长期定位施肥对玉米根际土壤团聚体有机碳与钾素含量及其相互关系的影响

  目的  探讨长期定位施肥对玉米根际土壤中不同形态钾素含量变化及其与团聚体组分有机碳含量间的耦合关系，为红壤合理施肥提供理论依据。  方法  依托红壤长期施肥定位试验（始于1986年），采集不施肥（CK）、氮磷肥（NP）、氮磷钾肥（NPK）、2倍氮磷钾肥（DNPK）和氮磷钾配施有机肥（NPKM）5个处理玉米根际土壤，测定不同粒级土壤团聚体的有机碳、交换性钾和非交换性钾含量，探明它们之间的相关关系。  结果  各施肥处理玉米根际土壤不同粒级团聚体组分中 > 2 mm组分均显著低于0.25 ~ 2 mm和 < 0.25 mm组分，但NPKM处理 > 2 mm的组分最高，< 0.25 mm组分则显著低于其他处理；而各团聚体组分间、同一粒级不同处理间全钾含量均无显著差异。与NP处理相比，NPK处理在 > 2 mm、0.25-2mm和 < 0.25mm团聚体的交换性钾含量分别增加了64.83%、31.12%和32.43%，非交换性钾含量分别提高了11.74%、16.86%和14.54%。相关分析表明，> 2 mm团聚体中有机碳与交换性钾、非交换性钾含量均呈现出显著的正相关关系（R2分别为0.72和0.77，P < 0.05），且 > 2 mm团聚体中有机碳含量增加0.1 g kg?1，交换性钾和非交换性钾含量分别提高5.69 mg kg?1和 2.37 mg kg?1。  结论  在南方红壤地区，长期有机无机肥配施是提高玉米根际土壤大团聚体比例的重要措施，且大团聚体中有机碳含量的增加促进了交换性钾和非交换性钾含量的提高，可为满足作物根系的钾素需求奠定基础。

Coupling Relationship of Organic Carbon and Potassium in Rhizosphere Aggregates of Maize under Long-term Fertilization

  Objective  The rhizosphere soil of maize was used to study the changes of potassium (K) under long-term K fertilization in order to solve the problem of K deficiency in red soil. The relationship between organic carbon (C) and K in the aggregate was also explored. It is expected to provide a theoretical basis for the rational application of K fertilizer in red soil.   Method  Relying on the long-term fertilization experiment of red soil (beginning in 1986), five treatments, including unfertilized control (CK), inorganic nitrogen and phosphorus (NP), inorganic NP and potassium (NPK), double NPK (DNPK) and inorganic NPK plus manure (NPKM) were selected to determine the organic C, exchangeable K and non-exchangeable K in each aggregate component of the rhizosphere. Then the correlation between organic C and K were conducted in the aggregate component.   Result  The results demonstrated that the proportion of aggregates > 2 mm was significantly lower than the proportions of 0.25-2 mm and < 0.25 mm in all treatments of maize rhizosphere soil. Among all treatments, the proportion of aggregates > 2 mm treated with NPKM was the highest, while the proportion of aggregates < 0.25 mm was significantly lower. At the same time, there was no significantly difference in the total K content of all aggregate component and all fertilization treatments. Compared with CK treatment, the content of organic C, exchangeable K and non-exchangeable potassium in aggregates > 2 mm treated with NPKM increased by 8.65%, 106.19% and 27.05%, respectively. Compared with NP treatment, the exchangeable K and non-exchangeable K content of aggregates > 2 mm in NPK treatment increased by 64.83% and 156.04%, respectively, and the increase by NPKM treatment was 11.74% and 23.47%, respectively. The correlation analysis showed that the organic C in > 2 mm aggregates had a significant positive correlation with exchangeable K and non-exchangeable K. Combining with the slope of the linear equation, it is found that when the organic C in the aggregates > 2 mm increased by 0.1 g kg?1, and the exchangeable K content increased by 5.69 mg kg?1 and 2.37 mg kg?1.   Conclusion  Long-term combined application of organic and inorganic fertilizers is a key measure to increase the proportion of macro-aggregates in the rhizosphere soil of maize in the southern red soil region, and the increase of the organic C content in the soil macro-aggregates promotes exchangeable K and non-exchangeable K content, which lays a foundation for satisfying the K demand of crop roots.