The Effects Of Nitrogen Management On Grain Yield,Nitrogen Use Efficiency And Nitrogen Loss Of Middle Rice In The Middle Of Yangtze River Basin Of China

The middle of Yangtze River Basin of China is one of the main rice producing regions in China.In this region,the poor synchrony between peak fertilizer nitrogen?N?availability and peak crop N demand caused by overfertilization and inappropriate timing of N fertilizer in rice production led to low nitrogen use efficiency?NUE?that can't meet the demands of green and efficient rice production.It's of great important to explore the effects of N fertilizer management on yield production,NUE and N fertilizer fate for achieving an optimized balance among rice yield,fertilization benefits and environmental protection,and thus promoting the sustainable production of rice.The field experiments were conducted to investigate the development of rice growth,population quality,grain yield,NUE,and the fate of applied-¹⁵N for Yangliangyou6?a super hybrid cultivar,YLY6?and Lvdao Q7?a high-yield inbred cultivar,LDQ7?,which were main varieties of middle rice in the middle of Yangtze River Basin of China,using10 combinations of N rates and splitting patterns at Huaqiao town,Wuxue County,Hubei Province,in 2013 and 2014.The experimental design was a split-plot arrangement with four replications,the main plots had different N treatments,the subplots had different rice varieties,and ¹⁵N fertilizer microplots were demarcated in subplots.The N rates ranged from 0 kg hm^-2to 250 kg hm^-2,and there were two to three kinds of N splitting patterns at midtillering?MT?stage and panicle initiation?PI?stage,with total N rates of 130 kg hm^-2,170 kg hm^-2,and 210 kg hm^-2.The following results were obtained:1. The grain yields of postponed N application patterns under middle N rates of 130kg hm^-2?170 kg hm^-2 were compareble with the seasonal highest yields.The highest yields of 9.74 t hm^-2 and 10.21 t hm^-2 for YLY6 in 2013 and 2014,respectively,were achieved under N rates of 210 kg hm^-2 and 250 kg hm^-2.And the highest yields of 8.55 t hm^-2 and 9.76 t hm^-2 for LDQ7 in 2013 and 2014,respectively,were achieved with an N rate of 210 kg hm^-2.In addition,N application patterns with postponed 40 kg N hm^-2 fertilizer from MT stage to PI stage under middle N rates of 130 kg hm^-2?170 kg hm^-2 had accelerated the yield increase of YLY6 in 2013 and 2014,and of LDQ7 in 2014 when compared to non-postponed N application patterns.Thus,the high yields of 9.70 t hm^-2and 9.68 t hm^-2 of YLY6 and 8.25 t hm^-2 and 9.49 t hm^-2 of LDQ7 under N treatments of90-40-40 kg hm^-2?N application amount at basal-midtillering-panicle initiation stage?in2013 and 90-0-40 kg hm^-2 in 2014,respectively,were comparable with the seasonal highest yields.2. Postponed N application patterns under middle N rates of 130 kg hm^-2?170 kg hm^-2 had remarkably improved the population quality,increased the dry matter accumulation from heading to maturity stage(DM_HD-MA)and increased the percentage of effective tillers for both rice varieties.Under N application patterns which postponed 40 kg N hm^-2fertilizer from MT stage to PI stage when N rates were lower than 170 kg hm^-2,although the leaf area index and leaf SPAD were lower than non-posponed N application patterns at PI stage,but both the two traits increased after PI stage.And thus,the dry matter accumulation at middle-late rice growth stages especially the DM_HD-MA was increased by10.2 g m^-2?178.0 g m^-2 when compared to non-posponed N application patterns(except YLY6 under N pattern of 90-0-40 kg hm^-2 in 2013),meanwhile,the percentage of effective tillers was increased by 0.73?8.32 percentage points.3. The plant N uptake at maturity stage were significantly influenced by N rates and N splitting patterns,which increased along with the incremental N rates when N rates were lower than 170 kg hm^-2,while it no longer increased even declined with further incremental N rates.Postponed N application patterns had increased the plant N uptake.The highest plant N uptake of 166.8 kg hm^-2 and 193.7 kg hm^-2 for YLY6 in 2013 and2014 and 157.5 kg hm^-2 for LDQ7 in 2013,respectively,were achieved under an N rate of210 kg hm^-2(90-40-80 kg hm^-2),the highest plant N uptake of 195.1 kg hm^-2 for LDQ7 in2014 was achieved at an N rate of 250 kg hm^-2(90-80-80 kg hm^-2).Compared to non-postponed N application patterns of 90-40-0 kg hm^-2,90-80-0 kg hm^-2 and 90-80-40kg hm^-2,the postponed N application patterns of 90-0-40 kg hm^-2,90-40-40 kg hm^-2 and90-40-80 kg hm^-2 had promoted the increase of plant N uptake from PI to MA stage,and thus had increased the plant N uptake at HD stage and MA stage by 0 kg hm^-2?30.7 kg hm^-2(except YLY6 under N pattern of 90-40-80 kg hm^-2 in 2013)and by 7.6 kg hm^-2?40.7 kg hm^-2.4. The N recovery efficiency?RE?calculated by traditional‘substraction calculating method'in 2013 and in 2014 were 13.35%?37.89%and 28.24%?60.26%for YLY6 and were 5.31%?24.43%and 12.65%?39.85%for LDQ7,respectivey.The influence of N rates on RE were statistically insignificant,while postponed N application patterns increased RE by 3.97?31.37 percentage points and by 4.20?21.23 percentage points,respectively in YLY6 and in LDQ7.The internal N use efficiency?IE_N?was the highest under an N rate of 90 kg hm^-2 which was comparable to IE_N under an N rate of 0 kg hm^-2,further incremental N rates decreased IE_N.Meanwhile,ponstponed N application patterns decreased IE_N by 3.80?15.10 percentage points and by 4.20?21.23 percentage points,respectively in YLY6 and in LDQ7,due to greater incremental range in plant N uptake than in grain yield.5. The ¹⁵N experiments demonstrated that the N recovery efficiency of ¹⁵N labeled fertilizer(RE-¹⁵N)was significantly influenced by N rates and N splitting patterns,which increased along with the incremental N rates when N rates were lower than 170 kg hm^-2,while it no longer increased even declined with further incremental N rates.Postponed N application patterns had increased the RE-¹⁵N.The RE-¹⁵N of 90-0-40 kg hm^-2 and90-40-40 kg hm^-2 were 26.8%?35.8%in YLY6 and were 21.3%?32.9%in LDQ7.The RE-¹⁵N had no significant difference between two varieties in 2013 with high temperature stress,whereas,the RE-¹⁵N was significantly higher in YLY6 than in LDQ7 in 2014 with high-yield climate conditions.6. The N residual percentage in soil of ¹⁵N labeled fertilizer?NRS%?and the N loss percentage of ¹⁵N labeled fertilizer?Loss%?had no significant diference between two varieties,which were 17.0%?27.3%and 40.4%?66.5%,respectively under each of the N treatments.The N rates and N splitting patterns significantly affected the N residual amount in soil of ¹⁵N labeled fertilizer?NRS?and the N loss amount of ¹⁵N labeled fertilizer?N loss?.The plant N uptake derived from fertilizer?PNdff?increased gradually with the incremental N fertilizer rates from 90 kg hm^-2 to 250 kg hm^-2,and the NRS reached the ceiling of approximately 48 kg hm^-2 at an N rate of 170 kg hm^-2 in both YLY6and LDQ7,while further incremental N rates sharpened the increase of N loss,and the highest N loss of 102.8 kg hm^-2?107.5 kg hm^-2 occurred when N application rate was 250kg hm^-2.Compared to non-postponed N application patterns of 90-40-0 kg hm^-2,90-80-0kg hm^-2 and 90-80-40 kg hm^-2,postponed N application patterns of 90-0-40 kg hm^-2,90-40-40 kg hm^-2 and 90-40-80 kg hm^-2 increased the PNdff and RE-¹⁵N,while decreased the NRS,NRS%,N loss and Loss%,simutaneously.In conclusion,the N rates and N splitting patterns significantly affected the rice population quality,dry matter accumulation,yield formation,NUE and N balance in rice field.Overfertilization and improper N splitting patterns would decline the grain yield,plant N uptake and IE_N,moreover,would cause huge amount of N fertilizer loss and low NUE.The N splitting patterns of 90-0-40 kg hm^-2 and 90-40-40 kg hm^-2 under N rates of130 kg hm^-2?170 kg hm^-2 would be recommended to the middle of Yangtze River Basin of China to increase rice yield and N use efficiency while reduce N fertilizer loss to ecosystem,simutaneouly.