Geostatistics-based Characterization Of The Spatial Distribution And Temporal Changes Of Soil Fertilities In The Region Around Taihu Lake In Jiangsu Province, China

The Taihu Region lies in Jiangsu Province. It is one of the most important industrial andagricultural developed areas in China. There is a growing concern about its seriousenvironmental issues due to long-term human effects on the manners and intensities of soilmaterial cycles in this area. So, it is of realistic significance to characterize current spatialdistribution and temporal changes of its soil fertilities during over 20 years. Thecharacterization will be very beneficial to enact effective and oriented measures forimproving the soil environment quality and promoting regional sustainable development ofagriculture and society. In this case study, the areas surveyed for change of soil fertilitiescovered total 12 counties and cities under the jurisdiction of Suzhou, Wuxi and Changzhoumunicipals around Taihu Region. The data of 2737 soil samples were collected in the year2004 from the same sites as used in the Second National Soil Survey which was conductedin the early of 1980s. The temporal and spatial variabilities of single factor andcomprehensive fertility index were analyzed by the aid of mathematic statistics and spatialanalysis methods in combination with global information system (GIS). The relationshipsbetween various soil types and soil parent materials and the temporal-spatial heterogeneityof soil fertility quality were also explored. The main results are described as follows:1. In 2004, the average pH was around 6.6 and soils with high pH were found in theNortheast parts in the survey area, while those with low pH were in the South parts. Theaverage contents of organic matter (OM) and total N (TN) were 24.84g/kg and 1.58g/kg,respectively. The strong random variability of OM and TN accounted for 30.31% and29.39% of total variability and showed moderate spatial auto-correlation. Similarly,available phosphorus (P) and potassium (K) displayed moderate spatial auto-correlation,but P was less than K in both the intensity and distance of auto-correlation, as well asthe anisotropic range. The average content of available P was 11.10 mg/kg and the soilswith available P higher than 3 mg/kg covered 94.14% of the soils in the entire area. Theavailable K in the soils ranged from 80 to 100 mg/kg with the average of 96.82 mg/kg.Comprehensive evaluation of soil fertility quality indicated that the soil fertility qualitywas in the grades of ClassⅡandⅢ. In general, fertilities of the surveyed soils,especially in the center and west parts, were in better conditions with soil quality indexranging from 0.8 to 2.21..2. There were significant differences of soil properties among the different subgroups ofsoils (P＜0.01). The soil chemical properties were also affected by soil parent materials.Statistical analyses showed that the soil type affected some parameters of soil chemicalproperties in the order: pH＞OM＞total N＞available K＞available P, while the parentmaterial effects were in the order: pH＞OM＞available K＞available P＞total N.3. Compared with the data of Second National Soil Survey conducted in the early of 1980s, the average contents of soil OM, total N, available P and K in the study area wereincreased by 2.49 g/kg, 0.19 g/kg,4.54 mg/kg and 9.50 mg/kg, respectively, while pHwas dropped from 6.93 to 6.60 in past 20 years.. Soils with decrease of pH occupied79.12% of the total area. Larger decrease of soil pH was found in the soils of countiesof Wujin, Wuxian, Kunshan and Wujin. Soil OM contents were increased in the soils ofJintan, Kunshan and Liyang, but tended to decrease in the soils of other countiesincluding Wujiang, Taicang, Wujin, Yixing and Wujiang. There were significantincreases of total N contents in the central and western parts of the region around theTaihu Lake, except the areas in Wujiang, Wuxian and Taicang where total N wasmaintained during past 20 years. Available P of soils in the south of Yixing county andin the northwest of Wuxi county was increased very largely, while it had slight decreasein the East of Wujin county. Available K of soils was increased in the south of Yixingand the north of Wuxi counties, but decreased in the north of Yixing, Taicang andZhangjia Gang counties. The overall fertilities of soils has been greatly improved in themost areas around the Taihu Lake region.The soil fertility index was raised to 0.5 in thesouth of Yixing, the northwest and southeast of Wujin, the east and west of Changshuand the west of Xishan counties. The south part of Wujiang county containing the areaof 17.8 km~2, accounting for 0.13% of the entire study region, was the only one showingthe drop of soil fertility index..4. Soil fertility varied with soil types. The change of soil fertility was found to be greatestin Yellow-red soils. Among all the chemical properties of Yellow-red soils, pH showedgreatest decrease, whereas OM, total N, available P and K were increased very largely.In gray fluvo-aquic soils, the change ranges were relatively smaller for pH, OM andtotal N than for available P and K. The contents of OM, total N, available P and Ktended to increase in the Yellow-brown soils, Yellow-brown soils with pan and thesubgroups of paddy soils,,while PH in the soils has slight decreases except Percogenicpaddy soils. Analyses of the effects of soil parent materials on change of soil fertilitiesdemonstrated that the soils developed on the Quaternary red clay and artificialaccumulated materials had most apparent change of soil fertilities in terms of somechemical properties. For soils derived from quartz sandstone, as well as in Yellow soils,their fertilities according to the contents of OM, total N and available P and K, wereimproved in generally during the past.. The changes of soil pH and available nutrientsof soils derived from fluvial-lacustrine deposit were shown to be moderate incomparison to the soils developed with the other soil parent materials.It was concluded from above results that the geostatistical method could be successfullyused in the evaluation of temporal and spatial change of fertilities of soils in the areawith medium size like the regions around the Taihu lake. The results also demonstratedthat the measures adopted during past 20 years in the region was basically appropriate inimproving soil quality and keeping sustainable development in agriculture.