| The experiment was conducted in the comprehensive demonstration base of rice and wheat science and technology in Shengao Town,Jiangyan District,Jiangsu Province in 2018-2019.The soil type was paddy soil with sticky texture.The previous crop of the experimental site was wheat,and the yield was about 7.16 t hm-2.The test material is Nanjing 9108,a late-maturing medium japonica.The experiment adopted split-zone design,with nitrogen application rate(N)as the main zone and topdressing leaf age(L)as the split zone.Two nitrogen fertilizer levels were set,with pure nitrogen of 180 kg hm-2(N1)and 225 kg hm-2(N2)respectively.Five topdressing leaf ages were set under each nitrogen fertilizer level,namely six leaf stage(L6)and seven leaf stage(L7)In N1 treatment,150 kg hm-2 of urea and 750 kg hm-2 of 45%compound fertilizer were applied once at each leaf age,and i1 N2 treatment,98 kg hm-2 of urea was applied after 7 days on the basis of N1 fertilization.37 kg hm-2 calcium superphosphate and 179.5 kg hm-2 potassium chloride were applied to the base fertilizer treated by Nl and N2,and the base fertilizer in each plot was spread before mechanical operation.The effects of different nitrogen fertilizer levels and different topdressing leaf ages on the yield and quality formation,dry matter production and nitrogen absorption and utilization of dry direct seeding rice were systematically compared,in order to provide data support for the simplified cultivation technology renewal of mechanical dry direct seeding rice with nitrogen reduction,high quality,high yield and light weight under the condition of straw returning to the field in double cropping area.The main research results are as follows:1.The results showed that rice yield showed a trend of first increased and then decreased with nitrogen application at bigger leaf age.Rice yield was significantly higher than other treatments when applying nitrogen fertilizer at the 8-leaf stage,and the yield was further improved with the increase of nitrogen application amount.Compare with the controls,nitrogen fertilizer in whole growth duration of 100 kg N hm-2 applied one time at 8-leaf stage could significantly increase rice yield by 5.10%and 8.65%,and reduced nitrogen fertilizer by 33.3%,whereras nitrogen fertilizer in whole growth duration of 225 kg N hm-2 applied two time at 8-leaf stage and 7 days later could significantly increase rice yield by 7.46%and 11.09%,and reduced the nitrogen by 16.7%,The reason was that,compared with the control,seed setting rate and 1000-grain weight,effective panicle number was significantly increased resulting in the increasing total spikelet amount per hectare and yield on the basis of maintaining larger panicle type.With nitrogen applied at bigger leaf age,the head rice rate,chalkiness and protein content of rice revealed an increasing trend,but the amylose content and taste value of rice showed a decreasing trend.Compare to the two controls,the processing quality of rice with the head rice rate was increased by 0.67%～2.23%with nitrogen fertilizer in whole growth duration applied at 8-leaf age;the appearance quality was improved with the chalkiness decreased by 3.6%～14.5%;the nutrition quality was better with protein content increased by 3.03%～14.08%;the cooking and eating quality showed a tendency of getting better with amylose content decreased by 4.23%～10.95%;and there was no insignificant difference in taste value.2.Under the research conditions,applying nitrogen fertilizer at L8 leaf age can maintain a high and stable leaf area index and total dry matter accumulation from heading to maturity.During the middle growth stage(jointing to heading stage),there were high dry matter accumulation and proportion,photo synthetic potential,population growth rate and net assimilation rate,and the photosynthetic potential remained at a high level after heading.At the same time,the efficient leaf area and grain-leaf ratio(spikelet/leaf,grain/leaf)of L8 treatment increased significantly at heading stage,and the specific leaf weight of the upper three leaves,the length and drape of the inverted two leaves were significantly higher than those of other treatments.L8 treatment maintained a high transport amount of photosynthetic substances in stems and sheaths from heading to milk maturity and from milk maturity to maturity,and its maximum output rate was significantly higher than other treatments.Therefore,the application of nitrogen fertilizer in combination with L8 treatment can significantly control the material production in the early growth stage of rice(from sowing to jointing stage),strengthen "small individuals" to achieve high-quality "small groups" in the middle and late growth stage,significantly improve the photosynthetic material production in the middle growth stage(jointing to heading stage),form a high-quality group with sufficient quantity and reasonable structure in heading stage,maintain high-level photo synthetic production characteristics,and significantly improve the dryness in the late growth stage(heading to maturity stage).3.This study showed that applying nitrogen fertilizer without base fertilizer and the whole process of nitrogen fertilizer at L8 leaf age could keep a high level of nitrogen accumulation in rice at heading and maturity,and it increased significantly with the increase of nitrogen application rate.In addition,the nitrogen transport quantity,transport rate and contribution rate of stem sheath and leaf treated by L8 were also at a high level.In terms of nitrogen use efficiency,L8 treatment had the highest nitrogen harvest index,nitrogen agronomy use efficiency and nitrogen partial productivity,but N2 treatment was significantly lower than N1 treatment with the increase of nitrogen application rate.Nitrogen absorption and utilization rate and nitrogen uptake per 100 kg of grain increased significantly with the increase of nitrogen application rate,while nitrogen physiological utilization rate decreased significantly with the increase of nitrogen application rate.Therefore,applying nitrogen fertilizer at L8 leaf age can ensure stable nitrogen absorption at early growth stage of rice,greatly improve nitrogen absorption at middle and late growth stage,and form the characteristics of "stable before,middle foot and excellent after",which is beneficial to the formation of high yield of rice. |
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