Effects Of Slow-release Urea,Conventional Urea And Its Combinations On Yield Formation,Nitrogen Uptake And Utilization Of Direct Seeding Rice

In order to find out the effects of slow-release urea,conventional urea and its combinations on the yield formation,the formation of panicles from the tillering,and nitrogen uptake and utilization characteristics in direct seeding rice.Two factors split-plot design experiments with high-quality indica hybrid rice Yixiangyou 2115 as material were conducted in 2017~2018.The main plot was two cultivation methods: direct seeding(CD)and hand-transplanting(CH),and the subplot was six N application ratios in total amount of150 kg/hm2,the ratio of conventional urea applied as basal N,tillering N and panicle N was 3:3:4(U30),the conventional urea applied as single basal N(U100),the slow-release urea applied as single basal N(S100),the ratios of slow-release urea(basal N)and conventional urea(panicle N)was 8:2(S80),6:4(S60),and 4:6(S40),and without N application as the control(CK).The effects of the combinations of slow-release urea and conventional urea on the yield and its formation,the tillering occurrence and panicle formation,the biomass accumulation,and nitrogen absorption and utilization traits during each growth stage of indica hybrid rice were investigated.The relationship between group quality indicators and yield and its composition were also analyzed.The main results are as follows:1 Effects of the combinations of slow-release urea and conventional urea on grain yield and its components of direct seeding riceAlthough the grain yield of direct seeding rice was higher than that of hand-transplanting rice by 2.75% and 0.76% in 2017 and 2018,respectively,there was no significant difference in grain yield between direct seeding rice and hand-transplanting rice was observed.The differences in 1000-grain weight and seed-setting rate between direct seeding rice and hand-transplanting rice showed not significant.Direct seeding rice had a significant advantage of the effective panicle number,while hand-transplanting had an advantage of grains per panicle.In addition,the constraint factor on yield formation of direct seeding rice and hand-transplanting rice was grain number per panicle and effective panicle number,respectively,which reflected in the total number of spikelets.The better coordination of effective panicle number and grain number per panicle was observed in the treatments of the optimal combination of slow-release urea and conventional urea.Theoptimal combination of slow-release urea and conventional urea could increase the grain yield of hybrid rice.Moreover,direct seeding rice and hand transplanting rice could achieve the highest yield in S40 and S80 at 12.11 t/hm2 and 10.98 t/hm2 in 2017,and 10.18t/hm2 and 10.01 t/hm2 in 2018,respectively,which increased the grain yield by 15.55% and5.40%(2017)and 4.76% and 6.01%(2018)as compared with the U30 treatment,In addition,the main stem and the effective tillering formed during 0~29 d after sowing showed the greatest contribution to the yield of direct seeding rice with the contribution rate ranged from 61.86% to 73.70%,while the effective tillering formed during 34~41d and 41~48d after sowing(that is,the effective tillering occurred during 11~25d after transplanting)contributed 56.83%~68.30% to the grain yield in hand transplanting rice.2 Effects of the combinations of slow-release urea and conventional urea on the tillering occurrence and panicle formation of direct seeding rice The number of effective stems of direct seeding rice formed during 0~29 d after sowing was the largest,which resulted in the highest rate of tillering and the proportion of panicles.The proportion of panicles transformed from the main stem,the tillering formed during0~29 d and 29~34 d after sowing was around 85%.The proportion of panicle transformed from the tillering occurred during 34~41d after sowing(before the peak of the tillering stage)was only 50% of the average value,while the proportion of panicle transformed from the tillering occurred during 41~48d after sowing is less than 10%.In hand transplanting,the maximum tillering number and effective tillering number of rice were observed during 41~48 days after sowing(one week before the tillering stage),the ratio of panicle and the tillering was 1/3 to 1/2,and the proportion of panicle transformed from tillering occurred during 48~55d after sowing rate was also less than 10%.The suitable amount of slow-release urea applied as the base fertilizer could not only meet the early control the population quantity of direct seeding rice but also achieve the control of medium-term in hand-transplanting rice.Reduced basal fertilizer application can effectively control the growth too fast and excessive of the population,increased the tillering number and keep proportion of panicle transformed from tillering over 60%(S60and S40)due to the high number of basic seedlings in direct seeding rice with regarding to the combination of slow release urea and conventional urea.The increase in the basal fertilizer application could promote the occurrence of tillering,and further increase theeffective panicle number under the premise of a certain number of populations in hand transplanting rice.3 Effects of the combinations of slow-release urea and conventional urea on the population quality characteristics of direct seeding riceDirect seeding rice had a larger C/N of plants and leaves,but a smaller SPAD value and lighter color of leaves than hand transplanting rice.The variation of the SPAD values of leaves at the different growth stages was also small.The growth rate,leaf area index(LAI)and the photosynthetic indexes such as chlorophyll content and net photosynthetic rate(Pn)of flag leaves of direct seeding rice were lower than that of hand transplanting rice at the middle and late stages.There was a significant positive correlation between LAI and Pn values and the total number of spikelets and grain yield in the middle and late stages.Direct seeding rice had a higher group photosynthetic rate(CAP)than hand transplanting rice at the medium-term,while the smaller difference was observed at the late stage.Also,there was a significant correlation between CAP and the total number of spikelets and yield at the middle-late stage.In addition,the C/N of plants and leaves during the whole growth period negatively correlated with the total number of spikelets and yield,especially at the fully tillering stage and the fully heading stage in both years.Direct seeding rice had little dependence on the basal fertilizer due to its population advantage.Thus,the increase in panicle fertilizer could delay the leaf senescence and ensure a higher Pn value,SPAD value and chlorophyll content of the flag leaves of direct seeding rice at the middle and late stage,which improved the high efficient LAI,CAP and photosynthetic production capacity of the population at the later stage in regarding to a limited nitrogen application rate.However,increasing the basal and tillering fertilizer application could effectively promote tillering occurrence to form a better rice population containing a certain number of effective panicle number,which laid a foundation for the highly efficient absorption of nutrients and rapid biomass accumulation in the later stage.4 Effects of the combinations of slow-release urea and conventional urea on the nitrogen absorption and utilization characteristics of direct seeding rice Compared with hand transplanting rice,direct seeding rice showed the multiple-plants tillering with the stronger nitrogen uptake capacity during the early stage,and the higher nitrogen accumulation during the seedling stage,the higher nitrogen transport rate of stemsand leaves,nitrogen dry matter and grain production efficiency and nitrogen partial productivity,but the lower nitrogen uptake capacity and nitrogen accumulation during the other periods and nitrogen apparent utilization.The effects of nitrogen management on nitrogen uptake,translation and utilization were greater than those of planting methods.Direct seeding rice had a lower utilization rate of basal fertilizer.Thus,increasing the panicle fertilizer and controlling nitrogen uptake in the early stage could reduce the nitrogen losses on ineffective populations,and increase the nitrogen accumulation rate after jointing stages,and improve the nitrogen accumulation from the fully heading stage to the maturity stage to achieve the higher nitrogen accumulation in panicle,nitrogen partial productivity,nitrogen agronomic utilization,and apparent utilization,especially in the treatment of CDS40,which increased the nitrogen accumulation by 28.99% and 15.65%at maturity stage,respectively,increased the nitrogen accumulation in panicle by 24.64%and 17.80%,respectively,increased the apparent nitrogen utilization by 32.05% and17.07%,respectively,in these two years when compared with U30.However,80% of slow-release urea applied as the basal fertilizer in hand transplanting rice could increase the accumulation of nitrogen in the early stage,and ensure the nutrient absorption capacity in the later stage.Also,the nitrogen utilization rate in S80 was superior higher than the conventional fertilization treatment(U30),and the apparent nitrogen utilization rate in S80 increased by 27.30% and 15.65% compared to U30,respectively in two years.In summary,the high-yielding populations' construction should be based on the differential demand for nitrogen in direct seeding rice and hand-transplanting rice.Then,combined with the high utilization rate of slow-release fertilizer and the rapid effect of urea to optimize nitrogen application methods to ensure the reasonable formation of stem and panicle,and to coordinate the population and individual and improve the nitrogen use efficiency.Hybrid rice variety Yixiangyou 2115 could have the highest yield at the ratios of4:6 and 8:2 for the basal fertilizer(slow-release urea)and panicle fertilizer(regular urea)in direct seeding rice and hand transplanting rice,respectively.