| In China nitrogen utilization efficiency(NUE) is relatively low which is only 30%-35% far under world average level because of the excessive usage of nitrogen fertilizer in irrigated low land rice systems. Large amounts of nitrogen fertilizer is lost by volatilization、denitrification、surface runoff leakage and so on, which caused ground water pollution、eutrophication and global worming. It is a presently studying hotspot that how to make the optimization of nitrogen management in rice according to crop nitrogen (N) demand, ensuring high yield, food security at the same time, to reduce the waste of unnecessary ferterlizer and to improve the NUE. At present, in nitrogen management the caculation of total nitrogen amount almost use the general NUE in the whole growth period, and then, allocate it based on the empirical dressing ratio with little consideration of the problem of different stages leading to vary NUE, meanwhile, the distribution ratio in growth period also don’t consider what the effects of different soil fertility causing not exact enough optimized N recommendation rates. Two trials:(1) two-years field experiment with two N rates of 150 (N1) and 300 (N2) kg hm-2 nitrogen applied and two distribution ratios that basal tillering fertilizer and panicle fertilizer of 8:2 (R1) and 5:5 (R2), and another treatment of no nitrogen applied as CK were conducted using two different high-yielding rice cultivars:Wuyunjing 23 (Japonica) and Yliangyou 2 (Hybrid indica). A sub-plot of 15N isotope tracing experiment with three duplications under the same treatment that was also set up in the field to ascertion optimum NUE at different rice growth stages and nitrogen management considering yield, environment and effectiveness by studying the effects of different nitrogen managements of nitrogen application amount and nitrogen application ratios on group quality, dry weight accumulation and translocation, yield formation, the N uptake and translocation at different rice growth stages, the residual N in soil, the contribution on the general NUE and yield and so on (i.e. during basal, tillering and panicle fertilization), soil N supply, residual N in soil, the contribution on yield and NUE.(2)It was conducted in a pot experiment using Wuyunjing 23 (Japonica) to study the effects of different nitrogen application ratios (6.67:3.33,6:4,5:5, 3.33:6.67)on yield, nitrogen uptake and utilization of rice under low, medium, high soil fertility. Furthermore, the optimum nitrogen application ratios under different soil conditions was explored. The research can provided more accurate parmerters of NUE, improving the precise and quantitative N application technology and theoretical system, and had the important theoretical and practical signifience for guiding N application in rice. The results were showed as followings:1 Effects different nitrogen managements on population quality, dry weight accumulation, nitrogen absorption and utilization and transport, yieldAt an appropriate postponing N application made rice yield increase, improved rice population and rate of dry matter accumulation, but the ratio of postponing N application that is optimum nitrogen application ratio of anterior and latter was based on the different cultivars and nitrogen application levels. At the same nitrogen applied ratio, there was no significant difference of nitrogen in grains among different nitrogen applied rate, but significantly lager than CK; At the same nitrogen applied rate, low nitrogen applied rate, postponing N application that was incereasing the ratio of panicle fertilizer could increase the amount and efficiency of nitrogen translocation for grain before anthesis and contribution on grain, high nitrogen applied rate, postponing N application decrease the index, but incease the amount of assimilation afther anthesis. N use efficiency and effectiveness are concerned, the most appropriate nitrogen fertilizer applying regime recommended is the treatment of its nitrogen fertilizer rate is 150 kg ha-1 and ratio of basal tillering fertilizer to panicle fertilizer is 5:5.2 Nitrogen absorption and utilization the effects at different stages-the outcome of 15N tracerThe results of 15N isotope tracing experiment revealed that basal nitrogen absorbed by rice was only 1.5%-11.5% before tillering fertilization (eight days after transplanting),6.6%-24.9%from tillering fertilization to panicle fertilization, and little after panicle fertilization. The overall recovery efficiency of basal N (NUEb) was low and ranged from 9.1% to 22.8%, not significantly affected by different cultivars and N treatments. Tillering fertilizer N was mainly absorbed from tillering fertilization to panicle fertilization, and no longer had effect after panicle fertilization. NUE of tillering N fertilizer (NUEt) was 17%-34%, which is almost the same as that of basal fertilizer. Compared with basal and tillering N fertilizers, NUE of panicle N fertilizer (NUEP) was the highest with a value of 54.0%=82.1%, and Wuyunjing 23 had lower NUE than Yliangyou 2. The translocation efficiency of Wuyunjing 23’s tillering ferilizer is the highest and Yliangyou 2 is panicle ferilizer. Both the basal nitrogen and tillering nitrogen had the same contibution on rice uptaking nitrogen. Among the total N uptake of rice, the contribution was 4.13%-10.59%(average 6.92%) for basal N fertilizer,3.98%-11.75%(average 7.58%) for tillering fertilizer,13.32%-37.56%(average 26.02%) for panicle fertilizer, and 45.71%-70.83% (average 59.91%) for the soil.The soil residual N rate of nitrogen fertilizer applied at different times was: basal nitrogen> tillering nitrogen> panicle nitrogen. Increasing nitrogen application amount, but decreased the total NUE in the whole growth period. Postponing N application decreased NUEp, but incereased the contribution of panicle nitrogen resulted for increasing the total NUE; Postponing N application also decreased the loss nitrogen and then decreased environment pollution. Therefore, in rice production, we should consier depend on crop N demand at different rice growth stages to make reasonable nitrogen application making NUEB, NUET and NUEP get optimum state and to improve the NUE of rice, ensure the yield while avoid the N loss.3 Explore the appropriate ratio of basal and tilliering nitrogen ferilizer and panicle fertilizer under different soil fertilityThe results of pot experiment showed that the yield of Wuyunjing 23 in response to soil fertility showed the trend of high fertility> medium fertility> low fertility; The appropraite N application ratio for the largest yield were 6:4 in low fertility,5:5 both in medium and high fertility. The nitrogen applied rates of the highest nitrogen utilization efficiency(NUE) in high, medium, low fertility were 240,240 and 360 kg ha-1. High fertility soil has higher available nitrogen, high soil N dependent rate, and then lower potential to increase yields; low fertility has low soil N dependent rate higher potential to increase yields. Considering high-yield and high effiency goals, it was recommended in this region that reduce basal and tillering nitrogen application rate in high fertility, but in low fertility should pay attention to the early fertilization to improve fertility by increasing basal and tillering nitrogen, therefore, it can increase yield and improve NUE. |
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