Characteristics Of Warm And Light Resource Utilization,Yield And Quality In Late Sowing Rice And Its Regulation

At present,the rice-wheat double-cropping production in the lower reaches of Jianghuai River has entered the "double-late cropping mode",which leads to great changes in the utilization of temperature and light resources in and between seasons of rice.It is of great significance to clarify the characteristics of the utilization of temperature and light resources and the formation of yield and quality of late sowing japonica rice and to put forward the regulation and control technical measures for high yield and good quality rice production.The experiment was conducted in the Diaoyu town of Xinghua City from 2018 to 2019.Rice was planted with late maturing medium japonica Nanjing 9108.In this study,under the condition of late sowing and late transplanting(sowing at June 12,transplanting at June 30).The machine transplanting mode was adopted,4 pure nitrogen application rates(N0:0 kg hm-2;N240:240 kg hm’2;N300:300 kg hm’2;N360:3 60 kg hm-2),and 3 types of seedling number planted in each hole(D3:3 seedlings,D4:4 seedlings,D5:5 seedlings)were set.The suitable sowing period(May 29)and the conventional nitrogen application rate and seedling number planted in each hole(N300D4)were applied as the control(CK),which aimed to explore the effects of nitrogen fertilizer and seedling number planted in each hole on the growth and yield formation of late-sown japonica rice,and provide theoretical basis for improving yield potential and resource use efficiency of late sowing and late transplanting japonica rice in central Jiangsu province.The main results are as follows:(1)With the delay of sowing date,the whole growth period of japonica rice was shortened,and the reaction from sowing to jointing stage was the most sensitive.During the whole growth period,the effective accumulated temperature and the total radiation decreased,and the average daily temperature increased higher during the seeding and jointing stages,and decreased after jointing.With the increase of nitrogen application rate,the heading and maturity stages of late sowing and late planting j aponica rice were all delayed,and the days of the whole growth period increased,which resulted in the increase of effective accumulated temperature and total radiation in the whole growth period.(2)The yield and its components of late sowing and late planting japonica rice were significantly affected by nitrogen application rate and number of hole planting seedlings.Compared with CK,the maximum population spikelets decreased by 11.94%and 8.12%in two years,respectively,which was the main reason for the decrease of sowing date.The highest yield of late sown and late transplanting japonica rice was N300D5 followed by N360D4.Increasing nitrogen application rate and number of hole planting seedlings could significantly increase the spikelet quantity of late sown and late transplanting japonica rice population.However,when the nitrogen application rate was up to 360 kg N hm-2,the seed setting rate and 1000-grain weight would significantly decrease,and the yield could not be further increased.Under the condition of late sowing and late planting,increasing the number of basic seedlings should be considered first,and then combining with the appropriate amount of nitrogen fertilizer can alleviate the yield loss.(3)The delay of sowing date resulted in insufficient dry matter accumulation in the middle and later stages of japonica rice growth,relatively low proportion of efficient leaf area at heading stage,and rapid leaf area attenuation rate after heading,which ultimately led to the decrease of photosynthetic potential,population growth rate and net assimilation rate at later growth stage.Leaf area index(LAI)and dry matter accumulation of late sowing and late planting japonica rice increased with the increase of nitrogen application rate and the number of hole planting seedlings.However,with the advance of growth process,rice overgrew with large population,serious shading and intense population competition at high nitrogen level,which led to the decrease of photosynthetic potential,population growth rate and net assimilation rate.(4)With the delay of sowing date,the length of apex trefoil of japonica rice shortened,the specific leaf weight decreased,and the basal Angle and drape of japonica rice increased,which was not conducive to the formation of ideal light exposure posture.The number of primary and secondary branches and grain density decreased.Stem reduced an internode,plant height decreased.Increasing nitrogen fertilizer and decreasing the number of hole seedlings could improve the plant type traits of late sowing and late planting japonica rice.(5)In late sowing period,the total nitrogen uptake and nitrogen use efficiency decreased.With the increase of nitrogen application rate and the number of seedlings in hole,the total nitrogen uptake at mature stage of the plant was significantly increased,and the nitrogen uptake at each organ of stem,leaf and ear showed an upward trend,but the nitrogen uptake ratio at ear decreased.With the increase of N application rate,N absorption and utilization rate,agronomic and physiological utilization rate increased firstly and then decreased.With the increase of the number of hole seedlings,N absorption and utilization rate increased under each N application rate,and agronomic and physiological utilization rate increased under the N application rate of N240 and N300.However,the agronomic and physiological utilization rates of 5 seedlings per hole were lower than those of 3 and 4 seedlings per hole under N application rate of N360.(6)With the delay of sowing date,the processing quality and appearance quality of japonica rice became better,while the nutritional quality,cooking and eating quality became worse.In the range of 0～300 kg hm-2 nitrogen application,increasing nitrogen application could increase the brown rice rate,milled rice rate and whole milled rice rate of late sowing and late planting japonica rice,and improve the processing quality.The appearance quality became worse when the application rate of nitrogen fertilizer was too high,and the appearance quality was the best under N240 treatment.With the increase of nitrogen application,the quality of nutrition becomes better and the cooking and eating quality becomes worse.The processing quality,appearance quality,cooking and eating quality became worse,the protein content increased,and the nutrition quality became better with the increase of the number of seedlings in the hole.Medium nitrogen and low density are effective cultivation measures to improve rice quality of late sowing and late planting japonica rice.