| Rice is one of the main food crops worldwide and plays an important role in global food production and consumption.Rice yield is comprehensively influenced by cultivation environment,soil nutrients and field management.Field management is easily controlled by human factors.Thus,the improvement of field management plays an important role in increasing rice yield.Rice-wheat rotation is the dominant farming system in the Yangtze River region of China,which can produce large amounts of straw residue.Crop straw and biogas residue that remains after the anaerobic fermentation of organic wastes,contain a lot of nutrients.Organic matter return not only solves environmental problems but also promotes the nutrient recycling and sustainable environmental development.Rice-duck farming,which is considered as an environment-friendly agricultural ecological model,has been widely applied and popularized in China and other Asian countries.Rice-duck farming can achieve the aim of stimulating the growth of rice,controlling diseases,insect pests and weeds,promoting material circulation and improving paddy environment by using ducks' continuous activities.Insect-proof net cultivation provide an ecological and effective approach for preventing the transfer and infection of insect pests,and controlling the harm of plant diseases with the coverage of insect-proof nets.The study took Nanjing9108 as experimental material to analysis the effects of insect-proof net cultivation,rice-duck farming and organic matter return on rice matter accumulation and nitrogen utilization,culm lodging resistance,greenhouse gas emissions and rice quality through designing insect-proof net cultivation,rice-duck farming and organic matter return treatments.Results of this study were presented as follows:1.Wheat straw and biogas residue return could improve rice leaf SPAD values,net photosynthetic rate(Pn)after the elongation stage(EG),dry matter and N accumulation after the EG,dry matter and N translocation after the heading stage(HD),and N recovery efficiency(NRE).Compared with inorganic nitrogen(N)fertilizer,wheat straw and biogas residue return increased the rice yield by 2.11-4.28%and 4.78-7.67%,respectively.Compared to conventional rice farming,rice-duck farming increased leaf photosynthetic capacity,dry matter and N accumulation,dry matter and N translocation after HD,NRE,and finally promoted the rice yield by 1.52-3.74%.Because of the coverage of insect-proof nets,insect-proof net cultivation declined the leaf Pn,dry matter accumulation and translocation,N absorption and translocation,and NRE.Compared with open field cultivation,insect-proof net cultivation decreased the rice yield by 2.48-4.98%.Organic matter return and rice-duck farming could increase dry matter and N accumulation at later stage of rice,dry matter and N translocation after HD,which were beneficial to improve the rice yield.2.Organic matter return increased culm diameter,wall thickness,substantial degree,bending moment at breaking and non-structural carbohydrates,cellulose,lignin of rice culm and leaf sheath,but decreased plant height,gravity center height,bending moment of whole plant and lodging index.Compared with inorganic nitrogen fertilizer,organic matter return increased culm bending load by 5.03-23.38%.Because of the ducks' stimulation effect on rice culm,rice-duck farming decreased rice plant height,gravity center height,lodging index and bending moment of whole plant,but increased culm diameter,wall thickness,culm dry weight,substantial degree,bending moment at breaking and non-structural carbohydrates,cellulose,lignin of rice culm and leaf sheath.Compared with conventional rice farming,rice-duck farming increased culm bending load by 9.65-20.37%,which indicates that rice-duck farming improved the mechanical strength of rice culm.Due to the insect-proof net mulching,insect-proof net cultivation improved rice culm lodging index,simultaneously increased plant height,gravity center height and bending moment of whole plant,while declined culm diameter,wall thickness,substantial degree and non-structural carbohydrates,cellulose,lignin of rice culm and leaf sheath.Insect-proof net cultivation decreased culm bending load by 7.95-13.42%,which wasn't beneficial to increase rice yield.In addition,plant height and gravity center height had positive correlations with lodging index,while culm diameter,wall thickness,substantial degree and bending load had negative correlations with lodging index.Therefore,decreasing plant height,increasing culm diameter,wall thickness and substantial degree were helpful for improving culm bending load,which is crucial for increasing rice lodging resistance.3.Wheat straw return increased methane emission flux,but decreased nitrous oxide emission flux and soil redox potential in paddy field.Compared with inorganic nitrogen fertilizer,wheat straw return improved the global warming potential by 96.89-123.02%,indicating wheat straw return enhanced greenhouse effect of paddy field.Because of the continuous activities of ducks,rice-duck farming increased soil redox potential and nitrous oxide emission flux but decreased methane emission flux.Compared with conventional rice farming,rice-duck farming declined the global warming potential by 8.72-14.18%.Insect-proof net cultivation had higher soil redox potential but lower methane and nitrous oxide emission fluxes than open field cultivation,insect-proof net cultivation decreased the global warming potential by 6.35-13.14%,this indicates rice-duck farming and insect-proof net cultivation would benefit for relieving global greenhouse effect.4.Compared with inorganic nitrogen fertilizer,organic matter return could increase milled rice rate and head rice rate,but decrease chalky grain rate,chalkiness and amylose content.Organic matter return also caused increases in rice protein,total amino acids,gel consistence,peak and breakdown viscosity,relative crystallinity but decreases in setback viscosity.In addition,wheat straw return decreased mineral element content in rice grain,while biogas residue return increased the contents of Ca?Fe?Mn?Zn and Cu in rice grain.Rice-duck farming and insect-proof net cultivation had higher milled rice rate,head rice rate,gel consistence,peak and breakdown viscosity,relative crystallinity but lower setback viscosity than corresponding conventional rice farming and open field cultivation treatments.Rice-duck farming and insect-proof net cultivation also increased rice protein and total amino acids but decreased amylose content.Rice-duck farming improved mineral element content of rice grain,while insect-proof net cultivation declined macro-element contents,and increased micro-element contents.In addition,rice amylose content had significantly negative correlations with relative crystallinity and breakdown viscosity but significantly positive correlation with setback viscosity.Significantly negative correlations were also found between prolamin content,prolamin/glutelin ratio and protein content,essential amino acids,total amino acids.Thus decreasing amylose content and prolamin content could promote the improvement of rice cooking and eating quality,and nutritional quality. |
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