麦（转基因抗虫）棉两熟周年秸秆还田的钾补偿效应及影响棉花产量形成的生态机制研究

In China, the planting area percentage of transgenic insect-resistant cotton has exceeded 70% in total cotton planting area. Although the yield of insect-resistant cotton is high, premature senescence caused by K deficiency occurs frequently and results in low yields and poor fiber quality. In this study, wheat-cotton double cropping mode with cycled straw returning to fields and K fertilizing location were designed. Besides, the experiments were carried out in two areas with different soil types at the lower reaches of Yangtze-river valley. We researched not only the effects of wheat-cotton double cropping mode with cycled straw returning to fields on physical and chemical properties, enzyme activity and microbial activity of soil, but also the responses of biomass accumulation and distribution, nutrition absorption of cotton and yield formation to the treatments. Therefore, according to the relationship, "K in straw of wheat and cotton- - K in soil- - K in cotton plant- - cotton yield formation", 1. The eco-effects of the compensation caused by wheat-cotton double cropping mode with cycled straw returning to fields on soil potassium was proposed definitely; 2. The accumulation and distribution of cotton biomass and nutrition under wheat-cotton double cropping mode with cycled straw returning to fields was illustrated; 3. The feasibility of K substituted or partly substituted by wheat-cotton double cropping mode with cycled straw returning to fields and the relevant substitution effects were both revealed. Consequently, building a theoretical basis, which is not only defined the optimal fertilization amount and fertilization method of transgenic insect-resistant cotton under wheat-cotton double cropping mode, but also improved straw utilization, has a great significance in futuristic transgenic insect-resistant cotton cultivation.

我国转基因抗虫棉已约占棉花种植总面积的70％以上，转基因抗虫棉载铃多产量高，但易发生钾因性早衰，导致棉花产量和纤维品质降低。本研究拟通过在长江流域下游棉区两种不同类型土壤（粘土、壤土）设置麦（转基因抗虫）棉两熟周年秸秆还田定位试验，从"麦棉秸秆钾素- - 土壤钾素- - 棉株钾素- - 棉花产量形成"之间的关系出发，基于麦（转基因抗虫）棉两熟周年秸秆还田对土壤理化性质、酶活性、微生物活性和棉花生物量与养分累积分配及产量形成的影响研究，明确麦棉两熟周年秸秆还田补偿土壤钾素的生态效应，揭示麦棉两熟周年秸秆还田棉花生物量与养分的累积分配规律，阐明利用麦棉周年秸秆还田补偿土壤钾素的可行性与补偿效果，为解决转基因抗虫棉缺钾性早衰、指导麦棉两熟制转基因抗虫棉钾肥施用、提高麦棉秸秆资源利用率提供理论依据。

我国钾肥大量依靠进口，而作物秸秆含钾量高且易释放，但其长期还田对棉花产量和土壤K库的影响，以及对钾肥的替代效应和生态效应尚不明确。本研究在长江流域的南京和大丰两地设置麦棉两熟秸秆还田和钾肥多年连续定位试验，研究麦棉周年秸秆还田对土壤物理性质、土壤养分变化、土壤微生态、棉花养分吸收与产量形成的影响，并通过与钾肥处理的比较，明确秸秆钾对钾肥的替代效应以及生态机制。结果显示：1）除第一年在大丰富钾土壤上麦棉秸秆还田对棉花产量影响不显著外，其余各年秸秆还田量越大增产幅度越高，全量还田优于半量还田、两季秸秆还田优于一季秸秆还田；还田第六年麦棉两季秸秆全量还田处理产量接近K150处理水平。秸秆还田在低钾土壤增产效果显著高于富钾土壤。2) 秸秆还田改善了土壤含水量、孔隙度和土壤有机质及水溶性碳含量等，但主要通过提高土壤速效钾含量，进而提高植株NPK养分吸收量，其中钾素吸收量提高极显著。棉花产量与棉株钾吸收量显著相关。3)小麦和棉花秸秆还田对参与土壤中碳、氮、磷、钾元素循环的大多数功能微生物数量及相关酶活性均起到显著的促进作用。而钾肥处理仅对K循环有关的微生物和养分影响显著，对C、N、P元素相关微生物和酶活性没有显著影响。4）秸秆还田与施钾均可以有效改善土壤钾素状况。显著提高土壤水溶性钾、交换性钾、非交换性钾含量，同时促进土壤非交换性钾释放，降低土壤钾素固定。相比化学钾肥，秸秆还田更多提高土壤非交换性钾含量，而化学钾肥有利于提高水溶性钾含量。麦棉全量秸秆还田可以基本补充土壤钾素亏缺、维持土壤钾素平衡，可以部分或全部替代钾肥，钾素替代率从还田第二年-第六年呈逐渐下降趋势，需补充的化肥量逐年增加。研究结果对改善转基因抗虫棉钾素管理与土壤钾库平衡、促进秸秆资源利用和棉花可持续发展，节本增效有重要的理论与实践意义。