| As the largest producer of rice stubble wheat in China,it is of great significance to promote the high-yield and high-efficiency production of rice stubble wheat in Jiangsu Province to ensure food security in the local region and China.The excessive application of quick-acting Nitrogen(N)fertilizer in the production process of rice stubble wheat has often led to a decrease in fertilizer utilization efficiency and the increase of costs,and exacerbated problems such as soil degradation,environmental pollution,resource waste,etc.How to improve fertilizer utilization efficiency and reduce fertilizer usage while ensuring high crop yield,so as to promote the sustainable development of agriculture has always been an important issue in crop production.Due to the advantages of labor-saving,high efficiency and environmental friendliness,slow-release N fertilizer(SRNF)provides an important idea for realizing synergy in labor-saving,yield-and efficiency-increasing in rice stubble wheat cultivation.In the past,SRNF is usually applied to wheat in a one-time basal application method.Although it saves manual input,the actual effect in production is controversial due to the difficulty in matching the nutrient supply from SRNF with the nutrient demand in the whole growth period of wheat.To further enhance the application effect of SRNF on rice stubble wheat,resin-coated urea(PCU),sulfur-coated urea(SCU)and urea-formaldehyde(UF)were used as materials to analyze the actual N supply dynamics of SRNF during the wheat growth period,and explore the synchronization between the N supply from twice-split application of SRNF and the N demand for the whole growth period of rice stubble wheat.According to the requirements of labor-saving,cost-saving,yield-increasing,efficiencyincreasing and quality-improving in production,four fertilization patterns were designed:SRNF applied once at pre-sowing(M1),SRNF applied at pre-sowing and urea applied at jointing(M2),SRNF applied twice at pre-sowing and re-greening(M3),SRNF combined with urea applied twice at pre-sowing and re-greening(M4),and the conventional high-yield fertilization method with urea fourth-split application was used as a control(CK).The effects of different fertilization methods on wheat population quality,yield components,quality,dry matter accumulation and transportation,plant senescence and filling physiology,lodging resistance,N efficiency and economic benefits of wheat,as well as their potential for N saving and efficiency increasing were analyzed.And demonstration experiments were conducted at multiple regions in Jiangsu Province to clarify the high-yield and ecological stability of different application methods of slow-release blended fertilizer in large-scale production.In addition,the regulatory mechanism of twice-split application of SRNF reducing N loss in wheat fields was discussed from the aspects such as soil N balance,N2O emission,soil enzyme activity and microbial community structure.The main results are as follows:1.The buried mesh bag method was used to determine the actual N release dynamics of different SRNFs under the condition of basal application and topdressing at re-greening and their synergistic effects with plant N uptake.The results showed that the N release of PCU in soil was slow-fast-slight,which followed an "S" shaped curve,while the N release of SCU was fast at first and then slowed down gradually,which showed an incerted "L" shaped curve.The N release by PCU or SCU one-time application was mainly concentrated before regreening,while PCU or SCU applied twice at pre-sowing and re-greening could continuously release N during the whole growth period of wheat,which significantly increased the N uptake at maturity compared with SRNF one-time application and CK,with an average increase of 13.64%and 15.83%in the two years,respectively.The Richards model parameters indicated that the two fast N release periods of PCU under basal fertilization and topdressing conditions was basically consistent with the two N demand peaks of wheat from tillering to overwintering and from jointing to booting,respectively.The N release rate during the two fast N release periods were both above 60%,which could fully meet the N absorption and utilization of wheat during the N demand peaks of wheat.2.PCU,SCU and UF applied once before sowing achieved similar or slightly reduced yield compared with CK,and avoided manual input of topdressing,but increased fertilizer costs,resulting in an average net benefit decrease of 357.71,1090.55 and 1433.99 yuan·hm-2,respectively.Among different fertilization patterns,both M3 and M4 were beneficial to coordinate population structure,increase total grain number,promote dry matter accumulation post-anthesis and delay leaf area index(LAI)decline,which promoted the synergistic increase of spike number and grain weight.M4 in PCU achieved the highest yield,N recovery efficiency(NRE)and net benefit,with an average increase of 12.92%,9.60 percentage points and 21.09%,respectively,compared with CK over the four years,which also increased NRE by 16.95 percentage points after reducing N by 20%,with the yield slightly higher than CK.In SCU,M3 was conducive to jointly improving yield,NRE and net benefit,with an average increase of 7.24%,7.16 percentage points and 11.43%,respectively,compared with CK over the four years,which could achieve similar yield and increase NRE by 10.63 percentage points compared with CK after reducing N by 15%.In UF,M3 had the highest yield and NRE in the two years,with an average increase of 8.30%and 4.86 percentage points,respectively,which was beneficial to increase yield and efficiency;while M2 replaced part of SRNF with urea,thus reducing fertilizer cost and achieving slightly higher average net benefit compared with M3.3.Twice-split application of different SRNFs supplied sufficient N in the later growth stage of wheat,which was beneficial to increase activities of CAT,POD and SOD in flag leaves post anthesis,reduce MDA accumulation,delay the decline of SPAD value,improve stomatal conductance and transpiration rate,reduce intercellular CO2 concentration of leaves at milking stage,thus enhancing net photosynthetic rate and promoting the accumulation of photosynthetic products and their transport to grains.PCU,SCU and UF applied twice could improve the grain filling process of wheat,prolong the effective filling duration and increase the average and maximum filling rate,which significantly increased the 1000-grain weight and yield of wheat compared with SRNF applied once.In addition,the photosynthetic performance,dry matter accumulation post-anthesis,effective filling duration and average filling rate of wheat in PCU were slightly better than those in SCU and UF.4.One-time application of PCU and SCU decreased N supply after re-greening,which reduced the length of the basal second internode,plant height and height of the center of gravity post-anthesis,but increased the fullness,diameter and stem wall thickness of the basal second internode,thereby enhancing stem snapping resistance and lodging resistance index.The actual lodging rates in one-time application of PCU and SCU were only 1.11 and 1.31,respectively,but the yield was significantly lower than that in PCU and SCU applied twice at pre-sowing and re-greening.Compared with urea applied twice,twice-split application of PCU and SCU increased yield by 14.75%and 12.45%,respectively,and showed higher diameter,stem wall thickness,fullness and snapping resistance of the basal second internode,which was beneficial to improve lodging resistance index at milking and dough stage,and balance the condradiction between lodging resistance and yield increase.5.Twice-split application of PCU,SCU and UF significantly decreased apparent N loss by 41.56%,34.13%and 15.39%,respectively,compared with urea applied twice,which was beneficial to increase plant N uptake and soil N residue after harvest,and reduce N loss through leaching and N2O emission.Compared with urea,PCU,SCU and UF applied twice increased plant N uptake by 18.67%,14.26%and 7.75%,and decreased cumulative N2O emission by 18.46%,8.39%and 9.58%,respectively.PCU significantly increased the activities of soil urease,nitrate reductase and nitrite reductase at maturity,and increased the relative abundance of bacteria involved in N cycle,such as Firmicutes,Actinobacteriota and Bacteroidota,reduced the relative abundance of Nitrospirota,which contributed to regulating the process of soil nitrification and denitrification,and controlling the concentration of NO3-.6.The application method of SRNF significantly affected the yield,N accumulation and transportation,and grain quality in wheat varieties for different end use.One-time application of PCU improved the N transport rate of wheat vegetative organs,especially the stem and sheath,but reduced the N accumulation post-anthesis,which decreased N absorption in grains.Compared with CK,PCU applied once before sowing did not significantly decreased wheat yield,but reduced the protein content,wet gluten content,sedimentation value,dough formation time and stability time,which failed to improve the quality of medium and strong gluten wheat but was conducive to ahcieving the quality standard of weak gluten wheat,so as to promote stable yield and quality improvement of weak gluten wheat.Compared with CK,PCU combined with urea applied twice increased yield and NRE by 4.91%～11.12%and 2.91～7.69 percentage points,respectively,which also enhanced N accumulation post-anthesis,and promoted N absorption and utilization in grains.The protein content,wet gluten content,sedimentation value,dough formation time and stability time in twice-split application of PCU combined with urea were not significantly decreased compared with CK,which was conducive to ahcieving the quality standard of medium and strong gluten wheat,and thus promoted the yield increase and quality improvement of medium and strong gluten wheat.7.The average yield in sulfur coated slow-release blended fertilizer(SBF)applied once in different regions of Jiangsu Province decreased by 4.70%and 3.10%compared with CK in the two years,respectively.The analysis of the coefficient of variation(CV)method indicated that the stability of yield and N agronomic efficiency(NAE)in one-time application of SBF was also at the lowest level under different ecological conditions.The average yield increase compared with CK in different regions of SBF applied at pre-sowing with urea applied at jointing was 3.11%and 3.94,respectively,while the average increase of NAE was 6.31%and 8.29%,respectively,which showed higher yield level and better stability than SBF applied once in different regions,but was lower than those of SBF applied twice.In different regions,twice-split application of SBF increased yield by 8.49%and 7.03%,increased NAE by 16.36%and 15.19%,and increased benefits by 901.59 and 672.08yuan·hm-2 in the two years,respectively.Twice-split application of SBF showed high yield level and stability in different regions,which was conducive to achieving the synergistic increase of yield,efficiency and benefit in large-scale production.In addition,with 15%N reduction,SBF applied twice had no significant difference in yield compared with CK,but increased NAE by 18.44%and 17.13%in the two years,respectively,showing the potential to save N and increase efficiency.8.In this study,the recommended application methods for different types of SRNF in rice stubble wheat production were 50%PCU mixed with 50%urea applied twice at presowing(60%)and re-greening(40%),100%SCU applied twice at pre-sowing(60%)and regreening(40%),60%UF applied at pre-sowing combined with 40%UF applied at re-greening or 40%urea applied at jointing,which were beneficial to promote the synergy of labor-saving,yield-and efficiency-increasing and benefit-raising in rice stubble wheat,promoted partial or full substitution of common urea,and showed the potential for fertilizer conservation and efficiency improvement. |
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