Spatial variation of soil nutrients and evaluation of integrated soil fertility in Torreya grandis cv. Merrillii region

A total of 121 topsoil samples(0-20 cm) were systematically collected from typical producing areas of Torreya grandis cv. Merrillii in Zhejiang Province. Geostatistics and Moran′s I were utilized to reveal the spatial heterogeneity of soil nutrients. Integrated soil fertility index(IFI) of Torreya grandis cv. Merrillii plantations were estimated and its driving factors were analyzed. The results indicated that soil pH was lower and the concentrations of organic matter(OM), available nitrogen(AN), available phosphorus(AP) and available potassium(AK) were higher, with average concentrations of 4.91 g/kg, 30.60 g/kg, 136.77 mg/kg, 15.02 mg/kg, and 153.42 mg/kg, respectively. Soil pH and nutrient elements had moderately spatial correlation. The minimum range value of pH was 3.29 km, and the ranges of OM, AN, AP and AK were 8.52 km, 5.84 km, 8.82 km and 6.49 km, respectively. The results of Kriging and the local Moran′s I showed that soil properties had the obviously spatial distribution patterns and locally spatial aggregation in the study area. The low pH values were located in the city of Keqiao and Shengzhou and high values in the city of Zhuji and Dongyang. The spatial distribution patterns of OM, AN, AP, AK were opposite. The low values were mainly in the city of Zhuji and Dongyang and high values were found in the city of Keqiao and Shengzhou. Soil pH and nutrients had moderately spatial auto-correlation. The scales of spatial variability were basically similar. The results of the integrated soil fertility evaluation indicated that the soil fertility level was higher in most areas, and the IFI was lower in Zhuji and Dongyang. In general, the soil acidification and nutrient imbalances in the producing areas of Torreya grandis cv. Merrillii in Zhejiang Province were serious, especially the excessively high AN concentration. The correlation analysis showed that the environmental variables had little effect on soil nutrients of Torreya grandis cv. Merrillii, while forest ages had the great effect on soil pH and nutrients. It can be observed that the soil nutrients in the study area were obviously affected by anthropogenic activities. Therefore, it is urgent to improve the fertilization management mode, to carry out soil acid improvement, and to make regional fertilization planning according to regional conditions.