| In terms of grain yield of wheat after rice in Lixiahe Agricultural Region of Jiangsu Province,there are significant gaps between local average yield level and high-yielding level,and also between average yield of local farmers and high-yielding level.It is important to narrow these gaps by studying the causes underlying these yield gaps.In the present study,Ningmai 13,a local wheat variety,was planted in five modes:basic mode(CK),nitrogen-free mode(MO),local traditional mode(M1),M2,and M3.Experiments with planting density and fertilizer management as the experimental factors were done to explore the regulation pathway of closing these yield gaps and to study the mechanism underlying the yield gaps and production efficiency.This study provided a theoretical basis and technical support for closing the yield gaps of wheat in Lixiahe Agricultural Region of Jiangsu Province.The main results are the following.1.Within the two experimental years,the average yield gap Ⅰ between M2 and M1 was 982.43 kg×hm-2;the average yield gap Ⅱbetween M3 and M1 was 580.13 kg·hm-2.The primary and secondary gaps of the three components of yield(spike number,number of grain per ear,1000-grain weight)was 18.24×104·hm-2,3 grains per spike and 0.62 g,and 6.58×104·hm-2,3.13 grains per spike and 0.29 g,respectively.Path analysis showed that the gap of number of grain per ear and grain weight are more influential on grain yield as compared with that of spike number.Tillering panicle rate,post-anthesis dry matter accumulation,potential source,leaf area duration from booting stage to milk-ripe stage were all lower in the local traditional modes,leading to lower grain yield.Within the two experimental years,the yield of M2 mode was the highest,followed by M3 mode.Therefore,M2 and M3 modes were identified as the high-yielding modes in this study.2.Nitrogen uptake accumulation during the whole wheat growing season under different cultivation patterns ranged from 200.00 to 240.00 kg·hm-2.The average value of primary and secondary gaps of agronomic efficiency of nitrogen,nitrogen partial factor productivity,nitrogen apparent recovery fraction and nitrogen physiological efficiency was 4.70 kg·kg-1,1.67 kg·kg-1,7.84%,5.80 kg·kg-1,and 5.19 kg·kg-1,4.95kg·kg-1,6.75%,and 7.43 kg·kg-1,respectively.The activities of NR,GS and GOGAT in flag leaves were highest in M2,followed by M3 and M1 at anthesis.The descending rate of activities of nitrogen metabolizing enzyme from anthesis to milk-ripe stage followed a descendant order of M1,M2,and M3.The M2 mode had the lowest cost,the highest yield and economic benefit in both two experimental years.Thus,M2 mode was confirmed as the high-yielding and high-benefit mode.The M3 mode was confirmed as the high-yielding and high-nitrogen-efficiency mode because its yield was second to M2 mode but the nitrogen utilization efficiency was the highest.3.15N labeling results showed that nitrogen efficiency was the highest when nitrogen was applied once at booting stage.When nitrogen was applied twice at jointing and booting stages,nitrogen efficiency was the highest,with significant higher nitrogen uptake and absorption ratio of wheat plants and less N loss as compared with one-time application.The amount of nitrogen absorbed by wheat plants with four times of nitrogen fertilizer application was significantly increased and N loss was significantly reduced to 16.14%.The nitrogen accumulation in leaves,stem sheaths,spike-stalk plus shell,and grains at mature stage occupied 7.01-8.51%、9.74-11.99%、3.61-5.23%和 25.55-27.27%of total nitrogen application,respectively.These results showed that closing the gap of nitrogen accumulation at jointing stage,anthesis stage and mature stage,increasing the nitrogen accumulation from booting to anthesis stage and from anthesis to mature,closing the gap of apparent nitrogen utilization efficiency and nitrogen physiological efficiency were the main targets for closing the yield gap.4.Compared with M1 mode,the utilization efficiency of heat and solar radiation resources at anthesis stage and milk-ripe stage was significantly improved in M2 and M3 modes.In the M2,M3 and M1 modes,the primary and secondary gap of SPAD and net photosynthesis rate of flag leaves on the 7th day after anthesis was 2.3 and 4.74 μmol·m-2·s-1，13 and 3.52μmol·m-2·s-1,respectively.Compared with M1 mode,M2 and M3 modes obviously reduced MDA content and enhanced the activities of SOD,POD and CAT in flag leaves after anthesis.The flag leaves aged slowly after anthesis with more green leaves and higher heat and solar radiation utilization rate,which was conductive to biomass accumulation after anthesis and grain yield formation.5.The results of three experimental sites in both 2 years unanimously showed that within certain ranges of planting density and nitrogen application,grain yield and spike number increased with the increases in planting density and nitrogen rate,and the number of grain per ear decreased with increased planting density,but there was no significant difference in gain weight.Within a certain planting density range at the same nitrogen rate,grain yield increased first and then decreased with the increase in planting density.Within the range of a certain nitrogen rate and at the same planting density,grain yield increased first and then decreased with increased nitrogen rate.The spike number,number of grain per ear and 1000-gain weight should be kept at about 480-520×104·hm-2,43-45 and 36g,respectively,to achieve a high-yielding population(7500 kg·hm-2)of Ningmai 13.The characteristics of this population are:the number of stem tillers at wintering stage,jointing stage,and anthesis was about 0.9-1.2,2.3-2.5,and 1.1-1.4 times of the final spike number;the percentage of ear-bearing tiller and stem was about 43%;biomass accumulation at anthesis,mature,and post-anthesis was higher than 12000 kg·hm-2,18000 kg·hm-2,and 6200 kg·hm-2,respectively;the leaf area index at booting,anthesis,and milk-ripe stage was about 5.4,4.6,and 1.8,respectively.6.According to the experimental results of two wheat growing seasons,it is suggested to use M2 mode to narrow yield gap between the local traditional mode in Lixiahe Agricultural area of Jiangsu Province(M1)and high-yielding level.Namely,the planting density,nitrogen application rate,and nitrogen application ratio of Ningmai 13 with the target yield above 7500 kg·hm-2 were as follows:Seeding from November 1 to 10 to get 150×104·hm-2 basic seedlings;the applied amount of N,P and K are kept at 270 kg·hm-2,112.5 kg·hm-2 and 112.5 kg·hm-2,respectively,with an nitrogen application ratio of 5:1:2:2 at the stages of basal,tillering,jointing，and booting.The high-yielding and high-nitrogen-efficiency mode M3 may also be used.Namely,the planting density,nitrogen rate and nitrogen application ratio of Ningmai 13 with the target yield above 7500 kg·hm-2 were as follows:Seeding from November 1 to 10 to get 210×104·hm-2 basic seedlings;the applied amount of N,P and K are kept at 240 kg·hm-2,112.5 kg·hm-2,and 112.5 kg·hm-2,respectively,with an nitrogen application ratio of 5:1:2:2 at the stages of basal,tillering,jointing,and booting. |
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