| A double cropping system is a dominant rotation system in the Yangtze River Basin of China,which mainly includes wheat(Triticum aestivium L.)-rice(Oryza sativa L.),oilseed rape(Brassica napus L.)-rice and early rice-late rice cropping systems.A higher intensity of these cropping systems with excess nutrient inputs,results in high nitrogen(N)loss during water-dry seasons and N deficiency.It is an immediate demand on optimizing N management to improve grain yield and quality,N utilization and maintaining soil fertility.The objectives of the dissertation are 1)assess the impacts of N management strategies on crop productivity,agronomic traits,and soil fertility in three rotation systems with three-year field experiments conducted at the Jingmen site in Hubei province and the Changsha site in Hunan province,2)to optimize appropriate N strategies among three rotation systems,and 3)to apply the process-based SPACSYS model for simulating productivity and adaptive strategies in the wheat-rice double cropping system under climate change.The experimental design includes N levels(N1:120 kg N ha-1,N2:150 kg N ha-1,N3:180 kg N ha-1),controlled release fertilizer(CR1:150 kg N ha-1 of controlled release urea as basal fertilizer,CR2:120 kg N ha-1of controlled release urea plus 30 kg N ha-1of urea),straw return(N2+SR:N2 incorporated previous season straw,CR2+SR:CR2 incorporated previous season straw,applying extra 30 kg N ha-1each rice season in wheat-rice and oilseed rape cropping system)and fertilization recommended by Nutrient Expert(NE).The research results help establish high yield cropping systems with minimized environmental impacts and develop adaptation strategies to climate change in the Yangtze River Basin of China.The results are as follows:1.Impacts of N management strategies on crop growth and development,grain yield and soil fertility for the wheat-rice cropping system.Controlled release urea(CR)significantly enhanced grain yield compared with other N treatments in the wheat-rice cropping system.Compared with local farm fertilizer(N2),CR2 and CR2+SR treatments achieved the highest yields for both wheat(1497 kg ha-1)and rice(1140 kg ha-1).The CR2 and CR2+SR treatments also significantly increased grain crude protein content for wheat and rice with the average of 14.9%and 18.3%,respectively,compared with N2.The wheat grain yield positively correlated with effective spikes,grain crude protein content,N use efficiency(NUE)and relative chlorophyll content,while negatively with N surplus.NUE of wheat under different N management treatments had a significant difference:a 13.2 and 18.2%increase,respectively,under CR1 and CR2 compared with N2.This may be because leaf chlorophyll content for wheat under CR2 was higher by 31.8%than that under N2 at booting stage.In addition,CR urea significantly decreased N surplus(wheat and rice:48.2 and 52.1 kg N ha-1)and increased NUE(68.7 and 72.5 kg kg-1).CR urea incorporated straw also played an important role in maintaining soil fertility in terms of soil organic matter(1%),total N(2%),available N(2%).However,the management could slightly cause soil acidification(0.4 of p H value).Generally,CR2 and CR2+SR for wheat and rice are superior for photosynthesis,yield,N surplus and NUE in the rotation system among all the N strategies.2.CR urea had a potential in increasing yield in the oilseed rape-rice cropping system.CR2 and CR2+SR increased grain yields of oilseed rape and rice by 291 and 708 kg ha-1,respectively,and crude protein content by 9.9 and 4.5%compared with local farmer practices,which was associated with maximum photosynthesis rates at anthesis for oilseed rape and tillering stage for rice.CR urea supplied enough nutrient in time for crops,thereby enhancing photosynthetic carbon metabolism in leaves and relative chlorophyll content.Furthermore,there was a significant correlation between NUE and crude protein content in the cropping system.Besides,the CR2 treatment for oilseed rape and rice played a key role in declining soil N surplus by 6.4 and 7.5 percentage points compared with N2,respectively.3.Impacts of N management strategies on productivity in the rice-rice cropping system.The combination of CR2+SR and N2+SR had obvious advantages in grain yield with an increase of 194 and 863 kg ha-1 in 2018;CR2+SR had a significant impact on the crude protein content in rice,and increased 0.2 and 2.9 g kg-1 compared with N2 treatment in 2017;CR2-CR1 enhanced N use efficiency in early rice and late rice with an increase of 0.5 and 15.8%;CR2+SR improved grain yield for rice due to release nutrient from CR urea and straw at booting and filling stage in appropriate environment condition.Leaf chlorophyll content under CR2+SR were increased by14.9 and 25.6% compared under N2;Straw return and CR urea played an important role in maintaining the sustainability of soil fertility.N2+SR obviously improved soil organic matter in early rice season with an average increase of 17.5%.It also indicated that straw return could provide certain nutrients through its decomposition or mineralization process,thereby improving soil physical and chemical properties,which is of great significance for maintaining the sustainable development of early rice-late rice system productivity.(4)The comprehensive evaluation index(EI)can directly reveal the advantages and disadvantages of different N fertilizer application strategies in crop yield,grain quality,and soil fertility.When considering high yield,the management combinations with CR2(wheat)-N3(rice),CR1(oilseed rape)-N3(rice) and CR2+SR(early rice)-CR1(late rice) have obvious advantages in improving crop yield in the cropping systems,respectively.Total net profit was ordered as:rice-rice(23,676 yuan ha-1)<wheat-rice(27,226 yuan ha-1)<oil-rice(27,792 yuan ha-1);When considering crop quality,total benefits under fertilizer recommendation by NE(wheat)–N3(rice)and CR2(oilseed rape)–CR1(rice)for wheat-rice and oilseed rape-rice were higher by 727 and 3659 yuan ha-1 than that under CR2(early rice)–CR1(late rice)for early-late rice cropping systems;When considering soil fertility,N2+SR(wheat)–CK(rice),CR1(oilseed rape)–CR2(rice)and N3(early rice)–N2+SR(late rice)are relatively high for the soil fertility levels among three rotations,and it was essential to maintain sustainability in land use.The oilseed rape-rice system was a competitive rotation system compared to the other cropping systems because total benefits reached 22,985 yuan ha-1.The results also revealed that the comprehensive evaluation index had good fitness to that of single attribute,indicating that the evaluation index was reliable.Properly managing N application by applying partial and full controlled release urea with or without straw incorporation for a specific crop system has the potential to be a better compromise among yield,grain quality and soil fertility in southern China.(5)Process-based simulation models are an effective tool to assess the potential impacts of climate change and agronomic practices not only on yield and N uptake but also nutrient cycling.The SPAVSYS(v6.0) model was applied to investigate the effects of climate change and fertilization on yield,N contribution efficiency before anthesis,N loss to water and nitrous oxide(N2O) emissions in the wheat–rice cropping system.The model was first evaluated using crop production and N accumulation data from three-year field experiments,and then applied to simulate production and N processes under three representative concentration pathway(RCP)scenarios at Jingmen,with projections for the years 2020 to 2100.Results indicated that N management as well as shifting sowing or transplantation dates could greatly mitigate the yield losses and N contribution efficiency(ANCE) reduction in rotation system.Delaying sowing dates of wheat and transplanting rice earlier could reduce N leaching losses.Unexpectedly,climate change indirectly increased N2O emissions,showing significant variation depending on the interaction with high N fertilization for rice pre-anthesis,indicating that emissions can be limited by restricting fertilizer application.Changing the dates when the growing seasons start,along with appropriate N management practices is a potential way to tackle climate change in the wheat-rice cropping system of China.In summary,our research results showed that optimized nitrogen management such as controlled release urea combined with common urea can significantly affect crop growth and development in double cropping system of three paddy fields and supply nitrogen nutrition in the later growing stage,which saved labor and increased crop yield,quality,economic benefits and nutrient utilization.On this basis,combined with straw returning to the field can increase the soil organic matter and effective nutrient content,and nitrogen nutrient released by the slow and controlled release urea can be used more effectively to maintain soil fertility.The comprehensive evaluation score coefficient(EI) based on the multi-index comprehensive evaluation method can be used to directly evaluate the pros and cons for different nitrogen fertilizer management,which has good guidance and practical value.After calibration and verification,SPACSYS can better simulate the crop growth in the crop rotation system and has good accuracy.The model can be used to study the impact of climate change on crop productivity and comprehensive adaptation strategies.Therefore,the author believes that above-mentioned optimized nitrogen management model combined with comprehensive evaluation index method and crop growth model could be used for evaluation and guidance of N management in double cropping system in the Yangtze River Basin.N application management provides a more reliable scientific basis,economic and ecological benefits. |
PDF Full Text Request