横断山北部生态脆弱区土壤磷素空间分布特征

Spatial distribution characteristics of the soil phosphorus in the ecological fragile area in the north of Hengduan Mountains

根据90个样点表层(0～20cm)土壤磷素的化验数据,在ArcGIS8.1平台上运用地统计学方法研究了横断山北部土壤磷素的空间分布特征及其影响因素.结果表明,该区土壤全磷和速效磷含量均属中上水平,全磷含量达1.20±0.66 g kg-1,速效磷含量达13.7±12.6mg kg-1.土壤全磷空间分布总体上呈团状或块状,高值区(1.8～2.8g kg-1)主要分布于雅砻江流域西岸甘孜、新龙段和金沙江白玉、巴塘段之间的区域,并向西北和东南方向逐渐减少,低值区(＜0.7g kg-1)则主要分布于稻城县南部以及莫拉山以南德格以北的一个狭长区域;速效磷空间分布总体上呈小团块状,高值区(28～55mg kg-1)主要分布于雅砻江中游的甘孜县东部和西部,并向西北和正南方向逐渐减少,低值区(＜12mg kg-1)则主要分布于研究区东南部和南部边缘.成土母质本身含磷量和风化程度的不同使得磷素空间分布存在一定的水平、垂直分布特征.土地利用方式、海拔和坡度通过气候差异或土壤侵蚀程度来影响磷素含量.

Phosphorus plays an important role in the course of plant growth, and is a key factor that influences crop output and so is an important index to evaluate soilfertility. Furthermore, it can contribute to nonpoint source pollution of surface waters. Many researches indicated that parent material and fertilization quantity were the two primary factors to determine soil phosphorus content. There had been many researches on the spatial distribution regarding soil phosphorus content and it＇s influencing factors in recent years, most of them focused on parent material, landform, land use, and soil erosion, but few researches for altitude, slope gradient. There were few large-scale researches for spatial distribution of soil phosphorus content, too. The study area is mainly located in the north of Hengduan Mountains and is a typical ecological fragile area in China, with the most complicated and converse landform. Analyzing the spatial distribution characteristics and influencing factors of soil phosphorus content by the software ArcGIS8.1 is an effective approach to enhancing soil fertility and preventing the ecological environment from being destroyed. The objective of this research was to provide an approach of making rational use of soil resources and reconstructing an ecological fragile environment in the area. Using stratified sampling method, 90 sample points in topsoil（0-20cm） were selected. The results showed that the average content of soil total phosphorus （STP） and soil available phosphorus （SAP） were 1.20±0.66 g kg^-1 and 13.7±12.63mg kg^-1, respectively. Based on the criteria for the classification of STP content which was set down during the second soil survey in the 1980s ,the percentages of grade Ⅰ （〉 1.0g kg^-1）, Ⅱ （0.8-1.0g kg^-1）, Ⅲ （0.6-0.8g kg^-1） and Ⅳ （0.4-0.6g kg^-1） were 83.52%0,11.97%,4.36% and 0.15%, respectively. According to the criteria for the classification of SAP content, the percentages of grade Ⅰ （〉40mg kg^-1）, Ⅱ （20- 40mg kg^-1）, Ⅲ （10-20mg kg^-1）, Ⅳ （5-10mg kg^-1） and Ⅴ （〈5mg kg^-1） were 0.84%,31.92%,64.08%,3.01% and 0. 15%, correspondingly. The spatial distribution of STP mainly appeared as droplets. The highest value region（1.5-2.8g kg^-1） mainly existed in the west bank （between the segment of Ganzi,Xinlong and Baiyu,Batang） of Yalong River, and reduced towards the northwest and the south. The lowest value region（0. 2-0. 9 g kg^-1） mainly existed in a long and narrow area which was in the south of Daocheng County, the south slope of Mola Mountain and the north of Dege County. The spatial distribution of SAP on the whole appeared as small droplets. The highest value region （28-55mg kg^-1） mainly existed in the east and west of Ganzi County which is located in the middle reaches of Yalong River, and declined towards the northwest and south. The lowest value region （1-12mg kg^-1） mainly lay to the southeast and south verge of the area. According to the analysis results of sample points, the STP content which derived from different parent material follows a pattern of.. residual and slope deposit of schist （1.81g kg^-1）〉 residual and slope deposit of limestone （1.71g kg^-1）〉 alluvial deposit （1.40g kg^-1）〉 diluvial deposit （1.26g kg^-1）〉 residual and slope deposit of granite （1.21g kg^-1）〉 residual and slope deposit of slate （1.15g kg^-1）. The SAP content which derived from different parent material follows the order of.. alluvial deposit （23.0mg kg^-1）〉 residual and slope deposit of limestone （16.8mg kg^-1）〉 residual and slope deposit of slate （14.1mg kg^-1）〉 diluvial deposit （13.8mg kg^-1）〉 residual and slope deposit of schist （3.9mg kg^-1）〉 residual and slope deposit of granite （3.7mg kg^-1）. Soil phosphorus content has a close relation to parent material, but a degree of weathering or nutrient release also influences it. In the north of Hengduan Mountains, the dominant agricultural land use types are grassland, forest land and cropland except the land which has not been used and water area, and the three land use types accounted for 61.72 %, 27.10% and 0. 62 % of the area, respectively. The SAP content in cropland is highest among the three land use types because of a small quantity of rainfall, high air temperature and use of phosphatic fertilizer. Because landform has impacted on the distribution of parent material and hydrothermal condition, the spatial distribution of soil phosphorus content appears to some extent as horizontal distribution and hypsometric characteristics. STP and SAP content increased along with increase in altitude, which represents hypsometric characteristics to a certain extent. Because soil erosion intensity and soil nutrient translocation were different in different range of slope gradient, SAP content increased along with augment of slope gradient, but STP didn＇t change substantially along with the change of slope gradient.