Mechanism Of High-efficient Water And Fertilizer Utilization By Winter Wheat Under Drip Fertigation

In the semi-arid regions of the world,irrigation and fertilization are essential for cereals growth and production because of water shortages and unfertile soils.However,inappropriate water and fertilizer management always causes unstable grain weight and yield,lower protein content and irrigation and fertilizer use efficiency.Understanding the grain macronutrient uptake requirements with increased grain yield is essential to optimize the irrigation and fertilizer management for high-yield and high-quality wheat production to meet the increasing future food demand.A four-year(2014–2018)experiment was conducted on winter wheat(Triticum aestivum L.‘Xinong 979')under drip fertigation,with three irrigation rates and three fertilization rates.And irrigation rates included normal irrigation level(W1),mild deficit irrigation(W2)and more severe deficit(W3),fertilization rates(N-P2O5-K2O)included F1(175-117-150 kg/hm~2),F2(125-84-108 kg/hm~2)and F3(75-50-65 kg/hm~2).A total of 10 treatments were included with the normal irrigation and no fertilizer application(W1NF).The mechanism of water and fertilizer saving for winter wheat production of increasing yield and quality was investigated.Suitable water deficit and fertilizer application amount were determined,in order to provide a reliable theoretical basis for winter wheat production.The results were as follows:(1)The response mechanism of physiological and photosynthetic characteristics of drip-fertigated winter wheat to water and fertilizer supplies were revealedThe chlorophyll a,chlorophyll b and total chlorophyll contents in leaves decreased,while chlorophyll a/b increased,with the increase of water stress.The content chlorophyll a,chlorophyll b and total chlorophyll contents were inhibited by low fertilizer rates.The F1 and F2 had no significant differences,however,were significantly higher than the F3 and NF(P<0.05).The coupling effect of irrigation and fertilization had a significant interaction on chlorophyll a and total chlorophyll content during the filling stage(P<0.01).Fertilization affected the leaf moisture content at the end of grain filling greatly.The increasing amount of fertilizer applied inhibited the decreased rate of the leaf moisture content.As water stress increased,diurnal variations of net photosynthetic rate(P_n),transpiration rate(T_r),stomatal conductance(G_s)and intercellular carbon dioxide concentration(Ci)reduced,but instantaneous water use efficiency enhanced.The P_n,T_r,G_s and Ci had a positive relationship with fertilization rates.As the growth period advanced,the P_n improved with increasing fertilization levels in the W1.However,excessive fertilization under the W2 or W3 inhibited photosynthetic rate.Insufficient fertilization caused early leaf senescence and decreased the net photosynthetic rate.Irrigation amount increased the transpiration rate.Effects of water stress on the transpiration rate were slightly discriminate at different growth stages,it was relatively small from jointing stage to the initial grain filling stage and strengthened afterwards.(2)Effects of water and fertilizer management on grain filling characteristics and grain weight of drip-fertigated winter wheat were determinedThe temporal dynamics of grain weight was simulated using determinate-growth equation.The appearance time of maximum filling rate(tm)and growth termination time(te)increased as fertilization rate increased,whereas the maximum and average filling rate increased and then had a slight decrease.The t_m and t_e decreased with the increase of water deficit.The mild water deficit and appropriate fertilization improved the grain filling,enough nutrients in glume and rachis transferred to grains,finally increased grain weight,the maximum grain weight percentage of spike weight(GPS)could reach about 80%.The GPS and spike moisture content(SMC)had extremely significant correlations with grain weight.GPS tended to decrease one week before maturity,and declined with the increase in water stress.SMC decreased in a parabolic form,and exhibited a dramatic decline about one week before maturity.With the increase of water or fertilizer supply,the grain weight firstly increased and then decreased,where the mild water deficit and appropriate fertilization improved grain filling and productivity of winter wheat.(3)Dynamic change and accumulation of grain macronutrient(N,P and K)concentrations in winter wheat under various drip fertigation regimes were evaluatedVarious drip fertigation strategies affected grain macronutrient uptake and utilization,and finally influenced yield and macronutrients concentration.The grain N concentration firstly decreased and then increased during grain filling.Specifically,it firstly increased and then decreased with the increase in fertilization rate,while it firstly decreased and then increased with increasing irrigation rate.The average of grain P concentration decreased with the increase in irrigation and fertilization rates.The grain K concentration showed a slow decline trend at the initial grain-filling stage until reaching a stable value at the mid-filling stage,and it increased with the increase in fertilization rate.Grain NPK uptake at maturity increased with increasing fertilization rate under normal irrigation,while the mild water deficit was found to promote grain NPK uptake.Grain N concentration and grain yield exhibited a positive relationship,and both irrigation and fertilization had significant effects on grain yield and NPK uptake.The grain protein content and N:P ratio were mainly affected by fertilization.(4)The regulation effects of water and fertilizer supplies on drip-fertigated winter wheat dry matter accumulation,partitioning and translocation were investigatedWater stress advanced the emergence of the maximum accumulation rate of dry matter.The maximum and average accumulation rate of dry matter were affected by the water stress negatively and fertilizer application rates positively.The type of year influenced the time and effective period of maximum growth rate of the aboveground dry matter.As water stress increased,the proportion of stem and grain improved and those of leaf and rachis+glume reduced.Fertilizer rates influenced the proportion of stem and grain negatively and those of leaf and rachis+glume positively.Irrigation and fertilization had a significant impact on the proportion of leaf and spike significantly.The increased fertilizer rates reduced dry matter translocation after anthesis(DMT)and improved post-anthesis dry matter accumulation(Post DM).(5)The characteristics of nutrient uptake,utilization and nutrient demand of drip-fertigated winter wheat on water and fertilizer supplies were analyzedWater stress inhibited total plant NPK uptake,and there were no significant differences between the W1 and W2.As sufficient water and fertilizer applied,the stem,leaf and rachis+glume obtained the higher the proportion of NP,while grain nitrogen and phosphorus harvest index(NHI and PHI)decreased.When the supply of water and fertilizer is insufficient,the NHI and PHI were increased,and the proportion of vegetative organs was relatively low.Fertilizer rates and water stress influenced the physiological utilization efficiency of NPK negatively and positively,respectively.The average nitrogen,phosphorus and potassium demand(GNR,GPR,and GKR)for 100 kg of grains in the four seasons ranged from 1.93 to 3.03 kg,from 0.37 to 0.41 kg and from 2.26 to 2.93 kg,respectively.The GNR and GKR were affected by water stress levels negatively and fertilizer rates positively.(6)The response of growth,yield and water and fertilizer use efficiency of drip-fertigated winter wheat to water and fertilizer supplies were clarifiedIrrigation and fertilization regulated the maximum and average growth rate of leaf area index(LAI).Fertilization extended the effective period of LAI.The type of year affected the thermal time and rate of LAI.With the increase of water stress,the growth was restrained,the plant height and LAI decreased,and then yield and its components decreased.The decline of yield leaded to the decline of partial factor productivity of fertilizer.The more serious the water deficit is,the more obvious the decline is.However,the irrigation water use efficiency first increased and then slightly decreased,while the W2 obtained the maximum value.As fertilizer application rates increased,which provided more nutrients,its plant height and LAI showed an increasing trend.More light was intercepted to increase assimilation.More yield and its components and irrigation use efficiency were improved.The increase of yield caused the improvement of irrigation water use efficiency,while on the basis of F2,the increase of fertilizer application amount continued to F1,the increase of yield is not significant,the marginal return decreases,the partial factor productivity of fertilizer decreases,and the partial productivity of F1 decreased 23.82%–30.52%,compared with F2.Therefore,the mild water deficit and appropriate fertilization rate improved the grain NPK uptake and production of winter wheat with higher grain protein content,which was conducive to the development of water-and fertilizer-saving agriculture.