| Jianghan Plain is one of the important wheat producing areas in the middle and lower reaches of the Yangtze River.The rice-wheat and water-drought rotation cropping pattern is adopted in this area,which has low yield per unit area and great potential for increasing wheat yield.Wheat is a kind of food crop that needs more nitrogen.Reasonable nitrogen fertilizer management plays an important role in wheat’s high quality,high yield and high efficiency.As an effective way to rationally utilize biomass resources and promote sustainable agricultural development,straw returning can improve soil physical and chemical properties,improve soil microbial activity and soil nutrient supply potential,promote crop growth and development,reduce nitrogen loss,and then increase crop yield and nitrogen fertilizer use efficiency.But at the same time,straw returning to the field may also cause competition with crops for nitrogen and lower seedling emergence rate,leading to the problem of production reduction.Therefore,it is necessary to study the effects of straw returning and nitrogen fertilizer management on the growth and development characteristics,yield and nitrogen absorption and utilization of rice stubble wheat in Jianghan Plain.In this study,a field experiment on straw returning and nitrogen fertilizer operation was carried out using Zhengmai 9023 as the material in rice-wheat growing area of Jianghan Plain from 2018 to 2020.(Four nitrogen application rates of 0,135,180 and225 kg·hm-2 were set up,represented by N0～N3.The basal and topdressing ratio of nitrogen fertilizer was set up at 10:0:0,7:3:0 and 1:1:1 while the topdressing periods were basal application,pre-winter topdressing and jointing topdressing,represented by M1～M3.)The effects of different nitrogen fertilization patterns on photosynthetic characteristics,population dynamics,yield,yield components and nitrogen absorption and utilization of rice stubble wheat under straw returning and non-returning conditions were studied in order to identify the optimal nitrogen fertilization patterns suitable for high-yield and efficient cultivation of rice stubble wheat in Jianghan Plain.The main research results are as follows:1.At the same nitrogen application rate,the treatments with a basal topdressing ratio of 10:0:0 and a basal topdressing ratio of 7:3:0（basal fertilizer:topdressing before winter）and 1:1:1（basal fertilizer:topdressing before winter:topdressing at jointing）had higher LAI at the wheat seedling stage.LAI of wheat in the late growth stage was higher in the treatment of jointing and topdressing),and the effect of N fertilizer deferral on LAI in the late growth stage of wheat without straw returning combined with higher N fertilizer was greater,which was significantly higher than that in the treatment of all N fertilizer.With the same basal ratio of nitrogen fertilizer,LAI of wheat population at each growth stage increased with the increase of nitrogen application rate,and the performance of wheat without straw returning to the field was consistent with that of wheat with straw returning.2.Compared with wheat without straw returning to the field,the SPAD value of flag leaf of wheat with straw returning to the field was higher in all stages,and the decrease of SPAD value of flag leaf was less after the middle grain filling.Under the same nitrogen application rate,the SPAD value of flag leaves of wheat was M1<M2<M3,and there was a significant difference between M3 treatment and M1 and M2treatment.With the same basal and topdressing ratio of nitrogen fertilizer,the SPAD value of flag leaf increased with the increase of nitrogen application rate.The SPAD value of flag leaves under N3M3 treatment was the highest in both wheat without straw returning to the field and wheat with straw returning to the field,but there was little or no significant difference with N2M3 treatment.The SPAD value of flag leaves under N2 treatment of wheat with straw returning to the field was significantly higher than that under N3 treatment of wheat without straw returning to the field.3.Compared with wheat without straw returning to the field,the maximum population tiller number of wheat with straw returning to the field may be lower or higher,while the effective tiller number and earhead rate at maturity stage are both higher.At the same nitrogen application rate,M1 treatment had a larger population in the early growth stage,M2 treatment had more effective tillers in the mature stage,and M3 treatment had a higher ear-forming rate.The effective tiller number at mature stage of wheat could be significantly increased by increasing nitrogen fertilizer with the same ratio of basal and topdressing.Wheat without straw returning to the field with N3M3treatment had a higher spike rate,while wheat with straw returning to the field with N2M3 treatment had a higher spike rate.4.Compared with the wheat without straw returning to the field,the dry matter accumulation of wheat with straw returning to the field was lower before winter,but higher at flowering and mature stages,and the dry matter accumulation of wheat with straw returning to the field was more conducive to promoting the dry matter accumulation after flowering.At the same nitrogen application rate,the dry matter accumulation in M1 treatment was higher at seedling stage,M2 treatment was higher at jointing stage to flowering stage,and M2 or M3 treatment was higher at maturity stage,which was significantly different from M1 treatment.At the same basal topdressing ratio,increasing nitrogen application rate could significantly improve the dry matter accumulation after anthesis and at maturity stage,and the dry matter accumulation at maturity stage was the highest for both wheat without straw returning and wheat with straw returning under N3M2.5.The grain yield and harvest index of wheat treated with straw returning combined with nitrogen fertilizer were higher than those of wheat without straw returning,and the grain yield increased by 10%on average compared with that of wheat without straw returning.Under the same nitrogen application rate,wheat yield,harvest index and grain number per panicle were M1<M2<M3,and M3 treatment was significantly higher than M1 treatment.The number of effective panicles in M2treatment was higher than that in M2 treatment,and the 1000-grain weight was decreased or increased first and then decreased with the increase of nitrogen fertilizer.The yield was N1<N2<N3,the effective panicle number and grain number per panicle increased with the increase of nitrogen application rate,and the 1000-grain weight decreased.The yield of wheat without straw returning to the field was the highest in the N3M3 treatment,and there was no significant difference in the yield between the N2M3 treatment and the N3M3 treatment.6.In the range of N application rate from 135 kg·hm-2 to 225 kg·hm-2,straw returning combined with N deferment could significantly increase the total N accumulation in plant and grain at maturity stage of wheat,which was beneficial to the N accumulation in plant before anthesis and the N transport from vegetative organs to grain after anthesis.Under the same basal and topdressing ratio of nitrogen fertilizer,plant N accumulation,grain N accumulation and post-flowering N output of vegetative organs increased with the increase of nitrogen application rate at flowering and mature stages.7.The average values of N apparent use efficiency,N agronomic use efficiency and N productivity of wheat with straw returned to the field were all higher,which were6.33%,3.71 kg·kg-1 and 2.28 kg·kg-1 higher than those of wheat without straw returned.At the same N application rate,N apparent use efficiency,N agronomy use efficiency and N productivity were significantly improved by N deferral.At the same basal topdressing ratio of N fertilizer,N apparent use efficiency increased or first increased and then decreased with the increase of N application rate,while N agronomic use efficiency and N productivity decreased.Considering the experimental conditions,wheat without straw returning to the field had stronger photosynthesis and better population structure under the treatment of nitrogen application rate of 225 kg·hm-2 and basal to topdressing ratio of 1:1:1,and wheat with straw returning to the field had stronger photosynthesis and better population structure under the treatment of nitrogen application rate of 180 kg·hm-2and basal to topdressing ratio of 1:1:1.It can meet the nutrient requirements of different growth stages of rice stubble wheat,promote the accumulation and transport of nitrogen,reduce the loss of nitrogen,improve the use efficiency of nitrogen fertilizer and nitrogen agronomy use efficiency,and obtain a higher wheat yield.It can be considered as a nitrogen fertilizer management model for rice stubble wheat in Jianghan Plain with both high yield and high nitrogen use efficiency. |
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