| In this study,a two-year field positioning experiments was conducted to examine differences in the growth and nutrient accumulation of green manure,growth and development,yield formation,nutrient accumulation of double cropping rice after green manure and characteristics of paddy soil in different mixed cropping systems of green manure(Astragalus sinicus,Astragalus sinicus+ Ro-phanus sativus L,Astragalus sinicus + Lolium perenne L,Astragalus sinicus,+ Ro-phanus sativus L + Lolium perenne L).Effects of mixed cropping and returning of various green manures replacing partial basal chemical nitrogen fertilizer(urea)on double cropping rice's yield formation and paddy soil characteristics were explored,and it aimed at screening the most reasonable mixed cropping system of green manures in paddy fields.Theoretical basis and technical supports for achieving efficient nutrient management in paddy fields,and overcoming soil barrier factors were provided.The main results are as follows:(1)Yield(dry base)of green manure,nitrogen(N)content and total nitrogen accumulating amount were all relatively higher in Astragalus sinicus monoculture system,and its nitrogen content of hay was higher 11.5%,18.0%,13.3% and 12.1%(averages in two years)than that of Astragalus sinicus + Ro-phanus sativus L,Astragalus sinicus + Lolium perenne L,Astragalus sinicus + Ro-phanus sativus L + Lolium perenne L and winter fallow treatment,respectively.There were no significant differences in P and K content among the treatments.The proportion of N of green manures replacing fertilizer N was 28.98%-39.68% in 2016 and 30.55%-39.47% in 2017.And the proportion of Astragalus sinicus monoculture treatment reached maximum,while that of Astragalus sinicus + Lolium perenne L treatment reached minimum.(2)Green manures replacing partial base application chemical fertilizer had no significant effect on rice tillering dynamics,while it was beneficial to improve leaf area index,leaf SPAD value and dry matter accumulation of rice in filling stage,then could increase effective panicle number and seed setting rate.There were certain differences between years,in general,Astragalus sinicus monoculture and Astragalus sinicus + Ro-phanus sativus L treatment showed well.(3)Green manures replacing partial base application chemical fertilizer treatments had yield-increasing effects,while there existed significant differences among different patterns.In 2016,both early and late rice could gain the best yield-increasing effect in Astragalus sinicus monoculture treatment(yield increased 7.3% and 8.5% than CK,respectively),and that in Astragalus sinicus + Ro-phanus sativus L treatment ranked second(yield increased 6.0% and 7.1% than CK,respectively).In 2017,both early and late rice had the best yield-increasing effect under the Astragalus sinicus + Ro-phanus sativus L treatment(yield increased 7.2% and 5.5% than CK,respectively),and that in Astragalus sinicus monoculture treatment ranked second(yield increased 5.5% and 4.7% than CK,respectively).(4)Green manures replacing partial basal chemical fertilizer had certain promoting effects on N absorption,utilization and accumulation of rice.There were better returning effects in Astragalus sinicus monoculture and Astragalus sinicus + Ro-phanus sativus L mixed cropping,which were beneficial to improve N absorption,utilization and accumulation amount in late stage of rice.(5)Green manure treatment had certain positive effects on improving available nitrogen content in double-cropping paddy soil.There were no obvious laws about differences of paddy soil available nitrogen content among the treatments after green manures returning in 2016,while the available nitrogen content in green manures returning treatment were all higher than winter fallow treatments' at maturity stage of early and late rice in 2017,and the increase amplitude ranked 0.53%-2.17%(averages of early and late rice),in which the content under Astragalus sinicus monoculture treatment was largest,and the content under Astragalus sinicus + Ro-phanus sativus L treatment mixed cropping ranked second.Green manure treatment had certain positive effects on improving the soil organic matter content in double-cropping rice soil,and the increase amplitude in Astragalus sinicus monoculture treatment was pretty big,and which was higher 1.16%and1.94%(averages of early and late rice)than that of winter fallow treatment in 2016 and 2017,respectively.Green manure treatment had certain positive effects on improving urease activity in double-cropping rice soil,and the increase amplitude in Astragalus sinicus monoculture and the Astragalus sinicus + Lolium perenne L treatment were bigger,and it was higher than that of winter fallow treatment by 1.91%-5.74% in 2016 and 3.25%-6.85% in 2017,respectively.(6)In various patterns,the available phosphorus content in paddy soil under the Astragalus sinicus + Lolium perenne L,Astragalus sinicus + Ro-phanus sativus L + Lolium perenne L treatments were higher,that of winter fallow treatment racked second,while that of Astragalus sinicus monoculture and Astragalus sinicus + Ro-phanus sativus L was lower,and which was lower 2.03%,2.72% and 2.07%,2.38%(averages of early and late rice)than that of winter fallow treatment in 2016 and 2017,respectively.Meanwhile,the available potassium content in paddy soil was higher in winter fallow treatment,that of Astragalus sinicus monoculture and Astragalus sinicus + Ro-phanus sativus L treatments at maturity stage was lower 6.05%,7.4% and 5.58%,6.75%(averages of early and late rice)than that of winter fallow treatment in 2016 and 2017,respectively.Comprehensively,returning green manures to field and replacing partial basal chemical nitrogen fertilizer had positive effect on yield-increasing of double cropping rice and improvement of paddy field fertility,and the effects of Astragalus sinicus monoculture and Astragalus sinicus + Ro-phanus sativus L treatment showed well. |
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