Response Of Rice Harvest Index And Factors Affecting Harvest Index To Different Water And Nitrogen Management Modes In Black Soil Region

The planting area and total production of rice in the black soil region of Northeast China both rank first in China,the black soil region is the main grain producing area in China.Improving rice harvest index is an important way to increase rice yield.Water management and nitrogen fertilizer application have important effects on the accumulation,transportation,and distribution of photosynthetic products in rice.Therefore,this study conducted field experiments to investigate the response of rice harvest index and its influencing factors to different water and nitrogen management modes.The research results are of great significance for improving rice yield and sustainable utilization of water and fertilizer resources in black soil areas.The experiment was conducted at the Rice Irrigation Experimental Station in Heilongjiang Province.The experiment set up three irrigation modes(F:flooded irrigation,C:controlled irrigation,W:“thin-shallow-wet-dry”irrigation)and four nitrogen application levels(N:110kg/hm~2,N1:99kg/hm~2,N2:88kg/hm~2,N3:77kg/hm~2).The experiment studied the response of rice plant height,tillering,tillering rate,net photosynthetic rate,SPAD value,accumulation and transportation of dry matter in aboveground parts,yield and its components,spikelet number at heading stage,leaf area index,grain-leaf ratio.The major conclusions of the research are as follows:(1)Under the same nitrogen application level,the HI of controlled irrigation and“thin-shallow-wet-dry”irrigation increased by 1.1%～5.13%and 1.58%～7.43%compared to flooded irrigaion,respectively.Under N and N3 nitrogen application level,the HI of“thin-shallow-wet-dry”irrigation was the highest,while the HI of controlled irrigation was the highest under N1 and N2 nitrogen application level.Under the same irrigation mode,the rice HI first increased and then decreased with the decrease of nitrogen application level,with the highest under N1 nitrogen application level.Under flooded irrigation,controlled irrigation and“thin-shallow-wet-dry”irrigation,N1 nitrogen application level was 6.85%～11.56%,4.71%～12.89%,and 2.31%～11.49%higher than the HI of other nitrogen application levels,respectively,with significant differences(P<0.05).Among all of the water and nitrogen management modes in this experiment,the HI of controlled irrigation with N1 nitrogen application level was the highest.(2)Under each nitrogen application level,the panicle formation rate of tillers was the highest under controlled irrigation and the lowest under flooded irrigation,indicating that controlled irrigation was beneficial to reducing redundant growth of rice.Under different nitrogen application levels,the dry matter transport rate,NSC transport rate,sugar-flower ratio,and grain-leaf ratio of rice under flooded irrigation were the lowest.Under the conventional nitrogen application level,the dry matter transport rate,NSC transport rate,sugar-flower ratio,and grain-leaf ratio of rice stem and leaf under“thin-shallow-wet-dry”irrigation were the highest;Under the nitrogen application levels of N1 and N2,the rice stem and leaf dry matter transport rate,NSC transport rate,sugar-flower ratio,and grain-leaf ratio at heading stage under controlled irrigation were the highest;The dry matter translocation rate,NSC translocation rate,and sugar-flower ratio at heading stage of rice under“thin-shallow-wet-dry”irrigation were the highest under N3 nitrogen application level.(3)Under different irrigation modes,the dry matter transport rate of stem and leaf,NSC transport rate,sugar-flower ratio,and grain-leaf ratio at heading stage increased first and then decreased with the decrease of nitrogen application level,and reached the highest at the N1 nitrogen application leve.Under flooded irrigation,controlled irrigation,and“thin-shallow-wet-dry”irrigation,the dry matter transport rates of stems and leaves under the N1 were 10.4%～33.25%,10.33%～31.77%,and 6.45%～28.91%higher than the other three nitrogen application levels,respectively,with significant differences(P<0.05).Compared with the other three nitrogen application levels,the NSC transport rate at N1 nitrogen application level increased by11.78%～21.43%,9.54%～23.19%,and 4.79%～17.51%,respectively,with significant differences(P<0.05).Compared with the other three nitrogen application levels,the sugar-flower ratio under N1 nitrogen application level was 6.04%～13.1%,3.95%～13.58%,and 2.62%～1.16%higher,respectively.Compared with the other three nitrogen application levels,the grain-leaf ratio at N1nitrogen application level was 10.75%～15.73%,2.97%～12.22%,and 0.98%～14.44%higher,respectively.(4)Under the same nitrogen application level,the yields of controlled irrigation and“thin-shallow-wet-dry”irrigation were 0.72%～8.36%and 0.02%～14.84%higher than that of flooded irrigation,respectively.Under N and N3 nitrogen application level,the highest yield was obtained under“thin-shallow-wet-dry”irrigation,while under N1 and N2 nitrogen application level,the highest yield was obtained under controlled irrigation.Under the three irrigation modes,rice yield showed a rule of first increasing and then decreasing with the decrease of nitrogen application level,and the highest yield was under N1 nitrogen application level,which were 19.46%～37.88%,13.35%～32.92%,and 6.21%～31.59%higher than other nitrogen application levels,respectively,with significant differences(P<0.05).In terms of water use efficiency,under flooded irrigation and controlled irrigation,water use efficiency first increased and then decreased with the decrease of nitrogen application level,and both were the highest under N1 nitrogen application level,1.41%～19.16%and 7.69%～20.57%higher than other nitrogen application levels,respectively.Under“thin-shallow-wet-dry”irrigation,water use efficiency decreased with the decrease of nitrogen application level,and under conventional nitrogen application level,water use efficiency was the highest,compared with the other three nitrogen application levels,the difference was significant(P<0.05).Under different nitrogen application levels,water use efficiency was the highest under controlled irrigation,and the lowest under flooded irrigation,with significant differences among the three irrigation modes(P<0.05).Among all the water and nitrogen management modes in the experiment,the yield and water use efficiency were both the highest under controlled irrigation with N1 nitrogen application level.To sum up,different irrigation modes should be adopted different nitrogen application levels to improve the rice harvest index in black soil rice cultivation areas.The variation range of harvest index in the black soil rice cultivation area is 0.545～0.622.Under each irrigation mode,the harvest index was the highest at N1 nitrogen reduction level,and was 0.608,0.622,and 0.621 under conventional flooding,controlled irrigation,and thin shallow wet sunlight irrigation,respectively.The research results also showed that in black soil rice planting areas,water and fertilizer resources can be saved through water and nitrogen regulation,and the grain-leaf ratio and sugar-flower ratio of rice at heading stage can be improved,as well as the panicle formation rate of stems and tillers and dry matter transport after anthesis,thereby improving the rice harvest index and achieving the goal of increasing yield.This research provides a theoretical basis for understanding the response of rice harvest index to different water and nitrogen management modes in the black soil of Northeast China,and guiding the cultivation mode of high yield and efficiency of rice.