| In recent years,with the improvement of people’s living standards,the market demand for japonica rice with good eating quality is growing.The rational application of N fertilizer is an important cultivation measure to increase rice yield and improve rice quality.The common fertilizer application methods in rice production include conventional N fertilizer split application,soil testing and formulated fertilization,etc.However,these methods require multiple fertilization.However,with the decrease of rural labor force and the increase of labor cost,rice production urgently needs one-time fertilization which can achieve stable yield and improve rice quality.Therefore,we carried out the experiment in the rice season(May～October)in 2018 and 2019.Under the rice mechanically transplanted pot-seedlings and pure N application rate of 270 kg hm-2,the late-maturing mid-japonica varieties Nanjing 9108 and Fengjing 1606 with good eating quality were used as field materials,and the CRU and conventional N fertilizer were combined at a fixed ratio of 5:5,while the CRU portion was composed of 2 kinds of CRU with different release periods.These combinations include 40%60d+10%40d,40%60d+10%80d,40%80d+10%100d,40%100d+10%80d,and 40%100d+10%120d,and they are recorded as 60+40,60+80,80+60,80+100,100+80 and 100+120 treatments respectively.The conventional split fertilization(CK)was used as the control.The effects of different mixed N fertilizer treatments on rice yield,population quality,N absorption and utilization and rice quality characteristics were systematically studied,in order to select a one-time mixed N fertilizer formula suitable for high yield and high-quality synergy of late-maturity medium japonica rice with good eating quality by mechanical transplanting of pot seedlings.1.Yield and population quality:compared with CK,the average yield of 100+80 treatment increased by 4.66%under Nanjing 9108 and 4.29%under Fengjing 1606,which was due to the significant increase in effective panicle and population spikelet,but no significant difference in grain number per panicle and seed setting rate.Except for Nanjing 9108 in 2019,the yield of 100+120 treatment is second only to that of 100+80 treatment.The yield of 80+60 and 80+100 treatments was not significantly different from that of CK in two years,while the yield of 60+40 and 60+80 treatments was significantly reduced compared with that of CK.Compared with CK,the N supply characteristics of mixed N fertilizer treatment were beneficial to promoting the occurrence of tillering and improving the population photosynthetic production capacity before jointing.However,during the jointing to heading stage,compared with CK,the nutrient supplies only treated with 100+80 and 100+120 could consolidate more tillers to form effective panicles,promote panicle differentiation and development,maintain or improve individual plant type of rice,increase leaf area index at heading stage,increase photosynthetic potential and stabilize population growth rate,laying the foundation for higher population photosynthetic production capacity after heading.Therefore,from heading to maturity,under higher photosynthetic potential and population growth rate,the dry matter accumulation in the shoot of population under the treatments of 100+80 and 100+120 increased significantly by 5.44%-8.58%compared with CK.Compared with other mixed N fertilizer treatments,except before jointing,the 100+80 and 100+120 treatments had higher population photosynthetic production capacity and larger spikelets,that is,the "source-sink" was increased coordinately.Therefore,the N release characteristics under one-time application of 100+80 and 100+120 formulations were most conducive to the formation of high-yielding population of late-maturing medium-japonica rice.2.Nitrogen uptake and utilization:Among all treatments,N accumulation in the shoot at maturity stage was the highest in 100+80 and 100+120 treatments,which increased by 2.95%～5.64%compared with CK,while the lowest in 60+40 and 60+80 treatments,which decreased by 4.2%-8.33%compared with CK.Compared with CK,the N accumulation and proportion at different growth stages under the treatments of 100+80 and 100+120 were the closest.Among the mixed N fertilizer treatments,the N accumulation and proportion under the treatments of 100+80 and 100+120 were the lowest from sowing to jointing stage,and were the highest at the two stages of jointing to heading and heading to maturity.More N accumulation from jointing to heading was beneficial to the formation of spikelet number and high yield.The above results indicated that the N release characteristics of these 2 treatments were the most suitable for N absorption in late maturing japonica rice.For N transport,the N transport amounts under 80+100,100+80 and CK treatments were all at high levels,while the value under 100+120 treatment was at the lowest level,which might be due to the apparent reduction of N transport amount due to more N accumulation after heading.In terms of N allocation,there was no significant difference between 80+60,80+100,100+80,100+120 and CK treatments in N accumulation of panicles at maturity stage.However,due to the larger sink capacity,N availability per unit sink capacity of 100+80 treatment was relatively lower than that of other treatments,which was closely related to the change of rice protein content.For N use efficiency,the partial productivity and agronomy N use efficiency of 100+80 treatments increased by 3.90%～4.92%and 9.42%～11.93%,respectively,compared with CK;the apparent N use efficiency of 100+80 and 100+120 treatments increased by 5.29%～7.21%and 5.79%-8.51%,respectively,compared with CK.Therefore,the N release of 100+80 and 100+120 formulas applied at one time was the best match with the N uptake of late maturing medium japonica rice,which was conducive to promoting the N uptake and accumulation and improving the N use efficiency.3.Rice quality:Compared with CK,60+40,60+80 and 100+80 treatments had lower protein content and higher amylose content of milled rice,while these 3 treatments had higher taste value and gel consistency,peak viscosity and breakdown value in RVA spectrum and viscosity in texture.The above index values of 80+60,80+100 and 100+120 treatments were all similar to CK.As for the processing quality,compared with CK,each mixed N fertilizer treatment failed to significantly improve these indexes.As for appearance quality,80+60 and 100+120 treatments were the best,while 60+40,60+80 and 100+80 treatments were the worst,but the chalkiness of 100+80 treatments showed no significant difference with CK.To sum up,under the condition of mechanical pot-seedling transplanting method,for the late-maturing medium japonica varieties with good eating quality rice—Nanjing 9108 and Fengjing 1606,100+80 treatment can not only achieve high yield and improve the N utilization efficiency,also can ensure the quality of rice,especially improve the eating quality.Therefore,it can be used as a one-time mixed N fertilizer formula for high yield and good quality coordination of late-maturity medium japonica rice with high good eating quality under the condition of mechanical pot-seedling transplanting. |
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