Study On Yield Effect And Physiology Of Different Sowing Dates Of Wheat After Rice In The Jianghan Plain

Jianghan Plain,located in the middle and lower reaches of the Yangtze River,is an important part of the wheat growing area in the middle and lower reaches of the Yangtze River in China.The wheat planting area in this area is vast,and rice wheat rotation is the main planting mode in this area.However,in recent years,the mechanized light and simplified rice cultivation methods,mainly mechanical transplanting and direct seeding rice,have been gradually popularized.At the same time,the late maturing rice varieties with high quality and high yield have been widely planted,resulting in the delay of rice harvest.At the same time,as the next crop of rice,the sowing date of wheat was delayed.Therefore,the traditional suitable sowing date of wheat has not been suitable for the actual production demand in this region.Therefore,this study was based on Jianghan Plain.Zhengmai 9023,which was widely sown in this area,was used as experimental material.8 sowing dates（sowing interval was 4 days）were set to study the yield and its components,growth period characteristics,population structure,dry matter and nitrogen accumulation,leaf growth characteristics and plant height differences of wheat under different sowing dates.In order to provide a theoretical basis for large-scale production of wheat in Jianghan Plain,this paper studied the growth and development characteristics of wheat（D1:24-Oct;D2:28-Oct;D3:1-Nov;D4:5-Nov;D5:9-Nov;D6:13-Nov;D7:17-Nov;D8:21-Nov）.The main results are as follows:1.After the first sowing date on 24-Oct,a higher yield can be obtained by appropriately delaying the sowing date.The yield reached the maximum value of each sowing date on 5-Nov（D4）,and the yield from 24-Oct to 9-Nov（D1～D5）could be maintained at 6000 kg·hm^-2or above.Compared with the previous sowing date,the yield would decrease significantly on 13-Nov（D6）and the later sowing date.If D1（24-Oct）was used as reference fitting in the two years,the yield decreased 0.1347%every day since the date of D1 broadcasting（P<0.05）;If D4（5-Nov）was used as the reference fitting,the yield decreased by 1.0810%every day since the delay of D4sowing period（P<0.01）.Under the condition of sowing date in this study,spike number and kernel number per spike of each sowing date showed a complementary change trend,and there was no significant difference in 1000-grain weight of each sowing date.With the delay of sowing date,the spike number of each sowing date showed the upward convex parabola of first increase and then decrease,while the kernel number per spike showed the downward concave parabola of first decrease and then increase.When sowing from 24-Oct to 9-Nov（D1～D5）,the change of spike number was stable,and a better yield level could be obtained.When sowing from 24-Oct to9-Nov（D1～D5）,we need to focus on increasing the number of kernel number per spike to further improve the yield.When sowing after 9-Nov（D6～D8）,we need to focus on improving the spike number to stabilize the yield.2.The adjustment of sowing date usually changes the climatic conditions of wheat growth process,thus affecting the growth period of wheat.Less rainfall during wheat sowing in Jianghan Plain has adverse effects on seed germination and emergence rate.With the delay of sowing date,the main growth stages were delayed and the duration of the whole growth period was shortened.Under the condition of two seasons,the growth period of wheat was shortened by 22 days.The duration difference of growth period among different sowing date treatments was mainly caused by the shortening of early vegetative growth stage,and the shortening days of growth period of each sowing date were lower than the delaying days of sowing date.3.With the continuous progress of growth and development,the tillers of wheat at each sowing date will gradually decrease from overwintering to maturity to first increase and then decrease（more than the maximum at jointing stage）,and the node of this transformation should be in the D4～D5.The maximum number of tillers at maturity stage was D4 or D5.When the sowing date was delayed to D7 and D8,the number of tillers decreased significantly.Therefore,a higher level of population number could be constructed by appropriately delaying the sowing date for 12-16 days after24-Oct.The maximum spike rate of wheat generally occurs at D5 or D6 when the sowing date is delayed.Different sowing dates of wheat in the construction of a reasonable population structure also need to increase the tiller ear rate to ensure that the high-yield population has the appropriate number of ears in the late growth period.High quality population and higher ear rate can narrow the population gap after the sowing date delay,and then narrow the yield gap.4.With the delay of sowing date,the maximum LAI of post-anthesis wheat advanced from 14 days after anthesis（D1）to 7 days after anthesis（D2～D6）and anthesis（D7～D8）,and the maximum value of SPAD will be delayed from 7 days（D1～D3）to 14 days after anthesis（D4～D8）with the delay of sowing date.The mean decrease of LAI in maturity of D4～D6 was 15.55%compared with that of anthesis,which was significantly lower than other sowing periods,and the SPAD value of D4sowing period was still at a higher level of 31.30 at 28d after anthesis.Therefore,the sowing time was postponed to D4,which could keep the higher leaf function of wheat after flowering,delay the leaf senescence and promote photosynthesis of leaves.With the delay of sowing time,the plant height of wheat showed a single peak curve.The maximum plant height was D3,and the later the sowing time was delayed,the greater the decline of plant height was,which was not conducive to the formation of good population structure.The internode length of the first part of the wheat under the spike is an important part of plant height,and also the main part that leads to the difference of plant height at each sowing date.5.The duration（T）of dry matter and nitrogen accumulation in wheat after entering the rapid accumulation stage and the average accumulation rate（V_t）of this stage have complementary effects,and they coordinate with each other to ensure that they are stable at the corresponding level.The average accumulation rate（V_t）and maximum accumulation rate（V_m）of dry matter in fast accumulation period of D1～D4 were significantly higher than those in delayed D5～D8,resulting in higher dry matter accumulation in mature period of D1～D4.Therefore,the coordination of characteristic parameters of dry matter accumulation dynamics in D1～D4 was good,which was conducive to rapid biomass accumulation and yield formation.However,the accumulation of N showed the opposite pattern.The average accumulation rate（V_t）and maximum accumulation rate（V_m）of nitrogen accumulation in D4～D7 were higher than those in other sowing dates,and the N accumulation in D4～D7 was also higher at maturity stage.Therefore,the coordination of the characteristic parameters of N accumulation dynamics of wheat at D4～D7 was good,which was conducive to the rapid N accumulation.The time for N accumulation to reach the maximum accumulation rate（before and after jointing）was earlier than that for dry matter accumulation（before and after booting）,indicating that the growth of biomass was based on the full absorption of nutrients.Therefore,it is necessary to apply N fertilizer at jointing stage to ensure the nutrient absorption of wheat dry matter and N in the rapid accumulation period.At the same time,M_D/J_D（dry matter accumulation at maturity stage/dry matter accumulation at jointing stage）,M_N/J_N（N accumulation at maturity stage/N accumulation at jointing stage）were significantly positively correlated with grain yield（P<0.05）.When M_D/J_Dand M_N/J_Nreached 3.08（P<0.05）and 1.62（P<0.05）respectively,the grain yield could reach 6000 kg·hm^-2or above.Based on the above results,the suitable sowing date range of wheat in the Jianghan Plain can be defined from 24-Oct to 9-Nov,and the production benefit is the best in this range.