Effect Of Nitrogen Topdressing And Chemical Control With Paclobutrazol In Spring On The Dynamics Of Growth And Development Of Winter Wheat

Effect of topdressing nitrogen in spring on growth and development of winterwheat has been repeatedly reported and paclobutrazol as chemical control agent iswidely used in wheat production. However, researches which combine the twotechniques to control the growth and yield of winter wheat had been reportedseldomly. The experiments were conducted during2011-2012in the core area of thenational science and technology project for food production (Gaocheng city), in whichexperimental material was the local winter wheat cultivar shimai18. With the totalnitrogen application of240kg/hm2and basal-topdressing ratio5:5, four differentcombination treatments, namely topdressing nitrogen+chemical control agent andtopdressing nitrogen+0chemical control agent at double ridges and jointingseparately, were carried out to explore the effects of the combination of topdressingnitrogen and paclobutrazol spraying in spring on dynamic of growth and developmentof winter wheat. The main results were summarized as follows:1、Topdressing nitrogen fertilizer and spraying paclobutrazol at jointing cansignificantly improve the material production ability after anthesis. By the method ofdelaying the degradation of chlorophyll a and b, the high light area and photosyntheticrate can be maintained during the late stage of wheat development, the accumulationof carbon assimilation, the transfer of soluble sugar accumulated by flag leaf to kerneland soluble sugar content of kernels all can be increased, which will keep adequatesupplies of the substrate for grain starch synthesis.2、Topdressing nitrogen fertilizer at jointing can significantly increase thenitrogen accumulation of wheat growth period, while there is no significant effect ofspraying paclobutrazol on nitrogen accumulation. Topdressing nitrogen at jointing isbeneficial to the transfer of nitrogen accumulated during the periods of pre-anthesisand increase the contribution rate of nitrogen accumulated after anthesis to grain.While at standing topdressing nitrogen can benefit the nitrogen accumulation afteranthesis and improve contribution rate of nitrogen to grain after anthesis; there is nosignificant impact of the paclobutrazol treatment on nitrogen transport. Comparingwith standing, topdressing nitrogen at the jointing makes higher protein content ofwheat grain and contributes to the high quality formation of wheat.3、It is advantageous to coordinate the individual contradiction and promote drymatter accumulation and transfer after anthesis by the method of topdressing nitrogen fertilizer at jointing and spraying paclobutrazol. This method is benefit to formhealthy individual and suitable groups at the early stage, reduce ineffective tilleringand peak seedling at the medium stage, decrease the loss of nutrition at early stageand form a group of high photosynthetic efficiency at the later stage. Thus variationsin the total number of stem changes gently in the whole development process.Tillerdynamics can be formed reasonably and the spike rates will be enhanced to achieveappropriate spikes. This method can improve the early accumulation of dry matter andthe transport rate after anthesis.4、Topdressing nitrogen fertilizer and spraying paclobutrazol at jointing cansignificantly promote the increase of grain number apparently. Topdressing nitrogen atjointing has obviously decreased the number of infertility spikelet, increased thestronger spikelet number and accelerated the formation of wheat florets. Sprayingpaclobutrazol can increase the number of wheat florets. Through topdressing nitrogenfertilizer and spraying paclobutrazol at jointing, endogenous hormones IAA and ABAcontent of young ear were decreased, however, at standing the ZR content of youngear will become higher at stamen and pistil differentiation stage.5、The yield and lodging resistance of wheat can all be enhanced by the methodof topdressing nitrogen fertilizer and spraying paclobutrazol at jointing. Topdressingnitrogen treatment can make higher increase of grain-filling rate after anthesis andpromote the formation of grain wheat. Topdressing nitrogen fertilizer and sprayingpaclobutrazol at jointing can also control of the growth of wheat at seedling, prolongthe maintain time of the larger LAI after anthesis, promote the growth of later period,optimize the structure of production, increase the grain yield, shorten1,2internodelength of wheat base, reduce the plant height and improve stem thickness, plumpnessand the lodging resistance.This paper indicates that when the total nitrogen application is240kg/hm2andthe basal-topdressing ratio is5:5, combining control of topdressing nitrogen andpaclobutrazol at jointing plays a key role in increasing production and lodgingresistance and is an effective way to improve the yield and lodging resistance ofsuper-high-yield winter wheat in Hebei province.