| Nitrogen is the most important nutrient element in rice production.The high yield of rice is closely related to the application of nitrogen fertilizer.As a simple cultivation technique,direct seeding has the advantages of time saving and labor saving.There are a lot of studies on the effect of nitrogen application rate on the growth and yield formation of rice,but there are few reports on the effect of nitrogen application rate on the growth and yield formation of direct seeding rice in cold regions.Therefore,it is of great significance to explore the effect of nitrogen application rate on the growth and yield formation of direct seeding rice in cold regions.The experiment was carried out in Acheng Practice Base of Northeast Agricultural University in 2020,with Suijing 18 and Longqingdao 21 as test materials.Five nitrogen fertilizer levels were set up,and the application rates of pure nitrogen per hectare were 0,50,100,150 and 200 kg,respectively,which were recorded as N0,N1,N2,N3 and N4.To explore the effects of different nitrogen application rates on the growth and development,dry matter accumulation and distribution,nitrogen absorption and utilization,grain filling characteristics,yield and its components of direct seeding rice in cold region.In order to provide theoretical basis and technical support for the formulation of technical measures of direct seeding cultivation and rational fertilization of direct seeding rice in cold region,the optimum nitrogen application rate was determined.The main results of this study are as follows :(1)Under different nitrogen rates,plant height,maximum tiller number,final tiller number,efficient leaf area index and leaf area attenuation rate of the two varieties were significantly affected.Compared with N1 treatment,plant height,maximum tiller number,final tiller number,efficient leaf area index and leaf area attenuation rate of N2,N3 and N4 treatments were significantly increased,but the difference between the final tiller number and the high-efficiency leaf area index of N3 and N4 treatments was not significant.N3 treatment was more conducive to the growth and development of direct seeding rice and the construction of high-yield population.N4 treatment increased the occurrence of ineffective tillers,reduced the spike rate,increased the leaf area attenuation rate and reduced the high-efficiency leaf area rate.(2)The effects of different nitrogen application rates on stem-sheath output,stem-sheath output rate and stem-sheath transformation contribution rate of the two varieties were significantly different.The stem-sheath output,stem-sheath output rate and stem-sheath transformation contribution rate of the two varieties showed N3 > N4 > N2 > N1,and the output rate of N3 treatment was significantly higher than that of other treatments.The increase of nitrogen application rate promoted the increase of stem and sheath dry matter output,but when the nitrogen application rate was too high,the leaf and stem sheath of rice grew too fast,and the spike grew slowly,resulting in the decrease of stem and sheath dry matter output,output rate and transformation contribution rate.Correlation analysis showed that dry matter of stem sheath between output and yield of rice was significantly positively related,and N3 treatment was more conducive to rice grain accumulation.(3)The effects of different nitrogen application rates on the distribution ratios of roots,stem sheaths,leaves and panicles of the two varieties at different growth stages were significantly different.With the increase of nitrogen application rate,the proportion of dry matter distribution in leaves increased,but the proportion of dry matter distribution in roots,stems,sheaths and panicles decreased.In mature panicle dry matter distribution ratio between the nitrogen treatment are to reduce with the increase of nitrogen application,and N4 interchange treatment was significantly lower than other nitrogen treatment.The difference between N1,N2 and N3 was not significant.The dry matter distribution ratio of stem sheath and panicles increased with the increase of nitrogen application rate.The increase in nitrogen application rate promoted the improvement of photosynthetic capacity of plants after heading,but when the amount of nitrogen cause leaf and stem sheath allocation proportion is too high,panicle allocation proportion is too low.N3 treatment was more conducive to the accumulation of photosynthetic products and the establishment of panicles in rice.(4)The effects of different nitrogen application rates on nitrogen output,nitrogen output rate,contribution rate of nitrogen transport and rice production efficiency of the two varieties were significant.Two varieties of nitrogen output and nitrogen output rate and transshipment nitrogen contribution rate of N3 > N4 > N2 > N1,and nitrogen output N3 treatment rate were significantly higher than that of other nitrogen treatment.The rice production efficiency of the two varieties decreased with the increase of nitrogen application rate,and the N4 treatment was significantly lower than other treatments.The increase of nitrogen application rate promoted the increase of nitrogen output,but when the nitrogen application rate was too high,the nitrogen accumulation in vegetative organs was excessive,and the nitrogen accumulation in panicles decreased.N3 treatment was more conducive to the nitrogen accumulation in panicles of rice.(5)Different n application rate on the two varieties of plant nitrogen utilization efficiency,nitrogen uptake agriculture utilization efficiency,nitrogen harvest index and nitrogen physiological utilization efficiency,nitrogen partial productivity significant difference,the influence of nitrogen absorption efficiency,nitrogen utilization rate of agronomy,nitrogen harvest index and nitrogen physiological utilization efficiency,nitrogen partial productivity decreased with increasing nitrogen application rate,and N4 interchange under the treatment of nitrogen agronomy efficiency and nitrogen harvest index was significantly lower than in other nitrogen treatment.(6)Under different nitrogen rates,the yield and yield components of the two varieties were significantly affected.The yield of two varieties showed N3 > N4 > N2 > N1,and N3 and N4 treatments were significantly higher than other treatments.There was no significant difference between N3 and N4 treatments.The effective panicle number and grain number per panicle increased with the increase of nitrogen application rate,and N3 and N4 treatments were significantly higher than other treatments.N3 and N4 interchange with no significant difference between grains and seed setting rate were characterized by N1 > N2 > N3 > N4 interchange,and N4 interchange was significantly lower than other nitrogen treatment.The increase of nitrogen application rate was beneficial to increase effective panicle number,promote spikelet differentiation and increase rice yield.However,when the nitrogen application rate was excessive,the excessive population led to the weakening of individual advantages,the prominent contradiction between yield components,and the decline of yield.N3 treatment was more conducive to coordinating the development of yield components and the increase of rice yield. |
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