施肥对洞庭湖平原水稻土团聚体特征及其有机碳分布的影响

【目的】团聚体是土壤重要的物理属性，也是土壤有机碳的主要固存场所。研究长期不同施肥对洞庭湖平原红壤性水稻土团聚体数量、稳定性、分形特征及其有机碳含量及分布的影响，为区域双季稻田施肥管理提供理论依据。【方法】以国家稻田土壤肥力与施肥效应长期试验为平台（1986—2013），运用湿筛法获得不同粒级水稳性团聚体，分析对照（不施肥，CK）、单施氮磷钾肥（NPK）、低量有机肥与氮磷钾肥配施（LOM，有机肥氮比例为30%）和高量有机肥与氮磷钾肥配施（HOM，有机肥氮比例为60%）4种处理影响下耕作层（0—20 cm）土壤粒径＞0.25 mm的水稳性团聚体数量（WR_0.25）、平均重量直径（MWD）、几何平均直径（GMD）、分形维数（D）及其有机碳含量与分布的变化特征。【结果】除粒径＞5 mm的土壤团聚体外，水稳性团聚体含量和团聚体对土壤有机碳的贡献率均随团聚体粒径减小呈现逐渐增加的趋势，而团聚体有机碳含量则呈现逐渐降低的变化趋势，其变化特征在不同处理间表现一致。长期不同施肥对2—5 mm和0.5—2 mm团聚体含量影响最大，与对照相比，施肥处理中上述两粒级团聚体含量分别增加35.5%—64.5%和6.2%—14.7%。施肥后团聚体的WR_0.25、MWD、GMD分别增加8.6%—12.5%、7.1%—15.1%、13.7%—28.4%，而D值降低2.3%—3.5%，说明长期施肥增强团聚体稳定性，改善团聚体结构。单施氮磷钾肥和氮磷钾肥配施有机肥均可显著提高各粒级团聚体中有机碳含量（P＜0.05），并始终表现出HOM强于LOM、LOM强于NPK的处理效应，与对照相比，HOM处理各级团聚体中有机碳含量较对照提高了22.1%—36.6%。水稳性大团聚体是土壤有机碳的主要载体，不同处理间＞0.25 mm团聚体中有机碳的分量占土壤有机碳的比例表现出HOM（83.5%）＞LOM（81.6%）＞NPK（79.2%）＞CK（69.9%）的顺序。施肥各处理均可显著提高＞5 mm、2—5 mm、0.5—2 mm三级团聚体中有机碳对土壤有机碳的贡献率，且主要影响土壤有机碳在2—5 mm和0.5—2 mm两级团聚体中的分配率。＞0.5 mm的各级团聚体含量与土壤有机碳含量呈极显著正相关（P＜0.01），说明施肥后土壤新增有机碳主要向＞0.5 mm的水稳性团聚体中富集。【结论】长期实行NPK平衡施肥及与有机肥配施有利于洞庭湖平原红壤性水稻土水稳性团粒结构的形成及大团聚体中有机碳的积累，与单施氮磷钾肥处理相比较，施用有机肥特别是高量有机肥与化学氮磷钾肥配施更有利于土壤良好结构体的形成和固碳能力的增强，是更优的稻田施肥模式。

Effects of Fertilization on Aggregate Characteristics and Organic Carbon Distribution in a Paddy Soil in Dongting Lake Plain of China

【Objective】 The objective of this study is to assess the capability of predatory mite carrying conidia and test the vitality of conidia, which will provide a theoretical basis for combining application of Beauveria bassiana with predatory mite against Frankliniella occidentalis.【Method】 Neoseiulus barkerimL B. bassiana suspensions, the potential of conidia carried by predator was observed under scanning electron microscope. The number of conidia carried by predator at different times (2, 12, 24 and 48 h) was counted under hemocytometer, and the vitality of conidia was tested by colonies counting. Moreover, the infection rates of conidia dispersed by predator at different times above were tested by bioassay.【Result】The treated predatory mites could carry conidia. After 2 h, one female adult predator carried 4.12×10⁴ conidia. The number of conidia carried was decreased gradually with time increasing, after 48 h, one predator carried 7.95×10³ conidia. The conidia dispersed by predators had vitality. After 2 h, the conidia dispersed by 10 predators formed 24 colonies on medium. The number of colonies was decreased gradually with time increasing, after 48 h, only 3 colonies could be formed. The conidia dispersed by predators were virulent to F. occidentalis. After 2 h, the conidia dispersed by 10 predators caused 75% mortality of adult F. occidentalis on the 10th day. The mortality of F. occidentalis was decreased gradually with time increasing, after 48 h, 25% mortality of adult F. occidentalis was caused. After 2, 12, 24 and 48 h, the mortalities of adult F. occidentalis over the 10 days displayed linear correlation. The lethal time (LT₅₀) after 2 h was 6.44 d, which was significantly lower than that after 48 h (9.83 d).【Conclusion】Predator mites can carry a large number of conidia within a short time, the conidia have vitality and can be dispersed and infected F. occidentalis, therefore, combined application of B. bassiana and predatory mite have a potential for control of F. occidentalis. adults were sprayed by 1.0×10⁸ conidia/