Effects Of Nitrogen Reduction On Rice Growth,Yield And Nitrogen Use Efficiency

Rice is an important food crop in our country,and maximizing rice yield is conducive to maintaining national food security.Nitrogen application rate significantly affected the growth and development of rice,and also have a certain impact on soil physical and chemical properties such as soil structure,organic matter and nutrient status.Excessive application of nitrogen fertilizer will not only increase production costs,environmental pollution,but also have an adverse impact on ecosystems and biodiversity.Water-saving and drought-resistant rice is a new type of rice that has the characteristics of high yield,quality and water use efficiency.In the past,researches on water-saving and drought-resistant rice mostly focused on water stress,and there was less research on reduced nitrogen application.In this pot experiment,using HY73（water-saving and drought-resistant rice,WDR）,CLYHZ and FLYX1（super rice,SR）as test materials,set up three nitrogen treatments,N0（no nitrogen application）,N1(nitrogen reduction by 36%,1.8g·pot^-1),N2(normal nitrogen application rate,2.8 g·pot^-1)to study the effects of reduced nitrogen application on agronomic characteristics,root and leaf growth characteristics,nitrogen absorption and utilization,and soil fertility of different rice varieties.The main results are as follows:（1）In HY73 and FLYX1,there was no significant difference between yield and its constituent factors of nitrogen reduction and normal nitrogen application.while FLYX1had the highest yield under N1 nitrogen fertilizer level,which was 44.06 g·pot^-1.Compared with normal nitrogen application,under nitrogen reduction conditions,the effective panicles per pot of HY73 and FLYX1 increased by 23.08%and 8.57%,respectively.And the seed setting rate and 1000-grain weight of FLYX1 increased by 7.25%and 5.03%,respectively.In different nitrogen treatments,the yield was CLYHZ>FLYX1>HY73.The effect of varieties on the number of effective panicles per pot was basically the same as the yield.HY73 was significantly lower than CLYHZ and FLYX1 by 52.51%～83.75%and36.59%～62.86%,respectively.（2）Except for individual treatments,in different varieties of rice,there was no significant difference between the quality of rice with nitrogen reduction and normal nitrogen application.In HY73,the chalkiness degree under N0 nitrogen fertilizer level was12.62%higher than that of FLYX1,the chalkiness under N1 nitrogen fertilizer level was significantly higher than that of SR,and the head milled rice rate under N2 nitrogen fertilizer level was slightly higher than that of SR.While the variety had no significant effect on brown rice rate,milled rice rate and amylose content.（3）Compared with normal nitrogen application,nitrogen reduction had no effect on the time of peak tillering number,leaf superoxide dismutase activity,leaf malondialdehyde content,root soluble sugar content and root proline at tillering stage.There were no significant differences in acid content,root morphology at tillering and heading stages,and total root absorption area at maturity stage.Under different nitrogen application treatments,the plant height,tiller number,total biomass,plant nitrogen uptake,ear dry matter distribution index,ear carbon-nitrogen ratio,root length,root diameter,root surface area and root volume of HY73 were basically lower than those of SR,while the stem dry matter distribution index was significantly higher than that of SR.Compared with SR,the content of osmotic adjustment substances and sucrose synthase activity in roots and leaves of HY73at grain filling stage were more sensitive to nitrogen fertilization.（4）In soil nutrient indicators,the effect of nitrogen application rate on the total nitrogen content,total carbon content and soil carbon to nitrogen ratio in the soil did not reach a significant level.Nitrogen reduction can increase soil p H at tillering stage,and decrease the content of soil available phosphorus and available potassium.The soil nutrients was also related to the characteristics of the variety.The overall performance was that the soil nutrients of HY73 was higher than that of SR.（5）Different rice varieties had different performances in nitrogen contribution rate（NCR）,nitrogen agronomic efficiency（NAE）and nitrogen partial factor productivity（NPFP）.Compared with N2,the nitrogen dry matter production efficiency（NDMPE）and soil nitrogen dependence rate（SNDR）of N1 increased by 12.13%～26.54%and 41.81%～90.90%,respectively,while the apparent utilization rate decreased by 9.09%～38.30%.Different rice varieties had different responses to nitrogen.Under the experimental conditions,the nitrogen utilization efficiency of SR was basically higher than that of WDR.The results of this study showed that nitrogen reduction can improve the morphological index of roots and leaves in the whole growth period and promote the absorption of nutrients,thereby increasing the yield.There were significant differences between WDR and SR in terms of root and leaf growth,yield,and nitrogen use efficiency.The basic performance was that SR was better than WDR,which may be related to variety characteristics,weather conditions（long-term extremes and low temperature rainfall from heading to filling stage）and soil type.