## 1 Introduction  
Prevention of soil pollution is an important part of ecological civilization. Compared with other pollutants, heavy metals remain in soil for a long time, transform slowly, accumulate easily, and can diffuse with runoff [1]. The accumulation of heavy metals in soil may inhibit soil function, cause toxicity to plants, contaminate the food chain, and promote the transfer of heavy metals to humans [2, 3]. The dry-hot valley is a partially arid valley-type region in southwestern China. It is one of the ecologically fragile areas characterized by high temperature, low humidity, dry climate and little rainfall, prominent water and heat contradictions, extreme lack of soil moisture and nutrients, serious soil erosion, and low vegetation coverage. The high contents of heavy metals in the dry-hot valley are attributable to the unique physical geography and farming system of the region. Under the unique dry-heat soil-forming environment, the background concentration of heavy metals in high-temperature soil is higher than that in other soil types [4]. Earlier studies have investigated the pollution status of heavy metals in dry-hot valley soils [5], but there is a lack of systematic studies on the pollution degree, spatial distribution patterns and sources of soil heavy metal pollution in dry-hot valleys. For the evaluation of soil heavy metal pollution, previous studies have proposed a variety of methods including Fuzzy Comprehensive Evaluation (FCE), Improved Weighted Index (IWI) [6], Geographical Accumulation Index (Igeo), and potential ecological risk index [7], and pollution load index [8]. There are multivariate statistical methods, GIS mapping method, isotope tracer method, positive matrix factorization (PMF), and absolute principal component score-multiple linear regression method (APCS-MLR) for the source appointment of soil heavy metals [9]. [PERSON] et al. [10] quantitatively analyze the sources of soil heavy metals in Guangrao, Shandong, using PMF and APCS/MLR. [PERSON] et al. [11] used PMF to conduct source appointment of soil heavy metals in typical areas of the Hexi Corridor. [PERSON] et al. [12] used APCS/MLR and analyzed the contribution rate of heavy metal sources in Xiamen urban soil.  
The slag field is the main source of soil heavy metal pollution in this study area. Different pollution sources contribute differently to the pollution characteristics of surrounding farmland soil and crops and ecological risks. The slag yard studied in this paper is currently stockpiled acid leaching nickel slag and gypsum slag. Therefore, clarification of the pollution source and contribution rate of soil heavy metals, objective and accurate evaluation of pollution status is of great significance for the control and restoration of soil heavy metal pollution in the affected area of slag field. In this study, the heavy metals were analyzed in the soil of the typical non-ferrous metal slag field in a dry-hot valley in Huili City, Sichuan Province, China. The contents of six heavy metals (Pb, As, Cu, Zn, Ni, Cr) and their associated soil properties were determined in the topsoil samples. Multivariate statistics-spatial analysis-soil pollution comprehensive evaluation and integrated research methods were used to obtain the visualized information of its spatial distribution characteristics and pollution degree. We expect to reveal spatial distribution of heavy metal from a single point to a larger area and from discrete to continuous quantitative description. Pearson correlation coefficient, canonical correspondence analysis (CCA), and PMF were used to qualitatively identify the sources of heavy metals in soil. The source contribution rate was quantitatively analyzed in order to provide a theoretical basis for the rational utilization of farmland soil and regional management and control of soil heavy metal pollution in the dry-hot valley.