Physiological Mechanism Of High Yield And High Resources Use Efficiency Of Dry Seeded Rice Under Different Water Managements

Labor shortageand water scarcityare threatening rice planting area and food security.To maintain rice production,improving rice yield potential and arable land use efficiency are both effective and strategic.In this sitiuation,with the advantages in less labor and water costs,and being more easily mechanized,dry seeding becomes valued and popular.So far,plenty of researches about dry seeded rice have been compeleted in world-wide,while the results varied,because of the different climate conditions.In order to evaluate the availability of dry seeded rice in Central China,a three-year field experiment was conducted in Wuxue,Hubei,from 2012 to 2014.In this study,four cultivars were tested under dry seeded aerobic rice,dry seeded flooded rice and transplanted flooded rice system.They were drought tolerant varieties: Lvhan1?LH1?& Hanyou3?HY3?and mega varieties: Huanghuazhan?HHZ?& Yangliangyou6?YLY6?.The detailed objectives of this study were:?1?to examine canopy structure,grain yield,grain quality,resourses use efficience and greenhouse gases emission of dry seeded rice under different water managements;?2?to clarify the physiological mechanisim of high yield and high efficiencies in dry seeded rice;?3?to identify the promising plant traits for adapting dry seeding system.The main results are as follows:?1?With a higher panicle number,dry seeded flooded rice was with a comparable grain yield(8.60 t ha^-1)with transplanted flooded rice(8.68 t ha^-1).While,grain yield was signigicantly lower under dry seeded aerobic rice(7.99 t ha^-1),even though the panicle number under dry seeded aerobic rice system was also higher.Under dry seeded aerobic rice and dry seeded flooded rice system,tiller number was much higher,while plant height,leaf area index and total aboveground biomass was lower than transplanted flooded rice at vegetative stage.After flowering,compared with the other planting patterns,functional leaves under dry seeded flooded rice senescenced earlier,which was related with lower dry matter accumulation during grain filling.?2?Dry seededaerobic rice and dry seeded flooded rice significantly enhanced water productivity by 50.0% and 14.5%,respectively,as compared with transplanted flooded rice.The higher water productivity in dry seeding rice system was accompanied with less irrigation times and less water input,especially in dry seeded aerbic rice.Nitrogen use efficiency for rice production in dry seeded flooded rice was 12.4% higher than transplanted flooded rice,thus the comparable yield with transplanted flooded rice was achieved in dry seeded flooded rice,even though nitrogen uptake in dry seeded flooded rice is low.While there was no consistent difference in nitrogen use efficiency for rice production between Dry seeded aerobic rice and transplanted flooded rice.?3?As content in milled rice under transplanted flooded rice was 0.3 mg kg-1,and Cd content in milled rice under dry seededflooded rice was 0.44 mg kg-1,which were both higher than the maximum limits ofpotentially toxic elements content in milled rice,while under dry seeding flooded rice,none of the potentially toxic elements in milled rice was higher than its threshold value.Milled rice under dry seeded aerobic rice was with significantly lower As and Mo content,and higher Zn,Mn,Ni,Cu,Cd and Co content,compared with transplanting flooded rice.No difference in grain quality was found between dry seeded flooded rice and transplanted flooded rice.Milling quality and appearance qualityunder dry seeded aerobic rice were improved,while the cooking quality was declined,compared with transplanting flooded rice.?4?Compared with transplanted flooded rice,CH4 emission underdry seeded aerobic rice and dry seeded flooded rice was declined by 97% and 67%,while N2 O emission was increased by 310% and 84%,in total,dry seeded flooded rice and dry seeded aerobic rice significantly reduced global warming potential by 71.4% and 94.8%,respectively.?5?With higher biomass accumulation,higher spikelets per panicle and moderate grain weight,grain yield of YLY6(9.7-10.5 t ha^-1)was higher than other three cultivars,in contrary,grain yield of LH1(6.4-8.2 t ha^-1)was the lowest among the tested cultivars,because of the lack of biomass accumulation and small panicle size;with a similar growth duration,HHZ achieved a higher grain yield,which was related to the higher sink size and higher harvest index of HHZ.These results suggest that being of a resource-saving and environment-friendly rice planting method,dry seeding flooded rice can be used as an alternative to transplanting flooded rice in Central China,when labor and water is limited for rice planting.The possibility has been proved by the comparable yield,higher water productivity,higher nitrogen use efficiency,lower potentially toxic elements content and lower global warming potential of dry seeding flooded rice.With a high water productivity and low global warming potential,dry seeding aerobic rice can be used to expand rice planting area,where transplanting rice is unattainable due to the lack of irrigation facilities and enough labors.The results also suggest that high yielding cultivars in transplanted flooded rice can also achieve high yield in dry seeded rice system;stable panicle size is benefit for increasing sink size,thus enhancing grain yield in dry seeded rice system;selecting stay green varieties may be an effective way to prolong the functional periods of top three leaves to increase dry matter accumulation after flowering.