Effects Of Sowing Date And Planting Density On Canopy Structure And Nitrogen Utilization Efifciency Of Winter Wheat

In this study, taking TN18with multi-grain number per spike and SN15with middlegrain number per spike as experimental materials, the effects of sowing dates （October7forD1, October15for D2） and planting densities (1.35million·hm^-2,2.70million·hm^-2,4.05million·hm^-2,5.40million·hm^-2for TN18;1.725million·hm^-2,3.45million·hm^-2,5.175million·hm^-2,6.90million·hm^-2for SN15) on the population dynamics, canopy architecture,the spatial-temporal distribution of root, grain yield and nitrogen use efficiency of winterwheat were investigated. The main results were shown as follows:1Effects of sowing date and planting density on population dynamics of wheatThe number of tillers, dry matter accumulation before anthesis and harvest index of twotypes of wheat cultivars decreased with the delay of sowing date, and these parametersmentioned above increased with the increase of planting density. After anthesis, no significantdecreases in dry matter production occurred with the delay of sowing date, but the increase ofplanting density had more or less effects on the dry matter production after anthesis indifferent treatments. For TN18sown at October7, no significant increases in dry matterproduction occurred with the increase of planting density, however, the dry matter productionafter anthesis increased significantly with with the increase of planting density for TN18sownat October15, SN15sown at October7and sown at October15.2Effects of sowing date and planting density on grain yield and its components of wheatThe effect of sowing date on spikes per m2, weight per103kernels and grain yield wassignificant; Planting density on yield and yield components was significantly affected. Theinteractions of sowing date and planting density on grain yield, spikes per m2and grains perspike were significant, but these on weight per103kernels were not significant. With planting density increasing, grain yield of two winter wheats sown at October7increased first and then decreased. Grain yield under2.70million·hm^-2for TN18and3.45million·hm^-2for SN15sown at October7were highest. Grain yield under4.05million·hm^-2for TN18and3.45million·hm^-2for SN15sown at October15were highest. while nosignificant difference exsited for parameter mentioned above between3.45million·hm^-2and5.175million·hm^-2for SN15. With the delay of sowing date, grain yield of two winter wheatsdecreased significantly.3Effects of sowing date and planting density on canopy architecture and photosynthesisCAP decreased with the delay of sowing date. Planting density affected more or lessCAP. The decreases in CAP under under2.70million·hm^-2for TN18and3.45million·hm^-2forSN15sown at October7, under4.05million·hm^-2for TN18and3.45million·hm^-2for SN15sown at October15were slower. And CAP of those threatments mentioned above were higherthan that of other three planting densities.CAP was positively significantly correlated with LAI and grain yield for two winterwheats. For TN18, LAI was positively significantly correlated with grain yield, while LAIwas not positively significantly correlated with grain yield until14days after anthesis.4Effects of planting density on the spatial-temporal distribution of root of late sown wheatThe root length density, total root absorbing area and active root absorbing area for TN18increased by raising planting density appropriatly and peaked under4.05million·hm^-2at allstages. Root length density, total root absorbing area and active root absorbing area for SN15achieved highest value under3.45million·hm^-2at booting and late grainfilling stages.5Effects of sowing date and planting density on uptake, distribution and nitrogen useefficiency of wheatAccumulation of nitrogen in grain per stem at maturity,amount of nitrogen in grain perstem from uptake of nitrogen after anthesis and contribution of nitrogen translocated to grainafter anthesis decreased with the increase of planting density and the delay of sowin date.Translocation proportion and contribution of nitrogen translocated to grain before anthesisincreased with the increase of planting density and the delay of sowing date, whiletranslocation amount of nitrogen stored in vegetative organs before anthesis increased withplanting density increasing and decreased with the delay of sowing date. Inorganic nitrogen accumulation in different depth of soil prifile at maturity decreasedwith increasing planting density appropriatly and increased with delaying sowing date.Nitrogen utilization efficiency increased with delaying sowing date, while nitrogenuptake efficiency and nitrogen partial factor productivity decreased with delaying sowing date.Nitrogen uptake efficiency and nitrogen partial factor productivity of two cultivars sown atOctober7increased first and then decreased with increasing the planting density. Theseparameters mentioned above under2.70million·hm^-2for TN18and3.45million·hm^-2forSN15sown at October7were highest. Nitrogen utilization efficiency increased first and thendecreased with increasing the planting density for TN18, while that decreased for SN15.Nitrogen utilization efficiency under2.70million·hm^-2for TN18and1.725million·hm^-2forSN15sown at October7were highest. For two cultivars sown at October15, nitrogen uptakeefficiency, nitrogen partial factor productivity and nitrogen utilization efficiency increasedwith increasing the planting density for TN18and these parameters were highest under5.40million·hm^-2for TN18; Nitrogen uptake efficiency and nitrogen partial factor productivityincreased first and then decreased with increasing the planting density and these parameterswere highest under3.45million·hm^-2for SN15; Nitrogen utilization efficiency decreased withincreasing the planting density and that were highest under1.725million·hm^-2for SN15.Taking grain yield, the relationship of canopy architecture and photosynthesis, thespatial-temporal distribution of root and nitrogen use efficiency into consideration, thetreatments under2.70million·hm^-2sown at October7,5.40million·hm^-2sown at October15for TN18and under3.45million·hm^-2sown at October7and sown at October15for SN15obtained higher grain yield and nitrogen use efficiency simultaneously.