我国不同水热梯度带土壤钾素生物有效性的分布规律及其作用机制

Potassium (K) plays a particularly crucial role in a number of physiological processes vital to growth, yield, quality, and stress resistance of all plants. Soil K is traditionally subdivided into three groups depending on its availability to plants: rapidly available, slowly available and structural forms. Various methods have been established to assess the available K (AK) in soils, e.g. extraction by 1 mol L-1 HCl, boiling in 0.5 mol L-1 or 1 mol L-1 HNO3, and sodium tetraphenylboron (NaTPB). However, in contrast to NaTPB, the acid extracting methods, on the one hand, underestimated the values of AK; on the other hand, extracted some structural K which cannot be utilized by plant. However, soil AK pools were estimated always using acid extracting methods in China. Therefore, quantification of AK using the method of NaTPB might facilitate prediction of long-term K release capacity in field balance calculations of soils. A new grading system for AK in soils based on K release rate from soils and plant growth indices was established by the method of NaTPB. According to this grading system, AK in soils was classified into three forms: high available K, medium available K and low available K. However, there is still a great deal of uncertainty and variation among these three AK forms and climate, topography and soil geochemistry, which has important implications for predicting plant/mineral interactions and soil sustainability.. The heterogeneous distribution of soil plant-available potassium, and its correlation with environment and soil geochemical characteristics of 285 soil samples in 31 sites will be investigated using the AK grading system along the hydrothermal gradients in China. Then the present study will be conducted to: (1) realize the heterogeneous distribution and causes of soil geochemistry along the hydro-thermic gradients; (2) discover the heterogeneity distribution of different plant availabilities of soil K along the hydro-thermic gradients and (3) reveal the effect mechanisms of environment and soil geochemical characteristics to soil plant-available potassium. The results of this study will help to form a basis data for the researches of soil K from transformation and its ecological cycle.

农田钾素供应不足导致土壤钾素成为作物钾素的重要来源，但当前对我国农田土壤有效钾库容量的估算过低，钾素生物有效性分级较为粗糙，气候、地形和地质化学背景对不同生物有效性钾素的作用机制也不明确。基于此，本研究拟采集我国7个水热梯度带内31个采样位置285个典型耕作层土样，利用常规土壤钾素测定方法和基于四苯硼钠法所建立的有效钾分级体系，对土壤钾素生物有效性和环境地球化学特征等的研究结果进行分析，探讨：（1）我国不同水热梯度带耕作层土壤地球化学特征的差异分布规律及成因；（2）不同水热梯度带耕作层不同生物有效性土壤钾素的分布特征；（3）环境地球化学特征对不同生物有效性土壤钾素的作用机制研究。以期为预测我国钾肥的市场需求、指导钾肥的合理分配和平衡施用提供基础数据和理论依据。

钾素是植物所必需的大量营养元素之一，但目前有关不同水热梯度带内钾素生物有效性分级以及气候、地形和地质化学背景对不同生物有效性钾素的作用机制尚不明确。本项目根据我国农业土壤分布的水热条件并结合考虑耕作制度、土壤类型、分布面积以及生产能力等，收集了我国由南而北2000km、至西向东3600km共8个水热梯度带的1985个耕作层土样。利用常规土壤钾素测定方法和基于四苯硼钠法所建立的有效钾分级体系，对土壤钾素生物有效性和环境地球化学特征等的研究结果进行分析。结果表明：（1）不同水热梯度带耕作层土壤地球化学特征分异明显，随着湿度和温度的增加，土壤pH值、CEC、交换性Mg、TN以及原生含钾矿物含量降低，有机质、交换性Al含量增加，TP变化不明显。（2）常规土壤有效钾（速效钾和缓效钾）和新建生物有效性分级钾形态（高效钾、中效钾、低效钾、最大量有效钾），其含量基本呈现随温度和湿度增加减少的趋势，且在南亚热带-湿润区和温带-干旱区内的土壤速效钾含量均值已趋近于土壤缺钾临界值，从空间分布来看，各不同有效性的钾素含钾较为丰富的农田土壤较多位于温带干旱区内，热带和南亚热带南部区域土壤有效钾含量均较低。（3）相比气候、土壤理化性质和含钾矿物，土壤速效钾更受控于地形因子；土壤缓效钾和全钾则更多的受气候因子的影响；土壤高效钾受气候因子和土壤理化性质影响较大，含钾矿物也会影响其分布，但与地形因子相关性较小；土壤中效钾除和缓效钾和速效钾相关外，仅受气候的影响；土壤最大量有效钾则同时受气候、地形、土壤理化性质和含钾矿物的影响。项目结果有助于了解我国农田土壤有效钾的空间分布特征及储量和明确土壤有效钾分布的控制因子，为指导不同水热梯度带内钾肥的合理分配和平衡施用提供了基础数据和一定的理论依据。