冷硝酸浸提法对表征富钾石灰性土壤有效钾的适用性研究

Research on the applicability of extraction method of available potassium using cool nitric acid in potassium-enriched calcareous soil

通过研究西北黄土区富钾石灰性土壤中钾素形态及各形态之间的关系，为“冷硝酸浸提土壤有效钾法”在富钾石灰性土壤上的适用性提供理论依据。以关中平原麦玉轮作不同秸秆还田模式多年定位试验农田土壤为供试材料，用2 mol·L-1冷硝酸浸提测定土壤有效钾，并以常规方法测得土壤钾素的其他7种组分，通过相关分析、主成分分析和通径分析，揭示上述8种组分间的关系。在麦玉轮作体系不同秸秆还田模式下，耕层土壤中各组分钾素含量均存在较大变异性，变异系数1．9%-33．8%，不同秸秆还田模式下差异不显著；冷硝酸浸提钾的含量分别约为速效钾和缓效钾含量的1．43和0．30倍，且与土壤速效钾存在极显著正相关关系（ r=0．82）；主成分分析表明，冷硝酸浸提钾与土壤速效钾同在第一主成分中，且均具有较高载荷；通径分析表明，冷硝酸浸提钾主要由土壤非特殊吸附钾、特殊吸附钾以及非交换性钾3种化学形态组成，其含量来自土壤交换性钾的贡献最大，与速效钾类似。冷硝酸浸提法可以作为表征石灰性富钾土壤有效钾水平的可靠方法，土壤交换性钾是土壤有效钾主要供方。

The purpose of this study was to provide theoretical basis for the applicability of“extraction method of available po-tassium （ K） using cool nitric acid” by evaluating K fractions and their relationships in K-enriched calcareous soil in northwest China. Soil samples were collected from different straw-returning modes plots in a winter wheat-summer maize rotation system treated as a long-term experiment in Guanzhong Plain. The available K in soils were extracted by cool nitric acid in 2 mol·L-1 and then determined. Conventional methods were also used to determine other 7 kinds of K variable in soils. The relationships among the above 8 fractions were clarified by three mathematic methods, i. e. correlation analysis, principal component analysis and path coefficient analysis. Results showed that large variability of each K fractions in surface soil and variable coefficients varied between 1. 9% and 33. 8%. No significant differences were found between different straw-returning modes. The content of K extracted by cool nitric acid was 1. 43 and 0. 30 times that of readily and slowly available K, respectively. Also, highly significantly positive correlation was found between K content extracted by cool nitric acid and readily available K in soils （ r=0. 82）. Meanwhile, the results of principal component analysis showed K extracted by cool nitric acid was in the first principal component with readily available K, where both had high loading. Additionally, the results of path coefficient analysis showed soil K extracted by cold nitric acid was composed by non-specifically adsorptive K, specifically adsorptive K and non-exchange-able K, and it was mainly contributed by exchangeable K, which similar with readily available K in soil. In conclusion, ex-traction method of available K using cool nitric acid could be used as a reliable method to measure the level of available K con-tent in K-enriched calcareous soil. Exchangeable K could be the main supplier to available K in soil.