Effects Of Nitrogen Fertilizer Management And Application Depth On Yield And Nitrogen Use Efficiency In Precision Hilldirect-seeded Rice

In order to study the effects of nitrogen application management and fertilization depth on yield and nitrogen use efficiency in mechanical hill-direct-seeded rice,two experiments were conducted in the farm of South China Agricultural University in the late season of 2016 and in the early season of 2017,respectively.There were three kinds of nitrogen application management viz,mechanical hill direct-seeded rice synchronous with deep placement of total quantity fertilizer as basal fertilizer?T1?,mechanical hill direct-seeded rice synchronous with deep placement of 75%total quantity fertilizer as basal fertilizer and 25%total quantity fertilizer as panicle fertilizer?T2?,combined mechanical hill direct-seeded rice with farmer's traditional broadcast fertilizer manually with 40%total fertilizer as basal fertilizer,30%as tillering fertilizer,and 30%as panicle fertilizer?T3?,No fertilization was regarded as a control?T0?,taken hybrid rice Wufengyou 615 and inbred Yuxiangyouzhan as experimental materials,respectively,in the field experiment,in the late season of 2016.Another experiment was about the fertilization depth.There were four different fertilization depths which were 0,4,8,12 cm,written as D0,D4,D8 and D12 in order,taken hybrid rice Tianyou998 and inbred rice Yuxiangyouzhan as materials,in the early season of 2017,No nitrogen fertilization was regarded as a control?CK?respectively.The effects of different treatments on yield,nitrogen recovery efficiency,some enzyme activities,grain qualities,and greenhouse gas emission?CH₄ and N₂O?were analyzed in order to provide a guidance for high yield,high efficiency,and high quality cultivation techniques of mechanically synchronous deep fertilization and precision hill direct-seeded rice.The main findings are as follows:?1?The results of nitrogen fertilizer application management showed that T1 could increase the number of effective panicle of the two rice varieties,the yields of Wufengyou615 and Yuxiangyouzhan increased by 43.29%and by 44.32%,respectively.T2 could improve grain number per panicle of the two rice varieties,yield increased by 49.64%in Wufengyou 615,and increased by 50.85%in Yuxiangyouzhan.The results of fertilization depth showed that D12 and D8 treatments significantly increased the effective panicle number,grain per the spike,and effectively promoted the increase of rice yield,then significantly increased yield.?2?T1 treatment could significantly improve glutamine synthetase activity?GS?at jointing stage and glutamate synthase activity?GOGAT?at heading stage in the leaves,respectively.D8 treatment also could notably increase GS activities in the leaves at jointing stage,heading stage and maturity stage,and GOGAT activity at jointing stage and mature stage.And nitrate reductase activity?NR?at maturity stage and the activity of GS and GOGAT were increased in roots at heading stage.D12 treatment could significantly increase GS at tillering stage and heading stage,nitrate NR and GS at jointing stage in the leaves.NR and GS were also improved in rice root at heading stage in the treatment of D12.?3?T1 treatment significantly improved nitrogen accumulation in leaves at mature stage,in the stems at the heading and mature stage,in the spikes at mature stage,and promoted the accumulation of phosphorus and potassium in the plants during mature stage,respectively.In T1 treatment,nitrogen absorption efficiency was near increased by 9.84%compared to T3,T1 also promoted the absorption and utilization efficiency of phosphorus and potassium.D12 treatment could significantly increase nitrogen accumulation of rice leaves at jointing stage,stem and sheath at heading stage,and rice panicle at maturity stage.D12 treatment significantly had higher 23.45%nitrogen agronomic efficiency and 29.45%nitrogen absorption efficiency than D0 treatment.The accumulation of phosphorus and potassium in rice leaves,stem and sheath,panicle,were also significantly increased by D8and D12 treatments,and phosphorus agronomic efficiency and phosphorus absorption efficiency,potassium agronomic efficiency,potassium absorption efficiency,were also increased,too.?4?T1 treatment could improve leaf area index of rice at jointing and heading stage,and promote the accumulation of aboveground dry matter at maturity stage.D8 and D12treatments,which were beneficial to the formation of root,could significantly increase the root volume and root surface,could also significantly increase leaf area index at heading stage and jointing stage,and promote the accumulation of aboveground dry matter at jointing stage,heading stage and maturation stage.?5?T1 treatment could significantly reduce rice chalky percentage,increase rice protein content of rice.D8 and D12 treatment could remarkably reduce rice chalk percentage and rice chalk granularity,and increase milled rice rate and whole milled rice rate.In general,the combination of T1 and D8,D12 contributed to the high quality rice.?6?T1 treatment could significantly inhibit the emission of CH₄ and N₂O during the whole growth period of rice,and apparently reduce the global warming potential of rice field.To sum up,the combination of T1 and the depth of fertilization is 8-12 cm were used as the better fertilization method to achieve the simultaneously improvement of yield and nitrogen use efficiency of mechanical precision hill direct seeding rice.