Effects Of Nitrogen Rate And Plant Density On Canopy Architecture And Its Function In Winter Wheat

In this study, T18, a winter wheat variety with multi-grain number per spike, and S15, a winter wheat variety with middle grain number per spike, were used as experimental materials for investigating the effects on the changes of population and grain yield, canopy architecture and ability of photosynthesis, the characteristic of culm and lodging resistance, the changes of NO3--N content in 0-200cm soil profile with time and space and fertilizer use efficiency under different nitrogen rate and plant density. The main results were as follows:1 Effects of nitrogen rate and plant density on the changes of population and grain yield in two types of wheat cultivars.The population of two types of wheat cultivars increased with the increasing of nitrogen rate and plant density in this study. The LAI and drymatter accumulation increased with increasing of itrogen rate and plant density for T18 in the whole growing stage. These were in same with T18 for S15 only during early and middle growing period but during late growing period the LAI and drymatter accumulation of high nitrogen and high density treatments were less than that of low nitrogen and low density treatments which both more than no nitrogen application treatments.With nitrogen rate and plant densit increasing, the total ears per unit area increased. Weight per 10³ kernels of T18 decreased with nitrogen rate increasing, and increased first and then decreased with plant density increasing. For S15, Weight per 10³ kernels of high nitrogen and high density treatments is less than that of low nitrogen and low density treatments which both more than no nitrogen application treatments. There existed significant interaction on grain yield between nitrogen rate and plant density. In the same plant density, the yield of T18 increased with the nitrogen rate increasing; in the same nitrogen rate, the yield of T18 increased first and then decreased with plant density increasing. For S15, the yield increased first and then decreased with nitrogen increasing in the same plant density; in the same nitrogen rate, the yield decreased with the plant density increasing. The treatment N300D300 gained the highest yield but was not significant to N240D225 and N180D225 for T18. For S15, the treatment N180D150 gained the highest yield and was significant to other treatments.Decreasing nitrogen rate and increasing plant density made reserves in vegetable organs before anthesis of wheat plant for translating to grain. Except for treatment of N180D150 the economic coefficient was not signicant among treatments of nitrogen application but all higher significantly than the treatments of no nitrogen application. So the yield elevation was achieved by increasing of dry matter weight not by improving the economic coefficient.2 The effects of nitrogen rate and plant density on canopy architecture and ability of photosynthesisFor T18, the flag leaf area of nitrogen application treatment was bigger than that of no nitrogen treatment. The flag leaf area was not affected significantly by plant density in the same nitrogen. The weight/area, nitrogen content, chlorophyll content, Pn, Cond, Tr, Fv/Fm,ΦPSII, SOD activity, POD activity, and CAT activity increased with the increasing of nitrogen rate and the decreasing of plant density; Ci of T18 increased with nitrogen rate and plant density increasing. The flag leaf area of S15 increased with the increasing of nitrogen and plant density. For S15, the weight/area, nitrogen content, chlorophyll content, Pn, Cond, Tr, Fv/Fm,ΦPSII, SOD activity, POD activity, and CAT activity increased first and then decreased with the increasing of nitrogen rate but decreased always with increasing of plant density; Ci of S15 increased with nitrogen rate and plant density increasing.There existed significant positive correlation between the Pn of flag leaf and the weight/area, nitrogen content, chlorophyll content in two types of wheat cultivars. For T18, there existed significant positive correlation between the Pn and area of flag leaf but not for S15.WLAI and TLAI increased with nitrogen rate and plant density increasing, and it was showed that N240D225>N180D225>N240D150>N180D150>N0D225>N0D150during the entire growing stage which was from anthesis to 14 days after anthesis for T18. For S15, they were in same with T18 during the early and middle filling stage. But during the late filling stage which from14 days after anthesis to maturity, WLAI and TLAI increased first and then decreased with the nitrogen rate increasing in the same plant density; and WLAI and TLAI of high density treatment was higher than low density treatment when no nitrogen applied, but it was contrary to the nitrogen application treatments. It was showed that N180D150>N180D225>N240D150>N240D225>N0D150>N0D225 for WLAI and TLAI of S15 during the late filling stage.For T18, LLAI increased with the increasing of nitrogen rate and plant density, and it was showed that N240D225>N180D225>N240D150>N180D150>N0D225>N0D150 in the whole filling stage. For S15, LLAI increased first and then decreased with increasing of nitrogen rate in the same plant density; LLAI decreased with plant density increasing in the same nitrogen rate, and it was showed that N180D150 > N180D225 > N240D150 >N240D225>N0D150>N0D225 during the whole filling stage.For T18, CAP increased with the increasing of nitrogen rate and plant density. There was no significant difference among N240D225,N180D180,N240D150, but they were all significant higher than 180D150,N0D225,N0D150. For S15, CAP increased first and then decreased with nitrogen rate increasing, CAP of high plant density was lower than that of low plant density in the same nitrogen rate. The CAP of N180D150 was higher significantly than other treatments.Lower leaf area index (LLAI) was positively significantly correlated with CAP and grain yield during the lower leaf stay-green stage , which consists of the lower two layers of leaves on the stem ; Top leaf area index (TLAI) consists of the top three layers of leaves on the stem and Whole leaf area index (WLAI) which consists of all of the leaves on the stem were positively significantly correlated with CAP and grain yield for T18 but not for S15 so the relationship were not certainly within 14 days after anthesis; TLAI and WLAI were positively significantly correlated with CAP and grain yield for two kind of wheat from 14 days after anthesis to maturity.3 Effects of nitrogen rate and plant density on the characteristic of culm and lodging resistance for S15The effects of nitrogen rate and plant density on lodging resistance related traits including morphological character, chemical components of basal internode, culm lodging resistance index, enzyme activities of lignin metabolism and grain yield of winter wheat were investigated. The results showed that grain yield were decreased and culm height of center of gravity and length of basal internode were raised as nitrogen rate increased from 180 kg·ha-1 to 240 kg·ha-1 or plant density increased from 150 ha-1 to 225 ha-1, while diameter, thickness, filling degree, mechanical strength of basal internode, and culm lodging resistance index were reduced. At the same time, cellulose content, lignin content, C/N ratio of basal internode were decreased but nitrogen content was increased with the increase of nitrogen rate or plant density. There existed significant interaction on lodging resistance between nitrogen rate and plant density, which led to worst lodging resistance in wheat plant under higher nitrogen rate plus higher plant density. Stepwize regression analysis indicated that nitrogen rate played a more important role in affecting lodging resistance compared with plant density. The highest kernels per spike, 1000 kernel weight and grain yield were gained with 180 kg·ha-1 nitrogen application rate plus 150 ha-1 basic seedlings. Therefore, proper combination with 180 kg·ha-1 nitrogen application rate plus 150 ha-1 basic seedlings could not only improve lodging resistance but also raise grain yield.4 Effects of nitrogen application on the changes of NO₃^--N content in 0-200cm soil profile with time.During the early growing stage, Content of NO₃^--N in 0-40cm soil profile is higher relatively. With nitrogen rate increasing, content of NO₃^--N in 0-40cm soil profile increased significantly but not significantly for that in 40-200cm. During the middle and late state, the peak value of NO₃^--N accumulation moved downwards obviously. The content NO₃^--N of 2009-2010 growing season was lower significantly than that of 2008-2009 growing season. It was showed reducing nitrogen amount successively in two growing seasons could decrease the content of NO₃^--N effectively.5. Efffect of interactions of nitrogen and density on fertilizer use efficiencyIn the early and middle growing stages of two types of wheat cultivars, nitrogen, phosphorus and potassium absorption volume improved with increasing of nitrogen rate and plant density. In the late stage of wheat, N, P and K uptake of T18 were still improved with increase of density and nitrogen, but for S15 showed that N, P and K uptake increased first and then decreased in the same plant density. There were significant positive correlations among N, P, K, and uptake of nitrogen could improve the absorption of phosphourus and potassium.In the same density condition, NUE, AEN, PEN and PFPN with the nitrogen rate increasing are increased for two types of wheat cultivars. In the same nitrogen levels, NUE, AEN, PEN and PFPN of T18 with the increasing of density increased and then decreased. NUE, AEN, PEN sand PFPN of S15 with the increasing of density decreased. For T18, increasing density appropriately could be increased NUE, AEN, PEN and PFPN at the same time, but increasing density was not conducive to improve NUE, AEN, PEN and PFPN of S15.For two ear types of wheat, in the same density conditions, PUE and KUE decreased with increasing of nitrogen rate. PFPP and PFPK of T18 increased with increasing nitrogen rate, but for S15 PFPP and PFPK increased and then decreased with nitrogen rate increasing. PUE, PFPP, KUE and PFPK of T18 increased and then decreased with the increase of density, but PUE, PFPP, KUE and PFPK of S15 decreased with the increasing of plant density in the same nitrogen rate.Under the experimental conditions, for T18, increasing density appropriately could increased PUE, PFPP, KUE, PFPK at the same time, but increasing density was not conducive to improve PUE, PFPP, KUE, PFPK of S15.As far as the relationship between yield, canopy structure and photosynthetic performance, between the morphological characteristics and lodging, changes of soil nitrate and fertilizer use efficiency were considered, N180D225 treatment of T18 and N180D150 of S15 were high-stable yield, ecological and efficient treatments of nitrogen and density combinations.