Effects Of Foliar Spraying Urea On Nitrogen Uptake, Utilization, Distribution, Physiological And Biochemical Characteristics Of Cotton

Crop foliar fertilization has the advantage of being absored rapidly, high utilization rate and strongtarget. In addition, it can avoid soil fixation and reduce environmental pollution, etc. It also has usefuleffect on disaster resistance and reduction. Currently, foliar fertilization technology has been widelyused in cotton production. And nitrogen fertilizer is one of the most commonly used foliar fertilizar.Wewant to provide technical and theoretical basis for foliar nitrogen application of cotton by exploring theeffects of foliar spraying urea on the characteristics of nitrogen absorption and utilization in cotton andunderstanding the mechanism to promote the growth of cotton. Therefore, we designed the followingtwo tests by using15N isotope tracer techniques in cotton seedling and blooming period. The first studywas undertaken on cotton cultivar CCRI79under field experimental condition which was foliar sprayedwith0%,0.5%,1%,2%four different concentrations of15N-urea solution during cotton seedling toinvestigate the effects of foliar spraying15N-urea on nitrogen uptake, utilization, physiological andbiochemical characteristics of cotton. The second study was undertaken on cotton cultivar CCRI79under field condition which was foliar sprayed with0%,1%,2%,3%,4%five different concentrationsof15N-urea solution during cotton blooming period to investigate the distribution of15N content invarious parts of cotton plant, the proportion of nitrogen uptake in vegetative organs and reproductiveorgans of cotton.Results of the first experiment:Foliage spraying15N-urea can significantly improve the15N content in cotton plant which isconsistent with the trend of time. And the15N content that uptake by cotton leaf increased graduallyovertime, between2～96h after foliage spraying urea. It reached the highest value after spraying96hthen it started to decline. And cotton plants can quickly absorb15N-urea by foliar sprayed. The averageabsorption rate of cotton leaf nitrogen has consistent trend among different treatment. And theabsorption rate appeared to reduce after spraying2～4h due to stomatal closure，But it reached thehighest value during4～6h in which sharply rising. It decline sharply during6～8h, fast during8～12h,and slowly after12h. It is0.23～0.29mg/(g.h) that is very high during0～12h. Cotton plant canmainly absorb the foliage nitrogen during0～12h after spraying. Foliar absorption can promote rootnitrogen uptake significantly and the nitrogen absorbed by root was quickly transported to the aerialparts for plants under the treatment of0.5%,1%urea concentration.During the urea spraying concentration of0%to1%, nitrate reductase, glutamine synthetaseactivity and chlorophyll content have consistent trend which increases with increasing concentration.The physiological and biochemical indexes peaked at the treatment of1%nitrogen concentration, thenthey began to decline. This suggests that spraying a suitable concentration of urea can significantlyincrease the nitriogen metabolism of the cotton plant, and can play a role in the carbon promoting bynitrogen. So it can facilitate photosynthesis.Results of the second experiment: During the urea spraying concentration of1%to4%, the15N content in roots, stems, leaves andflowers of cotton have consistent trend which increases with increasing concentration. By sprayingdifferent concentrations of15N-urea in boll of cotton, the distribution of15N content in all parts of thecotton plant is basically the same, which is of7.1%～8.3%in root,12.8%～13.2%in stems,47.4%～48.6%in leaves,31.4%～31.8%in boll. The ratio of foliage absorbed nitrogen used by cotton nutritionand reproductive growth is7:3approximatelyDuring the urea spraying concentration of1%to4%, nitrate reductase, glutamine synthetaseactivity, chlorophyll content, leaf area index and net photosynthetic rate have consistent trend whichincreases with increasing concentration. Every indicators of each treatment were significantly higherthan that of the control treatment. And the above indicators have reached the peak at the treatment of4%urea concentration. To sum up，in the blooming period of cotton, foliar nitrogen application can promotephotosynthesis by increasing the activity of nitrate reductase and glutamine synthetase, increasing thechlorophyll content, improving leaf area and forming a reasonable leaf area index of cotton group. Inshort, this approach can promote the cotton plant growth, increase cotton production. During the ureaspraying concentration of1%～4%, foliar uptake and root absorption of nitrogen can mutuallypromote each other, in Blooming period of cotton. And the suitable urea concentration for foliarapplication is3.24%in Blooming period of cotton.