有机肥等氮替代对双季稻根区土壤结构环境及根活力的影响

Effects of nitrogen substitution isonitrogen substitution on soil structural environment and root viability in the root zone of double-cropping rice

  • 摘要: 【目的】探究有机肥等氮替代对水稻根区土壤结构环境、土壤微生物量碳及水稻根系生长的影响,为南方集约化双季稻生产相匹配的减肥增效种植制度优化提供理论依据。【方法】依托广西南宁双季籼稻典型区环境,设不施肥对照(CK)、无机氮(T1,100%化肥)、无机氮+有机氮(T2,绿肥+化肥)和有机氮(T3,绿肥+生物炭+蚕沙+无氮化肥)4个定位处理。在水稻移栽后返青至晒田根系形成的关键期内,分别于移栽后7、14、21、35和42 d采集水稻植株和根区土壤样品,系统分析水稻根系生长及土壤团聚体结构和微生物量碳含量变化。【结果】等氮替代可促进土壤水稳性团聚体形成,增加微生物量碳含量。早稻季,各处理中小团聚体(II~V级)总含量表现为T2(21.44%)>T3(18.85%)>T1(13.4%)>CK(7.65%),T2和T3处理的微团聚体含量(VI~VII级)高于CK和T1处理,T2处理的土壤水稳性团聚体平均质量直径(MWD)低于其他处理;晚稻季,各处理中小团聚体(II~V级)总含量依次为T2(21.44%)>T3(18.85%)>CK(12.11%)>T1(7.70%),T2和T3处理的微团聚体(VI~VII级)含量较高、MWD较低;双季稻T2和T3处理的几何平均值径(GMD)均显著低于T1和CK处理(P<0.05,下同),微生物量碳含量依次为T2>T3>T1>CK。等氮替代改变水稻根体积与根系活力,增强了植株养分吸收力。早稻季,移栽后42 d根体积和根活跃吸收面积均表现为T2>T1>T3>CK;晚稻季,移栽后42 d根体积表现与早稻季一致,根活跃吸收面积表现为T1>T2>CK>T3。等氮替代影响水稻根冠比和干物质积累。早稻季,随移栽时间的延长,各处理的根冠比整体呈先升后降的变化趋势,均在水稻移栽后21 d出现峰值;晚稻季,各处理的根冠比峰值不明显。移栽后42 d,植株干物质重在各处理间差异显著,均表现为T2>T1>T3>CK。【结论】绿肥、生物炭与蚕沙可促进土壤水稳性团聚体形成,增大微生物量碳含量,利于稻根生长发育,与种植制度匹配的有机肥等氮替代生产模式可作为南方双季籼稻区集约化水稻减肥增效的重要优化措施。

     

    Abstract: 【Objective】The purpose of the study was to explore the effects of organic fertilizer isonitrogen substitution on the rice and root zone soil structural environment,soil microbial mass carbon,rice root growth,and to provide a theoretical basis for the optimization of reduced fertilizer enhanced efficiency planting system matched to intensive doublecropping rice production in the south.【Method】Based on the environment of a typical zone of double-cropping indica rice in Nanning,Guangxi,four types of localized treatments were set up:no fertilization control(CK),inorganic nitrogen (T1,100% chemical fertilizer),inorganic nitrogen with organic nitrogen(T2,green manure+chemical fertilizer),and organic nitrogen(T3,green manure+biochar+silkworm excrement+nitrogen-free chemical fertilizer). Rice plant samples and root zone soil samples were collected at 7,14,21,35 and 42 d after transplanting during the critical period from greening after transplanting to the formation of the root system in sunny fields. The growth of rice roots and changes in the structure of soil aggregates and microbial mass carbon content were systematically analyzed.【Result】Isonitrogen substitution promoted the formation of soil water-stable aggregates and increased the microbial mass carbon content. In the early rice season,the total content of small and medium-sized aggregates(classes II to V)in each treatment showed T2 (21.44%)>T3(18.85%)>T1(13.4%)>CK(7.65%). The content of microaggregates(classes VI to VII)was higher in the T2 and T3 treatments than that in the CK and T1 treatments,and the mean weight diameter(MWD)of soil waterstable aggregates in the T2 treatment was lower than that in the other treatments. In the late rice season,the total content of small and medium-sized aggregates(classes II to V)in each treatment was in the order of T2(21.44%)>T3(18.85%)> CK(12.11%)>T1(7.70%),with higher microaggregate content and lower MWD in the T2 and T3 treatments(classes VI to VII). Geometric mean diameter(GMD)of both T2 and T3 treatments of double-cropping rice was significantly lower than that of T1 and CK treatments(P<0.05,the same below),and microbial mass carbon content was in the order of T2> T3>T1>CK. Isonitrogen substitution changed rice root volume and root viability and enhanced plant nutrient uptake. In early rice season,42 d after transplanting,root volume performance and root active absorption area performance were T2> T1>T3>CK. In the late rice season,the root volume performance at 42 d after transplanting was consistent with that of the early rice season,and the root active absorbing area performance was T1>T2>CK>T3. Isonitrogen substitution affected the root shoot ratio and dry matter accumulation of rice. In the early rice season,with the prolongation of transplanting time,the root shoot ratio of each treatment showed an overall trend of increasing and then decreasing,all of which peaked at 21 d after rice transplanting. In the late rice season,the peak root shoot ratio was not significant in all treatments. At 42 d after transplanting,the dry matter weight of plants differed significantly among treatments,both showing T2>T1>T3>CK.【Conclusion】Green manure,biochar and silkworm excrement can promote the formation of soil waterstable aggregates,increase the microbial mass carbon content,and facilitate the growth and development of rice roots. Organic fertilizer isonitrogen substitution production model matching the planting system can be an important optimization measure for reducing fertilizer and increasing efficiency of intensive rice in southern double-cropping indica rice area.

     

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