,thus increasing post-anthesis photosynthetic capacity and delaying leaf senescence.Consequently,organic manure partial substitution for chemical fertilizer increased post-anthesis DM accumulation under WS and WW by 51.5 and 29.6%,WUE_B by 44.5 and 50.9%,grain number per plant by11.5 and 12.2%and 1000-grain weight by 7.3 and 3.6%,respectively,compared with control treatment.The grain yield under organic manure partial substitution for chemical fertilizer treatment increased by 23 and 15%,and water use efficiency?WUE_g?by 25 and 23%,respectively.The increased WUE under organic manure partial substitution for chemical fertilizer treatment was due to elevated photosynthesis,decreased T_r and g_s and improved transpiration efficiency.Our results suggest that the organic manure partial substitution for chemical fertilizer enabled plants to use water more efficiently under drought stress.